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oh95vx 05-11-2007 01:20 PM

Civic VX miss under load
 
I'm back again with more VX problems - sorry to say.

Right after I changed the L1H1 oxygen sensor about 6 weeks ago, she ran great - for a while. A couple weeks ago, I started to feel a bit of initial stumbling on acceleration. That's worsened to where it's a persistent miss.

Under even moderate acceleration I can feel frequent misfiring. The little girl just ain't got much go. Even in neutral, I can hear the miss in the exhaust note when I punch her throttle.

I have no CEL codes.

The exhaust smells odd. I'm not sure how to describe it.

Plugs (also ~6 weeks old) have some loose black carbon on the bases, just above the threads, but not much on the tips.

O2S also has a bit of carbon at its base, but the tip looks good (I think).

Ordinarily I'd suspect fuel delivery problems, and to be honest I don't recall when I last changed the fuel filter. However, the missing happens only after she's warmed up. When cold (and in open loop), she seems to run fine, suggesting something in the engine sensors or control is at fault. (Or am I wrong about that?)

ICM and coil were new a couple of months ago, just before the O2S. I didn't install them, however, so who knows what went in there?

New cap and rotor just after that.

TPS is smooth over its entire travel, no bumps or jumps, with resistance ranging from something like 2-3k to about 4.5k.

I just changed the MAP sensor. That was $75 for nothing. :thumbdown:

Timing light seems to show the distributor advance working, though I haven't tested it in gear with the wheels off the ground yet.

Could the replacement ICM be causing this? Any other possible culprits you can think of?

I appreciate the coaching. Thanks guys.

GasSavers_James 05-11-2007 01:36 PM

Wish I could help, but I am new to the VX. It sounds like you have replaced all of the usual culprits. Did you check the resistance of the plug wires, and dielectric grease the ends? You probably did this but did you set the right spark plug gap?
Mine does a similar thing. It only seems to miss under load once it has warmed up. However the difference is that it idles perfectly, and works perfectly once out of the lean burn mode. high rpm and low are fine if you put the throttle down and get it out of lean burn. It is worst at 1,700rpm under moderate lean burn load. I am hoping it is just the o2 sensor.

GasSavers_James 05-11-2007 01:39 PM

They are a sensitive automobile. Hopefully we can work together to diagnose problems and keep em running efficiently.
Just a note on how sensitive they are, mine idles beautifully at 550 rpm when all accessories are off, but turn the fan switch to 1 and that jumps to 800-900, probably burning quite a bit more fuel.

kwtorbe 05-11-2007 02:21 PM

I suggest a hotter spark plug if your plugs have carbon on them (they aren't oily are they?). I might guess at fuel injectors too. Have you checked the cap and rotor? The coil sometimes gets corrosion on it....The exhaust smell--is there any smoke?

My HX feels like it misses on the highway but a fellow HX owner and I determined it is the lean burn kicking on...

thisisntjared 05-11-2007 02:44 PM

50/50 shot its the fuel filter or dirty plugs. it could also be the distributor. how many miles are on the beast?

in the future change the cheaper parts first. MAP sensors do not readily go bad.

oh95vx 05-11-2007 03:14 PM

Cap and rotor are new.

"Could also be the distributor" - Hmmm. The ICM and coil are also new, about the only thing left in the distributor is the bearing, right? Or is there something else? How would I test it?

Plug wires are only about 2 years old if that, but I'll check 'em. No dielectric grease, but I'd expect the miss to be worse in wet weather if that were the problem, and wet or dry makes no difference.

Plugs are gapped right, or were when I put them in 6 weeks ago.

James, your VX sounds like mine was 2 months ago. She was smooth as butter at idle and under acceleration, but at any steady speed she missed and bucked. A new oxygen sensor fixed that, but now this.

BTW, 174,000 miles on her.

mrmad 05-11-2007 04:57 PM

Might not be a bad idea to get a compression/leakdown test just to ensure the rings/valves are in good health.

jadziasman 05-11-2007 06:23 PM

James,

The symptoms you describe suggest one of the following as the culprit of your engine miss at steady rpm under load.

1) The fuel injector timing is controlled by the ECM based on the 20 inputs it receives from the various sensors. The ECU contains memories for the basic discharge durations at various engine speeds and manifold pressures. The basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors to obtain the final discharge duration. lgnition timing is also controlled the same way but with fewer inputs. So it is possible that the ECM is trying to control fuel injection and ignition with bogus inputs. If so you will have to troubleshoot them one by one.

2) One of the cylinders has a deteriorating condition within the power cell. It could be something simple like carbon build up in the VX piston combustion bowl - which is pretty deep compared to other civic models. Or something more serious that is causing pre-ignition and additional carbon build up and wear. You said your compression test came out good in all cylinders which probably rules this scenario out.

In the case of my first VX with 155K miles, it was #2. I had a damaged cylinder that caused loss of power and poor mpg that deteriorated over time. An engine rebuild was the only solution I could come up with so I decided to sell it instead of repair it. Someone eventually did fix it but I'll never know the story - Carfax records indicated the car was still on the road three years after I sold it.

jadziasman 05-11-2007 06:28 PM

Oops - I meant our friend in Ohio not James specifically.

slurp812 05-11-2007 06:48 PM

Does that thing have an EGR valve? My 94 accord had clogged egr ports. ran like crap anywhere between 2 and 3000 rpms under light throttle. Also my plugs were showing a bit lean. But thats a lean burn engine, so I am not sure what the plugs should look like in an engine like that...

GasSavers_Ryland 05-11-2007 08:35 PM

sounds simaler to what I had when I had a faulty o2 sensor, lucky for me the parts store that I got it from remembered me, so I didn't even need my recepte to get a new one, after that it ran perfectly.

oh95vx 05-13-2007 12:56 PM

> Does that thing have an EGR valve?

It does. I pulled the vacuum hose off the EGR and plugged it to see if that made any difference. It didn't. I suppose that's not 100% definitive, though, as it's possible that the valve itself is leaking.

> sounds simaler to what I had when I had a faulty o2 sensor ...

I bought this O2S 6 weeks ago through Ebay, so I'd have to deal with a vendor in (IIRC) Detroit.

I hate to claim it's defective without any proof. Problem is, the only really good way I know of to test it is to substitute a known-good one. There's a test that involves voltages. I tried that on the old one and it passed even though it was junk. The voltage test is go/no go, but it won't identify an oxygen sensor that's out of calibration.

> The fuel injector timing is controlled by the ECM based on the 20 inputs
> it receives from the various sensors ... it is possible that the ECM is
> trying to control fuel injection and ignition with bogus inputs. If so
> you will have to troubleshoot them one by one.

Twenty of them! I had no idea.

This raises the same problem as above - the only way I know of to troubleshoot all those sensors this is to replace each sensor (and control) until the engine runs right. That could get pretty darn expensive. Too bad I don't have a spare VX for parts-swapping.

I just remembered something that makes me suspicious. I recall now that the problems with the poor running 6 weeks ago seemed to get worse right after the ICM and coil were replaced. Before, she'd run lousy at steady speeds and smoothed out when I accelerated. After the new ICM and coil, she missed ALL the time, including under acceleration.

Still, she ran well for a few weeks after I put in the new O2S. Puzzling.

jadziasman 05-13-2007 01:54 PM

It could be that it ran fine with the new O2 sensor until it got "fouled" with something in the exhaust gas that isn't supposed to be there. That's the most likely reason. Do you have the Helm manual in pdf form? You can download it if you search for 92 honda civic helm pdf. I don't remember the exact hit but it works. You don't get a table of contents with chapters separated into tabs though. Makes it hard to find stuff. Anyway, if you get the Helm manual it will guide you through the troubleshooting procedures without replacing sensors unnecessarily. Some procedures require a test jumper to test the input output circuits of the ECM. I don't know what this costs or where to get it. It is listed in the parts section of the fuel chapter. Your comment about the distributor work raises one remote possibility. The TDC/Crank/Cyl sensor may have been damaged or just isn't working right which could cause the problem. The CRANK sensor determines timing for fuel injection and ignition of each cylinder and also detects engine RPM. The TDC sensor determines ignition timing at start-up (cranking) and when crank angle is abnormal. The CYL sensor detects the position of No. 1 cylinder for sequential fuel injection to each cylinder. You will need to locate another TD-42U distributor to find out if this sensor is bad since cannot be replaced except with a rebuilt dizzy or new one. I have heard this sensor has caused problems in other VTEC civics. Keep trying and we'll keep helping. It sucks when the car you enjoy driving is sick.

oh95vx 05-13-2007 02:11 PM

Thanks for the ideas. I have the Helms on pdf, but its troubleshooting seems to only deal with problems that set CEL codes. That's never yet happened! On board diagnostics don't seem to be of much help here.

I see dozens of allegedly new and rebuilt TD-42U distributors for sale on Ebay, prices from $100 to $200. Some of them are no doubt cheap junk. Probably some are fine, and with unknown correlation between price and quality.

However, it really annoys me to think about just throwing new parts at this until something works. Not so much that it's expensive (which it is), but that there just HAS to be a better way.

One thing I have to somehow double-check is - this sounds stupid - basic timing. The crank pulley on this old girl is so rusty that I can't find the TDC and advance notches. I timed her by finding TDC with a dowel in cylinder #1, then using a piece of cardboard cut into a 16 degree angle with a protractor. Still can't find any of those notches. Can anybody think of a better (more accurate) way?

thisisntjared 05-14-2007 04:31 PM

Quote:

Originally Posted by thisisntjared (Post 51065)
50/50 shot its the fuel filter or dirty plugs.

????

Gary Palmer 05-15-2007 08:48 AM

OH95vx: I would suggest a couple of things.

First, I'd get another new set of plugs and try that. I have an 87 DX that has the lean burn carburator on it and I have one plug that gets chewed up a bit, for some reason. I think it's related to the lean burn mode, but I've finally gotten to a point where if the engine starts to idle a little rough, or i detect a slight miss, I pull that plug and replace it and then it's fine for awhile.

A second thought is you might try running dual point platinum plugs in the car. I used to have a Datsun pickup that idled lean and it ran like garbage, at idle. However when I put in dual point platinum plugs, it would idle like glass.

Third, if you swapped the ignitor and the coil out and it started running rougher, I'd suggest trying swapping the old coil back in.

Fourth, on Honda engines, the distributor ignitor was a weak link, at least in the year of my car. Their is supposed to be a Honda recall where they will replace the ignitor at no cost. I don't know if this is still in effect or not.

However, if your looking for a replacement, King Distributor sells a new, manufactured distributor, with the fix for the ignitor as a part of the distributor. The price is not much more than what any of the used or rebuilt distributors run, anyway and it comes with a lifetime warranty, so you shouldn't be having to fiddle with it anymore.

Fifth, on the car, with the setup you currently have, if you put a screwdriver into one of the plug wires, hold it close to the engine and have someone turn over the engine, how much of a gap will the spark jump. If it's working properly, you should be able to get a 1/4" to 3/8" gap between the screwdriver and the engine. On my car it had gotten to where I was only getting about 1/16" or less, to the point where it wasn't working right, but it was still working. If it's short, which is what I suspect, then the ignitor, or the ignition coil is marginal and needs to be replaced.

It could always be something else, but the fact it was running Ok, for a period of time, I would recommend checking these things first, before you go after any other possibilities.

mrmad 05-15-2007 09:20 AM

Here is a pretty good ignition troubleshooting guide. It is for Integras, but I would imagine that the distributers are similar enough to use it.

http://www.team-integra.net/sections...ArticleID=1112

VetteOwner 05-15-2007 04:03 PM

excessive oil in the exhaust will foul things up pretty good. could also be a clogged cat. does the exhaust smell like sulfer?(fireworks) so do a compression test (easy thing to do) will tell you if rings are leaking or valves are sticky/carbon build up will tell you if the headgaskets shot. have ya checked the oil level recently? too much will end up in the exhaust or if its mixed with coolant(ie blown headgasket) that can do unimaginable wonders.

GasSavers_James 05-16-2007 05:12 AM

I think I should do a compression test on mine, to check the valves. I can hear some valve noise (i think) when engine is cold under light to moderate load at lower rpms. It goes away once the engine is warm.

wehrd1 05-17-2007 07:25 AM

Quote:

Originally Posted by oh95vx (Post 51050)
I'm back again with more VX problems - sorry to say.

Right after I changed the L1H1 oxygen sensor about 6 weeks ago, she ran great - for a while. A couple weeks ago, I started to feel a bit of initial stumbling on acceleration. That's worsened to where it's a persistent miss.

Under even moderate acceleration I can feel frequent misfiring. The little girl just ain't got much go. Even in neutral, I can hear the miss in the exhaust note when I punch her throttle.

I have no CEL codes.

The exhaust smells odd. I'm not sure how to describe it.

Plugs (also ~6 weeks old) have some loose black carbon on the bases, just above the threads, but not much on the tips.

O2S also has a bit of carbon at its base, but the tip looks good (I think).

Ordinarily I'd suspect fuel delivery problems, and to be honest I don't recall when I last changed the fuel filter. However, the missing happens only after she's warmed up. When cold (and in open loop), she seems to run fine, suggesting something in the engine sensors or control is at fault. (Or am I wrong about that?)

ICM and coil were new a couple of months ago, just before the O2S. I didn't install them, however, so who knows what went in there?

New cap and rotor just after that.

TPS is smooth over its entire travel, no bumps or jumps, with resistance ranging from something like 2-3k to about 4.5k.

I just changed the MAP sensor. That was $75 for nothing. :thumbdown:

Timing light seems to show the distributor advance working, though I haven't tested it in gear with the wheels off the ground yet.

Could the replacement ICM be causing this? Any other possible culprits you can think of?

I appreciate the coaching. Thanks guys.

This is EXACTLY what mine is doing too. I just R&R'd the dizzy, the O2 sensor and put in the CORRECT plugs. 175Kmiles.

Runs like a champ at 70mph...and when cold runs great thru the gears. When it warms up however, it bogs down just before 3rd & 4th & 5th gear indicator lite lites, and tends to have a very noted 'stutter' in power under load.

And on that note....the gear shift indicator lite seems to lite at diff. rpms & mph ... This is while driving under the same type of load & acceleration scenarios. What's up with that?

Thanks guys!!!

oh95vx 05-17-2007 07:44 PM

Haven't had time to do anything on the car this week, but I've been wondering about the cat too. Still, I'd expect a constipated cat to make her run lousy even when cold, and she runs OK when first started. (Yes? No?)

Even though the plugs are only 6 weeks old they're Champions, so maybe I'll try a new set of the canonical NGKs. Then maybe r&r the distributor or at least the ICM (ignitor). Double check the timing.

I'm throwing parts at it after all; sigh. But my tags run out at the end of the month and it has to pass local smog before then.

One interesting thing. I read in another thread here about somebody who bought a used VX last autumn, and got 53 mpg driving it home at 75mph. I have NEVER gotten that kind of mpg. NEVER! Not even when she was brand new. In fact I've seldom done better than 48mpg, and I drive like your grandfather. Mixed driving, about 1/3 suburban (45 mph average) and 2/3 highway (60-65 average) gets me around 44-46 mpg (or did when she was running OK). That certainly beats a lot of other stuff on the road, old and new, but it's definitely not 50+.

I'm wondering if this car has EVER been right in the years I've owned it.

zpiloto 05-17-2007 07:52 PM

Quote:

Originally Posted by oh95vx (Post 51718)
Haven't had time to do anything on the car this week, but I've been wondering about the cat too. Still, I'd expect a constipated cat to make her run lousy even when cold, and she runs OK when first started. (Yes? No?)

Even though the plugs are only 6 weeks old they're Champions, so maybe I'll try a new set of the canonical NGKs. Then maybe r&r the distributor or at least the ICM (ignitor). Double check the timing.

I'm throwing parts at it after all; sigh. But my tags run out at the end of the month and it has to pass local smog before then.

One interesting thing. I read in another thread here about somebody who bought a used VX last autumn, and got 53 mpg driving it home at 75mph. I have NEVER gotten that kind of mpg. NEVER! Not even when she was brand new. In fact I've seldom done better than 48mpg, and I drive like your grandfather. Mixed driving, about 1/3 suburban (45 mph average) and 2/3 highway (60-65 average) gets me around 44-46 mpg (or did when she was running OK). That certainly beats a lot of other stuff on the road, old and new, but it's definitely not 50+.

I'm wondering if this car has EVER been right in the years I've owned it.

I think that VX might be the one that was purchased from one of the members here that was perched at the number 1 spot for a long time. I think it was sold with alot of aero mods left on and was in good running condition.
Need to be patience. It takes awhile to get a car where you want it. Also keep in mind that the commute is the make or break when it comes to mileage.

Gary Palmer 05-18-2007 10:39 AM

On the cat, it could be plugged or something, but I don't think that would have anything to do with your missing problem. I've had bad cat's on all 3 of our Honda's and the only way it showed up was when I got them smogged and they wouldn't pass. On all 3 of them, they would be about 110% over, but as soon as they got a new cat, they dropped to 10% or something really low.

I don't know about the mileage, but I think the VX you were talking about was purchased from a mechanic in AZ and then driven back to LA. He had a little trouble getting it smogged, but he hasn't posted, I don't think, since he got it passed.

Personally, I'm not sure why, but I think their is some variation from one vehicle to another. I hadn't been able to break about 37 mpg, with my 89 Civic Wagon, but it seems like some people are able to get better than that, no sweat. I've just resigned myself to doing the best I can. Right now it's getting either infinite mileage or no mileage, because it has some electrical issue that I haven't figured out.

oh95vx 05-18-2007 07:03 PM

Well, this is weird. I think my timing is backwards.

Tell me whether I'm crazy.

As far back as I can remember, gasoline engines have always had automatic spark advance. In the '60s and '70s, there was always a mechanical (centrifugal) advance that advanced the timing as rpm increased, and usually a vacuum advance that gave it an extra goosin' when you'd opened the throttle but rpm hadn't picked up yet.

Now, in my deformative years I spent a lot of time with my head under the hood of a '76 VW Rabbit. (Most people who owned '75 and '76 Rabbits got to know their engines pretty well.) It had good old fashioned points and condenser ignition.

In addition to a centrifugal and vacuum advance, it also had a vacuum retard. When manifold vacuum increased as you snapped the throttle closed, slowing down for that expressway exit, the retard diaphragm would do its thing, apparently as an emissions reduction strategy.

I know that microprocessor engine control has changed a lot of things, but it hasn't reversed the usual ignition advance / retard scheme, has it? 'Cause that's what my VX is doing. It's backwards. I swear.

When I blip the throttle, the timing *retards* for just a fraction of a second, from 16 deg BTDC to about TDC. Almost immediately it returns to the initial 16 deg BTC and stays there. There's very little if any advance as rpm builds, but when I let the throttle snap closed, the timing sometimes (not always) *advances* to about 20-25 degrees BTDC, then returns to the basic 16 deg BTC at idle.

I tested this in every forward gear with the wheels off the ground, thinking the timing might not act normally if it was in neutral. Same behavior.

That's not right, is it?

PS - I swapped out the plugs. The old ones were pitch black with carbon after only about 2,000 miles. Definitely something wrong here.

VetteOwner 05-18-2007 10:13 PM

lol yup u are right on the some kind of advance. my 80 chevette has vaccum advance and "had" a whole lotta emmisions crap that has been yanked. it just has basic stuff the engine needs to run efficently (it would fail an emmissions test even before the guy turned on the computer) but lucky for me i dont have emissions testing around here.

oh95vx 05-19-2007 11:20 AM

I checked the CKP, CYP and TDC sensors in the distributor by the Haynes method. They're all within the specified resistance range.

The TPS tests good.

I've changed out the MAP sensor.

Next step is to check the coolant temp sensor.

I can't think of any other sensors that affect timing other than the ones above. Can anybody else?

If I understand the ICM (ignitor) correctly, it really doesn't have any smarts of its own - all it does is fire the coil when the ECU tells it to. Anybody know whether that's right?

I did find a questionable connection to the ICM's ignition input terminal (green/yellow wire), where the shop that put in the new ICM 2000 miles ago crimped a new connector on the wire and did a shoddy job. However, fixing that connection didn't seem to make any difference. And I get the impression that all that terminal does is convey the command from the ECU to "fire the coil." (Right?)

So if I confirm that all the sensors are working correctly, about the only possibility left is a brain-damaged ECU, right? Wouldn't that be a rather bizarre kind of failure?

mrmad 05-19-2007 12:00 PM

"If I understand the ICM (ignitor) correctly, it really doesn't have any smarts of its own - all it does is fire the coil when the ECU tells it to. Anybody know whether that's right?"


You are right, the igniter is really a sophisticated switch. See the link below for a better explanation of the igniter works.

http://www.tegger.com/hondafaq/ignit...ion/index.html

I see where you say the plug wires are 2 years old. While they should last longer then that, they could be a source of the misfire.

oh95vx 05-19-2007 12:44 PM

Many thanks for the link on the igniter (ICM). That's about what I'd expected though it has a bit more intelligence than I thought in regulating dwell. (In the old days we adjusted dwell by changing the gap between the points; I suspect the term "dwell" derives from how many degress the distributor cam rotates while the points "dwell" together.)

I can check the plug wires, but it's hard not to put the principal blame on the bizarre things happening with timing advance. The timing light tells the story; it's simply NOT advancing when it should be. I have to think that either the ECU doesn't know that it should advance the spark because some sensor isn't telling it to, or the ECU itself is falling-down drunk.

Hard to believe that nobody has ever seen anything like this before ...

mrmad 05-19-2007 12:57 PM

Check out the VX ECU on EBAY. Hopefully it will stay low $.

http://cgi.ebay.com/ebaymotors/92-95...QQcmdZViewItem

GasSavers_TomO 05-20-2007 05:49 PM

If you do find your ECU to be defunct, I have a spare P07 (VX ECU) you can purchase.

usedgeo 05-24-2007 06:12 PM

First off I have never owned a Honda car so take this with a grain of salt. There has been some discussion of this problem but here is a little different path laid out that might lead to a solution.

First you have mentioned a miss. It seems like you are describing a miss at a specific cylinder. You would need to determine this by the rythm of the miss. If that is the case you should make a significant effort to determine which cylinder it is. You might determine this by plug color immediately after running with the miss or you might be able to detect an exhaust manifold temperature difference with an infrared thermometer. They are getting quite cheap. If you are talking a random miss then it could be anything and separating fuel and ignition problems can be difficult.

Second: If the miss is specific to one cylinder it will not likely be fruitful to replace components that are common to all cylinders. It might be but it is not likely. MAP, coil, ignitor, or ECU fall in this category. It would be more promising to determine the cylinder and then trade what components you can such as fuel injector, spark plug, or wire and see if the problem follows or stays.

Your description makes it sound like the missing occurs when it is going into lean burn. That is it after it warms up and you are cruising.

Third: I have never heard of a failure of the pin that locks the valves in the proper configuration but if the valves failed to change properly it could certainly cause a problem in lean burn. If the second valve is opening too much you will not get the proper swirl for the lean burn. It just crossed my mind but remember I have never worked on one of these.

Fourth: Diagnosing weak ignition. One time I had a Eureka moment. It took embarrassingly long for this concept to emerge from my unconcious as it is very simple. I noticed that when spark plug wires were old I often got shocked. When spark plug wires were new I could handle them carelessly with the engine running and not get shocked. A discharge will find the path of least resistance. What emerged from this was a dual spark gap. This only works if you have a separate coil feeding a distributor. Construct a simple spark gap arrangement on something that inuslates. Attach the coil wire to a central contact point. To one side of this arrange an adjustabe gap with a wire connected to ground. On the other side arrange an adjustable gap with the wire leading to the distributor. Please pardon the verbage I need a picture here.

http://xs215.xs.to/xs215/07215/first_proto.JPG

http://xs215.xs.to/xs215/07215/2nd_proto.JPG I know a wire is missing.

Anyway adjust the gap to ground very wide and the gap on to the distributor quite small. Start the engine. Open the gap to the distributor to about 1/4 inch. It should easily jump that gap with a blue spark. If the spark is weak and reddish you may have a problem. Bear in mind that if the coil output has no path to ground it may break down the insulation in the coil and in unlucky cases it can then follow the primary circuit back to expensive electronic components and damage them. At this time bring the ground close. On the first protoype this was just done by placing a plastic handled screwdriver bit between the wires to finess the gap. If one plug wire has higher resistance than the others with just a little finess you can adjust the gap so that the engine will miss on that cylinder but not on the others. This is only useful for finding high resistance problems. If you have a low resistance problem this is pretty useless. Sometimes Honda rotor insulation breaks down in the center and the current will go to ground through the center of the rotor. This will not help with that diagnosis unless it is placed in place of one of the spark plug wires.

Trivial Anectdote. About thirty years ago the head mechanic spent a couple hours trying to get a service tractor running. I was a new hire and had grown up in a repair shop. On my lunch break I used the first prototype to find a broken rotor. Fortunately these were mature people or I would have been in a spot of trouble.

For this thing to be useful you would need to play with it to develop a sense of the typical gaps and all. At one time I thought the thing had some usefulness but soon people won't know what a distributor is.
I tried to patent it through an outfit that was later featured on "60 minutes." That did not work out too well.

Pardon the length and if I mislead you I apologize.

oh95vx 05-26-2007 02:50 PM

Usedgo, I really like your spark tester. I'm going to make one of those up.

I don't think this is a case of a bad cylinder. I know that "loping" effect, and this isn't it. It misfires on all of 'em - all four plugs were black with carbon when I pulled them, and this was after only 2000 miles of use.

It's not just on the road, so I don't think it's a leanburn problem. I can hear the misfiring in the exhaust note just blipping the throttle in neutral in the driveway. But only after the engine's been running for a couple of minutes - it runs fine when I first start it, or at least seems to.

I thought "plugged cat" for a while, but I did a vacuum test, and it passed. I suppose I should really do an exhaust pressure test, the O2 sensor port would be the perfect place, but I don't know what tool to use. Could I use my compression tester, or will the hot exhaust gas kill it?

I have a used ECU here, thanks to the post by Mrmad. However, I'm kind of nervous about trying it before I'm sure everything else is OK, because I don't want to risk damaging it.

I really think something weird is going on with the ignition timing.

If anybody has a Civic (probably any engine would work about the same way) and a handy timing light, you could do me a BIG favor. Hook it up, fire up the engine (trans in neutral of course), aim the timing light at the timing mark, and blip the throttle. Tell me which way the timing mark appears to move when you open the throttle. Does it jerk toward the grille, or toward the firewall? And about how much does it move?

Oh, I also tried pulling the wire off the coolant temp sensor to see if the ECU's default map would work better (suggesting the CTS was bad), but it ran exactly the same.

Tearing my hair out here ... :confused:

mrmad 05-26-2007 06:11 PM

Got out the timing light on my Integra. The timing marks move towards the firewall as I made small blips in the throttle by pulling on the throttle cable. I couldn't see the tach needless to say, but I'm sure I wasn't getting it much above 2000rpm and the timing marks moved to where I couldn't see them. This is normal, remember a Honda engine turns counterclockwise when looking at the crank from the driver's side. I opened up a stock bin file from a P07 in Crome and the ignition advance on the low cam is:

16.5 degrees from 500rpm-1483rpm
18.0 degrees from 1484rpm-1795rpm
18.5 degrees from 1796rpm-1999rpm
18.75 degrees from 2000rpm-2311rpm
19.0 degrees from 2312rpm-3219rpm

The high cam has more advance, but I'm assuming you are not hitting vtec while blipping the throttle while parked.

The P72 ECU in my Integra advances alot faster (at 2500rpm, it's already at 36.5 degrees, which is why the marks jump to where I can't see them)

Hope all this helps.

oh95vx 05-26-2007 08:05 PM

Thanks a million times! I really appreciate your dragging out the timing light. It helps a LOT, confirming that what I'm seeing here is NOT normal.

My poor girl's timing RETARDS as I blip the throttle, the timing marks moving toward the radiator. Once the speed is steady at the new rpm timing moves back toward 16 btc. I don't see any significant advance at higher rpm.

Is there anything else BUT the ECU that could cause this? My understanding of the way this works is that the sensors report to the ECU, and the ECU alone decides when it's time to spark. Then it sends out a logic pulse that tells the ignitor to tickle the coil. That is - am I right that timing is 100% under the control of the ECU?

If so, the next question is, what would cause the ECU to lose its mind this way?

When the VX quit out on the road back in March or so, I had it towed to a shop (not much choice under the circumstances). They pronounced both coil and igniter DOA. The mechanic said that often the coil dies and takes the igniter (ICM) with it. I don't know whether that's true, but it scored him a few hundred bucks for replacing both.

If the coil whacked the ICM as it went down, maybe the ICM in turn knocked over the ECU. If so, I'd expect the ECU output to the ignitor to just go dead. However, it acts like its internal tables have gotten reversed or something.

You seem to know quite a bit about these ECUs. Any thoughts on what kind of failure could cause an ECU to somehow reverse spark advance?

And is there a possibility that something else still lurking there could fry the replacement ECU in the same way? Should I consider swapping out the distributor too?

mrmad 05-26-2007 08:53 PM

From what I understand, the main things controlling the timing are the TPS and MAP sensor, though nothing should ever get the timing less then the 16.5 degrees in the tables.

I see 3 possibilities.

1. Your ECU is messed up.
2. The VR (TDC) sensor in your distributer is messed up, so the ECU doesn't know where TDC is.
3. There is/are poor conections between the distributer and the ECU.

I would troubleshoot to eliminate these possibilites. I don't believe there would be anything latent in the wiring harness that could fry the new ECU (though this is just a guess). I only have a CRX OBD1 manual and an Integra manual, but you can measure the resistance on the TDC sensor to test them. I wouldn't put too much faith in the test, it is only measuring for resistance and isn't exactly showing the TDC sensor has a nice output when the engine is turning. I know you hate throwing $ and parts at it, but after testing your ECU, a different distributer would be a good idea.

Though unlikely, I suppose another possibility is poor grounds. As a precaution, I'd clean the ground terminals on the main ground to the engine block and to the head,

oh95vx 05-27-2007 04:23 AM

I did check the resistance of the TDC sensor - it was within the range in the manual, though as you say that's not definitive. Flaky grounds is an intriguing possibility I hadn't thought of.

I did find that the mech who changed out the ICM had crimped a new connector on the control wire, and had done a lousy job. It wasn't very solidly crimped. I put the ohmmeter on it and could see it intermittently go open as I wiggled the wire. But I've already fixed that, and it didn't seem to make any difference.

If the weather cooperates I'll check out some of this stuff today. Thanks!

oh95vx 05-27-2007 05:36 PM

Swapping out the ECU didn't help.

She still runs lousy. The timing still retards briefly when I open the throttle, then returns to 16 BTC. No apparent advance with increasing rpm.

Haven't tried it in gear with the wheels off the ground, but from the way it runs out on the road, I doubt that that will make any difference.

I've already replaced the MAP sensor. The engine-to-chassis ground jumper is a bit rusty but looks solid.

AFAIK, all that's left that affects timing is the distributor itself. I wonder what boneyards are getting for 'em these days.

Grrrr.

mrmad 05-27-2007 06:42 PM

That's a drag. It is odd you have these symptoms and either ECU is not throwing a CEL, but it does sound like you have a bad TDC sensor in your distributor. Have you checked to see if the VR sensor can be replaced without replacing the entire distributor?

I'd at least pull the TDC connector off your distributor and check to see if the contacts are clean before getting another one. On the bright side, at least distributors are easy to change.

VetteOwner 05-27-2007 08:43 PM

i really cant remeber but my friends civic had a random misfire code geting thrown. and it turns out it was his crank position sensor. now i have no idea if your car even has one.

oh95vx 05-27-2007 08:47 PM

Yeah, the lack of any CEL is what really gets me. I thought the diagnostics were supposed to complain if any of the sensors was out of range.

I tested the TDC sensor with an ohmmeter (as described in the Haynes manual) and it passed. The plug contacts looked pretty good then. I could give them a little squirt of contact cleaner, I suppose.

I think a reluctance pickup uses a magnet; if something weakened the magnet it might not work right. I wonder if there's a voltage output spec for that pickup somewhere.

Haynes says "if the [resistance] test results are not correct, replace the distributor," so I suppose the pickup isn't available as a separate part, at least not fro the dealer. But then you're supposed to replace the entire throttle body rather than just the MAP sensor, too, so maybe the pickup is available as an aftermarket part.

I'm really puzzled by this. I keep going over in my mind the admittedly rather meager knowledge I have of how these systems work, and it just doesn't make sense. Why on earth would the ignition *retard* instead of advance? And why no advance as the rpm increases?


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