Civic VX miss under load - Page 3

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

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 ...