VX exhaust manifold unique
 

I've seen the original VX exhaust manifold and it's unique among Honda manifolds; all the exhausts come straight out (90 degrees) to a central chamber where the O2 sensor is put in the centre, at the top. Then it goes down into a cat. That leads me to think that Honda wanted to put their 5 wire O2 sensor in the highest heat location. As the original VX manifold is hard to find, I'm going to try and modify a regular 4 into 1, locating the sensor in that 4 into 1 hotspot, at the top, then heat wrapping it to keep it hot. Has anybody done that?

Re: VX exhaust manifold unique
 

Yes a hot O2 sensor works better. I've also found that keeping the O2 sensor closer to the exhaust port give quicker response to changes in AF ratio, except you can't put a solo wideband in an individual runner so it has to be placed in the collector, preferably in a spot that doesn't hinder exhaust flow.

Re: VX exhaust manifold unique
 

Actually OP, if you makes you feel any better, most newer civics (1996+) have this EXACT exhaust design and the reason for this is by putting the catalytic converter closer and or using the catalytic converter like an exhaust manifold, it allows for quicker warm up temps.. My '98 Civic LX has this exact setup and considering the D-series engine hasn't substantially changed in design (save for increased deck height for more displacement, same bore size) since 88-05, I'd say you could just pick yourself up one of these OBD-II exhaust manifold catalytic converters (yes there actually is a distinction between OBD-I cats and OBD-II cats). OBD-I cats have a lower efficiency requirement compared to OBD-II cats, so OBD-II are always cleaner.

The civics that don't have this setup are the EX civics from when ever to at least 2000 model year.. Possibly in 2001 model year, they transitioned the EX to having the same catalytic converter setup as all of the other civics. Older Civic EXs have a separate exhaust manifold which bends and then connected to a catalytic converter further down stream, which allows for aftermarket upgrades, something the "newer design" doesn't allow for since the cat IS the manifold.

Re: VX exhaust manifold unique
 

This is correct. The VX engines from 1992-1995 and the DX/HX/LX engines from 1996-2000 all use that style of exhaust manifold, which raised the temperature of the catalyst more quickly than by placing it under the car. This allowed the VX to pass emissions (and the other engines to achieve a better emissions rating) during the cold startup test. I believe that the EX models did not have this style of exhaust manifold. I had a '99 Si, so I can say with certainty that the '99-'00 Si did not have it, either.

As far as buying/modifying an exhaust manifold, I would still try to buy a VX one rather than modify a 4-1. The VX manifold will give slightly higher backpressure. I know that the full-throttle performance will suffer slightly, but the mileage will be better. Some people on this site and others with a modified header in their VX suffered mileage drops when they swapped out, even when they kept the 5-wire O2 and OBDI cat.

Have you tried the WTB forum on this site? You may have better luck than you think.

Re: VX exhaust manifold unique
 

I just am trying to confirm if you both are saying that using the 96 cat/manifold will yield the same results as the original stock Vx cat/manifold to a t.

I purchased a new exhaust manifold and heat shields from Honda and a new cat from Bosal. Unfortunately the bolt patterns don't line up with my Vx manifold and they claim that it did so I have to return the parts with a company that sucks on returns. Partsgeek.com. I've had lots of good parts come from them but I'm worried about the return process based on consumer reports. Worse case is I send it back and they don't refund I'll dispute it I guess. My experience so far has been good though so hopefully it will be a smooth return, even though I have to cover shipping both ways, and they may try to hit me with a restocking fee :me:

Anyways back to topic. Will the 96 Lx/hx cat perform the exact same as a stock 92-95 Vx/Cx setup?

Re: VX exhaust manifold unique
 

If you're concerned about things not bolting up properly, going with a '96+ catalytic/maniverter from a DX civic will in fact bolt on and should output lower emissions. I plan to call the BAR (Bureau of Automotive Repair for California) and ask them if using a newer catalytic converter/exhaust manifold would pass smog or not. Considering that the design of the maniverter shouldn't have changed and identifying the difference between the '92-95 and '96+ would be difficult, even if it isn't a legal change, they won't detect it visually and will definitely not detect it at the tailpipe. Why are you replacing yours anyway?

Re: VX exhaust manifold unique
 

my 97 LX has the same set-up, and i believe you're correct that the EX does not.

the crack in my manifold has been patched, but it's still leaking. my thought was to buy an aftermarket one at some point, and sell my old one because the cat has value.

Re: VX exhaust manifold unique
 

The car sat for two years and rusted alot. I had the cat and manifold off the car for those two years but the car is still 19 years old with 220,000 on her. I just bought a brand new stock style exhaust system for her and I'm worried about the cat flaking off in the system and ruining the resonator and muffler. Looks like I may have to wait a few more months though.

I just am wondering if the 96 cat will yield the exact same results as m 92 VX. I know they blot right up, but I'm more converned with backpressure, o2 readings and MPG. I know they are very very similiar, but will they yield the exact same results?

Re: VX exhaust manifold unique
 

I wouldn't worry about that too much. Considering the age of the vehicle, I'd say you have other issues to worry about. If your car is rusted a lot, then you need to make sure you get rid of the rust on the manifold because the o2 sensor uses the manifold as a ground and a rusted manifold = weak or no signal.

Re: VX exhaust manifold unique
 

This got me thinking imz, I'll probably need to pull the shield away to access the manifold, but I remembered seeing rust around where it's exposed at the LAF on my vehicle.

Re: VX exhaust manifold unique
 

I'm sure most manifolds are rusted by this age and so on my car, I hope to get a video camera, record the scan gauge's data and use it as a before and after of the GPH, steady engine RPM, etc. My theory is, that occasionally, my car won't get a good signal from the o2 sensor so it enters failsafe mode which causes the engine to rev to around 750rpm instead of 670rpm..

Re: VX exhaust manifold unique
 

If it's staying in closed loop then you can definitely rule that out. If it's in open loop when that happens then it's a good possibility. Do you watch open/closed loop on the SG?

Re: VX exhaust manifold unique
 

No, it's in closed loop. "Signal Noise" is certainly a normal part in any electronic circuit, but when you have a rusted out manifold, any ground the o2 sensor has to the car would be very weak. If you read the helms manual, it mentions that when the computer receives erroneous data, it goes into "failsafe mode". This isn't necessarily going to trigger a check engine light. A lot of "bad signals" from the o2 sensor could still be within range and therefore there will be no fault code. I mean think of it like this, the difference between someone playing music on the telephone vs. a compact disc.

The only reason I know that the o2 sensor uses the manifold as a ground for its signal is that when I was testing out an o2 sensor, in order to get a signal on the multimeter, one probe was on a wire on the harness and one was on the body of the o2 sensor itself. Spark plugs use the body of the vehicle to complete the circuit, so it's not a stretch for an o2 sensor to do the same.

Re: VX exhaust manifold unique
 

Would one of the wires in the connectors help ground it?

Re: VX exhaust manifold unique
 

Just think of it like this. You have a spark plug.. Notice how you have only one wire running to the spark plug? But how is that possible if a circuit has an incoming and outgoing wire, or a point where you hook up the + and the -? That's because the part where you plug onto the spark plug is the + and the - on the spark plug is the body of the spark plug itself, which is screwed into the valve head which is on the engine which is grounded to the chassis. The O2 sensors on the manifold are heated, so they have more than one wire. I believe the o2 sensor to verify the catalyst efficiency has only a single wire. Some older vehicles also use a single wire o2 sensor for the manifold as well. Single wire o2 sensors are not heated and are narrow band. 4 wire o2 sensors are still narrow band o2 sensors but with a heater element to get them working asap. 5wire (really 7 wire I think) are wideband, heated o2 sensors. Nonetheless, they all utilize the body of the sensor itself to complete the circuit which sends the signal to the computer in regards to the Air Fuel Ratio. I believe the heater circuit is the only one that has a positive and negative wire coming out of the o2 sensor, possibly so that it doesn't interfere with the signal of the o2 sensor.

It's possible all this is an anachronism to the days of unheated o2 sensors and that they don't want to change the way they send the signal to the computer. For a more reliable signal, it would obviously make sense to just run dedicated + and - wires to the O2 sensor instead of using the body of the sensor itself to complete the circuit. They run dedicated + and - wires for the heater circuit but not for the signal part of the o2 sensor which is why a rusted manifold can certainly cause signal issues.

Most guys who work on cars are not very interested in the electronics part of the car and aren't able to infer repairs unless they're specifically told to do so. This is why if you ask most car guys what it means if a car battery is at 0V, they'll reply "it's dead, you need to replace it" when in fact, it's not dead, just severely discharged. The reason they think batteries with extremely low or no voltage are permanently "dead" is because battery chargers will refuse to charge batteries with a very low voltage. There are two reasons for this: 1. They don't want you charging 6v batteries with a 12v charger.. 2. If the voltage is extremely low, for all the charger knows, you don't have the battery charger hooked up at all and so you don't want the charger attempting to charge with 10amps+ of electricity when it isn't hooked up to a damned thing now do you? To get around this issue, just put a good battery with jumper cables in parallel to the bad battery. Hook up the battery charger and charge at a low amperage like 2amps. In about 12 hours, you can probably disconnect the good battery and just run the battery charger on the discharged battery itself and charge from there.

Re: VX exhaust manifold unique
 

So I guess I shouldn't put on this new NGK 24300 oxygen sensor until I get a new manifold? That would suck because the 96 dorman cat/manifold assembly is 200 dollars. I'm spent out at this point.

I just want to fix it right the first time. I'm just not 100 percent sure that the 96 cat/manifold combo will work to the exact same specs as the 92-95 Vx cat. I know they bolt up, I just wasn't sure if they will perform the same.

Re: VX exhaust manifold unique
 

why not try getting rid of the rust on your existing 92-95 manifold and see how things work. Do you have this '96 manifold or not? If you have a new manifold, just install it with the o2 sensor you have, if you don't, then just remove the rust from your existing manifold and install the new o2 sensor.

A "rusted out car" isn't going to make the catalytic converter fall apart and get into the muffler system. That would only happen if you crushed the catalytic converter with blunt force or something else.. If you're worried about rust showing up in your exhaust but don't feel like spending money to get a new manifold, then I suggest removing the existing manifold/catalytic converter, take out the part with the catalytic converter and then try removing the rust from the manifold. Let me know if you want ideas on how to remove the rust.

Re: VX exhaust manifold unique
 

I agree that external rust isn't going to do it, but there are other ways that a catalytic converter gets broken up and clogs the exhaust than just blunt force trauma. Breaking up and clogging is probably the most common failure for catalytic converters.

Re: VX exhaust manifold unique
 

While that's true, that wouldn't happen just because op had the car parked for a long period of time. Unless he has been chronically running the car rich, this wouldn't happen.

Re: VX exhaust manifold unique
 

Well I finally got around to running a ground to the O2 sensor on the exhaust manifold. Good news is, the idle is more stable, sticking with around 670 slightly edging up to 700 if the engine gets hot but when things cool down, it goes back to around 670. This is in contrast with before where I'd notice the car idle at 670 but then randomly the idle would jump to 750. I also noticed that after driving long periods of time and being stuck at a stop light, the idle wouldn't drop to 670 but would idle at 750. The only time I could get the car to idle at 670 was if I let the car warm up gently.

However, while working on the separate ground for the o2 sensor, I figured I'd take off the heat shield and take a look around, it turns out I have a cracked manifold and the crack is right at the spot where the o2 sensor is. I don't know if I told anyone on here this but before I added the ground to the o2 sensor, I used an ohm meter and measured the ohms from the o2 sensor to the battery. I noticed on a cold engine, the ohms was lower than when the exhaust manifold was heated up and on an engine that is heating up (while running) I can slowly see the ohms drop.. This might explain why running a separate ground wire to the o2 sensor would explain a more stable idle since there is now a more steady and clean signal. However the real issue at hand is that having a crack exhaust manifold could be letting in cold air (or so I have been told) and that could make the car read lean, dumping in more fuel. I was wondering why I could smell some fumes from the engine bay but then it would dissipate.

Re: VX exhaust manifold unique
 

So I can use a 96+ civic lx or dx manifold? My 92 VX manifold is cracked too.

Re: VX exhaust manifold unique
 

IF it fits, i would not use one--they're gonna have the same flaw. just patch it, or buy it aftermarket new. advance auto parts has some great coupons right now...$50 off $150 or $200, if it's still active. retailmenot.com has the codes.

Re: VX exhaust manifold unique
 

yeah, I'm thinking of fixing mine, but first I have to take it off, and I've never done that before.. JBweld is suppose to work pretty well but this crack IS where the o2 sensor meets.. I have no idea how it will turn out. If I could only be certain that a 2001+ maniverter would work on these cars without modification. The 2001+ maniverters are stainless steel.

Re: VX exhaust manifold unique
 

This car is my beater car... I seriously don't want to put much money into it. The body is pretty shot.

Anybody know of any aftermarket headers what will work with the VX? I think I'm just gonna get an ebay cheapy for $30.

As long as I get 40+mpg, I'll be happy... It currently get's 42mpg with a bad cracked manifold and possibly dying o2.

Re: VX exhaust manifold unique
 

yeah since the manifold is separate from the cat on the VX, you might just get a manifold unlike me who has to get an entire catalytic converter despite it working fine aside from the crack.

Re: VX exhaust manifold unique
 

how much will my FE be affected by using tube headers? the o2 bung will not be seeing from all 4 exhaust ports.

Re: VX exhaust manifold unique
 

I don't think you can use your existing catalytic converter with headers.. You'd have to get a cat that is compatible with headers.

Re: VX exhaust manifold unique
 

I know that. I will have to install one downstream.

$40 headers
$50 cat
$50 install

Still cheaper than a cast unit from a 96-00 that won't properly fit my oil-dip-stick.

Still didn't find an answer to this though...

Re: VX exhaust manifold unique
 

Though your car might be more likely to fail smog. The reason Honda put the catalytic converter near the engine wasn't to pass emissions when it was new, it was to make sure the car wouldn't fail emissions by the 100K mile mark. Most cars even with the most screwy of setups (imagine a catalytic converter that was mounted where the muffler would be!) will pass emissions in a brand new car... The reason why they moved the cat from the mid section of the car to the front is because a cat that gets nice and hot is one that works more efficiently and so, over time, despite the catalyst efficiency dropping due to age and being tainted, because of the ideal location, the car is still highly likely to pass emissions. Had the cat been down steam, like in place of the muffler, while the car would pass emissions when new, because it's on the border line, when the car ages a little bit, it'll fail..

So to conclude, it's really a good idea to stick with a setup that is close to stock especially with a lean-burn civic because otherwise your car may be failing smog sooner than you think. This is also why lean-burn was disabled for California civics, not because it'd fail smog when new, but would likely fail smog before the 150K mark which means warranty claims. Most automotive design is based upon making sure the car lasts the duration of the warranty period.

Re: VX exhaust manifold unique
 

okay. so can i use a good condition 96-00 dx/lx exhaust manifold without any problems? will i still be able to use my oil dipstick?

Re: VX exhaust manifold unique
 

I was looking through the service manual and I think they're mounted differently.. On the VX, it goes straight down while on the 96-00 it goes off to the side. I guess you're going to have to get a VX one after all. Maybe the 2001-2005 might work? Though I think the VX catalytic converter would be cheaper and since the newer engines are higher displacement due to a taller deck, the maniverters might be too long for your engine. I've never tried using a newer maniverter on a different year engine. Only reason I mention the 96-00 maniverter originally is because they're similar design and the bolt pattern on the d-series from 88-05 is unchanged.