Calling VX Owners/experts! Help w/ studdering...

[iceyinferno]

First off, thanks for all the wealth of knowledge that I've gained from this forum.

Unfortunately my wife's VX has had some issues in the past few weeks...so this is going to be a wall of text...and I'm hopeful that I can lay out all the information in a readable format.

About a month ago, my wife's VX had some terrible idling issues and was stalling out on occasion...ultimately diagnosed as low compression on cyl#3. I had a VX in my garage that I was doing some body work on that was rusted pretty badly, so instead of having down time on her car, I swapped in the engine that was in the car that wasn't driveable. Engine swapped over pretty quickly in a weekend without any major headaches. After the swap, mileage was down and it had intermittent studdering issues under lean burn mode. So I began troubleshooting. Before installing the engine in her car, I already had the following done to the engine: new head gasket, new valve seals, valves were verified as straight and true, head was decked and then reassembled and torqued down to spec. Brand new timing belt, water pump, distributor, cap, rotor, plugs and wires. Pistons were not removed as there was no indication on the cylinder walls that they should be. Engine has 200k miles. So I have spares for pretty much everything on the car...

The symptoms do not occur with less that 4lbs of vacuum, or at idle. They occur from 5lb to 15lb (noticeably) and when below 2500rpms. And from the information in the mpguino, seem to occur while in lean burn mode only. A new symptom that I just discovered this morning is that if I first get the studder by staying within the vacuum and rpm above and accelerate hard I do get about 4 audible misfires before the car switches out of lean burn and then accelerates normally.

Troubleshooting to try to eliminate the problem to this point other than replaced parts above has been to change plugs, wires, and dizzy. Cleaned and swapped EGR valve. Cleaned and swapped intake manifold. Swapped o2 sensors. Cleaned ground on tstat housing. Verified valves were within spec and adjusted spark timing. Only thing left that I can think of is to swap in the other set of injectors, but I ran out of time before work today. Compression check came back with the following numbers, which from what I understand are within spec: 1-165 2-160 3-150 4-170

Other than the injectors, which I plan on trying ASAP, does anyone have any idea where I should look next? What spark plugs are the VX owners running?

T/L D/R : Vx is having studdering issues, I've tried everything I can think of except injectors...what do I do next?

[California98Civic]

Well, that's a 12% difference in compression between #3 and #4, which is quite close to the 15% max., and I wonder if the lean burn function is more sensitive to lowered compression. Did you do a wet test too?

[iceyinferno]

I'm not familiar with the wet test, I'll check that out. I went ahead and swapped the injectors over from the other motor and got the same symptoms. I then disconnected the o2 sensor and drove it once more...everything is fine without lean burn mode. So I think I have a temporary fix, so long as leaving the o2 disconnected won't cause long term negative effects?!?

[2009Toyotoad]

Sounds like a minor vacuum leak at the intake manifold. It should be more apparent on lean burn cycle. Try a fresh gasket at the head. and check the TB gasket, because that one the leak should be very apparent and visible.

[iceyinferno]

Both the throttle body gasket and intake manifold gaskets were just replaced. I can verify everything is torqued to spec and check for vacuum leaks though. Thanks for the tip!

[92civicvx]

I ran into the same issue with my VX, ended up being valve lash too tight and o2 sensor were bad. I still have a very minor hicub every so often when in lean burn. Betting its something fuel related but got over 60mpg on my last tank so not chasing the problem till it get worse. Is your fuel pressure regulator working properly? Wouldn't hurt to replace the fuel filter either.

[iceyinferno]

Sorry, forgot to mention that the o2 sensor is brand new from Honda and that the fuel filter was replaced when the motor was swapped in. So far, driving without lean burn mode has been the best the car has run with this motor. I think for the short term I'm just going to leave it that way until I get some other projects off my plate.

[The donkey CRX]

Ice, We have two VXs and we also had this problem. In my experience if the problem goes away when you disconnect the 02 sensor, you have either a bad O2 sensor or you are not using the correct 5 wire sensor that Honda specs. You should be able to buy the correct O2 sensor on E-Bay for less than $200 dollars.(they are $500 from the dealer)

Also, our 92 VX was a California spec VX that had a 49 state ECU installed, but the incorrect 3 wire O2 sensor and would only run well with the O2 sensor disconnected. Not sure if you may have something like this in the history of your car.

The car will run OK with the O2 sensor disconnected, but your MPG will suffer.