Engine surging problem
Thread Starter
Melting Slicks
Joined: Oct 2001
Posts: 2,786
Likes: 22
From: Cary NC
Engine surging problem
I'm having a problem with the engine surging at certain rpms. I don't expect you folks to diagnose it over the internet but maybe you can point me to what kind of shop I should take it to. What kind of diagnostic equipment and test should I have run.
The car runs fine in almost all cases. Starts right up. Throws no codes. Driven daily. I do all basic maint and keep up with my schedule. Only mod is SLP Cold Air, Tb bypass, and FastChip. 92-LT1 w/A4 and 100K mi. Btw, I've pulled the Fastchip and put hte factory air breather back on. No change.
If I accelerate smoothly then it moves right along. If I punch it or push hard on the go pedal then the surge happens in 2 places. First time just below 3Krpm then again near 4Krpm. After 4Krpm it pulls really hard. That is the only indication I get. There is a faint smell of gas or oil after you get on it hard but that is about it.
What kind of diagnosis should I have done? Put it on a basic engine analyzer and check spark etc? Have and injector leak down test run? Fuel pressure etc? Not really sure where to start. Just did inspection sticker a couple of months ago and it passes the smog test just fine. Very low emissions.
Graham
The car runs fine in almost all cases. Starts right up. Throws no codes. Driven daily. I do all basic maint and keep up with my schedule. Only mod is SLP Cold Air, Tb bypass, and FastChip. 92-LT1 w/A4 and 100K mi. Btw, I've pulled the Fastchip and put hte factory air breather back on. No change.
If I accelerate smoothly then it moves right along. If I punch it or push hard on the go pedal then the surge happens in 2 places. First time just below 3Krpm then again near 4Krpm. After 4Krpm it pulls really hard. That is the only indication I get. There is a faint smell of gas or oil after you get on it hard but that is about it.
What kind of diagnosis should I have done? Put it on a basic engine analyzer and check spark etc? Have and injector leak down test run? Fuel pressure etc? Not really sure where to start. Just did inspection sticker a couple of months ago and it passes the smog test just fine. Very low emissions.
Graham
Burning Brakes
Joined: Jan 2004
Posts: 933
Likes: 0
From: Inland Empire CA
Re: Engine surging problem (vms4evr)
There's really no easy answer, but I would suspect the Opti-spark if it has 100k miles on it. There are also other things to be checked. If it is putting out any codes, I'd see what it is pointing to. Check O2 sensors. Replace the fuel filter if its really old. Make sure that the EGR valve is operating properly. Good luck on getting it figured out! :thumbs:
Thread Starter
Melting Slicks
Joined: Oct 2001
Posts: 2,786
Likes: 22
From: Cary NC
Re: Engine surging problem (WickedC4)
WickedC4
Nope it throws no codes. Starts right up cold or hot. Probably over due for a fuel filter. Only engine part ever replaced was the starter. So everything is original. Unless there is some diagnostic test that shows the Optispark I'm not going to just replace it. That's my problem. I want to find someone who has the right diagnostic equipement that shows whether it is a fuel or spark problem and where the culprit is. Everyone wants to blame the Opti. And given their reputation it's understandable. But I'm not going to just arbitrarily start yanking parts. Didn't think about the O2 sensors or the EGR. Also original parts.
Graham
Nope it throws no codes. Starts right up cold or hot. Probably over due for a fuel filter. Only engine part ever replaced was the starter. So everything is original. Unless there is some diagnostic test that shows the Optispark I'm not going to just replace it. That's my problem. I want to find someone who has the right diagnostic equipement that shows whether it is a fuel or spark problem and where the culprit is. Everyone wants to blame the Opti. And given their reputation it's understandable. But I'm not going to just arbitrarily start yanking parts. Didn't think about the O2 sensors or the EGR. Also original parts.
Graham
