GREGG 97Z

I have been trying to figure out why my car is missing throughout the rpm range lately and I think it may be a problem with the injectors being clogged. I was checking them last night by listening to each with a engine stethescope, touching it to each one while it's idling. They all had the rapid tick, tick that they should and all sounded normal. If they were clogged or even leaking for some reason would they still make the same normal ticking sound?

Also I have just replaced the fuel pressure regulator, filter and installed a new Walbro fuel pump. I replaced all these after this problem started and I noticed low fuel pressure and a stuck regulator, these problems all started after running the tank very low. After replacing all these things that I thought were the problem it's still running like crap even though the fuel pressure is now fine. The car will run ok for the first couple minutes then starts missing terribly throughout the rpm range, it's almost undrivable. It comes and goes though, sometimes it will be running ok for a while after its warmed with just a slight miss throughout the rpm range then I'll stop somewhere and go to start it again and it will suddenly stumble and miss like crazy. I don't understand how it can run this bad and the car has not thrown a single code?

slowpoke96z28

Does it miss when you are trying to maintain the same speed or under acceleration? What kind of tools do you have access to? What is this CPS signal removed you have listed in the mods section? I could tell you how to check the injectors, but I don't think that's the problem.

GREGG 97Z

It misses mainly under acceleration, at the same speed it feels ok. I have an Autoxray scan tool, I checked for codes last night and there were none. I didn't have long to work on it but I did see that it was still in open loop after warming up for at least 3-4 minutes which didn't seem normal, I'll have to look at it again tonight. The CPS is the crank position sensor, I removed it and had it programmed out of the PCM after installing the roller timing chain and new cam. It ran fine for several thousand miles with it removed, the motor uses it to detect misfires but it doesn't affect engine performance from what I was told. I don't think it's causing the problem although if it was there it would probably be setting a code right about now

slowpoke96z28

that explains why a 97 isn't showing the missfire code, now i have to rethink things. i was starting to think faulty PCM. What does the Auto-Xray say about the O2 sensors. now is the time i check for a lazy O2 sensor or water temp sender(in the water pump) to explain the time it takes to get to closed loop. the missfire sound like a standard ignition miss. what ever is causing a long time to get to closed loop is possibly causing a rich condition and already worn plugs are starting to missfire. Not saying that's the case, just a possibility. The funny thing about OBD I & II is that if a hard part starts to go bad, the pcm can compensate for it, until one of its(the pcm) inputs go bad. then it can't compensate correctly, and then you start seeing the the symptoms of the original failing part.

GREGG 97Z

I'll have to check the O2 and other readings tonight. I've been so busy lately I havn't had a lot of time to work on it. I just got the new fuel pump installed this weekend and did the filter and regulator the week before thinking they were the problem and it's still screwed up. Luckily it's not my only car or I'd probably just have it in the shop at this point. I havn't changed the plugs again at this point since I just did them about 3k miles ago during the cam swap. Maybe they have become fouled, thats probably the next thing I'll try after I check the scan readings. I'll let you know what I find, thanks for the help.