I'm getting a low rpm stumble when the engine is under load, especially noticeable in higher gears. I haven't ruled out ignition probs yet completely, but this doesn't feel like and ignition problem. Here's an example:

Cruising down the road in 5th or 6th gear, car starts to miss and hesitate some, and I give it a little extra gas and in just a second or two it catches and runs perfectly. Even throws you back in the seat some when it catches. Now this prob doesn't occur at WOT, and if I go WOT while it's stumbling, the problem immediatly goes away and it runs fine.

I reached back and squeezed the EGR to see if it was sticking, and although I could push the bellows in, I took quite a bit of force. Could that be what's causing my problem, and that's why it goes away under heavier throttle? If so, any way to test to see for sure?

Thanks in advance.

 

It's supposed to offer up some resistance when you push it in. When you pushed the diaphram in did the car sound like it was choking out, did the engine speed drop??

I'd start with the simple ignition stuff, plugs, wires, coil, coil wire, ect. This stumble that you're having, at what point in the RPM band does it happen??

 

Yeah, when I pushed the bellows in, it sounded like it was sorta choking out. And most of the stumbling usually occurs low in the RPM band, most of the time at or below 2k. Thanks for your help, by the way.

 

sounds like a plug wire problem if its missing and hesitating. Look of arcing. Do you have headers? I had similiar problems the worse it got the worse the car ran, then it eventually started backfiring at wot. Check your plug wires though, thats where i would start. -michael

 

I thought possibly plug wires, but wouldn't they cause hesitation and stumbling throughout the entire RPM band? I haven't had time to check them yet, and it's been ****ty weather, but sometime this weekend I'll check them out.

I plan on changing them and the plugs anyway, I just have to build some money back up. I just bought it last friday, paid it off all at once cash.

I changed the oil today, and sorta familiarized myself with the underside of an LT1. Looked around long enough to realize that changing plugs and wires is gonna be a real fun job.

 

Did you ever figure this out? Ive got the same problem.

 

No, I still haven't solved the problem yet. It gradually got worse for a while after I posted this, and started throwing an SES light when it got particularly bad. I don't have a code reader, so I don't know what code it was throwing.

I ruled out EGR though, so that's when I started looking for ignition related probs. I looked for signs of arcing on the wires, and they appeared to have been replaced within a short time before I bought it, along with the plugs. I even looked under the hood in the pitch dark, and didn't have a light show.

Opti seems to be a liable culprit.

I've been so busy lately that I haven't had time to do much work to my car. But I have been chasing thread after thread on here, looking for other possibilities.

Also, I've had another problem pop up as of yesterday. Sorta a periodic chirping/squeeling when letting out the clutch. Possibly a bad throw-out bearing?

 

You can disable the EGR valve from opening by plugging off it's vacuum supply. Take it for a test drive to see if there is any difference. It won't prove that it might not be closing all the way, but if it weren't, you idle would be a little rough.

 

My problem didnt start to happen untill i put in my ORP, didnt have the problem with the headers and the stock dual cat y-pipe.

If i plug the the hole in the header and also plug up the EGR tube would the problem go away? Or will i need to completely take off the valve and solonoid. My idle kind of cylces from rough to smooth. It will be rough, smooth out, and then go back the rough again a couple of times when im sitting at a red light or something.

 

Yeah, I ruled out the EGR like the way you described. It also seems to have the same problem with stumbling at idle. You can barely make it out unless you're behind it listening to the exhaust, or under the hood. It seems to stumble a bit, but if you leave it alone it'll eventually catch itself and idle perfectly.

 

Do you have stock manifolds or headers? Sounds like we have the same exact problem.

 

Nope, still running stock manifolds.

I've heard some people that had stumbling only when their car was at running temperature, but mine does it from the time I start it up.

 

Mine also does it all the time. Have you checked for broken bolts on the manifolds and a possible exhaust leak. Some people have had problems with the stock bolts breaking and causing leaks. I have what looks like an exhaust leak between the head and the header, but i cant here it, can only see a little black spot. I have new gaskets already, they will be going in this week. Ill let you if it helps any.

BTW, anyone reading this, i have a datamaster log of my car when its missing like this, and it looks like there is a possible problem with the short term and long term fuel trims, but i dont really know what im looking at. If someone wants to take a look at it let me know and i can email it to you. Could a EGR problems effect the fuel trim?

 

I've got a ticking coming from my drivers side of the engine. I dismissed it as a loud injector, or possibly something in the valvetrain, but it could possibly be an exhaust leak. I guess that would probably give the O2's bad readings, and cause it to richen the air/fuel mix.

I think we're finally starting to track the problem down.

 

Well, replaced the header gaskets and fixed all the leaks, but its still doing it.

My problem seems to be getting progressivly worse.

What is the best way to disable the EGR besides pulling the vacume hose to it. Im getting a funky idle so could that mean its not closing?