I'm having this studdering issue on my 91 Z28. It was only a slight problem at first, then I changed the fuel filter and added fuel injector cleaner. The problem went away for two days then slowly returned and proceeded to get worse until now where the car is almost undrivable. It even backfires (or possibly pings) sometimes. The problem was happening mostly on throttle increase and only for a second or two, but now I only get decent drivability when cruising. My computer throws a code for the EGR but only every other day or so and only when cruising over 55 mph. So far I have changed the cap, rotor, plugs, and wires, plus the fuel filter and injector cleaner and I even changed the O2 sensor to no avail. I hear you guys on these boards are the experts on Camaros so I ask you to please help!!

-Joe

 

Try installing a fuel pressure guage and watch what it does while it's running and acting up.

 

My L98 has a similar problem at WOT. It seems like it pings, even on 91. It turned out it was loosing fuel pressure at WOT. I replaced the fuel pump and it helped alot, but not enough. I am thinking about replacing the injectors in the spring when I take care of a few other odds and ends. If you get any headway, please post. I too am anxious to get this problem solved. Its been pissing me off for almost a year

Will

 

Also check the injector coils for a resistance of 14-16 ohms, if all are within spec, do an injector flow test.

 

How do I do the injector flow test?

-Joe

 

http://www.slponline.com/view_product.asp?P=23051

SLP has 25 lb/hr injectors for $99.95. You can't beat that. I am gonna p/u some myself and swap them out this spring.

Will

 

How about checking your EGR solenoid?

 

Just on a whim check your timing .Does it kinds hesitate when your take off and then run better at a higher RPM?If so it`s a pretty easy thing to check and I have seen this problem before , good luck and post back yer results eh?

 

I've had timing issues before, and this doesn't feel the same. With bad timing, your car runs crappy, but consitantly crappy. Sometimes, I'll hit the throttle and it wont hesitate at all. I'm pretty sure I'm not getting enough fuel to the engine. Maybe the injectors, maybe the fuel pump, I don't know. The problem is, it could be a lot of other things too such as a bad ECM or ignition coil(doubt it). I'll test the fuel pressure one of these days when I get some free time and if its good I'll buy those injectors from SLP. If that doesn't work, I'll probably end up taking it to a professional.

-Joe

 

You could have a bad pickup coil (inside the distributor). Check the timing mark as is (don't disconnect the EST bypass connector) and see if the timing mark jumps around. If you disconnect the EST bypass connector, does it run better? Yes to both may very well be a bad pickup coil.

EGR valves are also known to cause similar issues as well as simply, bad spark plug wires.

 

I had the exact same problem on my 91 L98, I tried everything I could think of, I went over the ignition and egr systems with a fine toothed comb, and in the end I replaced the fuel pump after I found the pressure was low, and it helped alot but still sputtered every now and then so I replaced the injectors and problem solved. For the record, I ran across one other 91 L98 that had the same problem, I told the owner of my experience and he replaced his pump and then injectors when the pump alone didn't fix it completely, and once again, problem solved. Hope this helps a little

 

I believe I have a coil seperate from my distributor. Either that, or the coil you speak of sits underneath the cap and rotor. I have seen coil-in-cap models and I think that is what you are refering to. If not, please correct me. I do not know how to check a timing mark or what an EST(electronic spark timing?) is. If you would please explain it to me, I would appreciate it. Also, from what I understand, EGR problems will usually cause you to stall at idle, or idle really rough, but then the problems ease off as you increase throttle. I have only a very slightly rough idle, but I have horrible problems when increasing throttle. This is what makes me think its a fuel issue. Spark plug wires are new, so thats not it. From what I'm hearing, the fuel injectors seem to be the primary suspect at this time.

 

ME TOO!! ok i have this hesitation problem also..only my car runs really good at higher RPM's particularly over like 1200r's. But when i am backing up or just starting out from a stop it will hesitate really bad and jerk like it wants to stall kinda..Once moving though it is fine. It does sometimes stall in reverse though rarely. I heard in this thread that it could be a timing problem?? this sounds like it might be it cause someone said that if it hesitates at low RPM and then runs good at high RPM it could be timing??
I am not sure on how to check the timing so i need some help!?!?

 

Yeah, thats what a timing issue feels like. Try to turn your distributor by hand. If you can, then your distributor hold down clamp has come loose and your timing has changed. You can time it by hand by listening to how your engine is idleing, or you can use a timing light. Another way is to move your #1 cylinder to top-dead-center and then positioning your rotor to face between your #1 and #8 wire on your cap. You will probably have to go with the first option, or have someone who is more experienced do it for you.

 

I really hope injectors are gonna solve my hesitation, because I just ordered some from SLP and I already have a new fuel system minus the injectors. Fingers Crossed

Will