'89 V6 Camaro: Hard start, restricted power and backfire

I've had two problems for some time now: a start problem that was no more than a nuisance in the mornings and a back fire problem that has been a bit more than a nuisance. When lightly accelerating at speeds up to around 40mph, the car would bog down a bit and backfire if bogging was allowed to continue...If I was driving harder (harsher acceleration), then the back-firing would become less of a problem.
I had a bad exhaust leek that I thought could be the cause of the backfire, I found that the exhaust manifold donut on the driver side of the engine was toast, so I replaced it...
After replacing the donut there was a noticeable drop in performance, the car became even harder to start when cold, and the backfire problem remained.
At the recommendation of a friend who had the same problem, I then had the original CAT replaced (problem lessened but remained). Then replaced the muffler (noticed little to no change).
I'm starting to think that there are multiple causes of this problem since the problem got worse when I fixed the exhaust leak, then a little better when I replaced the CAT and muffler. I figured I would try a full tune up next, but first I would like to know if the exhaust system includes any DOUBLE-WALLED sections of exhaust pipe that could collapse and cause this problem.
Any other suggestions would be helpful.


-Recent work includes: all new vacuum hoses, cleaned MAF, cleaned K&N air filters, fixed exhaust leak, new fuel filter, new CAT, and new muffler.
-Also battery and alternator are fairly new and have tested good.

So it turns out that the battery was actually bad, so I picked up a replacement under warranty... I still need to crank it a couple times to get the car started, but I wouldn't really call it a hard start problem anymore.
All that is left to fix is the lag in power and the backfiring.
I'm going to pick up a set of AC-Delco spark plugs plus a cap and rotor now.

I checked my spark plugs and I guess I replaced them more recently then I thought, so I didn't replace them because they are standard AC-Delco plugs for this car and are in great shape...I did however clean them off, double check the gap before reinstalling them. The wire set is also in great shape (only 1 or 2 yrs old). I also checked the cap and rotor which were also in great shape (same age as wires and plugs), so I took a fine file to the points inside the cap to clean off the small amount of oxidized deposits and reinstalled the cap and rotor set.
No change in performance could be noticed.

This is beginning to feel like I'm keeping a journal...:frown:
Does anyone have any suggestions?

Hmm, the problem got worse after you replaced the donut gasket? Are you sure the crossover pipe isn't crushed? Seen that quite a few times.

Crossover pipe? Do you mean the Y-pipe?
I assume by "crushed" you mean damaged from the outside...
The Y-Pipe looks fine on the outside, but I'm not sure if it is a double walled pipe or not...if it is double walled, then the inner wall could be collapsed...Do you know if this car has a double walled Y-pipe?

Yeah, y-pipe, and no, I don't think it's doubled. Are you sure no peices of the old gasket went into the cat and are blocking it up?

Its been a while…I took some time off from trying to fix my camaro, but I recently had a problem with my daily driver, so I decided to drive the camaro … it wouldn’t stay started…
My mechanic friend took a quick look at it after working on my sister’s car…he determined that my coolant temperature sensor was bad. He also told me to change my dizzy if there was any sign of rust or oxidation inside… it was the original dizzy… Needless to say I changed the heat sensor and the dizzy…Then the car wouldn’t stay started, so I changed the MAF sensor… I set the timing and the camaro runs great…until I reach 2000 rpm’s…then the car backfires. :banghead:
The camaro ONLY backfires at 2000 rpm’s… :confused:
Does anyone have any ideas why my camaro is backfiring at 2000 rpm’s?

Thanks all

I'd say the timing is a tick too far advanced? What did you set it too?

EDIT, however the original problems you discribe and now this sounds like a funky EGR pintle.

I set the timing as close to stock as I could, then I realized I stripped one of the screw holes that hold down the dizzy cap...so I left it as it was and I’m waiting for the Auto Zone hub to restock my dizzy.
I was trying to set it to the stock recommendation of 10 degrees before TDC, but I believe I was 1 degree off when I tightened down the dizzy and rechecked. So I am either at 9 degrees or 11 degrees before TDC…
...But I find it hard to believe that being 1 degree off could cause this car to backfire at exactly 2000 rpm’s AND only when I’m driving…

OK Wright, what exactly do you mean by “a funky EGR pintle”? :dunno:

OK Wright, what exactly do you mean by “a funky EGR pintle”? :dunno

The pintle that opens and closes to allow exhaust gas back in to the intake manifold could be carboned up, much the same like a IAC pintle.

Too far advanced engine timing

I dont see how being 1 degree off could cause this problem...the problem was already happening before I replaced the dizzy and at that time the timming was set to exactly 10 degrees before TDC...Which i believe is correct for this car.

I also just finished reinstalling the EGR valve. There was no buildup in the EGR valve and the valve iteslf seems to function properly.
The problem remains...also, it has started to backfire and hesitate when reving in park...naturally at or around 2000 rpms.

Keeping it simple for a sec, the tan wire is hooked back up to the ECM?

If you are refering to the tan wire that allows the ecm to control the dizzy, then yes that wire is connected.

Status update:
I changed the dizzy one more time and I got a new cap and rotor cause I figured, why not?:runaround:
I tried to set the timing at least five times today, but every time I get her to 10 degrees before TDC and I go to tighten down the bolt to lock the dizzy in place, I always manage to advance the timing a bit… I even tried setting the timing to 8 degrees before TDC and when I tightened it down I still ended up at 12 degrees… :banghead:
I think I keep knocking the dizzy ever so lightly when I try to set the timing because I don’t have the proper wrench which is contorted just for this application…Instead I have been using a stubby ratchet. :crying:
I gave up trying to set the timing for the day and took it for a short spin. The backfiring problem is still there, but seems better. Also, I think the lack/restriction of power may be a bit worse than before.
Any Ideas? :dunno:

Oh man, even with the proper distributer wrench, you still knock em around a bit. :banghead:

You know, I'm grabbing here a bit, maybe a plug problem, ie-wrong plugs, mis-gapped plugs or cracked?

Other than that, does the timing mark "jump" alot? Wondering if it's time for a timing chain. :uhoh:

Could it be that your manifold is bad (clogged) perhaps. Or maybe you're cat is plugged? something similar happened to my sisters grand prix.

Thanks for the responses guys. :biggrin:
I don’t think it is a plug problem. The plugs are AC Delco standard with about 2 years and maybe 12k miles on them. I pulled and inspected all 6 plugs when I replaced the dizzy. No cracks, little to no visible wear, correctly gapped, and only minimal black deposits which I cleaned off before reinstalling the plugs.
When the ECM is controlling the timing it jumps, but when the beige wire is unplugged and I am setting the timing it’s as stable as a rock…I replaced the timing chain and guide myself about 4 years back and this chain is doing good. :smokin:

Thanks for the thought izzydjinn, but I have already inspected the manifolds, replaced the bad donut, and replaced the cat and muffler…I was so sure that those repairs were going to fix the problem, but here I am a couple months later… :crying:

Im thinking about changing the plugs and wires again, but I feel like Im just throwing parts at it...:headshake

I just had a thought, when the ECM is controlling the timing, how far should the timing venture from the preset base timing? I only ask because when I use the timing light and the timing is being controlled by the ECM, I noticed that the timing is venturing quite a ways away from the base timing… Could this be a sign that there is a sensor sending bad information to the ECM and it is trying to compensate?

Off the top of my head, I think like 20-25*.

I think it may be going a bit further than that, but I guess that doesn't really mean anything...

Ok, carnal im just throwing it out there.......... Could it be that maybe just maybe the spark plug wire cables are crossed??????

crossed? You mean they aren't connected to the right plugs?....Its a good thought, but the problem started months, or even a year after the last time I changed the plugs and wires... So I don't think they are crossed... If I had changed the plugs later or if the I had connected the plugs wrone, then that could be the problem... I dont think that is the case, but I will check anyway :) Thanks for the idea...Any more ideas?

I checked my wire placement against the fireing order and it looks good....No crossed wires.

Update: I had a friend of mine looking at the camaro with me and he noticed the the backfiring seems to be comming out the intake...not the exhaust??? :eek7:
This is something I never realized before, but after having him rev the engine while I listened, he was right...There seems to be some detonation happening that is being forced out the intake...
ANY IDEAS??? :bricks1:

sounding more and more like a possible engine timing problem.

Yea, maybe...but how can it be a timing problem if the base timing is set properly and the computor is functioning properly?... I don't dissagree, I'm just stumped...
Ya see the car still backfires if I try to drive it with the beige wire disconnected...so even if the timing stays stable, the engine still backfires...:confused:

No, I mean engin timing, cam to crank. I knowyou say it's new(er) but it might of jumped on ya from the sound of it.

Hi ALL!
I know it has been a while...but I apologize and though I won’t bother you with the details, I have been especially busy…
A week ago, at the advice of a friend of mine, I unscrewed and checked the IAC…It was bad and I replaced it, but it was not the cause of the problem I have been experiencing…
About 3 days ago I found a reference to something that sounded remarkably familiar to my problem online…same generation firebird…the description said that the problem was caused by a bad fuel pump …producing only 20 to 23 pounds of pressure per square inch when the pump should have been producing about 40 pounds of pressure…
When my stepfather’s mechanic checked my fuel pressure he said it appeared to be holding steady at twenty-something (can’t remember exactly) pounds per square inch…he told me that was normal and that my pump was fine……obviously he was mistaken…:banghead:
Apparently he has been working at 1st NISSAN for too long…
I will be ordering a new pump tomorrow and after it arrives I will install it as soon as I have the opportunity… I will post an update after I have installed the new fuel pump.
Wish me luck :smooch:

Hope thats your culprit.