Diamondxx

I just recently purchased a beautiful 1990 vette with 99K miles on it.

I am not sure what exhaust system it has on it or if it has even been replaced(with aftermarket). My main concern is when I am driving around 45-50 (or a lot faster) and I let off the gas I get Mild/loud popping noises that sounds like it is coming from the exhaust/headers right off the engine and the car kinda sounds like it is going to die when this happens. It starts to feel like you are hitting the breaks on and off lightly when you are not. Could it possibly be bad injector replacement since they were replaced in the past?

Here is the sound the car makes with me revving the engine.



Here are the records of what has been replaced since 90'



There is also a page about the exhaust being replaced I suppose, don't know if it was OEM or Aftermarket



Thanks for the help guys!

leesvet

OUCH

OMG..thats even painful to read !

Whatever or why, is irrelevant at this point. Never do less than ALL injectors when replacing ANY. If there is one that's bad today, there WILL be another tomorrow.

The exhaust does not create the popping sounds..thats an engine malfunction. It can be from valves that are burnt/leaking OR injection that's too rich that's got unburnt fuel in the exhaust that's igniting during deceleration.

Your description of the "braking feel" is a little vague.
The TCC is supposed to "feel" like brakes as the engine brakes the car until it gets to stall speed OR until YOU touch the brake pedal. The TCC is actuated in 3rd gear but not in OD.

If your engine IS stalling when you let off the pedal, its probably the TCC that's keeping it alive as it dies/lights/dies again.
You need basic diagnostics.
Fuel pressure.
Ohms the inj
leak down/ pressure stability test
base timing

Its guessing at a problem on a computer controlled car without at least SOME test data to start formulating a picture of what the engine is doing...and why.

any stored codes?

if so, what?
ANY engine that's running as bad as described WILL have a code set. IF not, then its a sure thing the fuel system is NOT at peak efficiency.

BTW
if you are going to own and drive a vette that's got a history like that, you really really need to buy a FSM set so you can see whats BS and whats not. Besides, the FSM flow charts will answer almost ANY question that you have about a performance issue.
Shops see a corvette pull in their driveway................Cha--Ching !
You need to speak their language...or get taken to the cleaners, like the PO did. 90% of that work could have been done at home, or not done at all. Shops MAKE work when they have a "mark" in the 2nd bay...That car had a LOT of "maint" & "repair" for a 100K car....a LOT ! Yes, even dealers do this. (aka 'stealerships')

Diamondxx

After examining all the injectors look brand new so all 8 were replaced. Also the car runs amazing besides letting off the gas. Idle is perfect etc.... It had a load of maint done the lady that had it before me was a.rich head who got everything replaced a lot.

I'm not a super car person could you give me simple steps of what I need to go get done / do

Thanks

Also, it is not throwing any codes like on the dash

eatmydst1234

honestly, given that the mufflers look to me like they are the original style mufflers, possibly even the original i would crawl under and give them a goo look over and make sure there are no rust holes.. can't really tell from video but i thought i heard what sounds like an exhaust leak

Diamondxx

I will make a longer video tomorrow. Does this mean I will need to get a whole new exhaust system ? If this was the problem

DanielRicany

Does This Do It When Cold? How About If You Unplug The O2 Sensor? Can You Get A Scan Tool On There And Post The Results At Idle And At Deceleration?

eatmydst1234

IF it does turn out to be rusted mufflers, no. You can replace just the mufflers. Unless of course you want to replace the system.

If I were you I would swap those mufflers out for corvette specific dynomax super turbo mufflers. Slightly louder than stock but but not loud and in most cases little to no resonance.

Churchkey

Exhaust system is suspect, deceleration backfire is caused by the introduction of air into the system.
Cat still on the car? Right side of main cat has an air pipe is it connected?
If the exhaust system has been modified try disconnecting the air pump.

leesvet

yeah, I agree with the others that have mentioned a possible exhaust leak. I would think that would be obvious though.

It would have to be close to the engine, manifold joint or even header gasket. BUT,
That leak would be so LOUD and obnoxious during acceleration that you could not mistake it for anything else. This leak would have to be large and easy to find to draw enough fresh air inside the system to cause deceleration firing/burning IN the exhaust.
You should be able to get under the hood and rev it and listen.

If you rule out the exhaust, DO NOT assume the injectors are all NEW ! They DO wash them and they might have used the exact same replacements. They MAY NOT have changed any at all ! I have seen that particular SCAM from a dealership performed on my own mothers car. Carb rebuild and complete tune-up, and the funny thing was, the carb mounting nuts still had grease and dust all over them...as did the plugs and other "new tune-up parts"...
AGAIN< refer to your dealer maint log. It indicates ONLY 4 were changed.

leesvet

I'm not a super car person could you give me simple steps of what I need to go get done / do

If your engine IS stalling when you let off the pedal, its probably the TCC that's keeping it alive as it dies/lights/dies again.
You need basic diagnostics.
Fuel pressure.
Ohms the inj
leak down/ pressure stability test
base timing



Thanks

Also, it is not throwing any codes like on the dash[/QUOTE]


You need to learn the "code" system. It will not say CODE or show a number until prompted...
all it will do is activate the SES lite or Check Engine signal. THAT may not STAY lit. That is why YOU need to RETREIVE any STORED codes.
learn how. FSM is the way to do that. All it takes is a paper clip.
Once again, IF there are no stored codes or real time TDC displayed, the ONLY thing that can effect performance is the fuel system.
Refer to the above list of test if you feel that the engine is "not right".

When I see a possible fuel system fault and see only 4 inj changed...I see 4 more than should have been changed as well...make that 8 now.

Always change injectors in sets of 8 and always use the SAME inj that the engine was designed for. IF there are questions on fuel injectors, Call Jon.

eatmydst1234

I do agree with everything you said. I have had an exhaust leak on my car that wasn't audible from inside the car over all the other noises the car makes. But it would pop on decel, mine was leaking at the joint to cat on passenger side of car, there was a hole in the pipe on mine. You could hear with the hood up, or you you sat on passenger side of car. He may not know what to listen for.

HlhnEast

A Factory Service Manual is a wealth of info even if you cant do the repair. You can find out what it takes to do the job and can talk intelligently enough with mechanics so that hopefully they wont take advantage of you. Dont rely on Haynes or Chiltons as they are too generic.

Lee is spot on on the injectors, get a new/rebuilt set from Jon at FIC. He is well respected here for his work and customer service. Give him a call to ask questions.

Lee is also spot on about fueling issues not necessarily setting codes; If the engine isnt running properly and you have no codes, look to the fuel system

Here are a couple of useful links on Code retrieval and related.


http://www.corvettebuyers.com/c4vettes/codes.htm

http://www.corvettebuyers.com/c4vettes/ecm.htm

Baller

On the front of the engine on the passenger side will be the air pump diverter valve (I think that's what it's called). It will have hoses running from the exhaust manifolds into it as well as some wires.

It's function is to pump air into the exhaust when the engine is cold so the cats will heat up quicker. Once they are warm the air from the air pump is diverted down a tube that empties out at the bottom of the engine.

When the valve goes bad it will instead pump air into the exhaust on deceleration causing a lean condition that will cause unburnt fuel in the exhaust to ignite.

Disconnect the wiring plugged into it (I *think* it's the one closer to the center of the engine that is the one). This will prevent the diverter from opening into the exhaust at all.

See if that cures it.

Edit: Mine was going this as well and that's what it was. I just leave it unplugged as it doesn't hurt anything.

Diamondxx

Okay so I went by a mechanic, my Service ABS light came on. He had an OBD1 machine the only one in town and its very vague. It showed that I had a relay problem in my ABS or a power/grounding issue somewhere. He said basically he would have to get it and look at it one day since it isn't OBD2 it isn't very specific. We started it and he listened not a lot, but he said it sounded okay to him. Didn't mention anything about the exhaust didn't want a lot of money to be involved .

Here is an updated video that is better with the exhaust. Watch in HD for best sound quality.



sorry for the late reply I had somethings come up.

DanielRicany

Sounds awesome!