Bob2.0

Hi,
I've got a 94 coupe that has been running rough. At certain speeds its okay, but there is a very pronounced pulse all the time and I get crappy gas mileage. I changed the opti, plugs, wires, had the resistance checked on the injectors, always run the best gas, and can't get rid of it.

A friend told me to put a piece of paper in front of the exhaust, and on the drivers side, it blows the paper away on the passenger side it sucks it in and blows it out.

What is going on? And how much do you think it will take to fix it?

Bob from the Museum

RED-85-Z51

As i recall, the 94 had a shared main cat, so what it does on one side, it whould do on the other.

But a suck means a valve problem. Be it a burnt valve, bent valve, weak spring, bad seat...whatever.

as long as it is red

Your exhaust system has a front Y out of the manifolds, into a common cat and splits into 2 mufflers. More than likely one of the mufflers is dominant and is pulling air into the "sucking" muffler by way of a vacuum effect. Mash the gas and both sides of your exhaust will blow out. I really don't think you can diagnose an engine problem on the stock exhaust system like you described.

car5car

Check compression and spark plugs.

jmgtp

My 94 has a cat on each bank, no Y into a single cat - I imagine all 94s are the same unless mine is the oddball.

car5car

Do you have separate right and left exhausts?
Mine 94 has 2 cats, then pipes join together, then divide to 2 mufflers, 84 has common cat.

TLS_Addict

As I recall mine has a cat on each side as well....fugly looking things they are!

jmgtp

Yes separate right and left. The car has short tube headers, out of the headers it goes into what appears to be the stock cats, then into an X pipe before the resonator and dual out of the back of the resonator. I never had the stock exhaust. When I bought the car it had the short tubes installed and some rusting out flowmaster system. I replaced everything after the cats with the magnaflow system. The OP might want to check the cats out - if 1 was clogged it seems like it could possible cause this problem.

car5car

Stuck open exhaust valve will suck and show 0 compression.

MK 82

Do a compression check. 94 has true duals.

Tom400CFI

All of the above is wrong. All LTx cars have full dual exhaust w/dual cats. There is no such thing as a "dominant muffler". A clogged cat won't cause the symptoms described.





All of the above is right. Do a compression test. If one is low, then do a poor man's leak down to verify that the exhaust valve is leaking.

-Tom

C5rider

I'd have to agree with Tom. Let's do some checking to find out what the compression is and we can go from there. I think you're homing in on it Bob.

Andy