Nihilanthic

V6 (3.1, its a 1991 RS) was backfiring and sputtering and dropping RPMS for a few secs if you gave it too much throttle.

We (me and stepdad) replaced the whole ignition system except the plugs and wires, TPS, IAC, etc, and it didnt totally go away.... then the headgasket blows!

So, while we're worrying that the heads bent or cracked, he digs around and somehow figured out the cat being clogged up was causing it - the EGR looked like someone used it for a turbo manifold (or something, sheesh).

Well, cant replace the cat yet, so we just take the O2 sensor off the CAT. Its UNGODLY LOUD but it drives ok now. Too bad my ears are still ringing... so, I figure lets take the cat out and get it over with..GUT the damn thing.

So, after a one day struggle with the CAT converter involving a dremel tool and about 5 cutoff wheels, we put a slit in the part of the cat that slid over the y-pipe (previous owner felt like having a C-clamp on it hard as hell, ) and we gutted it completely with a hammer and a broomstick.

Sooo, pop it back on, damn proud of ourselves, we take it around and it backfires so loud people came running thinking something was going down! The NEW EGR is blown out from driving around with the "O2 sensor ventilation bypass" 'modification' and the CAT still essentially clogged to hell (there was NOTHING at the end of the muffler!), but still, the CAT is now TOTALLY empty. and theres a new headgasket on the pass. side bank.

So, what is it? The fact that the O2 sensor isnt hooked up? (new wire was just a little too short to reach the harness from the engine) Or is it the busted open EGR? Or is it something else with the (essentially brand new) spark? Or is it the fuel system? EDIT: the o2 sensor is now in the cat, just the wire isnt hooked up.

This is basically the only car I have to get my family to work and run my paper route with, I really wish it didnt backfire and pop like a old truck... and sometimes just stall out and need a cool down! At least Im not blowing out headgaskets anymore... oy.

FWIW, before this the car was reliable as hell, especially considering the previous owner didnt take care of it at all.

yupitsdadsbird

change the egr it might be dumpin too much exhaust into the intake........

Nihilanthic

I thought that... but could that cause a huge backfire like this? It backfired like a gun (or a big *** truck) from the cylinder, no flames out the exhaust or anything.

I'll do it and tell ya what happens though it might be a case of stupidity on my part not replacing it after I know its damn well blown out

BTW, gutting the cat really helps in making these 3.1v6's pull. This engine has got to be so corked up its crazy.

Dale

iTrader: (12)

I belive backfire is caused by incorrect timing, or the something to do with the valves being closed at the wrong times.

PhLaXuS

Yeah...the only time I've ever had a backfire with good timing was when my coil was dying. The car would miss several times in a row and then manage enough spark to burn what was left in the cylinders and exhaust pipe. BOOM! and big black smoke rings. New coil fixed that!

Another very likely thing is if you mixed up two plug wires...but then again that would just be bad timing as well...just REALLY bad. My bet's on timing.

Nihilanthic

Havent been able to touch it yet, but the coil was replaced before I made that post. Today I should get that damned O2 Sensor plugged in, the problem is being able to reach far enough to actually get it all the way in!

Could the spark control module be causing all of this? Coil is new, dizzy is new... and when its cold, I can stomp all over the gas, give it WOT and ride it out to redline and its fine... so how could it be the timing?

Im just absolutely amazed at how it can start sputtering and then backfire like a damn rifle because of the O2 sensor. If it IS that simple Im going to laugh a good one... and then wonder why GM gave us so little slack to try to plug in the O2 to the wiring harness.

Nihilanthic

Ok, plugged in O2 sensor. It was still warm from this mornings paper route, so I had to dodge the y-pipe... and to get the room to get my hand under there, I drove it up on a curb, then stuck my bottle jack under it, jackstand, got under, etc.

So, I push it in, squeeze it shut, and damn proud of myself go drive it around. It did the same crap as before! One time it stalled out, and when I restarted it it sounded like someone shot a gun it backfired so loud.

I can HEAR the damn EGR its so loud, so I might just block it off. As far as the extreme backfiring and studdering... Im totally confused. The timing isnt off at all. Its fine when cold and at idle, TOTALLY. How could the timing be messed up when it gets hot, but not when cold or at idle?

I replaced the coil and dizzy, is it the spark control module?

Nihilanthic

Ok... timing is FINE when cold (I whomped on that damn thing, really pulls harder with the gutted cat) and the o2 sensor is plugged in, and I am getting *NO* codes at all.

When its hot, it still ****s up. I figured trying to seafoam it cant hurt and well... it probably didnt hurt anything but it didnt amelorate the problem.

Its backfiring out the exhaust, LOUDLY like a cannon. The coil and distributer are new. I did see the EGR leaking like a **** when I seafoamed it, btw, smoke billowed rather visibly.

So... EGR is leaky, when hot it backfires out of the exhaust, but the dizzy and coil are new. Could the spark control module be acting up? Could it be my plugwires and plugs?

bru333

You need to fix that egr leak.
If the egr is letting air into the exhaust from a leak, the O2 sensor will indicate lean and add fuel that won't be burned in the engine.
The ecm only uses the O2 info when it is hot, so this would explain why it runs ok when cold.
With a '91 you'll throw a code if you just block the egr off.

Nihilanthic

Makes sense, but why did it do this before when the O2 wasnt even hooked up? And uh... did this have anything to do with my CAT being blocked up?

Or those few days where I had the O2 sensor out and vented my exhaust through the O2 bung while the cat was clogged before I unclogged it? lol.

bru333

Don't know.
But, I do know it is useless to try and troubleshoot a problem without fixing things you find along the way.
It may be a combination of things.
For example, my car was running terrible, turned out to be 2 bad sensors and dirty/leaking injectors. With each fix it would run better, and lead me to the next problem.

Nihilanthic

Well, I just heard that the fuzz is after me because I disturbed the GF of some cop making noise seafoaming the car (drizzling into the vacuum line going into the intake that was hooked up to the EGR) and making a buncha white smoke... and backfiring :P so testing this is going to require a trip to a big empty parkinglot while still cold!

BTW - is there any way to keep it in cold mode, like pulling a sensor somewhere? The fan is controlled by a hermostat I stuck into the radiator itself, seperately - even runs when the car is off. I just recently picked up an abandoned saturn wagon that had a Coolant Temp Sensor fail and thus was in warmup mode forever... but that was bad because the radiator fan never came on and it blew a hose (and burned my stepdad pretty bad). I replaced it and its PERFECT now, save for some only-from-a-saturn issues with 'popping' in reverse like Im learning how to drive a clutch that I'll deal with soon with some lucus and a fluid change.

Anyway, I wasn't speeding, there was no way it could even get up to 30 without stalling/shooting out a LOUD backfire/sputtering, but whatever. Part of me wants to part it out or sell it to someone whose willing to fix this (and doesnt live with condo commands who steal his satellite dish, tow his other car because it was too ugly, and call the cops because of a backfire!) and the other part of me wants to put a v8 in it.

So yeah, injectors are seafoamed, theyre not dirty... it has to be the EGR, or *SOMETHING* that is messing up the timing... spark control module. The O2 sensor is in and there is no check engine light thrown up at all... guess I gotta dodge the Cop's GF and eliminate down to what it is.

DeanE

It is the EGR. Mine is actually starting to stick and it will cause a very minor backfire when I first crack the TB open. Idle is going to hell and the power brakes is slightly hard at idle.

These EGR setups on the exhaust manifolds is a very poor design because the rubber diaphram up underneath them is so susceptible to tearing for the heat rising off them. I should have just put an new one on when I installed the headers a few months back instead of using the one off the stock manifolds.

hopefully when I get a new one it will last me longer than about 1-2 years like all the other have (and I am using the good AC Delco ones not the crappy Wells EGR's) Since I am now running ceramic coated headers.

Nihilanthic

Put on a new park control module (or wtf ever its called) and it runs fine now. EGR is still leaking, gonna fix that next.

Oh, and I think I somehow ballooned out the muffler with a damn backfire! LOL. It sure as hell spat out one of the tips.. the left one infact.

rough

park control moduel ??? Ignition control module ?