I recently gutted my catalytic converter on my 91 3.1L and put it back on the car and now the car will run very rough or not at all.
I checked the plugs which were all fouled and soaked in gas and it seems that the injectors are loading more fuel than needed. After I blew out all of the plugs, started the car, and idled just fine, then I took the car down the street and it shut off at the stop sign as soon as I pressed the gas pedal. Can anyone offer me insight as to how or why this is happening so that I do not have to order a new catalytic converter?

 

Welcome aboard Langdon.

As the older OBD 1 cars do NOT use a post catalytic convert O2 sensor, there's no way for the car to "know" what you did. There may be a slight decrease in backpressure, but not enough to cause the issues you are describing.

My guess would be something happened with the O2 in front of the cat. You damaged it, didn't get it plugged back in well, it didn't seal well and is leaking air (oxygen) into the system, or something along those lines. At least that's where I'd start looking.

Is your check engine light on?

 

My check engine light only comes on after the car shuts off on its own, but then when I start the car back up, it is gone for the few seconds that the car is running before shutting off again
The O2 sensor in front of the Cat was recently replaced and seems undamaged.
Could this maybe have anything to do with vacuum leaks?

 

When you put it back on the car, you didn't do anything incredibly stupid like hooking up a welder and welding the cat back on, without disconnecting the battery, did you?

The cat doesn't matter. You could take it off completely and leave the pipe open and it'd just be obnoxiously loud. Something else is going on.

 

No, I did not weld on the car with the battery still connected lol
The car has had issues with running rich before but every single sensor on the car has been replaced and it was only a very very small issue recently. Maybe gutting the cat made the existing problems worse?
I've been working on this car for a year now and cannot trace down the problem.

 

Changed the fuel injectors yet? V6s have the same troublesome Multec injectors as later V8s. My beater 91 V6 had about 20 different injectors in the 7 years I drove it. That was back when FWD 3.1L GM cars littered the junkyards, it was easy to grab a fuel rail or two and keep spares for when an injector got "funny". Now, I'd probably just replace them with a new set as preventive maintenance.

 

Why gut the cat? Fix the issue, enjoy the air you breathe.
You the same type of person who thinks disabling EGR is a good thing?
Carry on, mercy.

 

The V6 cats like to fail and melt the carpet. I've owned a handful of 6cyl thirdgens and have yet to see one with the original cat.

 

This helps the guy. Nothin like a good lecture to get your car runnin right. Geesh.

 

Geesh, figure out why it wasted the Cat, right?...or let's just let it run rich for?>?? Or let it run rich and waste the engine, my advice was spot on, yours?

 

Re: advice...

Oh wait, you gave none...move along please, you're in the way.

 

What useful advice did you give him? Yea, none.

He never stated why he gutted the cat, but from the original post it sounds like the improper running was at least a new issue after that. Even if it wasn't, if the cat's monolith is melted down or broken and blocking the exhaust it might be very difficult to get the rest running right without clearing that first, and I damned well wouldn't put a new one on without fixing the problem first. While at stock power levels it's easy to find a cat the flows enough not to be a major restriction, at higher power levels it is worth a few HP, and although you can use egr to manage detonation, this era was full of bad implementations that didn't do much of that and mostly just caused surging at cruise speeds. These and other reasons are legitimate reasons why someone with a clue would disable/remove either.

As far as the original problem, if you had a bad running engine and remove the cat made it worse I'd look at fuel delivery problems. If it ran fine and removing the cat made it worse, well that's not likely, if anything if the engine is OK then removing the cat will make it run the same or better, so you're looking for an unrelated problem. It sounds like you're saying that it runs fine when cold and then runs rich when warm- that implies that it's going rich when it tries to go closed loop, which means that you likely have an exhaust leak introducing outside air before the O2 sensor (or an open pipe very close behind it) or a bad O2 sensor. Although either bad enough to prevent it from running would typically set an engine code. That makes me suspect that there are multiple other things also wrong with it adding up to a badly running engine. You mention vacuum leaks, typically they can cause anything to run funny and be hard to diagnose (although in most cases the car will run lean except in special cases like if the FPR vacuum line is broken). Go through and replace all the hoses, gaskets, tighten any loose bolts... before wasting time looking for other things, a badly maintained car can become an instant piece of **** when people start throwing parts/fixes at it rather than fixing what is actually wrong. Same goes with the spark plugs, foul them a few times and no amount of cleaning will make it right, you need new plugs.

I think if anyone is going to give you a more accurate diagnosis you need to be clearer with your description:

1. what was it doing before messing with the cat?
2. why did you gut the cat?
3. what was it doing after messing with it?
4. what kind of shape is it in/known problems?
5. is it different when hot/cold?
6. when did it start?
7. etc...

 

Thank you for the useful information, a few months before I obtained the car the previous owner replaced all the sensors and injectors(with aftermarket) and a plethora of other miscellaneous things because when he got the car it did not run. It did not run right or as close to normal as possible until right before I got it and it was still running rich (with the cat). The car does not run any different whether it is cold or hot and it ran really well for about 6 or 7 months. then after I gutted the cat, this started happening which is similar to what the car was doing before I got it. (The cat was the original cat and when I took it off, it looked completely clogged.) When the car would start cold it would leave a black streak where the exhaust ran out on the concrete almost like rolling coal. I gutted the cat because I felt that it would help with the flow but I am ignorant about the entire car other than basic stuff. Many have told me it is a troublesome system with lots of problems but I figured I am just ignorant about it.

 

Well...What I said was find out the issue.

Next, re-read the title of the post.

Questions?

 

Actually you said: You never said to find out the issue. And I do have a question: How does, and I quote again, "enjoy the air you breathe." give him help to get his car running?

Bonus question: How does your question: "You the same type of person who thinks disabling EGR is a good thing?", give him help to get his car running?

Nothing I have stated here has, in any way, knocked or denigrated your post about wanting clean air. I am just asking questions because you asked if there were any questions.

Now, as for me, I live in a state that has no emission laws for checking and requiring factory emission equipment. So, I would remove my cat. I am instead going to put on a high flowing cat, and have already removed all of the smog pump crap.

 

Well, based on what you said it's unrelated to messing with the cat, but not really enough info to tell you what it is. Throwing sensors and crap at it without knowing what's wrong is really pretty stupid, even if it gets things running. With these cars worse than some because there have been a few people with issues with "new" sensors giving the wrong readings and some disagreement what pn's will work correctly.

If it's really that bad and you're really not getting a check engine light, that's weird. My top suspects would be to check EVERYTHING in the ignition system, replace the plugs (are they evenly fouled or are some worse than the others?), and check to make sure you don't have a leaking/ruptured diaphragm in the fuel pressure regulator, also check the fuel pressure but that would be pretty odd if it was too high, which is what would cause these symptoms. Honestly, these cars are not that complicated, someone that knows what they're doing would likely figure it out quickly if they saw it. Honestly, if that doesn't find something then I suspect that something has been replaced with an inappropriate part in it's history and you'll have to figure that out (like does it still have stock injectors? Any chance someone stuck oversize injectors in it without tuning it? Swapped cams without tuning for it? That kind of thing...)

 

LOL. Idiot.