FlyFast

I hate to ask this question here but the expertise is here.

Can anyone tell me how a clogged cat converter will act.

I have a 91 deville with the 4.9 85k miles. After 5 hours of running hard 75 or better I stopped at a light and the engine stumbled like it was running out of gas. The problem has gotten worse and only happens when the engine is warm an hour or so of run time. I have changed the fuel filter and am considering changine the fuel pump.

The problem only happens when the car had run for a couple of hours. Most of the time it happens going up a hill. The car will now bog down so that it will only run at a fast idle speed 1500 rpm and if you give it more gas it will stumble. Let the car sit for a while and it is ok until it gets hot again.

There are no error codes and when cold the car runs fine. The car is good for an hour or so around town. What do you do take it in and have the exhaust system changed? Anyother ideas?

Thanks

Go Big

I have had the same problem. Had to replace the converter and the problem was solved.

Airpacker

A clogged convertor will always be clogged. It doesn't have to get hot first. What you need to do is verify the fuel pressure when the problem occurs. A worn fuel pump will turn slower when hot and the pressure will drop. The fact that you say it happens on a hill could also indicate that the armature inside the fuel pump is rubbing on the case and slowing it down.

muffman

Yep its either clogged or not. You can take a pyrometer and take temp readings in front of and behind the cat. The temp behind the cat should always be about 100 F hotter than in front. If it is hotter in front than its clogged or the engine is running to rich for the converter to keep up and it will be clogged if not corrected soon. Make sure you get the engine hot before testing. There are also other methods of checking, back pressure test and visual.

Cord

iTrader: (2)

I saw one once. The engine would idle normally, but wouldn't rev. It actually sounded choked.

Sydwayz

iTrader: (1)

Yes, it does sound clogged. Someone should chime in here, but I think all CC are warrantied for 100K miles. When it gets REALLY in bad shape, you will see the CC begin to glow red, and could catch fire. I have seen it happen.

Do you have emissions inspections in your state? If not, I might be tempted just to remove it and hollow it out.

tanned fat looks better

I had a 91 seville that clogged so bad it wouldn't run. The mechanic broke loose the y pipe and it ran fine..............that's how he found it.

SmallPP

I'm an expert with this. Easiest way to tell is to remove your O2 sensor and install a pressure gauge. You can make one from an old O2 sensor and fitting. When I hooked it up to a Jeep with a clogged converter, the exhaust registered 25psi when the engine would start to run out of power. Exhaust pressure should only be a few psi at the most, but usually 1psi or less. You can tell with a vacuum gauge, but you must know exactly what you are looking for. Other items to check are fuel pressure and proper EGR operation. Your situation sounds like a faulty EGR system, as it only activates when the engine is warm, and during medium load such as freeway.

robyw1

Dude I'm gonna shove a potato up your exhaust and watch you go to Midas after you perform your test. The correct way to test a converter is have a shop pressure test it before and after the converter. if they vary more than 3 to 4 percent it's converter time.

Just kidding about the potato thing
Roby

FlyFast

Thanks for all the input. The car is fine cold for about an hour. It only happens running hard or in 107+ degree heat.

I thought it might be the ignition module. You know the thing with the special white grease under it so I changed the: ignition module and used the special grease, the cap, rotor, coil and pcv valve.

We do have emissions and am still considering changing out the cc. I wonder if a bigger one would give me better gas mileage?

I am also looking a buying a fuel pressure tester to check the fuel pressure.

The car is fine for short trips around town but when you need it the most it dies.

Thanks