Catalytic Converter???

[jeephack]

Recently, one of my Comanches has developed a severe backfiring problem.  Almost to the point of being undriveable.   1987  4.0

Fuel pressure is correct.  Spark is consistent.  New plugs.  Problem is so bad that I even went through the procedure to make sure  the

distributor was installed correctly.  I started it today and held it at high rpm for a couple of minutes.  Backfired the whole time.  

Afterwards, I noticed that the catalytic converter was extremely hot and smoking.  Smelled terrible also.  My question is, can a

clogged catalytic converter cause this kind of backfiring and terrible idling?

[onlyinajeep726]

Clogged cat could be the culprit.  Time to do one of Cruiser's Renix tips, #16.

 

16. Vacuum test for exhaust restriction

Your vacuum gauge should come with an instruction booklet outlining the procedure. Hook the vacuum gauge up to a source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum. Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle. Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a
second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

[jeephack]

Thanks onlyinajeep, I'll have to try this "IF" I can get it to idle long enough.  Thing is running so ragged

that it cuts off if I try to let it idle.

[onlyinajeep726]

You're welcome.

 

Where are you in NC, by the way?

[dasbulliwagen]

My experience with clogged converters is that they do NOT produce a backfire. They choke the engine speed and power at higher RPMs and in one of mine made it whistle through tiny gaps around the clamps as pressure before the converter increased so much that the exhaust woud find any way possible to get out. When Ive had backfires it was because of a burned exhaust valve, or you could have a stuck open injector loading the converter with fuel causing it to overheat and eventually meltdown. Just a few thing to think about.

[jeephack]

You're welcome.

 

Where are you in NC, by the way?

Cove City.  Know you've passed by the exit many times on 70.  

[jeephack]

My experience with clogged converters is that they do NOT produce a backfire. They choke the engine speed and power at higher RPMs and in one of mine made it whistle through tiny gaps around the clamps as pressure before the converter increased so much that the exhaust woud find any way possible to get out. When Ive had backfires it was because of a burned exhaust valve, or you could have a stuck open injector loading the converter with fuel causing it to overheat and eventually meltdown. Just a few thing to think about.

Thanks.  I'll look into these possibilities.  Funny thing is, it was running fine but it sat up for a month or so without being started.  When it was started again, the 

miss/backfire was there.

[onlyinajeep726]

Yea, I have.  Been a while though...  Pass it on the way to Atlantic Beach.