I replaced the old cat on this 1995 blazer, along with the muffler. I've changed out the FPR first and then another CPI unit. I have a very strong fuel smell from the exhaust and the cat turns glowing red after about a mile of driving or less and gets the muffler hot enough that there's something dripping onto the muffler from above/inside. When it is being revved up by a friend, I can feel the pressure building up from the exhaust pipe. Cat won't get red at idle, just when out on the road. When I turn the key to start, most times it starts right up, but lately I've been having to give it a pump at the floor to get it started or it won't start, usually just when the engine is warm. Spark plugs are normal, no fouling whatsoever. Checked the majority of the sensors for voltage and operation and they check out. Haven't checked the O2 sensor. Haven't totally checked out the fuel system. When accelerating, sounds like "buh, buh, buh, buh" like it's really struggling. Oh yeah, and this is the second EGR valve I've tried too. I've pulled the plenum about 10 times now. The only indication of a fuel leak is where the nut kit attaches to the manifold. On the inlet line, looks like a drop or two of fuel coming from the junction and this only comes from sitting overnight. Don't see it after driving. Am intending to get a fuel pressure tester to check the pressure. Can a O2 sensor cause such problems if its bad? Would disconnecting throw it into a closed loop and give default values? Any other ideas?

 

It is possible that you just got a bad cat. It is also possible that you still have a fuel leak causing a rich condition which will waste a cat if left alone.

I would start with a fuel pressure check, making sure to watch the pressure leak down after you have first turned the key on to prime the system, then turn the key off and observe.

 

Does the cat have its heat shields on, a cat can get up to 900*C or 1652*F.

 

Does have heat shields. What just seems weird is all the problems with the CPI I've read over time, you hardly ever hear about the Cat glowing red. Maybe their cats were already ate up. The old one on this blazer looked to melt right down the middle, then starting falling apart from there. I don't know. I plan on doing a pressure test shortly. Could there be a lot of fuel sitting in the cat from the last CPI leaking. How long would it take to burn off? What happened was, I took the blazer on a test drive (about fifteen miles) after installing the new FPR and cat. I guess it built up enough back-pressure that it blew a hole in the clogged up muffler from the chunks of old cat. I checked the internal back side of the cat when I put on the new muffler and it still looked fine. Don't know about the front portion. I also checked the rest of the lower exhaust to make sure of no obstructions. Nothing really has changed about the performance of this thing since I've bought it. Always feel like it's missing at idle (very slight) and then when I pull out of the drive, I get the stumbling under acceleration. You get it up to speed and it drives fine. Just idle and acceleration when it has problems, and of course the glowing cat after only one mile. Only recently did I get the no start unless I pump the pedal while starting. I'll post back shortly with the fuel pressure.

 

About to head out to get the gauge for the fuel pressure test. I just got back from the garage where the blazer is sitting. I was finally able to get some codes from this thing, being an OBD I, by jumping terminals 5 & 6. The codes I got were:

22 - Throttle Position Sensor
34 - MAP Sensor - Sensor Signal Voltage Low

Could either of these components cause the running rich conditions? I'm going to go ahead and run the pressure test for S&G's, but i really think I'm looking at something else here.

 

The fuel pressure held with the key on engine off at 57. With the engine running @ idle, the needle "flickered" from about 52 - 58. With the key off, the pressure held at 56-57 for about 15 minutes at which time I released pressure. Checked my plugs again and noticed that cylinders' 3 & 5 plugs are washed with fuel. All others looks normal. Am I looking at bad poppets? I pressurized the system with the poppets out of their holes lying on clean shop towels and noticed no leakage. So how are they dumping so much in those two cylinders with the engine running? Any ideas?

 

Pressures look good. It is possible that the poppet nozzles on 3 and 5 just are not firing properly.

The way the CPI system works is there is one centrally located electronic injector. When it opens, line pressure is fed to the poppet nozzles located down in the intake runners, opening the poppet nozzles. The poppet nozzles are rated at somewhere between 48 and 52 psi.

I would bet that if you were to energize the injector with the fuel pump powered, those two injectors would not have a very good spray pattern. That wouldn't cause the cat to glow red though. It just would mean that the fuel would not be properly atomized, affecting power on those cylinders affected.

 

So does that mean I may have spark problems on 3 & 5? (Distributor? Coil?) How would I begin to check that? The plugs look like if they have fired, they may not be doing it very much. Or maybe bad valves (springs)? But this thing has like perfect pressure readings for its mileage (246,XXX). 2 @ 175 (not 3&5) and the rest 180.