So I had the exhaust done on my '92 F150 5.0 a couple summers ago with all sorts of problems since and I believe it may all be inter-connected and related to a poor exhaust job. Everything is stainless steel and welded nicely but...

Last christmas the cat clogged so bad that the backpressure caused the truck to stall out and would not start up. After a month of trying to find the problem and $1000 in parts later we found it was simply the cat clogged beyond belief. It is now gutted.

I have since noticed that the air tube from the smog pump was welded in AFTER the cat, essentially rendering it useless. Wouldn't this have assisted the cat in burning raw fuel? It has now been deleted. I also noticed that the o2 sensor was placed on one side of the y pipe, rather than where the y pipe meets... would this cause an inaccurate reading due to the fact it is only receiving data from one bank of cylinders? I figured this would cause a lean condition dumping more fuel into the combustion chamber and ultimately into the exhaust and cat.

I'm just about ready to go back and say some non mentionable things to this supposedly highly reputable exhaust shop owner. Its under a 10 yr warranty but I'm thinking now that I have gutted the cat and cut the smog tube off it has been voided.

What are everyones thoughts? Am I way off in my assumptions? What should I do?

 

the A.I.R. tube should have been welded in BEFORE the cat. O2 sensor in the y-pipe one side or the other is fine as long as it's close to the where they meet before the cat.

 

Does a 92 SD have a 02 sensor, or is it just an exhaust temperature sensor?

 

EGT is a diesel thing, all EFI gas vehicles have at least one O2 sensor.

 

The stock exhaust system has 2 cats with the air tube connecting between them so maybe the tube is in the stock location and your muffler shop put the cat in the wrong place. Also note that modern honeycomb cats don't need extra air to work correctly.

No, the EFI system applies the same fuel map to all injectors and on batch fired vehicles those batches straddle both engine banks so it really doesn't matter if the O2 is only seeing one side of the motor.

 

That's good news about the O2, puts my mind at ease. I just figured that a more accurate reading would be received from all 8 cylinders. I will be switching to MAF soon, so I'm wondering if it will cause a problem at that point.

I'm not a huge fan of deleting smog equipment but the gutting of the cat was necessary to get the truck running and I just haven't put a new one in since... might just leave it.

 

From the factory the AIR tube goes in between the two cats. I'd say that the cat was either bad/defective or the truck is running rich. What kind of cat was it?

I have heard of guys running true duals and just putting the O2 sensor in just one bank or exhaust pipe and they say it works fine. I personally just don't see how it can, when its only reading off of half the engine.

 

The job of the o2 sensor is to sense either excess oxygen due to poor combustion (rich) which will also result in unburnt fuel in the exhaust stream, or little oxygen in the exhaust stream from to much oxygen in the combustion chamber creating too much heat and creating NOx gas(lean). If it measures lean or rich mixture then the eec adjusts, it has no provision to measure airflow or how much exhaust is passing by it(one pipe or two) and assuming that both sides of the engine are running very similar it works the same way on true duals as it would on a single pipe