Backfiring, loss of power

Tiny
ROACH.SPJR
  • MEMBER
  • 1991 FORD F-450
  • 7.5L
  • V8
  • 2WD
  • AUTOMATIC
  • 175,000 MILES
I have a 1991 - 34' motorhome with F-450 super duty 7.5l. I had it into a mechanic for some transmission hose repair because I thought that was the problem. After getting it fixed, on the way home I learned the catalytic converter was also gone. Neighbor cleaned the guts out of the catalytic converter (it has two large connections for intake and exhaust and two other connections with pipes attached, not sure what for.) And it seemed to run fine. Drove it 50 km and it started to backfire while decelerating, then lost all power as though the catalytic converter was still plugged. Most people tell me that the catalytic converter is not the problem, others tell me that the catalytic converter on this size needs the back pressure (perhaps for those other two connections) and cannot have the guts removed. Also but may not be connected, the automatic overdrive no longer works. Any ideas?
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Sunday, April 14th, 2019 AT 1:03 PM

3 Replies

Tiny
ASEMASTER6371
  • EXPERT
Good afternoon,

Gutting the converter was a bad idea. You need the converter for emission.

As far as the issue, yes, it could still be the converter as you cannot get all the guts out of it. From him gutting it, he may have missed a lot of broken pieces and they may have lodged themselves in the outlet not allowing the engine to breathe.

I would have a shop check the back pressure of the exhaust. I would not rely too much on peoples opinions who do not work on these units.

https://www.2carpros.com/articles/engine-backfires-while-running

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Roy
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Sunday, April 14th, 2019 AT 1:30 PM
Tiny
ROACH.SPJR
  • MEMBER
Thanks, although I do understand the environmental impact of removing the internals of a catalytic converter, and I do intend to replace it. What I'm concerned with is the mechanical impact of removing the internals, I'm trying to determine if this is the only problem or if there are more. As I said, this catalytic converter has four connections, two large (Inlet from engine, outlet to muffler) and two smaller connections about an inch in diameter on the sides of the catalytic converter. What is the purpose of these two additional pipes? Because there is no longer a back-pressure over the catalytic converter. Could this be the problem? Before any of this happened the engine idled smoothly now it hunts back and fourth a hundred or so RPM. The thing is, the last time I tried to get this corrected it cost me over $3,000.00, I drove 50 km for a camping trip and thankfully had CAA to tow me home.
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Sunday, April 14th, 2019 AT 3:19 PM
Tiny
ASEMASTER6371
  • EXPERT
They are air pumps connections for the air pump on the motor.

You need to have someone check this to confirm.

Roy
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Sunday, April 14th, 2019 AT 3:28 PM

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