86 GMC 454 cid. left exh. manifold red hot

luckylk · 11-12-2005, 07:41 PM

Hello, Any Ideas. I have a 1986 GMC 2500 with the 454 engine, no converters but does have air pumps on it and is carberated with 115000 miles on it. It has been runnig poor for the last year and I just let it go. But whe it cooled off it let me sit. It ran rough when cold last winter and better when warm but would take spells when it would cough and cut completly out and slight backfire . When it let me sit It had stalled while idling which was a first it would not restart and backfire pretty good. I though maybe jumped timing. did some checking and timing looked close. cap had one spot of carbon track. replaced and it started but still rough. so replaced plugs and wires which the wires were the main culpret. Still ran a little rough and slight backfire. Decided to pull carb and clean since I had never been off. only slightly dity. Once I put carb back on and runing at high idle while I check things out I notice the LEFT EXHAUST GOT RED HOT IN NO TIME FLAT. I though at first it was because I had vac line off and it was getting lots of air and at high idle. Any Ideas?

chevyguy · 11-13-2005, 11:58 AM

Timing.....

Truck_Man · 11-14-2005, 03:19 PM

could also be abstruction somewhere else in the exhaust on that side, this does'nt have any doublewaled pipes anywhere does it. My dad had a wall inside one of his pipes calapse once that coused this too happen but it was an older vehicle. Is there anyway something could have colapsed or come loose in a muffler and be blocking the exhust.

My escort had something colapse somewhere in the exauhst one time and it would backfire through the intake and not want to run. If your exahust manafold is turning red on one side thats a good indication of blockage in the exauhst on that side.

Im guessing that you have dual exaust on this, if so and you can get it to run for a couple of minutes go to the back and kind of put your hand up by the end of the exhaust pipe on each side and make sure you have good flow, be careful though if it has the tendency to backfire through the exauhst I would'nt do it this way.

The best way to do it though would be to have a back pressure test but you would have to have it towed into a mechanic to have this done.

I think there is a way to get an idea with a vacume guage too, but i dont know what type of reading you would look for on it. Chevy guy would probably know more about this.

luckylk · 11-14-2005, 08:34 PM

I had checked and changed the timeng and it made no difference. I also had checked the exhaust backpressure it seemed ok by feel. I pulled the exhaust down and things still got red. All the local mechanics had different opinions. A stop at the votech school got me the tip. The instructor insisted that the only thing that shoudl make things red hot that I had not checked was the air injection system. (AIR). Turns out this truck has a duel system one for each side. Left side was pumping to much air all the time. Bad diverter valve. That fixed it. Luckylk

chevyguy · 11-14-2005, 10:16 PM

Outstanding. glad to hear it is fixed.

11-12-2005, 07:41 PM	#1
luckylk Junior Member Join Date: Nov 2005 Posts: 2	86 GMC 454 cid. left exh. manifold red hot Hello, Any Ideas. I have a 1986 GMC 2500 with the 454 engine, no converters but does have air pumps on it and is carberated with 115000 miles on it. It has been runnig poor for the last year and I just let it go. But whe it cooled off it let me sit. It ran rough when cold last winter and better when warm but would take spells when it would cough and cut completly out and slight backfire . When it let me sit It had stalled while idling which was a first it would not restart and backfire pretty good. I though maybe jumped timing. did some checking and timing looked close. cap had one spot of carbon track. replaced and it started but still rough. so replaced plugs and wires which the wires were the main culpret. Still ran a little rough and slight backfire. Decided to pull carb and clean since I had never been off. only slightly dity. Once I put carb back on and runing at high idle while I check things out I notice the LEFT EXHAUST GOT RED HOT IN NO TIME FLAT. I though at first it was because I had vac line off and it was getting lots of air and at high idle. Any Ideas?

11-13-2005, 11:58 AM	#2
chevyguy Senior Member Join Date: Sep 2005 Location: ALABAMA Posts: 3,160	Timing..... __________________ When i die, i dont want to walk gracefully thu the pearly gates and turn in a unused body. i want to go sliding thru sideways and turn in a body that has been completely used up.

11-14-2005, 03:19 PM	#3
Truck_Man Senior Member Join Date: Oct 2005 Posts: 213	could also be abstruction somewhere else in the exhaust on that side, this does'nt have any doublewaled pipes anywhere does it. My dad had a wall inside one of his pipes calapse once that coused this too happen but it was an older vehicle. Is there anyway something could have colapsed or come loose in a muffler and be blocking the exhust. My escort had something colapse somewhere in the exauhst one time and it would backfire through the intake and not want to run. If your exahust manafold is turning red on one side thats a good indication of blockage in the exauhst on that side. Im guessing that you have dual exaust on this, if so and you can get it to run for a couple of minutes go to the back and kind of put your hand up by the end of the exhaust pipe on each side and make sure you have good flow, be careful though if it has the tendency to backfire through the exauhst I would'nt do it this way. The best way to do it though would be to have a back pressure test but you would have to have it towed into a mechanic to have this done. I think there is a way to get an idea with a vacume guage too, but i dont know what type of reading you would look for on it. Chevy guy would probably know more about this. Last edited by Truck_Man; 11-14-2005 at 03:40 PM.

11-14-2005, 08:34 PM	#4
luckylk Junior Member Join Date: Nov 2005 Posts: 2	I found the fix see below thanks to all that responded I had checked and changed the timeng and it made no difference. I also had checked the exhaust backpressure it seemed ok by feel. I pulled the exhaust down and things still got red. All the local mechanics had different opinions. A stop at the votech school got me the tip. The instructor insisted that the only thing that shoudl make things red hot that I had not checked was the air injection system. (AIR). Turns out this truck has a duel system one for each side. Left side was pumping to much air all the time. Bad diverter valve. That fixed it. Luckylk

11-14-2005, 10:16 PM	#5
chevyguy Senior Member Join Date: Sep 2005 Location: ALABAMA Posts: 3,160	Outstanding. glad to hear it is fixed. __________________ When i die, i dont want to walk gracefully thu the pearly gates and turn in a unused body. i want to go sliding thru sideways and turn in a body that has been completely used up.

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