| Cad 500 backfire through TB [message #371501] |
Sat, 28 October 2023 09:56  |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Senior Member |
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This is just an FYI to all in case it happens to you.
We attended the fall GMCMI conference in Corunna Michigan and had a great tlme. Following the conference we toured Michigan State Campgrounds for about a 2 week period of time. We went from one State Park to another and during that transition from one park to the next I began to notice a backfire through the TB (I am running a FiTech TB). It would happen at RPM's over 2500 with throttle pressures lower than 7 inches of vacuum. Over the 60+ years of being a mechanic, I recognized the symptoms as possible intake valve that was either not seating properly or a actual beginnings of a burned intake valve. Sounded/acted just like it. So following our Michigan trip, I feathered the throttle and made it home with anticipating that I may have to pull the heads for a valve job. The Cad 500 has about 45K miles on this rebuild. Not really looking forward to this as I do not have indoor storage and would be completing the task in approaching cold weather. I decided to check some easy things first. Check things like plug wires, distributor cap, rotor, Petronix pointless ignition, Fitech programing.......etc...etc. So, I made a list and started with plug wires first. I began with plug wire #8, drivers side back of the engine. I found it just barely hanging on to the plug, almost falling off. I pushed the plug wire back on and took the coach for a ride up the Irvington hill. The Backfire is gone. Before we left for Corunna I had changed out the transmission governor which is located directly below plug wire #8.
Lesson learned, sometimes it is the simplest things that get ya. Check the simplest first!
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: Cad 500 backfire through TB [message #371503 is a reply to message #371501] |
Sun, 29 October 2023 06:56  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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I call the easy ones 'quick and dirty'. Very little effort and often they work.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Cad 500 backfire through TB [message #371505 is a reply to message #371503] |
Wed, 01 November 2023 23:20 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I was reading Larry's posting at home yesterday and thinking it was getting cold in here. I checked the thermostat and it was 4 degrees lower than normal. The light was on calling for heat. I went downstairs to the furnace and it was just sitting doing nothing. I remembered Larry's posting and started wiggling wires and cables. Larry's good luck rubbed off and I found a loose connection inside a box housing the Honeywell chimney vent damper electronics. I wiggled it a little and it took off running. That box has not been opened in at least 25 years but now it has a loose connection inside.
Thanks Larry. Your good luck on your coach rubbed off on me. I had it going in 5 minutes and never had to get out a meter or any other tool. I do not know if it is permanently fixed, but I now know where to look if it fails again and it is warm in here.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
[Updated on: Fri, 03 November 2023 18:30] Report message to a moderator |
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