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Backfire

Tiny
TOMC12
  • MEMBER
  • 1992 CADILLAC DEVILLE
  • 4.9L
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
Sometimes engine runs okay. It backfires sometimes, and when it does, it sometimes blows the muffler. After getting through the backfire, the engine runs good, and strong. Sometimes it acts as though it is going to stop, and then it may backfire, and run fine.
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Thursday, November 9th, 2017 AT 10:19 AM

7 Replies

Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Often a back fire is cross firing ignition leads, or a burnt inlet valve can also cause this. just to be safe get a compression test done and if that is okay, replace the ignition leads, you may see the problem with the leads where they are bunched together. they can become display a white chalky coating on the leads. also, you can often see the sparks jumping, lift the bonnet at night in a dark place and run the engine, get someone to rev the engine up and down. often you can see the fire works under the bonnet, but do not touch as it is very high voltage +40,000 volts.

Here is a guide that may help

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

Cheers Mark
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Thursday, November 9th, 2017 AT 4:05 PM
Tiny
TOMC12
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  • 4 POSTS
Today engine ran pretty good until about sixty mph. After that seemed to be running out of power and missing as well as backfire, but not as much as usual.
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Friday, November 10th, 2017 AT 2:12 PM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
I would be checking the ignition leads probably high resistance and cross firing. This is where I would be starting.
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Friday, November 10th, 2017 AT 8:46 PM
Tiny
TOMC12
  • MEMBER
  • 4 POSTS
Here's what we've done on the 4.9 1992 Cadillac engine. Map Sensor, Temp Sensor, Plugs, Plug wires, Throttle Sensor, Oxygen Sensor, Converter, Muffler (Blew it) - Can't read these, but looks like Cap, Buttons. Backfires about 6 miles - until it warms up I guess, and then runs good. Made appointment to get new muffler, but afraid to. What now? Thanks, Tom Callahan
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Wednesday, November 22nd, 2017 AT 2:22 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,643 POSTS
It sounds like you have an ignition component that is cutting in and out which fills the exhaust with raw gas. Does the engine run okay with no misfires or cutting out for a short time?

Cheers, Ken
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Friday, November 24th, 2017 AT 6:47 PM
Tiny
TOMC12
  • MEMBER
  • 4 POSTS
YES IT DOES, It may misfire badly for about 6 miles, and then run good. It may cut out any time during this time however. It is hard to determine when it is going to cut out. It backfires terribly. I made appointment to get a new muffler after the oxygen sensor was installed, but cancelled after a backfire episode.

Thanks, Tom Callahan
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Saturday, November 25th, 2017 AT 8:52 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,643 POSTS
I would replace the ignition coil module and pickup coil in the distributor. Here is guide to show you how to do the job.

This is most likely the problem check out the diagrams (Below)

Please let us know what happens.

Cheers, Ken
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Sunday, November 26th, 2017 AT 1:53 PM

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