Backfire

Tiny
JESTERR
  • MEMBER
  • 1996 BUICK ESTATE WAGON
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 293,000 MILES
My car was backfiring constantly, at all times. I changed the distributor cap, and it was melted across three of the firing points on the cap. I replaced it, and now it is running much better, but still backfires somewhat on deceleration when the engine has been under significant load. I have removed both catalytic converters, and have not yet resealed the exhaust pipes. Prior to disconnecting the battery for this repair, it was giving four trouble codes. They were catalyst efficiency below threshold, random misfire, a code for the EGR Valve, and a code for one of the oxygen sensors(I cannot remember which one). I have owned this car for about a year and a half (It was a junkyard rescue). It already had the random misfire code, as well a noticeable misfire when I got it. The other codes have appeared during the time that I have owned it. I have a picture of the underside of the distributor cap, and can include it if necessary.
Friday, February 9th, 2018 AT 3:35 PM

5 Replies

Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
  • 1,853 POSTS
Backfiring where? Out the tailpipe or back out the intake manifold?
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Friday, February 9th, 2018 AT 4:19 PM
Tiny
JESTERR
  • MEMBER
  • 4 POSTS
I have removed the catalytic converters and have not replaced the pipe yet, so it is definitely not coming out of the tailpipe. Also, I left out on my original post, but my fuel sending unit went out about a year ago. I could not afford a new one at the time, and I worked at a salvage yard, so I paid a shade-tree mechanic to replace it with a used one for me because I did not feel like doing it. He took one out of a 1995 Roadmaster sedan. He told me they were the same, but I did not find out until later that they were not. It is the only used part I have ever put on my car, and I will certainly never do so again. That could be another possible issue.
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Friday, February 9th, 2018 AT 6:54 PM
Tiny
JESTERR
  • MEMBER
  • 4 POSTS
Also, I put it on an OBD II reader, and it said that the engine was running extremely rich on the driver side, and extremely lean on the passenger side.
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Friday, February 9th, 2018 AT 6:57 PM
Tiny
JESTERR
  • MEMBER
  • 4 POSTS
It appears to be backfiring from the driver's side, as best I can tell.
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Friday, February 9th, 2018 AT 6:57 PM
Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
  • 1,853 POSTS
Okay, let me rephrase that. Backfiring out the exhaust or out the intake, or in your case maybe both?
Out the exhaust for the drivers side and out the intake for the passenger side?
Anyhow, fix the banks too lean and too rich and you will probably fix the backfiring.
As far as the fuel level sending unit goes, unless the fuel pump was altered in some way, I do not see why that would be causing this.
Check you fuel pressure and check for a intake manifold vacuum leak on the lean side (passenger side).
If you have individual fuel injectors for each cylinder, smell each spark plug on the drivers side, cause you could have one bad leaking fuel injector causing that too rich and the backfiring out the exhaust on the drivers too rich side.
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Saturday, February 10th, 2018 AT 6:15 AM

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