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Backfire through carburetor

Tiny
CRAZY CRACKER
  • MEMBER
  • 1986 BUICK CENTURY
  • 2.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
Okay, first I had no fire to spark plugs so I changed the coil pack distributor cap, the rotor and the ICM. Now when I try to start it and press the gas it backfires in carburetor and starts a fire. What can it be?
Monday, October 23rd, 2017 AT 9:55 AM

16 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
Have you checked to make sure all the spark plug wires are routed correctly? That could cause your issue if there not routed correctly.
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Monday, October 23rd, 2017 AT 6:39 PM
Tiny
CRAZY CRACKER
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  • 10 POSTS
Yes, used a diagram found on internet to connect plug wires. Could bad temperature sensors cause this problem?
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Monday, October 23rd, 2017 AT 6:52 PM
Tiny
SATURNTECH9
  • MECHANIC
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No, a bad temperature sensor is not going to cause a back fire through the carburetor that is miss routed spark plug wires or it is out of time or the engine is really flooding out.
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Monday, October 23rd, 2017 AT 6:57 PM
Tiny
SATURNTECH9
  • MECHANIC
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So what happened that lead up to these events before you replaced all these parts? Tell me a story.
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Monday, October 23rd, 2017 AT 6:59 PM
Tiny
CRAZY CRACKER
  • MEMBER
  • 10 POSTS
I parked it on a Monday night and then on Tuesday morning it would not start all it did was crank but not start. So I check for fuel to carburetor and I could see it spray into carburetor but not start. So I checked for fire in which there was no fire coming to plugs so I changed coil pack and still no spark. Then I removed distributor cap and found rotor was melted on the side so I changed cap and rotor. That is when I tried starting it again and car started sputtering and when I press gas pedal fire shoots up from carburetor. I thought my friend had put the new ICM in, but I found the new ICM in my toolbox. Do you think the old ICM could cause this problem?
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Monday, October 23rd, 2017 AT 7:11 PM
Tiny
SATURNTECH9
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No, you would just have a spark issue a lack of or intermittent spark if it ran fine before. I highly suspect something is up with the spark plug wire routing. Sounds like the cap and the rotor was the original issue with the spark issues. I know you said you checked the routing and you said it was fine, but I have been told that before and it ended up being what I suggested that was already checked.
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Monday, October 23rd, 2017 AT 7:18 PM
Tiny
CRAZY CRACKER
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  • 10 POSTS
Okay, do you have correct firing order?
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Monday, October 23rd, 2017 AT 7:20 PM
Tiny
SATURNTECH9
  • MECHANIC
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I posted the firing order and spark plug routing on the distributor cap.
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Monday, October 23rd, 2017 AT 7:25 PM
Tiny
CRAZY CRACKER
  • MEMBER
  • 10 POSTS
So number one wire goes to the cap point front closest to drivers side and number three goes front side closest to passenger side.
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Monday, October 23rd, 2017 AT 7:33 PM
Tiny
SATURNTECH9
  • MECHANIC
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Yeah one, three, four, two, is that what you have?
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Monday, October 23rd, 2017 AT 8:00 PM
Tiny
CRAZY CRACKER
  • MEMBER
  • 10 POSTS
I think that is the way I have it, but it is after ten at night so I will have to double check tomorrow after work around 6:00 pm and then relay my findings to you. Thanks for all your help, tolerance and patience to a shade-tree guy.
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Monday, October 23rd, 2017 AT 8:05 PM
Tiny
SATURNTECH9
  • MECHANIC
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You are welcome. That is what we are here for. Talk to you soon.
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Monday, October 23rd, 2017 AT 8:19 PM
Tiny
CRAZY CRACKER
  • MEMBER
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Good afternoon, I checked the plug wires and yes they are correct. I am going to get new plugs and wires later this evening.
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Tuesday, October 24th, 2017 AT 2:08 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Okay let us know what happens.
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Wednesday, October 25th, 2017 AT 7:02 PM
Tiny
CRAZY CRACKER
  • MEMBER
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Changed plugs and wires still doing the same
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Thursday, October 26th, 2017 AT 8:05 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,959 POSTS
It sound like you may have a camshaft or valve issue. Can you do a compression test to see whats going on? Here is a guide to help you

https://www.2carpros.com/articles/how-to-test-engine-compression

Please let us know what happens so it will help others.

Cheers, Ken
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Friday, October 27th, 2017 AT 11:42 AM

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