Author Topic: 86' suburban-misfiring on acceleation  (Read 438 times)

Offline lorax

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86' suburban-misfiring on acceleation
« on: September 28, 2021, 05:02:33 PM »
Hey Chevy guru's, just joined, still tying to navigate this forum site. Let me know if this is right place.
1st I have 86' Suburban 3/4 ton 4x4 350.
trying to fix it up/keep it running.
Just installed "Glass Pack" Dual exhaust bolt on kit from  . Could be a coincidence but after completing the exhaust install, my truck is misfiring when I accelerate.....
Questions are:
1. Can a new exhaust system cause misfiring? I had a major exhaust leak before, but no misfiring....( NEW AMOUNT OF BACK PRESSURE)
2.If just coincidence, what are the most obvious things to check 1st?

I'll start here and see what you all have to say, thanks in advance.

William

Offline Shifty

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Re: 86' suburban-misfiring on acceleation
« Reply #1 on: September 28, 2021, 05:15:18 PM »
Check your passenger side exhaust manifold for cracks, very common problem.

And welcome!
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Offline lorax

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Re: 86' suburban-misfiring on acceleation
« Reply #2 on: September 29, 2021, 03:56:51 PM »
wouldn't it be load if there was a crack?  I will check.....

Offline bd

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Re: 86' suburban-misfiring on acceleation
« Reply #3 on: September 29, 2021, 04:40:42 PM »
The following steps should get you started.  Verify the firing order (1-8-4-3-6-5-7-2).  Check for active arcing between the spark plug wires and the exhaust manifolds (this is accomplished most easily in a dark location or at nighttime).  Make sure there are no cracked spark plugs.  Using a good flashlight, look deep into all of the spark plug wire boots at both ends of the wires.  Look for any greenish discoloration of the terminals or black soot accumulation.  Check the length of the wires for any gray-white ashy deposits, hard spots, or other indications of heat distress of the wire insulation.  How do the business ends of the spark plugs appear?  Are the electrodes rounded and burned back or sharp and clean?  Do the insulators appear fouled with carbon, oil, ash?  Are chunks of the insulators missing from around the center electrodes?  Post clear pics if you are unsure.  How many miles ago was the last tune-up performed?  Inspect the cap and rotor for terminal wear, housing cracks, and/or carbon tracks.
Rich
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Offline JohnnyPopper

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Re: 86' suburban-misfiring on acceleation
« Reply #4 on: September 29, 2021, 08:16:37 PM »
What is the state of the engine relative to temperature when this happens? Both hot and cold? Heat makes a difference sometimes.
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Offline lorax

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Re: 86' suburban-misfiring on acceleation
« Reply #5 on: October 11, 2021, 12:43:43 PM »
Thank you Rich, thats a very good place to start.  one of my suspicions is bad spark plug wires.
If I was to think this through logically. Engine needs Spark, Air and Fuel.
Air seems to be fine. 
Spark- was considering new plugs and wires. made sense to me that the wires could be arcing to some part of the engine. I'll most likely start with this.
Fuel- my thought was it's possible the fuel filter is clogged but seems unlikely. Or that my Fuel pump could be failing. but not sure why it'd run ok at freeway speed and then struggle at side street speeds.
and the wires are in order, they have been on for many years and this problem is only weeks old.

William

Offline lorax

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Re: 86' suburban-misfiring on acceleation
« Reply #6 on: October 11, 2021, 12:47:10 PM »
What is the state of the engine relative to temperature when this happens? Both hot and cold? Heat makes a difference sometimes.

Johnny, it appears to happen when engine is cold and warmed up.....