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GM 454 Backfires


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#1 timinclyde

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Posted 09 April 2014 - 01:56 PM

I have a 95 Bounder 28 with GM 454. I bought it used and discovered too late that it back fires under load during a hill climb. If I back off it stops but I also end up dropping down to 40-45 mph at times.

 

I have had several shops look at it and can't find the problem.

 

Any suggestions???


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#2 DickandLois

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Posted 09 April 2014 - 02:29 PM

Tim,

 

Welcome to the FMCA forum.

 

Good old 454's. Start by checking the vacuum advance unit mounted on the distributor. One needs to remover the Cap and the rotor to get a good look at at things, just be real careful not to pull off any of the plug wires if your not real familiar with the firing order of the cap connections.

Then connect a section of vacuum hose to the vacuum assemble, located on the passengers side, right side of the distributor. Pull a vacuum with your mouth, does the rod inside the distributor move in and out?

 

If not then the vacuum advance will not work. should everything work, then check the mechanical advance system. That is the system with the 2 springs one on each side are good and that the arms the springs are connected to mover freely in one direction and back again when released.

 

A drop of oil at each pivot point is good job while the rotor is off.

 

Post back your findings !

 

Should you not be familiar with this type system, seek some help.

 

Rich.


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#3 dave111451

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Posted 09 April 2014 - 04:57 PM

could also be caused by cracked or broken vacum hose.What condition are plug wires in ?

they eat plug wires due to the way plugs are nestled close to exhaust.    good luck

                                                                                                                              dave


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#4 kaypsmith

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Posted 09 April 2014 - 07:40 PM

All of the above are good. My first was a Southwind with the 454, my last resort was to go a high performance shop and purchase a very expensive set of plug wires, that was my final solution, and it work for me.

BTW, I had replaced with factory replacements three times before, with no good results.


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#5 hermanmullins

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Posted 10 April 2014 - 05:45 AM

This sounds like a need for an old Sun Diagnostics Machine. Scope and all, also a timing light. Find a shop that has a much older mechanic. He or she will have a vast knowledge older engines.

Herman
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"Fair winds and Following Seas"

Herman & Bobbie Mullins, F302225
Whitewright, TEXAS
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#6 thomasp

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Posted 10 April 2014 - 11:46 AM

I had the same problem, the shop told me it was the "stator". I do not now what that is, but that fixed the problem.


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#7 DickandLois

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Posted 10 April 2014 - 02:50 PM

Herman, Your making me feel old ! Not that I'm not, just got here allot faster then I thought I would !! :D :D

 

Rich. B)


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#8 WILDEBILL308

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Posted 12 April 2014 - 10:36 PM

After you have checked that the vacuum advance is working and set right look for vacuum leaks under load. A lean mixture will cause backfiring and missing. Have you checked the ignition module? Hear are a couple of links that might help.

 

http://www.summitrac...e-size/7-4l-454

 

 

https://www.youtube....h?v=OKCQPlr2k6c

 

Bill


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2003 Bounder 38N
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