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Unread 01-17-2013, 05:44 AM   #1
mj86
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1986 MJ Comanche 
 
Join Date: May 2012
Location: Flint, Mi
Posts: 17
back fire

I've changed distributer, plugs, wires, air filter, oil change, tune up. Still getting back fire, any ideas.
Thanks for any help
Mj86

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Unread 01-17-2013, 03:16 PM   #2
mj40
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1989 MJ Comanche 
 
Join Date: Jul 2011
Location: north bay/corbeil, ontario
Posts: 282
double check the firing order- no spec's on the truck???...so i cant give you this info- other than look at the intake for the firing order-4cyl 1342...6cyl-2.8l chev 123456 135 passangerside 246 driverside- make sure to start the wires on #1

check the timing??
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Unread 01-17-2013, 05:40 PM   #3
mj86
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1986 MJ Comanche 
 
Join Date: May 2012
Location: Flint, Mi
Posts: 17
fire order

It has a 2.5L. There is no rime or reason, it does it when it is hot and cold. Sometimes real loud and sometimes soft and sometimes it doesn't do it at all. So confused.

MJ86
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Unread 01-17-2013, 05:43 PM   #4
mj86
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1986 MJ Comanche 
 
Join Date: May 2012
Location: Flint, Mi
Posts: 17
MJ40, thanks for your help. I'm a true beginner when come to working on vehicles.
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Unread 01-17-2013, 06:14 PM   #5
mj40
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1989 MJ Comanche 
 
Join Date: Jul 2011
Location: north bay/corbeil, ontario
Posts: 282
need to know is it backfiring through the exhaust or the intake?
how does it idle/rpm? rough may have a bad intake or throttle body gasket
this link may help just to verify the base timing is ok...
http://www.4wdmechanix.com/Tuning-an...-TBI-Four.html
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Unread 01-22-2013, 04:29 AM   #6
cruiser54
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1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 9,811
There are some vacuum lines just below the throttle body that crack and rot. Also, remove the ground strap from the firewall, scrape the paint off, shine up the connector, and reinstall securely.
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