Backfiring through the exhaust - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tex_waco_usmc · 06-27-2013, 10:18 AM

At idle and low rpm the 86 with TBI 350 from an 87 is backfiring through the exhaust. I am thinking it needs a basic tune-up but what else should I be checking???

lunchbox99 · 06-27-2013, 11:45 AM

could have some carbon on the exhaust valve seat, might want to do a leak down on that cylinder, how many miles ??

manimal · 06-27-2013, 12:02 PM

Pull your plugs and look for carbon build up, but in the past when I had issues like that it was a burned exhaust valve. When the fuel/air is lit,it would back fire through the exhaust.

mrolds88 · 06-27-2013, 02:07 PM

Check plug wires also. If you have one thats worn, it can either ground out or jump to the next wire, firing it also. easy check in the dark.

tex_waco_usmc · 07-01-2013, 09:31 AM

Quote:

Originally Posted by lunchbox99

could have some carbon on the exhaust valve seat, might want to do a leak down on that cylinder, how many miles ??

Forgive my ignorance, but what is a leak down and how exactly is that done?

The drivetrain has 88K miles on it since it was new in 1987... Plugs didnt have carbon built up on them but did appear to be factory! LOL... Wires felt hard and had no ellacticity (sp?) to them... Ran out of daylight yesterday, going to finish the last three plugs and wires and believe it or not the wires I bought didnt come with a coil wire!

06-27-2013, 10:18 AM	#1
tex_waco_usmc Project Heaven in my 67!!! Join Date: Jan 2009 Location: Bosqueville, TX Posts: 899	Backfiring through the exhaust At idle and low rpm the 86 with TBI 350 from an 87 is backfiring through the exhaust. I am thinking it needs a basic tune-up but what else should I be checking???

06-27-2013, 11:45 AM	#2
lunchbox99 Registered User Join Date: Mar 2011 Location: Medford, Oregon Posts: 33	Re: Backfiring through the exhaust could have some carbon on the exhaust valve seat, might want to do a leak down on that cylinder, how many miles ?? __________________ 79' GMC stepside...the money pit! 355 aluminum partoit heads 2.02,lunati 268 flat tappet,comp roller rockers 1.6,hi-tech torque link intake(Jim McFarland),electric water pump,650 holley double pumper,msd 6al,msd street fire dizzy,doug's long tube headers(ceramic),3" exhaust(flowmaster 40)

06-27-2013, 12:02 PM	#3
manimal Registered User Join Date: Oct 2006 Location: Southern Kalifornia Posts: 3,066	Re: Backfiring through the exhaust Pull your plugs and look for carbon build up, but in the past when I had issues like that it was a burned exhaust valve. When the fuel/air is lit,it would back fire through the exhaust. __________________ ------------------------------------------------------ -Lance 2000 Chevy C2500, 5.7, 4L80e 1999 Suburban K2500, 7.4, 4L80e 1980 Camaro..son's car...PROJECT

06-27-2013, 02:07 PM	#4
mrolds88 Registered User Join Date: Jul 2011 Location: WV Posts: 946	Re: Backfiring through the exhaust Check plug wires also. If you have one thats worn, it can either ground out or jump to the next wire, firing it also. easy check in the dark. __________________ 72 GMC C2500 402/Th400 first truck (still have) 77 GMC C3500 CC dually Sold 70 C50 dump truck "Rusty" 87 K10 Suburban Sold 93 K2500 xcab 6.5TD 96 GMC K2500 Suburban 6.5 TD



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