engine backfire.

t-money80

Daily Driver
Mar 2, 2008
33
0
0
Granite City IL
Today when started my car it started backfiring through the exhaust while idling , not constant but intermitently. I pulled the valve covers and checked the rockers and locks all was ok . when i rev the engine and let off its not backfiring , just while idling . could this be caused from a bad coil ? Also the last time i drove the car was saturday and it ran fine . Its a 350 with a H.E.I Thanks.
 

DOUG213XRJ

MalibuRacing Junkie
Sep 18, 2006
4,661
1
38
West, MI
Does it have full exhaust or does it stop at the rear axle ?
 

DOUG213XRJ

MalibuRacing Junkie
Sep 18, 2006
4,661
1
38
West, MI
t-money80 said:
Stops at the axle .
Somtimes exhaust will pop with old mufflers and no tailpips. I wouldnt worry about it if its smoth driving down the road.
 

TNTS79

Dragway Regular
Jan 6, 2006
1,252
0
0
Illiniois
DOUG213XRJ said:
t-money80 said:
Stops at the axle .
Somtimes exhaust will pop with old mufflers and no tailpips. I wouldnt worry about it if its smoth driving down the road.

Never heard this before^^^^^^??
 

Supe

MalibuRacing Junkie
May 21, 2003
15,116
0
0
Charlotte, NC
Is it a backfire or just a light puff/pop out the pipes?
 

t-money80

Daily Driver
Mar 2, 2008
33
0
0
Granite City IL
when idling it has a faint pop/ping sound that sounds like its in the muffler. I checked some things and drove it now its starting to run rough and is missing at idle. If i rev it half way it gets better but still not like it should be. Tomorrow ill pull the plugs if they look ok i will do a compression check. This motor only has about 300 miles on it and has been runing good. Thanks
 

TNTS79

Dragway Regular
Jan 6, 2006
1,252
0
0
Illiniois
I would check the plugs, wires and cap/rotor. Might be a burnt boot or wire causing it...
 

t-money80

Daily Driver
Mar 2, 2008
33
0
0
Granite City IL
got the spark plugs out and all of them were dirty , the electrode and the gap was not that bad , but the top of the threads and down around the outside of the electrode / center of plug had carbon on them but it was real gummy. Recently i had the heads off because i broke a rocker stud , twice and wanted to get the heads checked and make sure i wasn't hitting the pistons with the valves or anything els. everything checked ok on the heads just replaced the studs. The tops of the piston had this gummy carbon on them as did the valves. The guy at the mach/shop said he thought it was sucking oil
from the intake because it had oil in the intake runners. When i put it back together i used some 3m yellow on the bottom edge and smeared some silicon around the ports on top . I checked the plugs after a few days and everything looked good, thought i had it fixed guess not . The guy that checked the heads is the one who did the work on them the first time along with the other machine work . Whats causing this sticky/gummy carbon or oil builed up ? Thanks for all the help.