Backfire on 1 cylinder

[tad240]

Need some help from you guys. Recently started my Marauder engined Cobra replica for the 1st time and found 2 problems. The engine is new but has been sitting for years.

Problem 1. One cylinder was not getting fuel so I replaced the injector - that cylinder works perfectly now. Problem 1 solved.

Problem 2. One cylinder is backfiring about every 10-15 seconds while idling - especially when the engine is cold and warming up. I have uncapped 4 into 4 headers so it was easy to ID the specific cylinder - getting a very loud pop with a flash of fire from only this cylinder. Any ideas? Another poorly performing injector? Any help would be appreciated.

I have not driven the car yet but have let it come up to temp sitting on jackstands. It seems to get better once warmed up but still concerns me that a cylinder backfires repeatedly.

Note: Please disregard the wires around the headers. Photo was taken during wiring phase.
http://i431.photobucket.com/albums/qq34/tad240/2008_1216DISNEY0026.jpg

[Paul T. Casey]

I don't think it's backfiring. What you have is unburned fuel in the exhaust which ignites when it sees enough oxygen. I think it's a common thing as I can hear mine a little when it's idling. Backfiring would be flames in the intake.

[CKMustangCobra]

Sounds like you aren't getting complete combustion. Spark plug gap correct? Timing correct? Enough voltage going to the coils? Good coils?

[omarauder]

Is there an O2 sensor in there to provide feedback to the engine computer? You might be getting the wrong fuel/air mixture.

[Marauderjack]

Probably an injector not seating well or has debris in it??:confused:

Did you run it with the side pipes on or just open headers??:confused:

If the motor set up a long time I would suspect all the injectors should be replaced......I have a complete set off my 04 Marauder I can send you to try if you like??:D

Marauderjack:burnout:

[Krytin]

Popping in exhaust at idle is a burnt or sticking exhaust valve.

[Marauderjack]

Popping in exhaust at idle is a burnt or sticking exhaust valve.

Could be but not likely a burned valve on a new motor??:confused:

[Krytin]

If it was sitting awhile there could be some sticking - especially if it gets better after it warms up. The bad thing would be rust/crud on the valve stem/guide.

If it keeps on sticking it will burn the valve!

[tad240]

Thanks for the input on my problem. I guess a sticking exhaust valve would be easily diagnosed with a compression check - do you all agree? Or do you think it may seal OK on some cycles but stick on others?

If it is a sticking valve, is it reasonably possible that it will work itself out if I run it some? I have only let the engine get warmed up once and then it was not for long - it just idled for about 10 minutes total. I'm thinking that running it more may solve the problem since it got better once warmed up. Any tips that may help resolve if that turns out to be the problem - short of removing the head?

Thanks!

[ImpalaSlayer]

do you indeed have an 02 sensor installed? i know when i took my exhaust off i started the car for ***** n giggles and it ran like crap and didnt sound good so only ran it for a few seconds. just my 2 cents.

[Zack]

***** just made it through the swear filter.



***** ***** ***** *****

[tad240]

No O2 sensor installed. Agree that it will not run too well since it has never been run and the EEC needs to learn. But - I thought that the O2 did not do anything until the sensor gets hot enough to go into closed loop mode. Not sure how long that would normally take. I just thought it was odd that the same cylinder kept popping.

[Krytin]

You could try to get a visual of the valves for the cylinder in question. I don't know how much you can actually see with the valve cover off and/or the the header off but w/push rod motors I have removed said parts and cranked the motor over w/remote starter to see if there were any iregularities.

Long term running/under load with a valve off the seat will burn the valve.