Backfire! Why?

[David D]

Hey guys, I cannot figure out why my 7mgte is back fireing in between shifts.
Its pretty embarrassing. I have good denso plugs and the timming is set to 10degs advanced. Could my cank pulley be slipping under a load causing it to run late and backfire?
any info, or insight would be greatly apprecaited.

thanks again.

 

[gaboonviper85]

Set timing to spec...check codes...check spark gap, any fuel mods?, and what blow off valve are you useing?

 

[roadboy]

hmm...how embarrassing?
not for me lol, mine backfires due to a bit of foul on the spark plugs, since i ran a bov vented, but will be re-reouted soon.

 

[mcpcola]

reset timing to spec and it could be a number of reasons such as Leaking fuel injector, running rich, fowled plugs, ETC ETC. you need to make sure you have good plugs and that its consuming all the fuel during the burn not after. Back firing generally is timing related be it cam or spark.

 

[WhtMa71]

Could my cank pulley be slipping under a load causing it to run late and backfire?

No.

Backfiring as in a pop sometimes when you shift? Most turbo Supra's do this.

Every now and then I will get a fireball when I shift. My timing is right on, plugs are fairly new.. Just have a 3" turbo back exhaust, intake and boost is at 10 psi. Everything else is stock..

 

[jetjock]

^ As configured your engine should not do this. Ever. Something is wrong. Likely the decel cutoff isn't working or the dashpot is busted/set up wrong.

It'd be helpful if the OP would clarify exactly what's happening. Backfire is an induction system event. Afterfire (also known as muffler explosion) is an exhaust system event...

 

[lintlars]

Do you have a wide band I had this issue when I was running WAY to rich what fuel mods do you have ? if your running a upgraded fuel pump did you drill the j-tube?
And no its not normal

 

[CajunKenny]

Mine does the same thing. I'm venting to atmosphere and my only fuel mod is an Aeromotive AFPR. Well, and an FCD if you want to count that...

I have brand new NGK's gapped to spec. I'm at 10 psi and mods are in my sig.

Sorry if it seems I'm trying to thread jack. I'm not, I just thought my details may help in some way.

EDIT: My timing is also set to stock spec.

 

[WhtMa71]

^ As configured your engine should not do this. Ever. Something is wrong. Likely the decel cutoff isn't working or the dashpot is busted/set up wrong.

It'd be helpful if the OP would clarify exactly what's happening. Backfire is an induction system event. Afterfire (also known as muffler explosion) is an exhaust system event...

Hmm.. I'll check the dashpot and throttle linkage stuff tomorrow. I am having a problem sometimes with my my throttle getting hung open at small pedal increments when the engine is stone cold. Sometimes when I first drive it in the morning it will stay/go up to ~2000rpm while I shift instead of dropping back down. A blip of the throttle makes it return. Goes away when it's warm.

How would I go about checking to see if decel cutoff is working properly and how would it be fixed?

Sorry to thread-jack.

 

[David D]

Just to be clear this is deffinatly an exhaust explosion, which only ocurrs in between shifts. I am running a HKS BOV and a 3in down pipe and 10lbs of boost. Other than that everything is stock...what is the stock timming setting? mine is at 10degs advanced

 

[jetjock]

David: Stock timing is 10 BTDC with the diag bock jumped. If that BOV isn't recirced it could be the problem.

Eric: Fix the sticky throttle and check that the TPS is set right. Do the dashpot last. Can't have any exhaust leaks either...

 

[WhtMa71]

A BOV venting to atmosphere will make make your engine load up when shifting and usually cause an afterfire or just a big puff of black smoke when you shift. It could also cause your engine to die if you just lift off the gas while in neutral.

I have the stock bypass valve still routed back into the accordion pipe.

Thanks JJ.

 

[tbcmorris]

10 before top dead center??

 

[LilMissMkIII]

I wish there was someone that lived near me that knew how to check and diagnose all this stuff... My car is having a VERY similar issue since it came back from the shop, but i have no idea where to start with diagnosing and fixing it

 

[jetjock]

Yes, BTDC. I should have worded that differently. Fixed...

 

[David D]

Yes, BTDC. I should have worded that differently. Fixed...

Are you saying that stock timming is 10 degs retarded or 10 degs advance?

 

[7msupradude]

No.

Backfiring as in a pop sometimes when you shift? Most turbo Supra's do this.

Every now and then I will get a fireball when I shift. My timing is right on, plugs are fairly new.. Just have a 3" turbo back exhaust, intake and boost is at 10 psi. Everything else is stock..

Ill second that, supras naturally run rich, so they naturally backfire after a nice boost. No worries, you can't tell me you dont love a flame here and there, it spooks rice off. Oh, and if you arent running a bypass valve, and rather a BOV, then you're obviously running a lot more rich, and it will backfire more (or stall

 

[jdub]

Are you saying that stock timming is 10 degs retarded or 10 degs advance?

10 deg BTDC = advanced...i.e. using a timing light, the crank index is pointing at the "10" on the timing cover with TE1 & E1 jumped on the diagnostic block.

A non-recirculated BOV can easily cause this.

 

[DBN]

since the bov vents to the air and the airflow sensor has already accounted for that air goin in it sends more fuel than air thus a rich mixture... please correct me if im wrong im just tryin to help.

 

[Frank Rizzo]

You need to shift faster