7mgte backfire

[bosco659]

This has been haunting me for as long as I can remember but I thought I'd try to pick everyone's brain one more time.

My car continues to backfire when I shift gears. It actually backfires when I get back on the throttle after shifting slowly especially at low RPM's. If I shift quickly and over 3000 rpm, it does not backfire. Seems like a build up of fuel between shifts that re ignites.

I think it is worse since I installed my aluminum flywheel as the engine speed drops rapidly between shifts.

Here's the specs on the engine:

550's
Walbro and fpr
CT26 54 trim
15 lbs boost
3" exhaust with CAT
Lexus afm
BOV vented to atmosphere
Apexi SAFC version 1 - pulling up to 22% fuel at wot and full boost

Checked for vacuum, exhaust and intake leaks and none found
Reset TPS
Throttle linkage dash pot ok
AFR's 14.5 at idle and cruising. 11.0 to 11.5 under boost.
Can't recall fuel pressure

The only thing that I have never changed is the ECU.

Lmk what you think.

Thx

 

[Mikael_7m]

have you tried recirculating your BOV? backfires will occur when you vent to atmosphere. Probably not as much as yours though...

 

[jdmfreak]

You don't have 2step enabled and not calibrated correctly do you??

 

[jetjock]

A backfire is an induction system event. Afterfire/muffler explosion involves the exhaust system. Which is it?

 

[bosco659]

You don't have 2step enabled and not calibrated correctly do you??

Not sure what you mean by this. Can you explain? Thx

 

[bosco659]

A backfire is an induction system event. Afterfire/muffler explosion involves the exhaust system. Which is it?

Not sure which one it is. I would assume that the muffler explosion would involve some flames? I have never had no one report flames from the exhaust. Would this then lead me to believe that it is truly a backfire?

Can you comment on probable causes of either condition? Thx

 

[jdmfreak]

Does it "backfire" if you hold in the clutch and rev it high?

 

[IndigoMKII]

Interesting, the stock ECU cuts off the injectors above 2k rpm without any throttle right?

Sounds like the timing is off somewhere.

 

[bosco659]

Does it "backfire" if you hold in the clutch and rev it high?

No it doesn't.

 

[Poodles]

It's a muffler explosion and it's because you're running a vented BOV.

/thread

 

[bosco659]

It's a muffler explosion and it's because you're running a vented BOV.

/thread

Thx. Maybe try to recirculate the bov over the winter. Car has always done this but now that I think of it I had always been venting to atmosphere when this has occurred.