Car backfiring when boost limit hits

[3jcelica]

Hi,

I have this problem that the car backfires when I hit the boost limit (12psi), may also happen when I back off from this amount of boost.

I susspect this may be caused by running rich. but would like to see other peoples thoughts

Thanks

Roger

[Cuzzo]

what car / motor

[beerhead]

It could be a poor quality spark. A 4agte I wired would take 10 psi on 1ZZFE coilpacks, but once we wound the boost to 15psi as soon as it boosted it'd pop and fart and make a terrible noise. If the coil / leads and spark plugs are good it could be time to start thinking about an ignition upgrade.

[3jcelica]

cuzzo,

3tgteu running CT26, after market computer, recently dynoed at 130rwkw at 12 psi.

beerhead,

Currently the engine runs wasted spark using a crank sensor and 8 dual post coils, new leads, new plugs. Ignition is pretty strong in my opinon, what can be done to further strengthen it? different coils (currently using hyundai)?

I do know that my AFR is pretty rich across the range at about 12:1

Roger

[beerhead]

Sounds like the ignition side is good. You could try tweaking the dwell time of the coils if they're set at 1 or 2 ms, you could try 3 or 4ms as an experiment. What kind of igniters does your setup run?

[CrUZida]

Have a look to see if the ECU cuts fuel or ignition at boost cut/rev limit.
If it cuts ignition there is problem #1.

Have a look at the decel fuel cut values.
If it doesn't cut fuel on decel there is problem #2

Are you running a cat?
If not, there is problem #3


If the above 3 are not a cause, I'm out of ideas

[3jcelica]

CrUZida,

Spot on with number one. I put a boost cut in some time ago (long time between drives) to save my clutch. The boost cut is obviously cutting the ignition. So I took it out and all is fine.

decel is working fine at the moment.

Thanks guys for your help.

The reason I put it in was to save the clutch which was just starting to slip, after removing the boost cut I proceded to fry the clutch completely.

If running high boost say 18 psi and I was to hit such a boost cut what damage would I be doing?

Thanks

Roger

[Kyosho]

Cut outs such as rev limiters etc, with excessive "bouncing" do damage to oil pumps from what I've heard...
Also, cutting ignition has been known before to explode mufflers, and it melts cats...

[CrUZida]

As above, ignition cut is not a good thing. Fuel cut is the better way to do it (if you have that option)

[DRFT86]

yeah i got the same problem