Popping on decel

[DMCTurbo]

A couple weekends ago my sled began to decel pop once getting out of the throttle after 1320' pulls. Data logging shows it was still making boost and RPM however it seems that the performance has dropped off. Fuel pressure set at 47psi key on and the closed loop was pulling fuel as per the logs. Temps outside were warm, above freezing.

Has anyone experienced this? I haven't looked at the sled yet but will start by checking my header for cracks/leaks. Could a boost leak cause this? I tested for boost leaks at the beginning of the season and am confident it's not my issue.

Any help would be appreciated.

Thanks.

DMC

 

[Turboflash]

1. IMO, yes, check for boost leaks.
2. Pop is usually raw fuel in exhaust system. Can ECU/closed loop pull fuel fast enough when cutting throttle after WOT for 1320'?
3. Maybe try turning down FP a bit. What is WOT AFR @ 47 psi FP?
4. Any chance MAP is getting slow or lazy? If it's slow when TPS and boost comes down, it might be slow to tell ECU to cut injector pulse down.
5. Any chance TPS setting needs adjusting?
6. Any chance FPR isn't reacting correctly to throttle cut?

 

[74Nitro]

I would look for exhaust leaks as you mentioned. If you hold the throttle open slightly while decelerating does it still do it?

 

[DMCTurbo]

I would look for exhaust leaks as you mentioned. If you hold the throttle open slightly while decelerating does it still do it?

No pretty sure it stops.

 

[DMCTurbo]

1. IMO, yes, check for boost leaks.
2. Pop is usually raw fuel in exhaust system. Can ECU/closed loop pull fuel fast enough when cutting throttle after WOT for 1320'?
3. Maybe try turning down FP a bit. What is WOT AFR @ 47 psi FP?
4. Any chance MAP is getting slow or lazy? If it's slow when TPS and boost comes down, it might be slow to tell ECU to cut injector pulse down.
5. Any chance TPS setting needs adjusting?
6. Any chance FPR isn't reacting correctly to throttle cut?

1. I'll check for boost leaks for sure regardless.
2. Never popped all winter till a couple weeks ago.
3. AFR set to 12.1 with closed loop.
4. How would I know the map is getting slow?
5. TPS code came in once last weekend just after a cold start then went away and never came back.
6. How would I know if it wasn't reacting correctly?

 

[justinator]

Exhaust leaks are usually the culprit. Put a glove on and plug your exhaust and it should stall pretty quickly. Try with cold exhaust and again when exhaust is hot. The closed loop does nothing at closed throttle position so its possible its a little rich with the warm weather when you kill throttle and the unburnt fuel ignites in the pipe and you get popping but I would bet on an exhaust leak.

 

[DMCTurbo]

Exhaust leaks are usually the culprit. Put a glove on and plug your exhaust and it should stall pretty quickly. Try with cold exhaust and again when exhaust is hot. The closed loop does nothing at closed throttle position so its possible its a little rich with the warm weather when you kill throttle and the unburnt fuel ignites in the pipe and you get popping but I would bet on an exhaust leak.

I'm hoping that's all it is. Fleecer told me the glove trick as well so I'll give that a shot when I get a chance. Thanks.

 

[Turboflash]

1. I'll check for boost leaks for sure regardless.
2. Never popped all winter till a couple weeks ago.
3. AFR set to 12.1 with closed loop.
4. How would I know the map is getting slow?
5. TPS code came in once last weekend just after a cold start then went away and never came back.
6. How would I know if it wasn't reacting correctly?

Any chance you've got moisture/water in signal line to MAP or waste gate?

 

[SidewinderConvert]

I'm hoping that's all it is. Fleecer told me the glove trick as well so I'll give that a shot when I get a chance. Thanks.

Use a good leather glove and nothing with nylon in it if the exhaust is hot. Ask me how I know....

 

[max rolph]

after those common chks, you may have spit a shim from valve

 

[Fleecer]

If there are no boost/exhaust leaks, I would go to the TPS sensor next. When you cut the throttle, the sensor may not be responding to ECU input.

 

[Turboflash]

1. I'll check for boost leaks for sure regardless.
2. Never popped all winter till a couple weeks ago.
3. AFR set to 12.1 with closed loop.
4. How would I know the map is getting slow?
5. TPS code came in once last weekend just after a cold start then went away and never came back.
6. How would I know if it wasn't reacting correctly?

MAP - I usually trade out with another sled (that's running correctly) to see if it makes any difference.
TPS - DVOM and compare voltage to spec.
1st see if you have exhaust leak as you plan.

 

[sideshowBob]

Back firing on decel was a symptom of a leaking exhaust on Apexs so definitely worth checking on your SW.
If you put the gage into diagnostic mode and check the TPS readings the voltage increase/decrease should be smooth with no lag or spikes as you open and close the throttle with the engine off.

 

[DMCTurbo]

Back firing on decel was a symptom of a leaking exhaust on Apexs so definitely worth checking on your SW.
If you put the gage into diagnostic mode and check the TPS readings the voltage increase/decrease should be smooth with no lag or spikes as you open and close the throttle with the engine off.

Refresh my memory on how to put it into diagnostic mode. Thanks Bob.

 

[DMCTurbo]

Any chance you've got moisture/water in signal line to MAP or waste gate?

Not sure, it's possible, will check that too.