Car stumbles/sputters/backfires on heavy acceleration between shifts

[Canebrake]

Like the thread title says, the car seems to stumble or stutters between shifts under heavy acceleration. From 75% to 100% throttle, in between 2-3 and 3-4 shifts. When it happens, I let out of the throttle and the car returns to normal within 1-2 seconds. Sometimes I push in the clutch again, sometimes I leave it in gear and just decelerate in gear. Afterwards, I can resume applying throttle and she accelerates without issue throughout the RPM range.

I haven't done this much at all for fear of damaging something, but just enough to get an idea of what is happening, when and under what conditions.

It acts like a spark or timing issue to me, but I'm not sure. Could this be spark blowout? Or does it seem more like a fuel related issue, like PPRV or FPDM? The car has a KB Boost A Pump and Boost A Spark, and other mods are in sig. The traction control is off, the car is not running hot, the intercooler pump is working, etc.

I am going to run a datalog on the XCal3 this afternoon and see what I can find. I am going to email it to the tuner, who is actually Jeff (formerly of Modular Powerhouse) at Mo's Performance in Dallas GA and get his input as well.

Any help and guidance would be greatly appreciated.

Thanks

 

[jm@ReischePerf]

Sounds like the typical hesitation issue. Sometimes it shows up all of the sudden. Might want to log and see if you're losing any voltage. PPRV deleted?

 

[quikcobra]

Maf?

 

[SVT03Chris]

Post up the data log once you do it.

Fuel pressure?

 

[unforgiven]

PPRV still in there?

 

[Canebrake]

Sounds like the typical hesitation issue. Sometimes it shows up all of the sudden. Might want to log and see if you're losing any voltage. PPRV deleted?

Regarding the PPRV: I don't think so, but I'd have to drop the tank to be sure, right? Where might I check for voltage drop? In the pump wiring? I wonder if the KB BAP might be wired improperly or poorly, since I have no idea who did the install.

If we assume for a second the BAP isnt working properly, (fuse blown, voltage drop, etc.) and the fuel pumps are maxing their duty cycle, would that cause the car to behave the way it is?

I'll be logging it this evening after work.

Maf?

It's possible, but since I have the SCT 2400 I wouldnt think it was pegging the MAF. It would have to be something else causing an issue I would think. I'll inspect the wiring to be sure.


Thanks for the help, keep the info and suggestions coming!

 

[unforgiven]

After my Whipple install, my car acted exactly as you described. I had Ford remove the PPRV and that eliminated the problem.

 

[Parts-is-Parts]

There is a way to remedy this problem in the tune (without removing the PRVV) but I dont know the fix.
ModularPowerhouse knows for sure.....anyone have the info?

 

[Canebrake]

After my Whipple install, my car acted exactly as you described. I had Ford remove the PPRV and that eliminated the problem.

I thought it may be PPRV related but wanted to be sure. I was going to do the PPRV delete eventually, but I didn't want to just throw money at the problem.

On a side note, I planned on changing the plugs this week anyway and I was going to check the gap on the ones already in there. I went with NGK
TR7ix's. Should be gapped at .032" correct?

 

[jm@ReischePerf]

Should be gapped at .032" correct?

That should work.

As far as the voltage I would just check to see that the car is making at least 12.5V at WOT. Low voltage directly correlates to higher FPDC and the higher FPDC gets the more likely hesitation will occur. Definitely check the wiring to make sure the connections are good. The most common way to fix or reduce this hesitation is to remove the PPRV but, like the others have said, it is possible to correct it in the tune. Whether or not a tune fix will work on every car is debatable though.

 

[Canebrake]

Well I datalogged it the other day on the way home and emailed the results to Mo's Speed Shop this morning. It did show the hesitation/backfiring this time, but not as badly. The only thing different that I know of was the ambient temps were 10-15 degrees cooler than when I first got the car and noticed the issue.

I'm curious to see what Jeff says and if he can find it in the tune. I checked the wiring at the MAF and it seems fine. The wiring in the back end I will check tonight and I plan to R&R the plugs tonight since its rainy, and see how they read.

Regarding the voltage, I'll likely pull a datalog at WOT and see if there is voltage drop at the pumps/FPDM. If anything, I'll bite the bullet and delete the PPRV this weekend.

 

[Canebrake]

I finally got the new tune from Mo's the other day. It didn't take care of the issue. I'm going to see if Jeff can take another look at the tune file and see if we can work it out. I guess the next step is to do the PPRV delete and see if that takes care of it.

 

[jm@ReischePerf]

I guess the next step is to do the PPRV delete and see if that takes care of it.

Generally on a twinscrew setup it's just better to take it out.