Hesitation - SRT Forums

hardcore · 10-04-2009, 09:13 PM

I have searched and my problem doesn't seem to be shared by any other threads.

I have no hesitation problems at full throttle at all.

Every once in a while, after a low boost(5-10psi) at part throttle running through 2nd and 3rd then going immediately to cruising in higher gears at low throttle, the car will buck, hesitate and back fire. The long term fuel trims go from a normal -1.X to -10 to -18 and air fuel ratios go way rich. After a little bit, it will go away and driveability will return to normal.

During the low throttle, low boost runs i will see long term trims go to -13 as the computer tries to keep the afr's stoic with the extra fuel from the boost referenced fuel pressure regulator.

I had this problem when I was on a DTEC tune and still have the problem now that I am on a Dsport tune.

I never had the problem on the stock turbo/stock injectors with the FPR hooked up.

Mods:
GT3071R
255 walbro fuel pump
fuel pump re-wire
DW 650's
Aeromotive FPR with vacuum reference connected, base pressure 50psi.
WOT box w/2-step
DTEC (only doing boost control now)
D-sport tune on a S1 computer w/ 3bar sensors
The stock solenoids have been completely removed, so the TIP just sees ambient pressure.

Plugs are good I replace them between 3K and 6K miles. They look very good when i change them, ie no fowling. Wires were replaced about 10K ago. The coil pack is stock. Compression on all cylinders is 170ish.

Does anyone have any input on this problem? I have been thinking that this could be caused by the boost reference hooked up on my FPR and that a proper tune on some 750's(eliminating the boost refrence) will resolve the problem.

Thanks for the advice.

I could also try to get a log file of this, but it is hit or miss. If anyone would like me to do this, just let me know and tell me which parameters to log.

Thanks.

UpShiftSRT4 · 10-04-2009, 09:28 PM

A friend of mine had the same exact symptoms for the past few weeks with his big turbo Subaru and it turned out to be a poor seal of some sort at the fuel pump. This was essentially a vacuum leak that caused intermittent fuel pressure during cruising.

Just something to think about, but not 100%

goats srt · 10-04-2009, 09:28 PM

It could be the 50psi of fuel cause I know I had it when my fuel psi was down try turning it up to 58-60 just to see if it goes away or it could be the up stream 02 senser

Mindmelt101 · 10-04-2009, 09:38 PM

Quote: Originally Posted by hardcore

I have searched and my problem doesn't seem to be shared by any other threads.

I have no hesitation problems at full throttle at all.

Every once in a while, after a low boost(5-10psi) at part throttle running through 2nd and 3rd then going immediately to cruising in higher gears at low throttle, the car will buck, hesitate and back fire. The long term fuel trims go from a normal -1.X to -10 to -18 and air fuel ratios go way rich. After a little bit, it will go away and driveability will return to normal.

During the low throttle, low boost runs i will see long term trims go to -13 as the computer tries to keep the afr's stoic with the extra fuel from the boost referenced fuel pressure regulator.

I had this problem when I was on a DTEC tune and still have the problem now that I am on a Dsport tune.

I never had the problem on the stock turbo/stock injectors with the FPR hooked up.

Mods:
GT3071R
255 walbro fuel pump
fuel pump re-wire
DW 650's
Aeromotive FPR with vacuum reference connected, base pressure 50psi.
WOT box w/2-step
DTEC (only doing boost control now)
D-sport tune on a S1 computer w/ 3bar sensors
The stock solenoids have been completely removed, so the TIP just sees ambient pressure.

Plugs are good I replace them between 3K and 6K miles. They look very good when i change them, ie no fowling. Wires were replaced about 10K ago. The coil pack is stock. Compression on all cylinders is 170ish.

Does anyone have any input on this problem? I have been thinking that this could be caused by the boost reference hooked up on my FPR and that a proper tune on some 750's(eliminating the boost refrence) will resolve the problem.

Thanks for the advice.

I could also try to get a log file of this, but it is hit or miss. If anyone would like me to do this, just let me know and tell me which parameters to log.

Thanks.

Yes a proper tune would fix your issue.

hardcore · 10-04-2009, 10:58 PM

Mindmelt - would you reccomend keeping or eliminating the boost refrence on the FPR and going with a larger injector? Right now the car has a custom ragetune that I have had to pull a bunch of fuel out of in order for it to work at WOT on my setup. Have you seen this problem before, what is the root cause of the hestiation?

Upshift - 2 years ago when I installed the FPR, i noticed that my fuel pressure drops to 0 quickly after turning the car off. I don't have any fuel leaks and no problems at full throttle, but this always made me wonder.

Goats - What setup did you have the problem on and when did you see the hesitation? Same as what I described? I hesitate to add more base fuel pressure because the fuel system will be running at 80+psi under full boost at 58-60 base. The car has 60K on it, so it's not impossible that the oxygen sensor could be going, but it seems that the computer is getting an accurate signal and compensating accordingly to an overly rich condition.

Thanks

Mindmelt101 · 10-05-2009, 09:44 AM

Quote: Originally Posted by hardcore

Mindmelt - would you reccomend keeping or eliminating the boost refrence on the FPR and going with a larger injector? Right now the car has a custom ragetune that I have had to pull a bunch of fuel out of in order for it to work at WOT on my setup. Have you seen this problem before, what is the root cause of the hestiation?

Something tells me it's in the tune. What I would do is put all the fuel back and set your base pressure to 58psi static then check your adaptives and see what they look like. Then go from there.

If you have a rising rate FPR that can be accomodated for it's just easier without having the reference hooked up to it. Then again I've done them either way. What size injectors do you have?

ptperformance · 10-05-2009, 09:48 AM

Quote: Originally Posted by hardcore

I have searched and my problem doesn't seem to be shared by any other threads.

I have no hesitation problems at full throttle at all.

Every once in a while, after a low boost(5-10psi) at part throttle running through 2nd and 3rd then going immediately to cruising in higher gears at low throttle, the car will buck, hesitate and back fire. The long term fuel trims go from a normal -1.X to -10 to -18 and air fuel ratios go way rich. After a little bit, it will go away and driveability will return to normal.

During the low throttle, low boost runs i will see long term trims go to -13 as the computer tries to keep the afr's stoic with the extra fuel from the boost referenced fuel pressure regulator.

I had this problem when I was on a DTEC tune and still have the problem now that I am on a Dsport tune.

I never had the problem on the stock turbo/stock injectors with the FPR hooked up.

Mods:
GT3071R
255 walbro fuel pump
fuel pump re-wire
DW 650's
Aeromotive FPR with vacuum reference connected, base pressure 50psi.
WOT box w/2-step
DTEC (only doing boost control now)
D-sport tune on a S1 computer w/ 3bar sensors
The stock solenoids have been completely removed, so the TIP just sees ambient pressure.

Plugs are good I replace them between 3K and 6K miles. They look very good when i change them, ie no fowling. Wires were replaced about 10K ago. The coil pack is stock. Compression on all cylinders is 170ish.

Does anyone have any input on this problem? I have been thinking that this could be caused by the boost reference hooked up on my FPR and that a proper tune on some 750's(eliminating the boost refrence) will resolve the problem.

Thanks for the advice.

I could also try to get a log file of this, but it is hit or miss. If anyone would like me to do this, just let me know and tell me which parameters to log.

Thanks.

Pull it off vacuum reference and go to a boost only reference on the RR FPR. the transition from vacuum to boost is very difficult to tune for with the DSP, it can be done but we almost always have our canned tune customers switch this around due to the problems that come with tuning it.

If you wouldn't mind getting a log sent over I would be willing to look at. Send me an email (with details) and I will get you the PID's I would like to see.

tunes@pt-performance.com

Thanks.

hardcore · 10-05-2009, 10:24 PM

Mindmelt - 650cc's with a base pressure set at 50psi idle. You bring up a good point as well, i will give it a try and see what happens.

PTP - I'll shoot you an e-mail and sorry for the confusion about the 'vacuum refrence'.

The FPR is connected before the throttle body, so it is only seeing positive pressure, no vacuum.

Thanks