my buddy has this weird issue with his cobra. it has a 5.0 stroker bottom end, and when he shifts hardly, after the shift the car will stutter. So tonight we took a datalog, keep in mind this is my first time doing this, and im not sure i got the right parameters. I decided to look at the fuel since when we added more fuel to the tune, it seemed to fix the issue a little bit. Tell me what you guys are seeing
Tell me if you can see a problem in this DL?
- Thread starter mossbergman
- Start date
Have you done the PPRV delete ?
Off hand i see a low batt voltage reading which can cause even less voltage to drive the fuel pump once it makes it in back. It looks as though your fuel issue may be getting caused by low voltage to the pump causing the fuel pressure drop. The spikes/dips, can also be caused by a fuel pump voltage table that needs adjusting.
+1 or you are maxing the pump out or it is going bad. I recommend logging fuel pump duty cycle. What car is this for again? Forced induction? Specs?
The car is actually mine, it's na. Fuel system consists of walbro 255, stock rails, 39 lb injectors. Motor is forged high compression 10.8 compression, 98 cobra intake cams, 03 cobra heads. Car never "hesitated" before the new motor. I thought it was the fuel pump so I put the walbro in. Car still does it. Car was tuned locally. I replaced the sensor in the rail also. When the tune is richend via the handheld it doesnt stutter near as often. Any help would be appreciated.
ok thanks for the input. we were maybe thinking that the pump driver in the trunk might be on the way out? I think its just as likely in the tune as well
whats that? im afraid im uneducated on that mod
what deverick (devcon said)
whoa look at this guy getting in the thread!!!:loser: lol
Have any way to take a look at A/F? Or STFT (O2 Sensors)? You could have a rich or lean tip in issue. You would need to log a wideband or STFT 1 and 2. "Sounds" like it is mechanically sound. I think the tuner needs to take another look at it to make sure the MAF Xfer function is correct and the LWFM (Load with failed MAF) was setup correctly.
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As stated above, next time we datalog we can moniter the stft and ltft and get somewhat of an idea for the commanded a/f ratio. I would have Chris touch up the tune if that driver doesn't fix it
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sounds like a good idea. Here's a video of what It does...sorry about the quality
B4901C73-82BF-4DB7-8590-47764EFF2A51-1605-000001A55B5D3A5F.mp4 video by Devcon7 - Photobucket
Look at how your fuel pressure rises before you shift to the next gear, pressure drops between your shifting and rise again after you shift. You did not log your tps signals. I bet you are lifting of the throttle between shifts, that will cause the pumps to turn off, then on when you complete the shift but it takes a fraction of a second for the pumps to get the pressure back up.
You need to learn to shift faster and you won't have the problem or don't let off the gas all the way. Simple.
I used to have the problem in the beginning but not anymore. The only time i have the problem is open tracking when i am off the throttle for a second or two and go wot, it does it so bad that in the slow corners it will break the rear tires loose and i have to counter steer so i won't spin the car.
If you have a boost-a-pump the issues is even worse. On my car the fuel pressure spikes to around 80psi when i let off the gas. Yours looks like it spikes to about 65psi.
You need to learn to shift faster and you won't have the problem or don't let off the gas all the way. Simple.
I used to have the problem in the beginning but not anymore. The only time i have the problem is open tracking when i am off the throttle for a second or two and go wot, it does it so bad that in the slow corners it will break the rear tires loose and i have to counter steer so i won't spin the car.
If you have a boost-a-pump the issues is even worse. On my car the fuel pressure spikes to around 80psi when i let off the gas. Yours looks like it spikes to about 65psi.
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I never had this problem before the motor swap/tune or with any of my previous mustangs/sports cars. I don't have a BAP, and I do lift off the throttle...I have never power-shifted it in fear of wrecking a good tranny. Do you believe clipping the fuel pressure could possibly alleviate the problem??
Id go ahead and do the inevitable and convert the car to a return style fuel system LOL
I speed shift and i never have the problem. You just need to learn to shift faster. I did hear that a good tuner could clip the spikes so that it will fix the problem. It just takes time and an experienced tuner.
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