FI Tuning Question

[only_1]

I have a 16 GT PP with a KB SC kit. I am running a Sai Li fuel system for E85. I have a remote tune done with data logging. One of my problems I have is that I have terrible throttle response, especially when warm. If I stab the throttle it bogs quite badly. It takes about a second for the rpm to start picking up.
My biggest issue though is that if I try to take off without slipping the clutch with a higher RPM, it bucks really hard. In first, it throws me back and forth in my seat madly. When I am deep in the throttle it does really well. When I am cruising with little throttle input, I think I can feel the hunting back and forth if I am under 3000 rpm.

Lastly, it hunts for idle at every cold start.

Would this be a result of bad tuning?

Would this be a result of driveline play?
-I have some play in the rear differential, which I haven't found a spec yet to say if its excessive.

Thanks for your help.

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[LxMike]

Data log and send to your tuner....

 

[only_1]

Data log and send to your tuner....

I have. It hasn't gotten any better.

 

[Jackson1320]

I have. It hasn't gotten any better.

The idle hunt to me is a sign of bad tuning but has it always done it or did it develop. The throttle response would be bad tuning if it is only problem but all of it can be related. Any codes?

 

[beetle6986]

I have a 16 GT PP with a KB SC kit. I am running a Sai Li fuel system for E85. I have a remote tune done with data logging. One of my problems I have is that I have terrible throttle response, especially when warm. If I stab the throttle it bogs quite badly. It takes about a second for the rpm to start picking up.

Lastly, it hunts for idle at every cold start.

My Roush charged car used to fall on its face when you first stab the gas. I got a VMP tune and that resolved the issue. I think my car also hunts for idle for a few seconds on cold starts. However, it's nothing alarming and I think some of my other cars do that a bit also when first started.

 

[only_1]

The idle hunt to me is a sign of bad tuning but has it always done it or did it develop. The throttle response would be bad tuning if it is only problem but all of it can be related. Any codes?

No codes.

 

[only_1]

My Roush charged car used to fall on its face when you first stab the gas. I got a VMP tune and that resolved the issue. I think my car also hunts for idle for a few seconds on cold starts. However, it's nothing alarming and I think some of my other cars do that a bit also when first started.

Yeah the hunting on startup isn't a big issue. I just wanted to describe all the issues in case they would be connected. Something in the mechanical build I was overlooking or something? I could/would absolutely believe I messed something up putting it together.

 

[beetle6986]

Yeah the hunting on startup isn't a big issue. I just wanted to describe all the issues in case they would be connected. Something in the mechanical build I was overlooking or something? I could/would absolutely believe I messed something up putting it together.

I think I do also noticed a slight bit of unsteadiness when cruising around 2k rpm. so slight that I don't think a passenger wouldn't notice.

 

[Jackson1320]

Yeah the hunting on startup isn't a big issue. I just wanted to describe all the issues in case they would be connected. Something in the mechanical build I was overlooking or something? I could/would absolutely believe I messed something up putting it together.

Anyone who built their own engine has thought back wondering if they messed up anytime something happened. Did you know what you were doing?
Did you cut corners? Did you check everything as you built it? You know if there’s a chance that you messed up or not just be honest with yourself.

 

[only_1]

Still fighting this, and the tuner has not made any progress. Stepping back, it acts like a bad throttle position sensor or play in the throttle body. I swapped out the rubber rear sub bushings, and diff bushings. That did help the chassis immensely. Still no codes, and pulls hard when deep in the throttle.

 

[turbofiveoh]

If I were working on this car here's the process I'd follow:

First, I would pressure test the engine to make sure there are no vacuum leaks.

Next, check the throttle function. Confirm the throttle is working properly but removing the intake tube and have a friend sit in the car and sweep the accelerator pedal while you are watching the throttle blade move. The throttle blade should move smoothly through the corresponding range. If the throttle blade is moving erratically that may be the source of your issue.

For good measure I would check the fuel system to make sure that the fuel pressure is increasing based on MAP and that there are no pinhole leaks in the system.

If the car passes the health and wellness check mechanically then I'd move to the tune.

To address the bogging issue I'd check the AFR reaction to rapid throttle changes. This will tell me if the problem is related to tip in fuel tuning, non-synchronized fueling requirements, or even possibly a slow responding map sensor. E85 generally requires some major adjustments to the relevant fuel trim/adjustment maps.

For the rough cold start idle I'd check O2 control settings for open and closed loop and also inspect/test the O2 sensors. The engine should start in open loop and move to closed loop after some amount of time (usually less than a minute). From there I'd check the cold start enrichment tables. Cold starting on E85 can present some unique challenges and generally requires a lot more fuel than one would think.

Good luck.

 

[Jackson1320]

What are you using for tuning? Can you log it? Also what are you using to check codes? Some code readers can see codes that are coming up but have not thrown a code, Like forscan. Logging live data can make a big difference

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