How to adjust tune to improve driveability pulling away from a stop?

TheFleshRocket

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I recently finished a TVS upgrade on my '04. It got a 2.8 pulley, VMP MAF and pump booster, 60# injectors, and a BBK 65mm DBTB. My only complaint is driveability when pulling away from a stop during normal driving. (Like at a stoplight or stop sign or whatever.)

Previously, when my car had a 2.76 Eaton, I could ease out the clutch and feed in a little throttle to put the RPM just a bit over idle, and it would pull away smoothly. Now, I have to be somewhat aggressive on the throttle, or the engine will stall. I find that I have to rev to 1500-2000, blipping the throttle to keep the RPM in that range, while engaging the clutch. Once the clutch is engaged, driveability seems fine, though I don't ever really lug the engine down to idle speed when in gear.

I'd mentioned this to my tuner early in the tuning process and he made some changes which made it better, but obviously not good. Now you might be thinking, "it's probably that crappy BBK throttle body", but here's the thing--when the engine is cold, like after I start it up first thing in the morning, pulling away from a stop is just as easy and smooth as it was back when I had the 2.76 Eaton. (After a few minutes, it starts being touchy again.) Obviously when the engine is cold, it's running a little richer, and the IAC is keeping the idle a little higher too, so one of those parameters can be modified to fix the issue when the engine is warm.

Since my tuner apparently thinks he's already done whatever can be done to fix the issue, I'd like to be able to tell him specifically what should be changed in order to improve driveability pulling away from a stop. Any input would be appreciated.
 

gt347mustang

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Any input would be appreciated.

Where are you located? Who did the tune?

Have you been able to recreate the issue with the tuner in the vehicle data logging? If so, there's no reason he shouldn't be able to correct it.

There's no one single item to change, the tuner needs to ensure spark/fuel/airflow are all working correctly and in harmony from idle to part throttle transition.
 

TheFleshRocket

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I'm in Carbondale, IL, and had the tune done remotely. The tuner had me take the following datalogs:
--idle, 2 minutes
--1500rpm, 30 seconds; 2000rpm, 30 seconds; 2500rpm; 30 seconds; 3000rpm, 30 seconds
--2nd gear light acceleration from idle to 3000rpm
--WOT run from 2000rpm - redline (I usually do 3rd gear)

I haven't done any datalogging of the car pulling away from a dead stop. I guess I'll tell him that it's still an issue and ask what he wants me to datalog in order to help get it resolved.
 

SVT_Troy

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Who’s your tuner? I know two really good remote tuners that’s are known here and I think you would be good with either. Kevin Dunn aka 04Sleeper and Malcolm. I just finished my 93 tune with Kevin and my car has never ran smoother!

I thought no you should tell your tuner again and if he can’t fix it find another.


Sent from my iPhone using svtperformance.com
 

01yellercobra

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It can still be the throttle body. When it gets warm things expand and could cause sticky issues. My Accufab tended to be better when it was cold until I did some adjustments. I'd try a known good throttle body just to eliminate the variable.

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TheFleshRocket

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I got an updated tune from my tuner and it's much better. Not as good as it was with the Eaton and stock throttle body, but 80% of the way there, I'd say. He said he "added a bit more spark in a couple areas down low" but wasn't more specific than that. I've since replied to him, asking if he could modify the tune with a bit more of whatever he did.
 

TheFleshRocket

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I just had a thought--I wonder if the issue isn't due to how the TPS sits on the BBK. It seems like the TPS is slightly "depressed" when connected to the BBK--instead of the sensor being all the way bottomed, it's slightly off of bottom, or so it seems. So maybe the PCM thinks that the car is at 5% throttle (for example) when it's really at 0%. Is there some way to see the raw TPS readings so I can see if it's above 0% when at idle?
 

TheFleshRocket

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I just queued up the "absolute throttle position" PID on my OBD2 reader, and it shows 16.5% at idle and 93.3% at WOT. So I bet that's the problem. I bet if I dug out my stock TB, it would show closer to 0% and 100%.

EDIT - I disconnected the TPS from the TB. With no input (idle), it registered 8.2% and at WOT, it registered the same 93.3% as it did while mounted to the BBK.

When I reinstalled the TPS, I set it as far back as I could, and it read 14.9% at idle. I adjusted the throttle stop screw out about 1/2 a turn, but the TPS never got any lower than 14.9%.
 
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Rich'sTRsvt

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You want to adjust the TPS sensor to as close to 0.98 volts as you can. I don't recall the wires to check any more as it has been a while, you should be able to find something on here with a search. I was able to get it to 0.98 volts with my BBK but I didn't have any of the troubles you have had with yours.
 

TheFleshRocket

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I switched to TPS voltage and ran the tests again.
Idle = 15.3% throttle = 0.76V (apparently the sensor has "moved" a bit since last night)
WOT = 93.3% throttle = 4.65V

Is it problematic that the idle voltage is less than 0.98?
 

ctgreddy

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It may not be problematic however it also might not be helping the issue.

I had the same exact problem on my car. Except I didn’t really know what to change because I tune it myself and just not enough experience. However I put an auto in my car now and the problem is gone. I know that’s not a realistic cure for 99% of people just throwing it out there.
 

TheFleshRocket

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I chatted with my tuner and got an updated revision, which made the issue just about completely gone. It's now good enough that it's not worth messing with any more.

I also reset and adjusted the TPS so that it was at ~0.97v at idle, which had no noticeable effect on idle quality or driveability.
 

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