RPM Surge (except with A/C) with FAST 102 + 102mm TB

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03-03-2024
thehemi

1 Attachment(s)

RPM Surge (except with A/C) with FAST 102 + 102mm TB

Background: Mostly stock LS1 with FAST LSXR 102, 102mm TB and 100mm MAF

I'm currently doing all this testing in SD mode with MAF disabled. In case it matters.

In gear while cruising, it'll actually accelerate (slowly) with no throttle. Out of gear it'll surge to 3000+ rpm. With clutch depressed it'll come back down to normal idle levels. I have not been able to identify any vacuum leaks.

Due to the new TB, I performed the TPS relearn process (once). I cannot get TPS voltage below 0.71V. I keep reading this should be closer to 0.50V, but I cannot get it that low. IAC count is 0 at idle. Idle is reasonable at 850-900 rpm.

An interesting thing I noticed today...

With the A/C off, it experiences the above surge.
With the A/C on, it does NOT experience the surge.

Does this difference in behavior with the A/C running point to anything?

I wasn't expecting this A/C curve ball, so I wasn't logging anything related to A/C. I'm going to add it to my channels for next test drives. If there's anything else I should add for logging which might help, let me know.

Thanks,
Scott
03-03-2024
horsepowerguru427

Have you tuned your air models for the changes or even changed data for the larger TB? You cant get idle right if your air model isnt correct.
03-03-2024
thehemi

Quote:

Originally Posted by horsepowerguru427

Have you tuned your air models for the changes or even changed data for the larger TB? You cant get idle right if your air model isnt correct.

No, I'm trying to figure out what I need to adjust for the larger TB.

I just find it odd it runs fine with the A/C on, but not with A/C off.

Thanks,
Scott
03-04-2024
Alvin

Quote:

Originally Posted by thehemi

Background: Mostly stock LS1 with FAST LSXR 102, 102mm TB and 100mm MAF

I'm currently doing all this testing in SD mode with MAF disabled. In case it matters.

In gear while cruising, it'll actually accelerate (slowly) with no throttle. Out of gear it'll surge to 3000+ rpm. With clutch depressed it'll come back down to normal idle levels. I have not been able to identify any vacuum leaks.

Due to the new TB, I performed the TPS relearn process (once). I cannot get TPS voltage below 0.71V. I keep reading this should be closer to 0.50V, but I cannot get it that low. IAC count is 0 at idle. Idle is reasonable at 850-900 rpm.

An interesting thing I noticed today...

With the A/C off, it experiences the above surge.
With the A/C on, it does NOT experience the surge.

Does this difference in behavior with the A/C running point to anything?

I wasn't expecting this A/C curve ball, so I wasn't logging anything related to A/C. I'm going to add it to my channels for next test drives. If there's anything else I should add for logging which might help, let me know.

Thanks,
Scott

IAC at zero means the IAC is all the way closed.. IT can't go any lower to lower the idle. The blade position needs to be mechanically closed more with the throttle stop. Or a smaller hole in the throttle body blade.

You are using the correct spot on the belcrank for the throttle cable right? There are two. if you use the wrong one it will hold the blade open a bit.
03-04-2024
horsepowerguru427

2 Attachment(s)

Posting the tune would help:banghead: Assuming its a P01 like my 02 z28 LS1, Raise your BRAF 2g/sec across the board from stock and then change ETC scalar from .0255 to .0210 and adjust your IAC steps vs Effective area by shifting tables over to the right as shown in the screenshots i posted. After this you need to tune the air models and then come back to idle tuning if its happier. If its not happier then go ahead and adjust idle based on the second link i posted. After your VE and MAF is all tuned accurately youll have to circle back to idle tuning to get it spot on. Heres a few links thatll get you straightened out for idle.

https://www.performancetrucks.net/forums/tuning-diagnostics-electronics-wiring-161/tuning-101-tuning-dummies-plus-krambos-idle-tuning-tips-tricks-373848/

https://forum.hptuners.com/showthrea...e-(w-pictures)
03-04-2024
edcmat-l1

Depending on the vehicle you may have an adjustable throttle cable (F body). Chances are the throttle cable needs to be adjusted because it's holding the throttle blade from returning to the stop. This is the first thing you need to check. Is the blade set screw against the stop? If it isn't, try to close it further and I bet you'll feel yourself pulling on the throttle cable.

Once you have the blade on the stop, you'll need to adjust it to get your IAC counts/TPS voltage/idle RPM right.

Then from there dial in all your airflow numbers. You'll most likely have to circle back and adjust your BRAF/IAC position numbers after.
03-04-2024
thehemi

Quote:

Originally Posted by edcmat-l1

Depending on the vehicle you may have an adjustable throttle cable (F body). Chances are the throttle cable needs to be adjusted because it's holding the throttle blade from returning to the stop.

Thanks for the advice/suggestions, everyone.

I do appear to be throttle cable limited instead of the throttle stop. This is a 2001 Camaro SS. Let me work on addressing that first and see if I can get the IAC counts right, and then I will start digesting the rest of the suggestions. I appreciate the help!

Thanks,
Scott
03-04-2024
edcmat-l1

Quote:

Originally Posted by thehemi

Thanks for the advice/suggestions, everyone.

I do appear to be throttle cable limited instead of the throttle stop. This is a 2001 Camaro SS. Let me work on addressing that first and see if I can get the IAC counts right, and then I will start digesting the rest of the suggestions. I appreciate the help!

Thanks,
Scott

Follow the throttle cable back from the throttle body. About a foot worth of cable from the T-body you'll see a little black plastic square piece in the middle of the cable. That is the adjustment.
03-05-2024
thehemi

After adjusting the throttle cable, idle is 785-815 (commanded 800) and IAC is 36. I think that's perfect.

I went on a test drive to check on the RPM surge and the car is actually driving great. There was no RPM surging!

With it running really good, do I still consider the IAC Step and ETC Scalar changes? Or just move on to VE tables?

I really appreciate the help! It felt great to go driving without any issues!

Thanks,
Scott
03-06-2024
edcmat-l1

You know the deal. Post a data log.
03-06-2024
Alvin

Quote:

Originally Posted by thehemi

After adjusting the throttle cable, idle is 785-815 (commanded 800) and IAC is 36. I think that's perfect.

I went on a test drive to check on the RPM surge and the car is actually driving great. There was no RPM surging!

With it running really good, do I still consider the IAC Step and ETC Scalar changes? Or just move on to VE tables?

I really appreciate the help! It felt great to go driving without any issues!

Thanks,
Scott

ETC scalar is for fly by wire cars only. It doesn't do anything for cable cars.
03-06-2024
thehemi

2 Attachment(s)

Quote:

Originally Posted by edcmat-l1

You know the deal. Post a data log.

Fair enough! I'm attaching my current tune and yesterday's data log.

Thanks,
Scott