LS2 only runs right EXACTLY every third ignition cycle

[patooyee]

2006 LS2 out of Chevy Trailblazer SS in a rock buggy running E40 ECM. Running stock tune without VATS or emissions. Has been running this way for years now. Runs great, exactly as it should, only EXACTLY every third ignition cycle. The other two ignition cycles it runs like crap, apparently in some sort of reduced power mode, but there are no codes or check engine lights. When it's running right, it will continue running right until you shut it off. To get it to run right again, you simply flip the ignition switch on and off twice and then on again. If you try to run it on the first or second cycle, you get reduced power. We've come to just flip the ignition switch twice every time before starting it out of muscle memory. It's 100% reliable in the pattern. The only way the pattern is broken is if you disconnect the battery, which starts the pattern over. If you shut it down and then flip the ignition on and off once and then try to start it again months later, it will still be waiting on the 2nd cycle before it will give you the normal power on the third.

Weird, right? Any ideas?

[blindsquirrel]

I have an idea, how about post the tune file, and a log of when it runs bad, and a log of when it runs right, and a list of all the parts being used (intake tubing? MAF? fuel system/regulator/rail pressure?) and I guess the wiring harness will always have to be an unknown but those things would be an absolute bare minimum to start with.

[patooyee]

Not my buggy but I'll try to get some logs from it this weekend. Is there anything specific that you'd like me to log beyond the standard stuff?

Stock MAF
Stock Fuel rails and injectors
Corvette regulator
58 psi at the rail both when running right and in reduced power
Does have custom intake tubing but nothing about it is changing every third key cycle or battery disconnect.
The harness is custom and was done by a third party. I will say that we're not impressed with it, but again, nothing about it is changing every third key cycle or battery disconnect.

Tune attached.

buggy no vats no emissions 2-23-18.hpt

[blindsquirrel]

screenshot.10-11-2023 22.31.06.png

[patooyee]

Yes, it has a th350 trans / no tcm.

[blindsquirrel]

Tune file has a TCM in it. OS is 24235341. How did that get into the file if it's removed?

You can't turn an auto trans ECM OS into a manual trans OS just by flipping the trans type to manual.

This should be SPS'ed as a 2006 SSR, that one was built with a manual trans option and uses the same service number (12596679). 1GCES14HX6B121492 or 1GCES14H36B121608 are both confirmed manual optioned SSRs.

[blindsquirrel]

screenshot.10-11-2023 23.45.20.png

[patooyee]

Tune file has a TCM in it. OS is 24235341. How did that get into the file if it's removed?

You can't turn an auto trans ECM OS into a manual trans OS just by flipping the trans type to manual.

This should be SPS'ed as a 2006 SSR, that one was built with a manual trans option and uses the same service number (12596679). 1GCES14HX6B121492 or 1GCES14H36B121608 are both confirmed manual optioned SSRs.

That is how I've done every conversion I've ever done and it has never been an issue. I've probably done 10 that way and the rest worked fine. If it's looking for a tcm, wouldn't it throw a code saying so?

[edcmat-l1]

Pretty sure this is why it's not setting a code. Just a guess LOL

[patooyee]

Pretty sure this is why it's not setting a code. Just a guess LOL

I'll re-enable that code and it should pop up if the theory is correct then.

[patooyee]

Tune file has a TCM in it. OS is 24235341. How did that get into the file if it's removed?

You can't turn an auto trans ECM OS into a manual trans OS just by flipping the trans type to manual.

This should be SPS'ed as a 2006 SSR, that one was built with a manual trans option and uses the same service number (12596679). 1GCES14HX6B121492 or 1GCES14H36B121608 are both confirmed manual optioned SSRs.

I'm not trying to argue with you, I'm happy to try your suggestion. But I'm also trying to learn something. So can I not just use this option?

Untitled.jpg

[edcmat-l1]

No.

Easiest thing for you to do is grab a 06 Vette or GTO manual trans calibration off the repository and do a write entire.

[blindsquirrel]

'06 Vette is E38, and '05 Vette's E40 is a different service number and can't be flashed to the '06 12596679 E40. GTOs have a lot of Aussie-based weirdness in them, the SSR is the same truck as the Trailblazer just with a different body and a factory manual trans option.

How did the TCM OS get into the tune file? Was the file created before the swap was done, when the TCM was still present in the harness? 'Cause if somebody had done a 'read entire' after it was chopped out it wouldn't be in the tune file.

[TheMechanic]

Got one for an 05. Manual trans SSR

E40-2005-SSR-6.0-manual-12596734.hpt

[edcmat-l1]

'06 Vette is E38, and '05 Vette's E40 is a different service number and can't be flashed to the '06 12596679 E40. GTOs have a lot of Aussie-based weirdness in them, the SSR is the same truck as the Trailblazer just with a different body and a factory manual trans option.

How did the TCM OS get into the tune file? Was the file created before the swap was done, when the TCM was still present in the harness? 'Cause if somebody had done a 'read entire' after it was chopped out it wouldn't be in the tune file.

Yep you're right my bad. I forgot the E40 was one year only in the Vette.

[patooyee]

How did the TCM OS get into the tune file? Was the file created before the swap was done, when the TCM was still present in the harness? 'Cause if somebody had done a 'read entire' after it was chopped out it wouldn't be in the tune file.

It's my friend's buggy. He purchased it without engine. He had the complete donor TBSS. Yes, I read entire from the original TBSS, removed VATS and emissions, and wrote it all back into the e40 after he installed the engine into the buggy. It has been years since this was all done all I'm trying to recall it all in sequence correctly.

Coincidentally, my personal buggy engine at the time was an 05 SSR LS2 with e40 and manual trans. I'll post that file later when I'm back at my computer. I looked at it this morning before I left the house though and there was no tcm.

I'm curious what the red circled option i posted earlier does if not meant for this specific purpose?

[blindsquirrel]

Got one for an 05. Manual trans SSR

E40-2005-SSR-6.0-manual-12596734.hpt

2005 and 2006 are different service numbers and calibrations don't interchange between them. And, it needs to be SPSed not HPTed, so the 2006 VINs up above are all that's usable or needed (and the tools/means to do the SPSing).

[blindsquirrel]

I'm curious what the red circled option i posted earlier does if not meant for this specific purpose?

Nothing you can do in HP Tuners will convert the auto trans ECM OS into a manual trans ECM OS. Not even a write-entire with a manual file, because HPT only writes 6 of the 8 segments in the ECM. It must be flashed with a stock GM calibration using dealer-type tools, and that's done by feeding a VIN from the desired vehicle into GM's SPS. The two VINs up above are both the correct year and confirmed by the TIS lookup service to be manual trans-built trucks (trying to look up the TCM calibration on something that wasn't built with a TCM gives the 'sps.exception.no-valid-cop' error message).

[Alvin]

I'm honestly not sure that leaving this as a TBSS with no automatic is a issue other than not getting VSS into the computer ever.

I"m trying to think if I've done a swap or something like this and I can't think of one. I feel like I did some jet boats this way. I just can't remember at this point.

I suspect there is a code popping up after a few key cycles and whatever that is.. causes the engine to run better. A log would be helpful.

[patooyee]

2005 and 2006 are different service numbers and calibrations don't interchange between them. And, it needs to be SPSed not HPTed, so the 2006 VINs up above are all that's usable or needed (and the tools/means to do the SPSing).

Thanks again for your help. I'm not sure this is worth paying a dealer to do to my buddy, but I'll make sure he knows it's an option. I'm going to his place on Wed. evening to re-enable that TCM code to see if it pops up. But i do have a few questions just for my own educational purposes:

1. What does SPS stand for? (I searched the acronym list and it's not there.)
2. What does that red circled option do? What's it there for?
3. Is converting auto to manual using the switch in the ECM possible on older ECM's? While this was the only E40 I've ever done this way, I've done it that way on every 411 I've ever done and none have ever had any issues.
4. How / from where are you getting these service numbers?