1994 LT1 ~ Eliminate VSS?

[dave w]

I'm wondering if anyone has suggestions / ideas on how to eliminate the VSS for a 1994 LT1 PCM. I'm working on a LT1 powered off-road application, see pictures below.

Thanks,
dave w

[steveo]

zero the min speed for closed loop idle thing, so it'll be in normal idle mode all the time.

for BLM, with no VSS, it will be stuck in cell 17/18 all the time. to get around that, set the minimum ccp to enable blm (i forget the exact name, im at work) to 0%, and disable the CCP by setting the enable temperature out of range. i assume you dont require the CCP solenoid anyway.

i'd probably disable DFCO, although i doubt it would enable on you, better safe than sorry.

that's about it, should work fine. you'll have no iac speed follower or whatever, but who cares.

that's about it; i've tested it before, i ran without a vss for a few weeks while i was waiting for a pigtail, barely even noticed.

[dave w]

zero the min speed for closed loop idle thing, so it'll be in normal idle mode all the time.

for BLM, with no VSS, it will be stuck in cell 17/18 all the time. to get around that, set the minimum ccp to enable blm (i forget the exact name, im at work) to 0%, and disable the CCP by setting the enable temperature out of range. i assume you dont require the CCP solenoid anyway.

i'd probably disable DFCO, although i doubt it would enable on you, better safe than sorry.

that's about it, should work fine. you'll have no iac speed follower or whatever, but who cares.

that's about it; i've tested it before, i ran without a vss for a few weeks while i was waiting for a pigtail, barely even noticed.

Awesome!

Thanks!

dave w

[steveo]

i forgot to mention, do be aware that you'll have no cell 16-18 anymore if you use my blm workaround; that means it'll idle/decel/whatever in whatever cell it lands in, which is not designed behavior... this may require altering your blm cell boundaries.

i also found it best to place high vacuum into its own group of cells so engine braking doesn't corrupt regular driving cells, and just ensure hot idle is in a cell that doesnt have a lot of other activity.

[EagleMark]

With the BLM cell memory being effected reworking the BLM cell boundaries is a great idea. Not so much an issue with older ECM that don't have seperate cells for idle, DFCO etc... that the LT1 PCM has.

But this would effect the usual BLM data logging for VE fueling adjustments? Hmmm... I wonder if doing the VE fueling would be better by swapping over to STFT (INT)? Just thinking out load... may not be necessary as the data log would be showing the BLM in correct cell, but the PCM memory of the BLM would not be in correct cell... so INT would forever be changing the cell it's stuck in making BLM not accurate?

[EagleMark]

You know, thinking about the way the LT1 has more BLM cells for Idle, Off, DFCO, etc... and no VSS it will always be in 17/18 as steveo mentioned. So both INT and BLM are going to be a never ending change depending on what engine is doing, either idle or cruise or load all in same cells. So both INT and BLM data logs for VE or MAF fueling is not going to be good at all.

If it's a stock engine with relatively stock incoming air tube to MAF? I don't think it would even need tuning. Without MAF or modified engine tuning would have to be done with WB.

Unless I'm not thinking clearly and someone corrects me?

[steveo]

nah. you just force it to use ordinary driving range cells (0-15) as i mentioned.

[dave w]

I've completed most of the mods outlined above. I'm also deleting the MAF.

Where do I find the "blm workaround"?

dave w

[steveo]

there that'll do it

[dave w]

there that'll do it

Thank you!

dave w