Help with cruise control after LS swap

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DocHanson

DocHanson

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Apr 4, 2025
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Location
Amarillo, TX
I need help solving a very annoying issue with cruise control. I have also posted this on the HPtuner forum. Any leads on someone that could help would be greatly appreciated!

I have a 1987 60 series that I have swapped in a 6.0 LQ9 DBW setup, I kept the stock 5 speed manual transmission (H55f). I bought the wiring harness from BP automotive and have a Dakota digital cruise control panel.

Over the last several months I have spent an exorbitant amount of money and time trying to diagnosing the issue. Currently, I have cruise in 4th gear but when I change to 5th the PCM locks out cruise. As you know, the transmission is analog, so I cannot figure out why cruise doesn't work in 5th gear. BP automotive did their best and over the course of 4 months, we exchanged 100+ emails with several iterations of tunes but they finally threw in the towel. I can supply a copy of the latest tune if that would be helpful for anyone. (I can't attach the file because IH8mud doesn't recognize the file format)

I would be more than happy to pay a professional to take a look and help me diagnose the issue.

thanks for any insight.

-Gabe

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I know nothing about LS PCMs but I've researched LS swaps for a possible swap in my 60. Is there some sort of minimum RPM for CC to work? In your case, is it the RPM drop going into 5th taking you below some minimum value? I would think the VSS signal doesn't know gear selection so that shouldn't matter. Good luck.
 
sims said:
I know nothing about LS PCMs but I've researched LS swaps for a possible swap in my 60. Is there some sort of minimum RPM for CC to work? In your case, is it the RPM drop going into 5th taking you below some minimum value? I would think the VSS signal doesn't know gear selection so that shouldn't matter. Good luck.
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Yes but I’ve tried in all rpm ranges and no dice.
 
I haven’t done cruise control before but the ecu has a set a parameters and as long as it meets them it will work. The question is what’s not being met. If you can find what those requirements are then in live data you’d be able to watch those inputs and see what happing when you’re going into 5th. Might be worth finding a local tuner that can help if you don’t have the tools for it.

From a quick google it needs VSS and RPM so it’s possible the signal isn’t clean or if your ecu isn’t calibrated for the gears and rolling diameter of the tire then it goes out of parameters.
 
I hadn’t thought about the tire diameter.

After several rounds of trouble shooting, it’s currently programmed as a manual transmission (nv3500). I have the gear ratios programmed from the h55f but it doesn’t have a way to program in all 5 gears. It only has parameters for a 4speed.

I am a fairly competent wrench but I’m out of my wheel house when it comes to the tuning side of things. I’d like to find an expert that I could pay to look over my current tune parameters to see if anything is out of sorts.

I’ve reached out to a few guys and have a local guy, but no one seems to have a solution. BP automotive gave it their best shot but finally threw in the towel after 100 emails and 3 months of trouble shooting. Even put a post on HP Tuners forum with no response.

If anyone can recommend an expert I’d be all ears.
 
DocHanson said:
I hadn’t thought about the tire diameter.

After several rounds of trouble shooting, it’s currently programmed as a manual transmission (nv3500). I have the gear ratios programmed from the h55f but it doesn’t have a way to program in all 5 gears. It only has parameters for a 4speed.

I am a fairly competent wrench but I’m out of my wheel house when it comes to the tuning side of things. I’d like to find an expert that I could pay to look over my current tune parameters to see if anything is out of sorts.

I’ve reached out to a few guys and have a local guy, but no one seems to have a solution. BP automotive gave it their best shot but finally threw in the towel after 100 emails and 3 months of trouble shooting. Even put a post on HP Tuners forum with no response.

If anyone can recommend an expert I’d be all ears.
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So if I understand this right, the calibration only has slots for 4 gear ratios? So I'm guessing you have 1st-4th of the H55F programmed? Try programming 2nd-5th instead. I bet the PCM is looking for a valid "cruise ratio".
 
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Lead Head said:
So if I understand this right, the calibration only has slots for 4 gear ratios? So I'm guessing you have 1st-4th of the H55F programmed? Try programming 2nd-5th instead. I bet the PCM is looking for a valid "cruise ratio".
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Correct, only 4 slots

Good thought but we have tried every combination of ratios. Even tried skip shifting to keep from confusing PCM… no dice

Thanks for replying though!
 
are you able to program it to run off of a nv4500? that would give you the 5 gears. or like the other in this thread said, program gears 2-4. it sounds like the RPM is too low for the pcm to register the cruise, especially if its working in other gears. So that means your tac module and brake pedal wiring is working right.
 
dbbowen said:
are you able to program it to run off of a nv4500? that would give you the 5 gears. or like the other in this thread said, program gears 2-4. it sounds like the RPM is too low for the pcm to register the cruise, especially if its working in other gears. So that means your tac module and brake pedal wiring is working right.
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I don t think it’s an RPM issue. When cruise works (4th gear) it works with anything above 45mph, I’ve tested it with RPM ranging from 2k to 3k. Tried the same in 5th rpm ranging between 2k and 2,500 and no dice

I agree that it’s not a wiring or hardware issue, otherwise it wouldn’t work in 4th.

This is where I’m stuck, I don’t know the hptuner software well enough to know how to navigate or change parameters. I assume BP automotive knew what they were doing but I’d like someone to look over my tune and see what they think. Happy to pay for someone’s time if they can help
 
DocHanson said:
I don t think it’s an RPM issue. When cruise works (4th gear) it works with anything above 45mph, I’ve tested it with RPM ranging from 2k to 3k. Tried the same in 5th rpm ranging between 2k and 2,500 and no dice

I agree that it’s not a wiring or hardware issue, otherwise it wouldn’t work in 4th.

This is where I’m stuck, I don’t know the hptuner software well enough to know how to navigate or change parameters. I assume BP automotive knew what they were doing but I’d like someone to look over my tune and see what they think. Happy to pay for someone’s time if they can help
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imo your best bet would be to take it to someone with a dyno and get a full tune. youll probably pick up a few hp while youre there. Whats weird about your situation is that since your trans is analog, theres not really any way it knows youre in 5th gear
 
Do you have a VSS? What about a clutch pedal position switch? Do you have the necessary brake pedal switch hooked up? It looks like cruise requires both a normally open AND a normally closed brake switch input.

The TAC module also needs to be hooked up to the brake lamp circuit apparently, as well.
 
Lead Head said:
Do you have a VSS? What about a clutch pedal position switch? Do you have the necessary brake pedal switch hooked up? It looks like cruise requires both a normally open AND a normally closed brake switch input.

The TAC module also needs to be hooked up to the brake lamp circuit apparently, as well.
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Yep, have all of the above. Cruise works great in 4th gear, but nothing in 5th
 
DocHanson said:
Yep, have all of the above. Cruise works great in 4th gear, but nothing in 5th
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Did some searching. Lots of people have this issue where cruise only works in 4th after doing a manual swap. The computer seems to be calculating what gear the transmission is in by looking at engine speed vs. vss. If the computer can't find a matching ratio, you don't get cruise. The only way it works, is if your manual transmission has the same gear ratios as whatever transmission segment you swapped in (ZF6, nv3500, etc...). All of those transmissions have a 1:1 direct ratio, so the PCM sees that as valid, and allows cruise to work.

The general consensus seems to be that there is another set of transmission gear ratio inputs in the transmission or engine side of things that HPTuners doesn't expose that needs to be changed.

A workaround seems to be setting the vehicle for an automatic transmission. That seems to get cruise to work again.
 
Lead Head said:
Did some searching. Lots of people have this issue where cruise only works in 4th after doing a manual swap. The computer seems to be calculating what gear the transmission is in by looking at engine speed vs. vss. If the computer can't find a matching ratio, you don't get cruise. The only way it works, is if your manual transmission has the same gear ratios as whatever transmission segment you swapped in (ZF6, nv3500, etc...). All of those transmissions have a 1:1 direct ratio, so the PCM sees that as valid, and allows cruise to work.

The general consensus seems to be that there is another set of transmission gear ratio inputs in the transmission or engine side of things that HPTuners doesn't expose that needs to be changed.

A workaround seems to be setting the vehicle for an automatic transmission. That seems to get cruise to work again.
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Your google skills are better than mine my friend! Thank you for this, I will explore this option and report back!
 
toy_tek said:
What’s the trade-off doing this?

Subscribed - have a Gen4 LS I’ll be swapping in later this year with my H55
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From what I’ve read the gen 4 PCMs are much more forgiving. And worst case, you can add a stand alone unit like the Dakota digital vcm-101for your application.

Good luck!
 
Just a thought; Have you tried to get up to speed in 5th then set the CC. This seems like it should work. Sorry if this is way to obvious.
Dyno
 
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