J_dude

Hey all,
I’ve done some searching and I can’t find anyone with an issue like this, I can turn on my cruise, set it at 90 km/h, it will work fine. But if I hit accel and slowly speed up it will get up to around 97-99 and then just shut off. And it will not work above 100 km/h, just won’t hold.
Now, when I bought the truck the cruise didn’t work at all, and I found out why, there was a vacuum line that had been cut/broken and was capped off. It was on of the ones that go to the little... um... thing? under the driver side battery box (I’m assuming it’s the cruise module or something). So I replaced that line and went for a drive, see above scenario for the results of that test lol. Anyway it just has never worked properly so I have had to become very good at holding a steady speed for very long periods of time haha
But recently, after buying a car that actually has cruise that works, I have become spoiled and now I want this thing FIXED lol so I’m trying to figure out how to start diagnosing this issue, I don’t even know where to start.
Any help greatly appreciated! Thanks!

Jude

(oh yeah, I have also replaced that THING under the DS battery box with no improvement)

AlpineRAM

If the cruise kicks off at a certain speed it's because the software in the PCM has a limiter set.
I know that it was illegal to sell vehicles that would go illegal speeds on the highway in cruise control in some regions.
Maybe a dealer with an old tech can help you.

AlpineRAM

Something else that you can check- if your wheels are unbalanced or out of round there is a speed where the frequency of the shake is just right- and your brake pedal moves, cancelling the cruise.
Try lifting and holding the pedal up with your left foot and see if you get more speed out of your cruise.

J_dude

So I tried this^ and no improvement. I’ve tried using the cruise on many different roads in varying states of disrepair and it always cuts out at around the same speed, regardless of road conditions so I had my doubts but thought hey why not give t a try lol. Actually on my way home from work yesterday I tried it and it wouldnt even get up to 98, was cutting out around 90 but I think that might’ve had something o do with the truck being cold at the moment.

J_dude

Also if it is a limiter in the pcm I will need to get someone to hook up the computer and delete it right? I’ll have to ask the local mechanic about it tomorrow, he has an old Cummins too and knows quite a bit about em.

Thanks!
Jude

bigbaddog

Just a thought here but where did this truck start it's life [us or Canada]. Was just thinking about if it had a mismatched bunch of electrical parts. Was just thinking and I everybody that knows me knows it is NOT my strong suit. Mike

J_dude

Good question, as far as I know it’s always been a Canadian truck, however I’ve never verified and I’ve only had it for a year and a half now so I suppose it could be a possibility. Is it possible if it somehow was limited to 99mph and then switched to km/h it would still shut it off at 99 even though it’s not actually the same speed? That doesn’t sound like it should work that way. I’m with ya on the thinkin thing, I think I’m confusing myself here.