so finished installing my 4.05 trans, only issue I got is in cruise control my car speeds up and slows down constantly. will boost 3 psi, then goto -20 vacuum, then go to -10, then hang a bit, then do it again. anyone ever seen this issue?

 

Almost sounds like the speed your wheels are moving is disagreeing with the rpm it's at. Is there any settings that hpt can adjust? Like the final drive ratio so the computer recognizes the speed vs rpm?

 

How big of speed changes are you seeing? Is it just a couple of k? Or is it more significant?

 

like 3 kms or so. its possible it could be from the cracked oil separator I found, tried to fix it but it broke again so vacuum leak. I went back to stock setup bypassing separator, see how it works tomorrow.

 

other than that idk. Hp tuners has a final drive option but its set to 1.0 on tune and on stock tune so I don't think that should be changed. I'm hoping its just the vacuum leak I had there, I'm tired of trouble shooting already

 

Well fixing the vacuum leak didn't work

 

Check to see what the final drive is set to on the LSJ tune.
You may need to change it to that.

 

It's an Lnf.

 

And?

He put the trans in from the LSJ. Check a LSJ tune for final drive setting. Put that value into the LNF tune. See if problem is fixed.

 

Where would u do that in Hp tuners. There are no options under transmission, and the only place it has final drive settings is under speedo, which is set to 1.0 it's like that on stock tune as well, what would u change it to

 

It's like I'm pushing the gas then letting go, so weird

 

It sounds kind of like when you put the car in third and go like 100 and set the cruise and ts just super sensitive making minor speed adjustments maybe it's just more sensitive with the lower final drive and needs adjustments in that regard.

 

That's not what I thought you meant. And I was just stating it for the record.

 

I have no tune files on my work computer and forgot my laptop; I will try to look when I go home.

 

Minor adjustments doesn't need to boost to 5 psi then fall to -20 vac. If it would stay within -10 to -5 like normal yes, but not what it's doing

 

I'm saying what is normally a minor adjustment is being multiplied by the new gear ratio so it's no longer minor. I'm sure someone has had experience with that. It must be in the tune.

 

Ah yes. I wonder if anyone else with that trans has had this issue. I need an lsj tune to see what their speedo final drive is set at

 

I will look when I get home; couple hours.

 

I dont know about an lsj but all the stock base tunes ive looked at have the FD set to 1.0

 

I have an l61/f23, but it sounds like everything is constant. My FDR is/was set to 1.0 in the tune as well. when I swapped to a new FDR, the speedo and everything related stayed correct without any changes to the tune. It just goes on pulses per mile of the sensor, which reads "after" the final drive. So final drive should not affect how the sensor reads, since it measures output revolutions. The only thing you should have to edit under the "speedo" tab is the PPM if you change tire sizes (if you want the speedo to be accurate).

I don't have cruise (so I can't confirm 100%), but I don't see that being the issue. I haven't heard of anyone having these issues when swapping FDR.

The car runs 100% except for cruise?

 

did you reset your trims after you fixed the leak? just a thought

 

Trims are good but I'll try again. The leak was there even with old trans I believe. I'll try to change maf. And reset ecu

 

I went through it; it's not the tune. FD doesn't matter in it.

 

Have you played with your throttle sensitivity at all? Not sure if that would effect it under cruise or not

 

Alternative thought did you break your speeds sensor or not scree it in all the way on the new trans?0