pcm adjustment
 

When I had my harness done 3 years ago the programmer/Harness modifier asked me for info on my truck such as rear end ratio. a/c etc. I gave him all the info and I assume he programmed it into my pcm. Well come to find out I gave him the incorrect info on the rear end ratio. I have a 3.70 and he programed a 3.07. When I contacted him 3 years ago I asked him to change it, He replied drive it and see how it works. Well, I tried contacting him and he doesn't respond, I live in Houston and been asking around and can't find anyone who will take my pcm and reprogram it with the correct ratio. Does anyone know of anyone who I can send my pcm to that can do this. I can't believe it can be that difficult. I don't want a 700 dollar tune just a ratio change. Or am I asking for something that is does not affect my daily driving or can't be done.

Re: pcm adjustment
 

Have you tried Brendan at LT1Swap.com? He's about the cheapest for simple tunes like that.
https://lt1swap.com/programming.htm

Re: pcm adjustment
 

sent him a email today

Re: pcm adjustment
 

I would drive it and see what the shift points are like along with the torque converter lock up. I like to have the 4th gear engage and TCC lock up after 45 mph. Helps prevent lugging the engine.

Re: pcm adjustment
 

i been diving it for over 2 years, Not sure how i would know when the converter locks up. My reason for changing the ratio in the PCM is the gas milage is not good, Around 12mpg. I think maybe I am never getting into overdrive because the ratio and the computer are not working together, I don't have a tach

Re: pcm adjustment
 

Someone will correct me if I'm wrong but I think the only thing the improper ratio setting would effect would be the speedometer.
You may be able to benefit from someone with HP Tuners that could take some real time readings to see why it's mileage is so bad.

Re: pcm adjustment
 

I am running a manual speedo with original cable off the back of my 460L, I had a guy on ebay machine my tail housing to make this work.
As far as HP Tuners still trying to find someone to look at it but in Houston they all want around 700 to do a tune and I am not sure if I need a full tune I am not racing it just driving like a old man.

Re: pcm adjustment
 

Since you don't have a tach it's a bit harder to tell when the converter locks up but you should be able to count the shifts 1-4 and then there you should be able to hear/feel a small drop in rpm.

Re: pcm adjustment
 

The only problem with having someone else do it you will have to pay for more credits. (usually around $100) If the person that originally tuned it changes it, all you would have to pay for is his time to do it. It would only take about 15 minutes to do it. It would take longer to hook the computer up than it would to change the ratio perimeters.

LockDoc
'

Re: pcm adjustment
 

Someone will correct me if I'm wrong but I think the only thing the improper ratio setting would effect would be the speedometer.

An incorrect speedometer reading isn't the only issue. Shift timing is also affected.
The computer reads, speed, throttle or engine load and engine and transmission temperatures to schedule shift quality and timing. If it is cold out the transmission shifts late till it warms up.
Tuners can change the speedometer reading which affects the transmission. They can also set WOT shift rpm and this can be different for each gear. The computer also anticipates shifts and raises the transmission's line pressure before the shift and then reduces after the shift. Not even touching on "torque management" which will reduce engine power for the shift.
Kind of crazy isn't it?

My truck ran night and day different after the tune. I hated to do it as I considered it overpriced. Afterwards, I thought I received every penny worth as the truck ran so much better.
I drove it home, from the tuners, on the back roads and embarrassed myself in front of the cows.... It was a blast.

You didn't mention if your tune was on a dyno or if your motor has an aftermarket camshaft.
I had a small exhaust leak 6 inches below the O2 sensor and the tuner knew and even could tell me what side it was on.
The details the OEM's go through to get this correct is astounding. The smallest item like an exhaust or vacuum leak upsets the system.
Do you have an exhaust leak any where slightly down stream or anywhere upstream from the O2 sensor. That will wreck havoc with how your motor runs.
Cheers

Re: pcm adjustment
 

Many of the tuners have the unlimited license for HP Tuners for the Gen III PCM's, I'd have to go look at HP Tuners website to see how many credits you need for a particular type before you end up unlimited, but it's likely a 'tuner' would not need to purchase any credits.

Ok I looked briefly, here's a thread on it - https://forum.hptuners.com/showthrea...ed-gm-gen-3-v8

There are new tools out there besides HP tuners that allow you to tune for free also. For example...

I had my harness touch my exhaust and it grounded out one of the injector trigger wires from the PCM, caused the injector to stay open all the time. Was lucky to not hydrolock the engine with fuel. I was getting white 'smoke'(fuel) out one tail pipe. Tail pipe smelled like gas.

I fixed the harness and the engine ran fine, but I had a code that I could not get rid of. Something related to injector trigger can't remember the number.

I troubleshooted it down the the only possible problem being the PCM. If I swapped the PCM, that would mean I would have to buy more credits from HP Tuners for the new PCM.

I ended up buying a OBDLink LX and used PCM Hammer to clone my old PCM to the replacement. Worked great and that code has not returned.

That really opened my eyes, if I had another swap vehicle with a Gen III engine, I could just make another clone of my PCM and wouldn't need more credits.

Re: pcm adjustment
 

Yes, I knew there was an unlimited version. I have HP Tuners but I only modify ECM's for myself and a few friends. I don't do enough with it to justify an unlimited account. I will have to read up on the OBDLink LX.

Thanks.
LockDoc
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Re: pcm adjustment
 

I sent my pcm and harness to someone in CAl. They ask my for-tire size. rear ratio and other things. Got it back in the mail. hooked it up and that is all I know. they programmed 3.07 instead of 3.70. I called them at the time they said drive it and if you still want it changed call us. I did no response. There's got to be someone out there I can send my PCM to that can make this change for less then a full tune.

Re: pcm adjustment
 

Search "mail order tunes" over on LS1tech.com. There are a number of companies that possibly could help you.

Re: pcm adjustment
 

Get the OBD Link cable and just do it yourself.
If you were local I’d have you bring the PCM by and I’d show you how to change it. It’s really simple.