More PCM tune questions

[dhanger]

I know PCM tuning is discussed ad nauseum all over the place but it's a bit difficult to pull together everything I need to know specifically for my case. I just had the tranny rebuilt and I'd like to have the tuning done mostly for the benefit of the tranny plus the performance improvement.

My TB is the only ride for me and my wife so I can't go without it long enough to send it in and have it done. I contacted Jeremy at Lime Swap about a loaner or junkyard PCM and here's what he told me:

8) I no longer offer the loaner service. You can send me a junkyard PCM, but the make, model, year, and gear ratio all have to match

So I plan to grab one from the pick and pull but not sure of myself. As I understand it the gear ratio is listed as an RPO code in the glove box? I found an RPO spreadsheet here so I'm assuming that's my best option to clear that up. Based on the attached photo and cross referencing the spreadsheet I see GT4/3.73 ratio, so I'm pretty sure I have that covered. Also what's the easiest way to check the model year, I don't see model years in the RPO list. The VIN has it I'm sure but don't know how to decode it.

I'm planning to ask for the air injection codes deleted, I've owned the vehicle for 20 years and never had a related DTC show up for that but I'd like to be proactive about it and knock it out before it happens. Any other favorites I should ask for on my 2004 TB LS? I'm not planning any mods so not looking for anything unusual. I did ask Jeremy about Passlock, his reply:

1) I would leave passlock stock on a Trailblazer. This option is mostly for folks with a Colorado, as those systems fail a lot.

Any comments on that?

Thanks,
Dan

 

[dhanger]

Okay, I did find the model year in the VIN code so that question is answered:

VIN-to-Year Chart | ALLDATA

The VIN (Vehicle Identification Number) is a serial number used to identify an individual vehicle. The VIN for each vehicle is unique.

www.alldata.com

 

[Mooseman]

Also what's the easiest way to check the model year, I don't see model years in the RPO list. The VIN has it I'm sure but don't know how to decode it.

That would be in the VIN itself, 10th digit. In the pic is a 2004.
(you answered that one yourself while I was typing )

I'm planning to ask for the air injection codes deleted, I've owned the vehicle for 20 years and never had a related DTC show up for that but I'd like to be proactive about it and knock it out before it happens. Any other favorites I should ask for on my 2004 TB LS?

Definitely kill the SAIS codes. Next would be the fan codes so you can use a thermal fan clutch from a 2008 instead of the failure prone electro-viscous fan clutch when yours does fail. I'd have the shift firmness increased to a medium just to reduce heat and wear from comfy slipping clutches. Then, have the TCC lock up 100% instead of slipping to lockup to reduce wear of the TCC and the valve in the valve body. It will feel like a 5th gear. Have torque management removed so the engine feels snappier. Never regretted that one . If you want, you can also have the 100 mph speed limiter removed.

Unless you live in an area prone to auto theft, I'd still have the Passlock taken out. It can, and has failed on our platform too. You still have to do the 30 minute security relearn with the "new" PCM.

Be sure to try the new PCM in your truck before sending it just to be sure it works after the security relearn (you won't have to redo it again when it comes back). You will need a CASE relearn requiring a high-end bi-directional scan tool or a Tech 2 or you'll have to take it to a shop or dealer that can do it. You will be able to drive it.

Be sure to keep your old PCM as a spare. It will work without anything to be done to it.

 

[dhanger]

Be sure to try the new PCM in your truck before sending it just to be sure it works after the security relearn (you won't have to redo it again when it comes back). You will need a CASE relearn requiring a high-end bi-directional scan tool or a Tech 2 or you'll have to take it to a shop or dealer that can do it. You will be able to drive it.

Thanks, that's the kind of info I was looking for. Regarding the CASE relearn, I understand that if the crankshaft position sensor is replaced the relearn procedure is required also. I have never replaced the sensor; since I have to do the relearn anyway is there any reason I should make a pre-emptive strike and replace the sensor at the same time?

 

[Mooseman]

Because the crank angle is specific to each engine, the used PCM will have the learned angle from the junker and may not be the same as yours. You could replace the crank sensor however I haven't heard of many of these failing. You could try it for a while and see if it trips a code for it. It won't prevent the engine from running. It's only to report when the timing chain is over-stretched.

 

[dhanger]

I see, so I infer that the whole reason the PCM has to do the relearn is *because* of the inherently wrong angle. I think I'll just skip replacing the sensor and only do it when necessary.

Thanks for the help on this issue.