I was asked about the differences between the programming for the 3.7L and the 3.5L. This may not mean anything to some of you, but here are the major differences in PCM programming between the 3.5L and 3.7L (auto tranny):

1) The 3.7L has a little higher idle in gear when cold and high temps (241F and over).

2) The MAF calibration table is about 8% higher, but the 3.7L has a new MAF.

3) The VE tables are different (as expected with a slightly different displacement). The low, mid, and high cam threshold angles are a little higher with the 3.7L.

4) The deceleration fuel cutoff is disabled for 3rd and 4th gears with the 3.7L. For my tuning, I only disabled the DFCO cutoff in 4th gear. Sometimes when going down a hill, I’ll put the tranny in 3rd and let the compression slow me down instead of riding the brakes, and the DFCO in 3rd helps.

5) Open loop A/F is a little different.

6) Closed loop enable is much quicker with the 3.7L. The closed loop delay time is now zero.

7) The WOT A/F is a little leaner with the 3.7L.

8) The lowest COT temperature threshold is 9F higher with the 3.7L.

9) The high octane timing table is generally higher with the 3.7L with the exception at low RPMs (idle and lower).

10) IAT timing adder pulls out about 1 degree more timing above 176F with the 3.7L.

11) The cat lightoff is a little different.

12) The 3.7L has lower burst knock retard (base vs CylairDelta).

13) The ETC max vs RPM vs Max torque is less restrictive with the 3.7L.

14) The tranny shifts to a higher gear for lower TPS’s with the 3.7L. I’m guessing this was done to try and improve MPG with the higher torque 3.7L.

15) The 1->2 and the 2->3 shifts are softer with the 3.7L.

16) The torque converter locks at lower speeds with the 3.7L.

17) The torque reduction during shifts is less with the 3.7L.

 

Good informatiom..So can that 3.7L factory tune still be improved on?


Imoved this threadhere, to keep this kind of good information with the topic for easier searching.

 

I think the 3.7L programming can be improved upon. Maybe Alvin can chime in on how much gain they are seeing with the 3.7L.

 

CHP, that's a great post, with a real insight into the things that a PCM controls. Thanks. And yes , I would like to hear what Alvin has to say on both what GM has improved upon and what he can improve from there.

 

i asked kelly a month or so ago
she said there was no difference in the tune
now chevyhighperformance has got me thinking
im in the group buy but id like to have kelly or alvin
chime in on this 3.7 difference
i still want the tune if its gonna be worth it

 

I'd be curious also.

 

Curious as well with 2 days left for the buy lol.

 

I'm sorry, I meant to say that there is not a big difference in the tables that we change from 06 to 07 (i.e. we modify the same things, just by different values).

We've already got 2007 tunes on the ground, people seem to enjoy them as much as the 2006's. If it came from GM, it can be improved upon

 

Kelly, I got my PCM installed over the weekend, I dropped off my PCM to ship to you, should see it by Thursday. Looking forward to getting my unit back and feeling the results.

thanks again to the gang and PCMforless and to Hummer Forums for a heck of a deal.

 

Good to get feedback. Everything about PCMforless seems top notch!