3.7L vs 3.5L programming differences
 

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.

Re: 3.7L vs 3.5L programming differences
 

CHP,
Item # 14 is interesting on the MPG attempt. Understand the MPG table on the 3.7 is -1 mpg below the 3.5 engine.

Re: 3.7L vs 3.5L programming differences
 

I had the 06 now have 07 and mpg is better! Can tell right away just on my normal daily driver routine of fill-ups. weill get stats after full breakin
thanks for the data

Re: 3.7L vs 3.5L programming differences
 

I know nothing of what is being discussed, and am always eager to learn more.:excited:
I've been asking questions about the GM Performance exhaust I had installed by the dealer, and read the posts regarding the PCM programming. I think, I will need to have the dealer service look into the PCM, and tune it to work better with this new exhaust. :confused:

I understand the EFI, requires the PCM to maintain motor function, and that the days of Carburetors, and pneumatic engine controls are gone, but how does one know the correct program for "re-tuning" the PCM to increase performance on any of these factory settings?

And more over, if the H3, for example can get better performance with a re-tune of the PCM, why doesn't the factory make it the best setting to start? Seems like it's counter-productive to build a car or truck, and set the PCM with programs that don't get the best performance out of the motor.:(

Anyone's thoughts?

Re: 3.7L vs 3.5L programming differences
 

PETER PRINCIPLE...

Re: 3.7L vs 3.5L programming differences
 

Evidently you have not heard of CAFE or EPA. There is more to producing a calibration than making it fast(er) for someone. It is a find balancing act on these vehicels, with EPA being number ONE. The vehicle must pass all required emission (this includes the California air resource board- CARB requirements for CA and some other NE states). Second is the balancing act between fuel milage and performance. Yes, it is a Hummer, but GM wants to (needs to) get the best possible fuel mileage while keeping a decent power rating.