What happens at 3500 RPM?

[mpyusko]

I get a power surge. It almost feels like a downshift, but it's not.

 

[Dropped88]

This a tbi or vortec?

 

[thegawd]

bad tps?

 

[Schurkey]

I get a power surge. It almost feels like a downshift, but it's not.

First Guess: Torque converter clutch disengaging.

 

[mpyusko]

Votrec 7400.
I mean it's consistent. first and second gear at least. (Never wound it out that high in 3rd). It hist ~3500 RPM and then there is a surge of power/acceleration. Kinda cool, but kinda strange. It's been doing it forever, I've had this truck for 8 years. Several Tune-ups, new TPS, IAC, EGR, and other stuff, so I don't think it's related to that.

 

[Schurkey]

If it's doing it in first and second gear, it's not the torque converter clutch.

Connect a scan tool, look at the data stream around the time you feel the "surge".

 

[L31MaxExpress]

If it's doing it in first and second gear, it's not the torque converter clutch.

Connect a scan tool, look at the data stream around the time you feel the "surge".

4L80Es lock the converter in 2nd gear, even at WOT.

My guess however is that he is finally reaching the programmed time or rpm delay for power enrichment to kick in and he is feeling the air/fuel mixture richen up and the PCM advancing the timing. Some 350s as well as the 7.4 and 8.1 have a very long delay before they finally get into power enrichment. 6.0Ls also have a very long PE delay. GMs way of trying to get some fuel mileage out of the heavy GCVW trucks.

 

[L31MaxExpress]

Factory 0411 L31 van tune had a pretty pronounced PE fuel delay. Back when I had first swapped to an 0411 and it still had the delay in place. Really woke up around 2,800-3,000 rpm in 1st gear. Engine tone would change and it would just open up and take off. Air/fuel mixture richens from 14.7:1 to about 12:1 and the timing gets bumped about 6° more advanced resulting in a big bump in torque output. TUNE is a must to fix it. Eliminating the PE delay knocked nearly 3 tenths of a second off my 1/8 mile time on a stock L31 van. Power Enrichment came on around 25-30 mph.

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[mpyusko]

Ya know I've always said the truck is kinda amazing. "It's like the more power it needs, the more it creates". My example our old minivan was pretty zippy, but when you loaded it up with 8 people, it was a slug. The truck though.... I had a half-cord of firewood, 6 people and camping gear in it and you didn't even notice a difference. So this PE kicking in kinda makes sense for what I'm feeling. It literally takes me from .8 G to .88 G accelerating (yeah.... I put an accelerometer on it to measure it. LoL)