No power until +/- 2500 RPM

[supajut]

Hey, this is the tune from my buddies 02 GMC 5.3. We are having a hard time with gains down low. The truck has a small cam, LTs + ORY, Efans, CAI, and a high flowing muffler. The truck wont even burn the tires off the line and doesn't really start pulling until around 2500 RPMs. Is there something we are missing. The truck was tuned with a LC1, the VE is almost spot on. It has never been able to burn the tires without a substaintial amount of brake. Any advise will greatly be appreciated.

J

[ElecTech]

You can try incresing the PE Enrichment rate to try and get max enrichment ramped in sooner and make sure that you don't have any timing retard at the lower rpms. Also, keep in mind that tire size can be a factor with how a truck, or car for that matter "feels" down low. I get alot of guys with larger tires but still running stock gears ask me why I cant make it accelerate faster. The PCM and tuning software will only give you what you have, no more. Hope this helps.

[supajut]

Yeah thanks, I understand that. I am just confused what tuning differences there are on some 5.3 trucks that make some have gobs of torque and some lack all low end power. Granted it is cammed, but it is a "baby" cam. I am just wondering if there is a power limiter that I missed. Anyhow, THANKS!

J

[blkgoat]

It takes longer for air to flow through LTs as well. I don't see significant gains in hp until 3000 rpm.

[EC_Tune]

You got a TON of timing down low and probably pulling all of it back out (and leaving it out for a long time) because of KR. Get that a little closer to stock and monitor KR down low.

You didn't mention a converter or anything else done to the trans?

[jknox]

Does a run look something like this attachment? This is one of my first-ever runs at a local track last friday night (truck needs a driver mod more than anything else right now!).

You see it flash to 1800 (stock stall), then at 2500 you see it start pulling harder.

Only perf mods at this point are my lame tuning, opened up airbox, and efans. Air sucked (high humidity, 85*), IAT was 100*. Tune is still on stock high-octane spark table. Changes are primarily VE, PE, trans pressure tables, abuse mode off, 25% TM reduction, and wot shift points. Ended up a little lean (13.1:1), ran a 10.50 @ 68.59 (1/8 mile).

Mind you, I don't know what it means yet, but I see it too...

[7420NW7TH]

If you have a stock converter you probably need something with a higher stall to go with that cam. Also, what gear are you running? And what are the specs on your cam?

[EC_Tune]

Looks like the PCM is running off the LO Spark table.

[jknox]

Not sure which of us you're referring to, but my tune has high copied over to low (I have learned some things ). And looking at supajut's file, he does too. Mind you his is pretty different from mine...

[jimmyblue]

Look to see whether burst knock retard is activating on
you, earlier 5.3 with the cable throttle that I messed with
had burst knock delta CylAir thresholds that were too low
and it pulled a bunch of timing anytime the RPM was trying
to rise fast (basically, the VE table slope you traverse was
making the delta w/ RPM large).

Trucks also had a crappy PE enable setup, mode delay and
high enable TPS and slow ramp and used low timing to cover
it (too bad about performance but enjoy that extra MPG
while towing gutlessly).

I would log all spark retard related PIDs one time and see
which (if any) may be meddling. And commanded fuel air
multiplier so you can see if you are getting PE on cue or
if she's witholding.

[supajut]

WOW, sorry guys!!! Been on Vacation, still am. Will check into these things and post back up. THANKS!!

[supajut]

OK, we logged the timing and put the values closer to stock. No KR is being pulled and no noticable difference. We logged the PE and it isn't kicking in until around 3600 RPM, is this common or is this the major limiting factor? EC the trans has a servo and a shift kit, he is saving for a stall..... The gears are 3.73 with stock tires. I don't have the cam card infront of me..... I think its around 212 with 550 lift. Jimmy we set the values higher in the burst knock so it won't come into play. I guess we need some help in the PE department. Thanks guys!!!

[jknox]

Don't know why it would be taking *that* bleepin' long, but you can speed it up. Looking at the original tune you posted, set PE Enable torque to 0, and Enrichment Rate to 4.

If you've got ve in line and the knock is gone then lean it out some! Right now you're commanding 11.4:1 at 4400+ (stock tables suck). I didn't see you say you've got a supercharger on this thing.