tut5079

It has fairly new hardened pushrods and beehive springs and I am getting no float but thanks keep the ideas coming one of them is hopefuly gonna be the right one lol.

Blown02Sierra

well the pressure is dropping no doubt at the top end, but not a significant amount so i would believe that you have enough air (I think you may be reaching your turbo's limits, but i dont know much about turbos).... Where is you're IAT sensor? Is it still the stock one in the maf? If so, is your maf before or after your turbo? If it were before, i would definitely say heat soak and/or knock retard because your iat readings look mighty solid and i would expect more heat, even from a turbo.

tut5079

That reading was not from the truck it was just the ambient in the shop ,my IAT is after the IC and they were from 68-83 during the pull.I am coming to the same conclusion that I might be out of turbo

Dirty Dave

What exhaust housing on the turbo? If it is the .68 that could be the problem. My truck did the same thing. My dyno sheet showed a dramatic drop off at 5200rrpms. When my turbo bearings went out I upgraded to a mp t70 with a .96 housing Now it pulls hard up to 6000 with no drop off. The spool up is a little slower but I am very happy with it.

Dirty Dave

What kind of dyno was the truck on? Does the truck still have cats on it.

tut5079

Yup the turbo is a standard STS so it should have the .68 and yes it does still have cats on.The dyno was a Dyno Dynamics .What size engine have you got the t70 on Dave ?

Dirty Dave

Its a 5.3. My truck was also dynoed on a dyno dynamics dyno it made 546hp and 600ft with 12lbs and a fifty shot.With the 60-1 with a .68 housing. It was done before it hit 5200 rpms. First i would check the back pressure before and after the cats if they are restricted it feels like what you are describing. I put a off road y pipe on mine. I bought it from jegs for around 180 bucks. If i were you I would get a .81 exhaust housing and a off road y pipe. Make sure its not pulling to much timing mine never goes below 16 degrees, I am running meth My a/f runs 11.5-1 with out the meth and 10.8-1 with the meth. The truck makes a lot more power with the mpt70 and now pulls all the way up to 6000 rpms.

James B.

iTrader: (1)

With boost it is better to DROP baseline fuel pressure. GM likes 4.0 BAR baseline fuel pressure when just about every fuel injector around is rated at 3.0 BAR baseline fuel pressure. If you think about it, the fuel pressure regulator continues to raise fuel pressure relative to manifold pressure even beyond 105kPa of manifold pressure. Once you've passed that point the fuel system is running at a higer fuel pressure than it was intended to. Any fuel pump will deliver a higher volume of fuel at lower pressure. If the injectors are large enough to support a decrease in baseline pressure, you can actually get MORE flow fuel with a lower pressure because the pump won't be fighting as much backpressure. You might look into swapping out the 4-Bar FPR for a 3-Bar one and retuning for that. I don't have any experience doing this on the Gen-III/IV engine so I don't have any part numbers to suggest.