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Why Is My Truck Running Lean?

tyler.m.13

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tyler.m.13 Enthusiast

tyler.m.13

Posted
Posted

I recently installed a more agressive cam, ls2 heads, built tranny, and a higher stall converter in my 2004 GMC Z71 Sierra. (5.3 stock intake and fuel system) I took the truck to the shop to have it dyno tuned today and found a problem. Through the several pulls that weremade I only made 270hp & 268 ftlbs of tourqe at the wheels. This sound good but the computer showed that my injectors were running at full capacity. The tech said this was because my engine was starving for fuel. ( running way lean) At the RPM's the truck was running the injectors shoul have been at about 60% capacity. He tuned everything where it would run better but left the injectors at 100% to get the most power out of it. He said that I should change my fuel pump and filter and after I did it should run pretty rich. If it started running rich this would point out that I had fixed the problem bc the injectors were still turned way up. If this turned out to be the problem I was to bring the truck back to him and let him reset the injector capacity to the correct setting fo rmy application. But I changed the fuel pump/filter to no avail. (2004 sierras have a fuel filter that is integrated into the fuel pump) The truck is still running lean even with the injevtors cranked all the way up. Could this b a fuel pressure regulator problem? If so, where is the fuel pressure regulator located? Anybody else have any ideas? I need to get the truck back to the dyno shop asap. Thanks!

stlavsa Senior Enthusiast

stlavsa

Posted
Posted

Maybe its running lean because you just installed higher flowing head and bigger cams and now theres more air combustion chamber and your stock fuel system cant keep up? Are you sure the solution isnt bigger injectors?

dlstewart01 Senior Enthusiast

dlstewart01

Posted
Posted

Injector slope can be tuned for richer or leaner operation up to a point. Sounds like yours are maxed out. If that is the case bigger injectors could be the answer. Changing the fuel pump will not help if your injectors are maxed out. .Same for regulator. You can only squirt so much fuel through a given nozzle. I believe I would find another speed shop...

txab Senior Enthusiast

txab

Posted
Posted
Injector slope can be tuned for richer or leaner operation up to a point. Sounds like yours are maxed out. If that is the case bigger injectors could be the answer. Changing the fuel pump will not help if your injectors are maxed out. .Same for regulator. You can only squirt so much fuel through a given nozzle. I believe I would find another speed shop...

 

+1

 

Have you even checked your pump pressure? If pump is at max output of pressure/volumn, then putting a new one in doesn't seem to be the way to go

Mike@Diablosport Enthusiast

Mike@Diablosport

Posted
Posted

Ideally, the tuner should have monitored fuel pressure to see if that was the culprit, rather than throwing parts at it.

 

If you monitor fuel pump pressure, and injector duty cycle, you will know where the problem lies most of the time.

 

the stock 5.3 injectors are certainly good for way more than 270 rwhp.

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