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Running Lean! Help!

tyler.m.13

By tyler.m.13
in Ask A GM Technician

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tyler.m.13 Enthusiast

tyler.m.13

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(I am not asking "will this part fit on my truck". Just to clarify so it doesnt scare off any of you technicians when the first phrase you read is about a new camshaft) 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!

vettelovralexand Enthusiast

vettelovralexand

Posted
Posted
(I am not asking "will this part fit on my truck". Just to clarify so it doesnt scare off any of you technicians when the first phrase you read is about a new camshaft) 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!

 

Could be a regulator, but more than likely just a weak fuel pump. Seems to be a common issue.

tyler.m.13 Enthusiast

tyler.m.13

Posted
  • Author
Posted
(I am not asking "will this part fit on my truck". Just to clarify so it doesnt scare off any of you technicians when the first phrase you read is about a new camshaft) 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!

 

Could be a regulator, but more than likely just a weak fuel pump. Seems to be a common issue.

 

 

 

Well it ended up being the fuel pump. I guess the computer just took a while to recognize that it had the fuel pressure needed. Thanks for the comment though.

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