I have a 1997 K1500 with a new 5.7L Vortec 5 speed transmission that had 0 miles on both when I installed them a couple months ago. I bought the truck as a roller and never heard the old motor run so I am not sure if these problems were present before. I am having multiple problems with this truck and trying to get it running like it should. It has a surge at idle when I first start the truck for about 10 seconds it fluctuates between 500-1,000 rpm and then levels out at 600-700. It is fine until I start driving it then the throttle will rev back up to 1,000 like the cruise is stuck or the throttle is stuck open. I have replaced the IAC, and TPS. I installed an aftermarket gauge column with the oil pressure and another for the coolant temperature. When I put the new motor in I put new plugs, wires, cap, and rotor. I am running it with the cats still and some aftermarket short tube headers and a 2 1/2 exhaust with flowmasters. The other issue I have is intermittent and feels like it is loosing fuel pressure but I tested it with a gauge and it reads 52PSI but it also was not acting up at the time. I could be driving down the road and it will start bucking like crazy but very intermittantly. I would think if it were the cap and rotor it would act like that all the time and the same goes with the plugs and wires. I consider myself to be very mechanically savvy but this one has me stupmed. I have even gone to a frind of mine and we hooked a brick up to it and he does not se any codes that would help him pinpoint what the problem is. Thank You, Jeff
Your fuel pressure should be 60-66 psi with csi and 56-62with sfi. That may be part of your problem. Alsoc clean the throttleplateon both sides and the iac hole. Also your injector lines could be cracked if under the nmanifold. That could cause the up and down revving.
If the fuel pressure is less than 55 psi (379 kPa) at idle, it falls into the following 3 areas: ? The pressure is regulated but less than 55 psi (379 kPa). The amount of fuel reaching the injector is sufficient, but the pressure is too low. The system will run lean, hard starting cold, no start, overall poor
performance, and may set a DTC. See NO START DIAGNOSIS .
? A restricted flow causing pressure drop. Normally, a vehicle with a fuel pressure of less than 44 psi (300 kPa) at idle is inoperable. However, if the pressure drop occurs only while driving, the engine will
normally surge then stop running as the pressure begins to drop rapidly. This is most likely caused by a restricted fuel line or plugged fuel filter.
January, 6, 2012 AT 9:54 PM
Sorry forgot to mention I replaced the fuel pump and fuel filter about 2 months ago because I was having the same systoms. When I changed the pump it did run better. Do you think the pump might have gone bad again? It was a Bosch I bought from Advance Auto.
January, 6, 2012 AT 9:59 PM
Someof those trucks needed a pump with a different connector as the harness wasn't any good about the last footor so the pump should have come with a new harness to wire in. You might try a filter change if you didn't do it then and also check for injector lines cracked under the manifold.