truck will not go over 30mph when it does code comes up for multiple misfires and you
are unable to throttle down anymore. have checked everything for air leak. nothing comes
up. just replaces header gasket and exhaust manifold gaskets. code p300 keeps coming
up have also replaced fuel filter. believe it might be the fuel pump. any answers?
Maybe check your spark plugs too.
I have changed all spark plugs and wires.
Maybe your computer needs to be remapped.
1998 GMC Sierra 1500 SLE Extended Cab 5.0 Liter Engine. I have a similar situation. I replaced Coil and it's controller. spark plus, wire and rotor and rotor cap. Changed oil and etc. Air Filter also. I even replaced the distributor itself to be on the safe side. Mine gets the Error Codes P0102, P0108, and P1351 They may be the error codes from before me repairing all that. But I thought I cleared them back then. I just fired it up and it stayed running once until the engine heated up but before that if I did not keep my foot on the pedal it died. It can not go below 1000 rpm without chugging out so I have to keep it manually above 1000 rpm. I had a local mechanic friend of mine say he knew what it was. He said it was a fuel filter. But if that was the case, why did it start and run for a while and I mean a while and while it is running the tachometer readings kept jumping faster than and slower than I had it running. It feels like it misses also but I cleared the codes and it take a couple weeks to get the codes to come back and I can't drive it to get that.
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