1998 chevy1/2 ton 4x4 missfire 5.7 po300

[bucklure71@hotmail]

I purchased truck 8 months ago 154000 and in the first month it died in town the fuel pump died I replaced with new one flushed tank and installed a new fuel filter now with 160000 I started my truck thur morning and went back inside for about ten min when I went back outside the truck was running rough and the check engine light was on I pluged it in and it showed po301 # 1 cyl missfire I did a tune up on it plugs, dist, rotor, wires were new and cleared codes when I started it it ran the same and check engine light came back on now the code shows po300 multiple missfire it seems to be fuel because it has good spark and 145lbs compresion = to the other 7cyl the next morning 18*F I started it up it acted like it was running on 4 cyl it wouldn't even pull itself forward or back I don't own a fuel tester that goes high enough to test this fuel system but it almost seems that it was ice in an injector line in between upper and lower intake but after puting the truck in my shop and warming it to 65* f overnight it started up and ran rough # 1 cyl missfireing but the other seven picked back up I put sea foam and fuel dryer in it no difference still showing multiple missfire. I can completely remove # 1 plug wire and it will arc but the engine doesn't sound any different but any ice in the line would melt as engine warmed up. I was hopeing not to have to remove the upper intake .If some one has any ideas plese dont hesitat to send thanks

[bracketshark]

Did you get this fixed? I'm interested in the fix.

[Danielswan]

I have a buddy that had the same problem while out on the road. it kept changing wich cylinder was misfiring. it turned out to be his multiport fuel injector assy, about 900 dollars to have a mech do it, the bummer is it looks like a dualport from the top of the engine so it dont seem like the injectors but when you remove the FALSE intake you can find the injectors all connected to one brain.

[asguti]

This seems to be a common problem with the 5.7L Vortec.. The same thing is happening to my Suburban

[termite88]

i had a similar problem with my 98 K1500 5.7 and it was caused by the 4 o2 sensors being bad and making the fuel to air mixture too lean. it was misfiring on random cylinders and throwing codes. i replaced the o2 sensors and the problem disappeared.

[Bmullin]

i to have the same problem shakes like crazy going up a hill any suggestions would be helpfull!