Help with 98 Chevy 5.7 misfire not running right

110

Asked by Feb 03, 2015 at 01:50 PM about the 1998 Chevrolet C/K 1500 Silverado Extended Cab LB RWD

Question type: Maintenance & Repair

Hello. I have a 98 chevy 1500 5.7. The truck doesnt run right at all. Msifres bad under acceleration. Idle ok when misses when reving and accelerating. I did a full tune up including plugs, wires, cap rotor and a new distributor. With key on i have about 60psi fuel pressure but idleing i only had 50psi. I put a complete new fuel pump unit in and changed fuel filter. Same problem. no different fuel pressure. I changed and replaced the spider injector with the new updated system. changed all intake gaskets. That didnt make a difference either. Replaced tps sensor and map sensor. Removed egr valve and it isnt sticking or anything. I cleaned it and used new gasket and put back on. Still same. I know these trucks need 60psi when idling. Cant figure out why i only have 50. I replaced everything in the system. I removed the fuel line where id goes into the spider system and plugged it and have 80psi when i turn the key. then i disconnected the return line by the distributor and plugged it and had 90psi there when idling but engine ran the same. i dont know where to look next. please help
Thank you
Jon

10 Answers

110

also to add, i was getting a p300 misfire and a p122 tps sensor code. thought it had a bad sensor thats why i replaced it. sensor code hasnt come back yet but just did that this morning and still messing around with it. could i have a bad spider injector causing the low fuel pressure?

4 people found this helpful.
40

What's the battery and alto stir like? If one or the other is bad it may not be getting enough voltage.

2 people found this helpful.
40

I have a 98 1500 with 5.7. Have same issue. I have replaced everything I can think of and still misfiring. My next move is to replace timing chain. Hopefully that'll fix it. Did you ever figure out your problem?

4 people found this helpful.

i had the same problem. i then took it to a shop and they emptied my gas out of my tank, put new gas in, then it worked fine. they told me not to get gas anymore from places with old tanks.

20

I have the same problem did you find out what was wrong.

2 people found this helpful.

Exhaust obstuction?

do a compression check on that cylinder if it is anything less than 110 its probably the valves for that cylinder, but to make sure do a leak down test too.

I have a 99 suburban showing cylinder six is dead but i am getting fire from distributor to plug but cylinder is dead any explanation for this

Ttt

I had same problem 97 5.7 vortec. Replaced cam and crank sensors repaired wiring to crank sensor, much better. I put it on co. Outer and it said can and crank sensors were not in sync with eachother adjusted timing got it down to 2 degrees, it can be - 2 or +2 but no more than 2

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