multiple misfires
4x4trucks
04-19-2005, 11:12 PM
Hello, I have had problems trying to diagnose this problem. The truck misfires under load and lighly at idle and very rarely in park at high rpm. Any time I accelerate slightly it misses, when I accelerate hard it misses bad. I have replaced plugs, wires, dist. cap, rotor, coil, icm and fuel filter. Could it be the map sensor? the maf? it ran slightly better with the maf sensor unplugged. Thank you for any help.
2000CAYukon
04-20-2005, 06:33 PM
What year and engine? Do you know what the fuel pressure is at, especially under load.
//2000CAYukon
//2000CAYukon
4x4trucks
04-21-2005, 12:25 AM
[QUOTE=2000CAYukon]What year and engine? Do you know what the fuel pressure is at, especially under load.
//2000CAYukon[/QUOTE
year is 96, engine is 350 or 5.7 vortech, i have no idea what the fuel pressure is in either state. would this be a good place to start checking and what would cause this problem other than fuel pump? engine has the throtte body towards front of intake manifold and fuel control behind it with injectors. upper plenum (plastic) and so on.
//2000CAYukon[/QUOTE
year is 96, engine is 350 or 5.7 vortech, i have no idea what the fuel pressure is in either state. would this be a good place to start checking and what would cause this problem other than fuel pump? engine has the throtte body towards front of intake manifold and fuel control behind it with injectors. upper plenum (plastic) and so on.
2000CAYukon
04-21-2005, 01:53 PM
Your 96 does have a test port on the fuel rail to test the pressure. You want to make sure that the pressure is within spec when troubleshooting a misfire.
You also want to check the timing; however, you need a scantool to do it on the 96-99 Vortec engines.
//2000CAYukon
You also want to check the timing; however, you need a scantool to do it on the 96-99 Vortec engines.
//2000CAYukon
lweford
04-21-2005, 09:36 PM
Hello, I have had problems trying to diagnose this problem. The truck misfires under load and lighly at idle and very rarely in park at high rpm. Any time I accelerate slightly it misses, when I accelerate hard it misses bad. I have replaced plugs, wires, dist. cap, rotor, coil, icm and fuel filter. Could it be the map sensor? the maf? it ran slightly better with the maf sensor unplugged. Thank you for any help.
I ran into this same problem once. I replaced everthing on the truck that delt with the ignition. Even replaced the entire distributor after replacing all the parts iside the old one. I also was in the process of ordering a new computer but hen a friend that has the same truck said "lets just put my plug wires and distributor on your truck just to see". Well this cleared it right up. Turns out AutoZone had sold me a set of wires that were bad right out of the box. I returned them and and bought the Bosch and haven't had a problem since.
I ran into this same problem once. I replaced everthing on the truck that delt with the ignition. Even replaced the entire distributor after replacing all the parts iside the old one. I also was in the process of ordering a new computer but hen a friend that has the same truck said "lets just put my plug wires and distributor on your truck just to see". Well this cleared it right up. Turns out AutoZone had sold me a set of wires that were bad right out of the box. I returned them and and bought the Bosch and haven't had a problem since.
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