tac1
Red Skull Member
- Joined
- Jun 21, 2020
- Member Number
- 2142
- Messages
- 76
I bought a cheap 2001 2500hd truck a couple weeks back think of using it as a winter beater and maybe swap donor down the road. Truck has plenty of issues, the main one being a cylinder #4 PO304 misfire with flashing check engine light.
Truck is 100% stock 252k miles lq4 6.0/Nv4500 (older 3/4 ton so no afm/dod junk on it)
PO 304 is the only code shown, the truck has a miss, less noticeable at idle but pretty clear under load in 4/5th gear. I've had a few of these trucks. here is what I tried so far in troubleshooting.
1) Verified had spark on #4 with a spark tester
2) Swap coil, spark plug, and plug wire from #4 to #2 = Misfire stayed on #4
3) Friend brought over a fancy scan tool and we ran a test that pulsed the injectors while you watched the fuel pressure drop on a manual gage. All injector except #4 were dropping 11-12 psi, #4 was only dropping 4-5psi. I though we found the answer, I checked injector wiring with a noid light all seemed ok. Fuel pressure was good we did find the fuel pressure regulator was shot.
I intended to swap injectors on #2 & 4 to see what happens but when I pulled the rail several injector tips and the top part with the little screen fell apart, so I put in 4 reman injectors on the passenger side bank. To fish the injector tips off the top of the valves I pulled the intake and put new gaskets on it. I cleaned and looked at the fuel rail, everything looked fine
Back together truck still has a #4 misfire, screen shot after a short drive.
4) I ran a compression test, surprised to find 175-180 psi on all 8 cylinders
5) Ran a leak down test on #2 and #4 both showed really good results ~5% on my cheap tester I'm not sure I trust but I did not hear any air leaking on the intake or exhaust.
6) Pulled the valve cover on the passenger bank. No broken valve springs, rocker arms are tight (lashed), and I took a crude min max rocker arm measurement on 2,4,6 intake and exhaust rocker arms to check cam lift. All were with in a few thousands.
7) Last ditch to rule out electronics I checked resistance on the coil connectors and injector plug push pull and wiggling on the harness, checked all the pins, and even overlaid the signal wires of the coil and injector directly from the ecm connector. No change
I'm kind of lost at this point. Truck is drivable and I have a cheap scan tool or toque pro to monitor/try any suggestions. Truck is not really needed so I'm not wanting to throw a bunch of money at it currently.
Truck is 100% stock 252k miles lq4 6.0/Nv4500 (older 3/4 ton so no afm/dod junk on it)
PO 304 is the only code shown, the truck has a miss, less noticeable at idle but pretty clear under load in 4/5th gear. I've had a few of these trucks. here is what I tried so far in troubleshooting.
1) Verified had spark on #4 with a spark tester
2) Swap coil, spark plug, and plug wire from #4 to #2 = Misfire stayed on #4
3) Friend brought over a fancy scan tool and we ran a test that pulsed the injectors while you watched the fuel pressure drop on a manual gage. All injector except #4 were dropping 11-12 psi, #4 was only dropping 4-5psi. I though we found the answer, I checked injector wiring with a noid light all seemed ok. Fuel pressure was good we did find the fuel pressure regulator was shot.
I intended to swap injectors on #2 & 4 to see what happens but when I pulled the rail several injector tips and the top part with the little screen fell apart, so I put in 4 reman injectors on the passenger side bank. To fish the injector tips off the top of the valves I pulled the intake and put new gaskets on it. I cleaned and looked at the fuel rail, everything looked fine
Back together truck still has a #4 misfire, screen shot after a short drive.
4) I ran a compression test, surprised to find 175-180 psi on all 8 cylinders
5) Ran a leak down test on #2 and #4 both showed really good results ~5% on my cheap tester I'm not sure I trust but I did not hear any air leaking on the intake or exhaust.
6) Pulled the valve cover on the passenger bank. No broken valve springs, rocker arms are tight (lashed), and I took a crude min max rocker arm measurement on 2,4,6 intake and exhaust rocker arms to check cam lift. All were with in a few thousands.
7) Last ditch to rule out electronics I checked resistance on the coil connectors and injector plug push pull and wiggling on the harness, checked all the pins, and even overlaid the signal wires of the coil and injector directly from the ecm connector. No change
I'm kind of lost at this point. Truck is drivable and I have a cheap scan tool or toque pro to monitor/try any suggestions. Truck is not really needed so I'm not wanting to throw a bunch of money at it currently.
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