RKCRLR
Newbie
My 2000 7.4L Vortec K3500 won’t start.
It has 96,555 total miles on it. I replaced the engine 2 years ago with an ATK remanufactured long block and I’ve only put 2000 miles on it since then. I also replaced the complete distributor (including cap, rotor, cam sensor, etc.), spark plugs, and wires (including coil wire) then. I did not replace the ignition coil or crankshaft position sensor.
Not long after I put the engine in I noticed it would occasionally backfire through the intake when trying to start cold. I would then have to crank if for a while before it would fire. It cranked unevenly almost like some cylinders had low compression or a weak fire. Once it started it would run rough like not all cylinders were firing for a few seconds and then smooth out. It would run fine after that.
It is also occasionally takes a while to start when it is hot. I suspect this is due to a leaky fuel pressure regulator diaphragm. I wish I had realized this while I had the engine out but have been too lazy to replace it.
About a month ago I took it for about a 50 mile round trip. It started cutting out a little at the beginning of the trip, felt almost like a fuel problem but it was intermittent. By the end of the trip it was running fine. I was low on fuel so I filled the tank towards the end of the trip hoping I had gotten water or contamination in the old fuel. I checked for codes when I got home but there were none stored and the check engine light had never came on.
Yesterday I took if for a short trip. Initially it was fine but the engine started dying when I let off the gas to stop. Initially it would restart and drive. But then it would only run at a low speed and was cutting out. It got to a point that it wouldn’t restart and had to get towed home. The check engine light would go out when I had managed to start the engine and there were no codes stored after I got home (but the battery had accidentally disconnected during towing).
The engine turns over unevenly but with a rhythm. It sounds like one cylinder is trying to fire but perhaps too soon. It will sometimes almost stop the cranking. Sometimes I get a backfire through the intake.
The fuel pressure is 58 psi when the pump is running and 48 psi once it stops. I haven’t timed how long the pressure takes to bleed to zero but it is quite a while. I don't see any evidence of water in the fuel.
Cylinder #1 has a spark verified by a spark plug testing light.
I removed the resonator and tried spraying starting fluid in the intake. It didn’t make it fire (but made it backfire good enough to blow the PCV tube off).
I have a OBDLink MX+ reader and Torque Pro. Is there anything I can do with it for diagnostics if the engine won’t start?
I thought I’d ask for suggestions here before digging into it further. I’d prefer ways to test vs just blindly replacing parts.
It has 96,555 total miles on it. I replaced the engine 2 years ago with an ATK remanufactured long block and I’ve only put 2000 miles on it since then. I also replaced the complete distributor (including cap, rotor, cam sensor, etc.), spark plugs, and wires (including coil wire) then. I did not replace the ignition coil or crankshaft position sensor.
Not long after I put the engine in I noticed it would occasionally backfire through the intake when trying to start cold. I would then have to crank if for a while before it would fire. It cranked unevenly almost like some cylinders had low compression or a weak fire. Once it started it would run rough like not all cylinders were firing for a few seconds and then smooth out. It would run fine after that.
It is also occasionally takes a while to start when it is hot. I suspect this is due to a leaky fuel pressure regulator diaphragm. I wish I had realized this while I had the engine out but have been too lazy to replace it.
About a month ago I took it for about a 50 mile round trip. It started cutting out a little at the beginning of the trip, felt almost like a fuel problem but it was intermittent. By the end of the trip it was running fine. I was low on fuel so I filled the tank towards the end of the trip hoping I had gotten water or contamination in the old fuel. I checked for codes when I got home but there were none stored and the check engine light had never came on.
Yesterday I took if for a short trip. Initially it was fine but the engine started dying when I let off the gas to stop. Initially it would restart and drive. But then it would only run at a low speed and was cutting out. It got to a point that it wouldn’t restart and had to get towed home. The check engine light would go out when I had managed to start the engine and there were no codes stored after I got home (but the battery had accidentally disconnected during towing).
The engine turns over unevenly but with a rhythm. It sounds like one cylinder is trying to fire but perhaps too soon. It will sometimes almost stop the cranking. Sometimes I get a backfire through the intake.
The fuel pressure is 58 psi when the pump is running and 48 psi once it stops. I haven’t timed how long the pressure takes to bleed to zero but it is quite a while. I don't see any evidence of water in the fuel.
Cylinder #1 has a spark verified by a spark plug testing light.
I removed the resonator and tried spraying starting fluid in the intake. It didn’t make it fire (but made it backfire good enough to blow the PCV tube off).
I have a OBDLink MX+ reader and Torque Pro. Is there anything I can do with it for diagnostics if the engine won’t start?
I thought I’d ask for suggestions here before digging into it further. I’d prefer ways to test vs just blindly replacing parts.