2000 7.4L Vortec K3500 turns over but won’t start

[RKCRLR]

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.

 

[Schurkey]

Connect scan tool, see what it shows for RPM when cranking. Look at coolant temp, MAP, CMP Retard/Offset, and anything else that looks abnormal in the data stream.

Some folks have suggested pulling the #3 plug wire on Vortecs that don't start, apparently that's the weak-point in the distributor cap.

You DID dial-in the distributor position with your scan tool, when you replaced the distributor...right?

Have you pulled all the plugs to see what condition they're in? Checked for spark at all eight plugs?

If you have compression on all eight, spark to all eight, and a reasonably free-flowing exhaust (catalyst not melted or plugged) then it's likely you have fuel system trouble.

 

[stutaeng]

It kinda sounds like the distributor was not installed correctly from the engine install. But I think a CEL would be thrown by now.

But yeah, you need to look at all sensors while cranking to see what the ECU is looking. Something's got to be acting up.

 

[RKCRLR]

Connect scan tool, see what it shows for RPM when cranking. Look at coolant temp, MAP, CMP Retard/Offset, and anything else that looks abnormal in the data stream.

I don't have a scan tool. Is this something with a bluetooth OBDII reader (OBDLink MX+) and Torque Pro or similar app if the engine won't start?

Some folks have suggested pulling the #3 plug wire on Vortecs that don't start, apparently that's the weak-point in the distributor cap.

I'll try that.

You DID dial-in the distributor position with your scan tool, when you replaced the distributor...right?

I used Torque Pro to set the cam retard. I borrowed a professional scanner to do the crankshaft relearn procedure (even though I didn't have any codes) and verify the cam retard. I don't easily have access to that tool anymore. But if that was the problem why would I just now have problems to this extent?

Have you pulled all the plugs to see what condition they're in? Checked for spark at all eight plugs?

Not yet, but I'll probably do that as one of the next steps. And do a compression check while I'm at it. But compression shouldn't come and go unless it is a sticking valve. And the engine should still start if one cylinder was having compression problems.

If you have compression on all eight, spark to all eight, and a reasonably free-flowing exhaust (catalyst not melted or plugged) then it's likely you have fuel system trouble.

But if it was a fuel problem wouldn't I be able to make it fire using starting fluid?

 

[Schurkey]

I don't have a scan tool.

Need to fix that situation.

But if it was a fuel problem wouldn't I be able to make it fire using starting fluid?

Not if the injectors leak, and it's flooded/plugs fouled.

 

[RKCRLR]

So I checked the spark on #3 cylinder and it was sparking about 4 times per revolution.
I pulled the distributor cap and I can see a faint arc trace between the center post and the thick section that insulates the conductor going to the #3 post. So off to the parts store for a new cap.

Everything went fairly smoothly during the cap removal (although time consuming) other than getting the torx driver to align into the cap screw closest to the manifold. It took me about half an hour to get it out.
Is there a trick to getting that screw back in without dropping it? I can't believe the screws aren't captive in the cap

 

[HotWheelsBurban]

So I checked the spark on #3 cylinder and it was sparking about 4 times per revolution.
I pulled the distributor cap and I can see a faint arc trace between the center post and the thick section that insulates the conductor going to the #3 post. So off to the parts store for a new cap.

Everything went fairly smoothly during the cap removal (although time consuming) other than getting the torx driver to align into the cap screw closest to the manifold. It took me about half an hour to get it out.
Is there a trick to getting that screw back in without dropping it? I can't believe the screws aren't captive in the cap

On my 5.7 vortec I use a small magnetic tool next to the torx driver. So far that's worked. Not much room back there on a 350 either.....
I would recommend a Blue Streak or Accel cap. They're made of better plastic and they have brass contacts instead of the aluminum ones most brands have. I have the Accel cap on mine, it's worth the extra $$. My Burb used to eat rotors, as long as I was using the cheap white rotors. Put a Blue Streak rotor in 2 years ago, still working great. The white rotors would last about 6 months at the most.

 

[RKCRLR]

On my 5.7 vortec I use a small magnetic tool next to the torx driver. So far that's worked. Not much room back there on a 350 either.....
I would recommend a Blue Streak or Accel cap. They're made of better plastic and they have brass contacts instead of the aluminum ones most brands have. I have the Accel cap on mine, it's worth the extra $$. My Burb used to eat rotors, as long as I was using the cheap white rotors. Put a Blue Streak rotor in 2 years ago, still working great. The white rotors would last about 6 months at the most.

The distributor has a lifetime warranty. The parts store will let me replace just the cap and rotor under warranty (I don't want to replace the whole distributor). I'm going to give this one more chance. If I have another problem I'm going to put my original distributor back in (there is nothing wrong with it) with a quality cap and rotor.

 

[RKCRLR]

I put the new distributor cap and rotor on and it started right up.

So, for anyone else that finds thread with symptoms similar to mine, check to see if the spark at #3 cylinder is firing multiple times per revolution when cranking. If so, replace the distributor cap.

 

[HotWheelsBurban]

Good to know! My current Burb had an intermittent no start when we got it in 2013. Probably part of why PO got rid of it....One of the things that was likely already going on, was that the cap/rotor was damaged and was trying to fire 2 cylinders simultaneously. That's not good for anything, especially the starter. Ended up having the flexplate/flywheel replaced, after doing the cap and rotor, and replacing several starters. The people who had this truck before us probably didn't spend any money on it, and it had some problems which I've mostly got sorted. Biggest problem now is the blower doesn't work on any speed; think it's probably the dashboard switch. Have other things to do in the dashboard so I want to do all work at once. Long as it starts, stops and goes where and when we need it to, right now I'm good.
Glad you got it figured out!