99 k1500 5.7 motor has 1,700 miles on it. Cranked it one morning for work and it was shuttering like crazy. Took the car to work came home and it was only shuttering a little bit and had a p0307 code up. Drove it for a minute and the light went off and it drove fine. Got in it the next morning for work and same thing. Here I am a few days later with no answers. Checked compression on #7 and I’m sitting at 170 psi. New ignition coil, new plugs, wires and fuel filter. Check fuel pressure and it’s around 55 with ignition on and sits at 62 while running. Also cleaned the injectors and it did nothing. Need help and need it fast. I have a lawn care company and I need my truck running to make money. Any suggestions will help!
Hey it’s me again 2 hours later. I ran another compression test on it, hooked my distributor back up put the plug in and cranked it. Still had the code but wasn’t running rough. Cleared the code and got it on the highway and floored it. Code hasn’t come back yet, but it’s done this before. Could it be something with the distributor. Wasn’t sure if maybe I jiggled something and got back to where it should be.

 

If it disappeared after the plug wire was reconnected, I’d be looking for signs of the plug wire grounding out/arcing along the routing path and/or loose connections at both ends.

Apply a thin film of dielectric grease to the plug and cap to make sure the wire seats completely.

 

yeah I tried that. Ended up changing distributor cap and all the plug wires and it still does it. But honestly I’m starting to think it’s bad gas. I can let it run off and on for a while and then It’s like something clicks and it’s fine. I can clear the code and it does fine until I let it sit over night. Last night I got it run like new, got in it this morning for work and I could barely get out of the driveway.

 

Is it also setting a P0300 for random misfires?

If not, It’s unlikely bad gas is to blame - if it were fuel quality, it would be misfiring on more than just one cylinder.

Are you noticing a heavy fuel smell, like it’s flooding?

Was the engine a complete assembly or did you have to swap/replace the intake and injectors? The injector assemblies on these are known for being problematic, even when new.

 

yeah I’m pretty sure it’s just bad gas. It throws a p0307 and p0300 at different times. But never at the same time. Last time it came up it was just random misfire.

no I did have to put injectors and Intake on the motor. They’re new injectors that did fine for the first 1,000 miles so I tested them and they’re fine. I’m guessing you were going to say it could be a bad intake gasket right? I thought so too so I checked it as best I could and I’m not seeing or hear any bad spots on it.
As for the gas smell there’s a faint smell but nothing that was really concerning.

 

I was just curious about the parts swapping, particularly if it was a used injector assembly because they’re so susceptible to failure.

What about the distributor? Was it new or used?

 

no it was a new injector assembly and distributor.

 

Quick update. I’ve figured out that if it’s a cold start it has a misfire. If I let it run and get to operating temp, clear the code and restart the motor, the mis is gone. Checked fuel pressure again and with key on it jumps to 50 and slowly leaks down. Not sure if that helps anyone, but would love to know if you have anymore ideas. Also noticed a slightly bit more of an exhaust smell while it’s warming up.

 

It depends on how much pressure it’s losing and how quickly. If it’s immediately dropping 10 PSI or more, the fuel pump is the likely culprit. If it’s dropping less than 5 PSI and then stabilizing, it’s nothing to be concerned about.