5.7 Vortec Hard start when warm

[JBis]

2000 c3500 5.7 vortec.

All items replaced so far are gm genuine or delco.
ICM, coil, cap, rotor, fuel pressure regulator, oil sending unit (one wire type), crank position sensor, temp sens

Truck came with updated injectors.

Code reader says cannot connect to ecu, but has power. So is there a chance for computer to be bad?


Problem: after running engine up to temp then letting sit for at least an hour and up to about 4 hours, engine cranks for up to 8 seconds, has lousy start, then dies. P1351 pops up and I have a handful of delco ICMs now.
If I hold the gas pedal to the floor, the truck will start and not die, so I’m suspecting something to do with flooding.

I’m ready to buy a pre flashed computer, I don’t know what to do from here.

 

[east302]

Did you change the temperature sensor (by the thermostat) or the gauge sender on the driver cylinder head. The first one could cause the hard hot start like that since the computer uses the temperature data from it. Too bad your scanner won’t connect - you’d be looking to see what temperature the sensor is reporting.

 

[JBis]

Did you change the temperature sensor (by the thermostat) or the gauge sender on the driver cylinder head. The first one could cause the hard hot start like that since the computer uses the temperature data from it. Too bad your scanner won’t connect - you’d be looking to see what temperature the sensor is reporting.

yep the sensor, not the sender. Holding the throttle to the floor helps it start though. MAF has also been replaced. Going to look tomorrow for what pins I should test in the ecu to see if a wire broke.

 

[east302]

The GM manual will have a diagnostic procedure for when a scanner won’t connect. PDFs can be downloaded at this link:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

I don’t know if 2000 is available, but 1999 is in post #77 and should be close enough.

Have you checked fuel pressure? Spec is 60-66 psi key on, engine off. Since it does better flooring the gas (clear-flood mode, temporarily pauses injector pulses) it could be a leaking injector.

 

[Schurkey]

2000 c3500 5.7 vortec.

All items replaced so far are gm genuine or delco.
ICM, coil, cap, rotor, fuel pressure regulator, oil sending unit (one wire type), crank position sensor, temp sens

Plug wires, spark plugs verified good?

Oil pressure sending unit for the fuel pump?

Is there a relearn procedure for the crank sensor?

Truck came with updated injectors.

Any idea what brand?

Code reader says cannot connect to ecu, but has power. So is there a chance for computer to be bad?

What "code reader"?

Any chance of coming up with a real scan tool?

Problem: after running engine up to temp then letting sit for at least an hour and up to about 4 hours, engine cranks for up to 8 seconds, has lousy start, then dies. P1351 pops up

Follow the service manual procedure for P1351.

The GM manual will have a diagnostic procedure for when a scanner won’t connect.

Yup.

Have you checked fuel pressure? Spec is 60-66 psi key on, engine off. Since it does better flooring the gas (clear-flood mode, temporarily pauses injector pulses) it could be a leaking injector.

Also a good idea.

 

[JBis]

Have you checked fuel pressure? Spec is 60-66 psi key on, engine off. Since it does better flooring the gas (clear-flood mode, temporarily pauses injector pulses) it could be a leaking injector.

The check port is stripped.

Plug wires, spark plugs verified good?

All new.

Oil pressure sending unit for the fuel pump?

New. Gm unit, this isn’t the one where it has fuel pump relay going through it either.

Any idea what brand?

Replaced the injectors twice now. First time, it would fire right up even in problem conditions, but cyl. 3 is missing, the new spider had a bad injector and I could see a rust spot on the injector port. Replaced it again with another unit, all cylinders are firing, but problem persists. I don’t know is standard from rock auto gave me some horrible luck, or if it’s something else.

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Cyl 3 injector on the first new set. Ran horribly, lean codes and everything and ruined the plug. I replaced all plugs, wires, cap and rotor with Delphi or ac parts.
changing the injectors again, lean codes went away. I don’t know if the new one is leaking or what. Something I noticed was when I was releasing the gas pressure, the fuel was pretty hot. I’m able to get the spider out and have the truck running within an hour now.

Any chance of coming up with a real scan tool?

Got a bafx, coolant temp sens is good so that’s at least one box checked.