No start, ECU / Injector Pulse issue?

454RV

MEMBER
1998 CHEVROLET EXPRESS
7.4L
V8
2WD
AUTOMATIC
80,000 MILES

The truck is our clean and well-maintained RV. Driven all over the US issue free over the past year. It was running in the driveway for a trip, when it sputtered to a stop. Crank, but no start. Will only run on starter fluid.

-All fuses are good.
-60 psi fuel pressure at rail
-Replaced crank position sensor inside distributor
-Oil pressure gauge shows pressure during crank
-Haven't pulled manifold to get at injectors, but seems there is no injector pulse.
-Replaced ECU with one from junk yard. Defeated security. Truck started and ran poorly for a few minutes. Then stalled and would not restart.
-Replaced ECU with one from reprogram website. Defeated security, but has never started.
-Handheld scanners seem unable to properly connect to ECU to read trouble codes. They read some data from OBD2 port, but freeze up when trying to pull codes. Have tried a couple different ones. This was never an issue before and used these same scanners on this vehicle previously.

Any suggestions would be greatly appreciated!

1998 Chevrolet 3500 Van.

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,867 POSTS

Hi,

Have you checked the ECM fuse in the under-hood fuse box? In addition to the fuse itself, are you sure there is power to and from it?

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

I attached two pics below. Pic 1 shows the ECM 1 fuse which is located in the under-hood fuse box. Check that first,

If that checks good, go to the injector harness. My manual isn't showing the wire color at the injector itself, but a pink wire from the aforementioned fuse supplies power with the key on. See if they are getting power. I'm questioning the power supply because there are a few different splices in the wiring that may have failed.

If there is power, then we have an ECM issue. The ECM provides a ground path to complete the circuit and fire an injector. If we have power, this is my concern.

What to do at that point is this. Disconnect one of the injectors. Note the colors in pic 2 and select one that is the opposite of the power supply. That will be the ground path. Take a test light and connect one end to the battery positive and the other to the ground path wire for that injector. Have someone crank the engine to see if the test light pulses on and off. It should.

Let me know what you find.

Take care,

Joe

See pics below.

Images (Click to make bigger)