No Injector Pulse when Hot

[XJ1100]

I have a 97 Jimmy 4.3 with TBI. After driving for 20 miles or so in hot weather, the truck stumbles and dies. After which I have no injector pulse.After letting it cool down an hour or so it will start back up.I have NO problems when the weather is cool.
I borrowed a scan tool from a friend and found the injector pulse problem.I have good spark at the plugs.
I started having the problem last fall. A friend had another 97 jimmy he was rebuilding the motor. We pulled the PCM out of his and we hooked it up in mine and it fired right up. We thought that I just needed to replace the PCM. I recently replaced the PCM but I still have the same problem.
A few questions I have is... When the new PCM is "Flashed" should The "PROM" from my old PCM be installed first. I don't have any factory theft devices on this truck. I bought the PCM aftermarket and I installed my PROM just before I left the store.
Does the fuel pump have to put out a certain amout of pressure in order to get an injector pulse?
Is there a common wire or connector problem that could cause a no pulse??
Also. Today I went out and started the truck and let it idle for an hour or so to let it get hot. After turning the key off and turning it back on I had NO "service engine soon" light with key "ON" engine off. If I unplug the "Black" plug from the PCM and plug it back in, the light will work properly again. BUT if I start the truck and turn it back off, the light will not come back on again until I perform the same routine.
I replace the fuel pump last spring. I put in a new crank sensor in (just because) last summer when I had a new oil pan gasket and front cover gasket installed.
T.I.A.


Is there a "Flow" chart available to check for voltage at certain areas when this happens???

[old_master]

Originally Posted by XJ1100

....Does the fuel pump have to put out a certain amout of pressure in order to get an injector pulse?

Is there a common wire or connector problem that could cause a no pulse??

Fuel pressure has no effect on injector pulse, there is no fuel pressure sensor. Ignition and injector pulse are both triggered by the crankshaft position sensor, therefore if you have ignition pulse, (spark at the coil), the PCM is receiving a signal from the crankshaft position sensor. The connector at the injector assembly would be a likely spot to look for a loose connection. If that's ok, trace the wiring back to the PCM. Check for battery voltage at the injector connector when it acts up. If that's ok, check for a pulsed ground while cranking. That will at least tell you what circuit is causing the problem.

The 3 pink wires should show battery voltage when the ignition is in the RUN and START positions. They are all fed from the ECM 1 15amp fuse in the underhood fuse panel.

The PCM provides pulsed ground to the other six wires, (each has a black stripe), when the engine is cranking and running.