98 1/2 e450 crank/no start/stalls

MattB · March 6, 2012

I'm stuck hard on this one, hopefully someone can provide guidance. It's a 98 1/2 E450 with a 7.3. Came in as a crank/no start. Pulled codes. P1663, P1667, P1668, P1670 present. Ran the PPT's and went further. I've load tested both PCM powers, 5 PCM grounds, IDM power, IDM ground, the FDCS wire, CI wire, feedback wire, and signal return from PCM to IDM. At this point I replaced the IDM. It started and ran for a minute, then stalled out. Swapped in a known good PCM. It will now run for anywhere from 5 minutes to 1.5 hours, then stumble and catch itself or die.

At this point I disconnected all 3 wire sensors on the engine except CMP. Still acts up. Probed VREF at PCM, holds 5 volts during stall event. Was told to watch VSS during event and see if it spikes. It holds 0 mph during stall. Disconnected alternator and still stalls out. PCM diode is oriented correctly, and I have 12v to PCM.

After a few stalls, I will usually lose communication with IDS, but the van will still start and run. When it stalls, I don't have glowplug or WIF light illuminated in IC indicating that PCM wasn't reset or losing power. I verified pinfit with the rotunda probe kit on every pin at PCM and IDM. I don't see any harness chafe, and wiggle test reveals nothing. CMP looks new.

If you made it through reading all that, I appreciate it. Please let me know what I might be missing. Hotline was stumped. They escalated it to some special team, and I think I have them stumped. FSE isn't an option due to vehicle age.

EDIT: It's a school bus conversion

MattB · March 7, 2012

Anybody? Forgot to mention it dies instantly like the key is turned off. No fuel knock or anything. ICP falls out after RPM drops, not before.

Keith Browning · March 7, 2012

Sure sounds electrical. Just for giggles, disconnect the fuel heater. According to the WSM it still shares the PCM and IDM relay circuits in 1998.5. I know failed heaters usually cause the fuse to open but I have seen the heater not blow the fuse and eat up the current in the circuit. This could make one or both relays open... even if momentary. When I have seen this it was causing erratic stalling. I also suspect that engine vibration plays a role in this scenario.

Just thought I would put this out there. Good Luck!

MattB · March 7, 2012

I'll give it a shot this morning and let you know. Thanks!

MattB · March 7, 2012

Still stalls out with fuel heater disconnected. We also disconnected the glowplug relay command wires, and the connector on the trans for the solenoids. Monitoring datalogger, PRNDL holds park during stall.