weird ignition problem 95 TS

[Jeffrv]

My 1995 TS with 3.8 just quit driving down the road, would not restart. had to be towed home.
Fuel pressure just meets specs at 41 PSI engine off ( Gm says 41 to 47), but has been that way for some time. Put Actron scan tool on, got a code 361, EST not toggling. GM has no code 361, but based on past experience, this has usually pointed to a defective ignition module, and I thought that was that. While testing, scan tool kept losing communications and having to be reset. Finally I unplugged power source of tool, and engine immediately quit and would not restart. Resetting scan tool would allow engine to restart, albeit very rough. Doing a wiggle test of engine wiring harness makes no change. Crank sensor was replaced, about 12 years ago, so it not the trouble prone OEM; cam sensor about 10 years ago by a garage who was unsuccessful in solving a driveability issue.
Issue here is why would scan tool affect engine operation has anyone else had similar experiences?
Jeff

[brcidd]

I've seen my scan tool not allow an engine to even crank- unplug it and it cranks and starts- saw it on a '97 U-van and just saw it last week on 2004 Lesabre...have seen it cause instrument clusters to go wild on Chryslers and Jeeps- speedometers flutter, gas guage goofy- unplug scan tool and all is fine.

So it has to do with data line and communications- doesn't always happen. I remember wasting 2 or 3 hours dubugging why a Pontiac Transport would not crank- when finally, I unplug scan tool and it starts right up...WTF....You never forget to unplug the tool first, now.....

[Jeffrv]

Update:
Van back running now. I did replace ignition module, would not start, but at least didn't throw that code again. Googled car wont run without scan tool, got a few hits, none from GM cars. However, the recurring theme was OBD II ( and this van has that oddball OBD II packaged in OBD I guise) and loss of ground link in PCM circuit. Apparently the scan tool will allow a poor ground connection, enough to just get engine started, but once scan tool removed, engine will quit. Checked all fuses, power connections, and disconnected and reconnected battery. Lo and behold, the ground wire located under the ignition module was frayed through- repaired it all well again.
Jeff

[sergeimoskva]

Hello !
Watch the wire from ignition module to PCM

[LMP]

Well the wire bundle going to PCM plug C111 has an history of wires breaking close to the plug.
Ahhh..I see you are aware of that........

[sergeimoskva]

Hi !
I meant the, it is one of the the reasons of malfunction

[Jeffrv]

In this case, it was a defective wire on the ground stud under the ignition module. Yes aware of the engine wire bundle issues, which is why I did the wiggle test on the engine harness, paying particular attention to the area around the engine side of the bulkhead connector. Not the problem this time.
Jeff

[LMP]

Originally Posted by Jeffrv

...defective wire on the ground stud under the ignition module....

Thanks for the update....will record that for eventual issues...
Wiring problems at this age ..I would not qualify as "normal"....but , let's say, explanable. After recent issues (solved) with the wire bundle from passenger door to body, some more have come recently. I cannot lock doors (unlock OK) from the driver side now, just from passenger's. A little soldering will take care , when I have time...