1997 Wrangler cutting out (solved)

[Hanks_Hotrods]

Any ideas on a random cutting out situation? Check engine light flashes when it cuts out, but never stores code, scanner disconnects do unable to watch data to see anything. Tech and speedometer jump during event also. Seems to be load related, but will get worse as it gets warmer, or after a longer drive
Stuff I’ve done =

•New battery cables
•New crankshaft position sensor (does the same thing with a used oem one, used aftermarket, and new aftermarket)
•New distributor pickup
•New coil
•Verified fuel pressure during event
•Verified voltage out of fuse #11 during event
•Cleaned grounding points
•Bypsssed ADS relay, no change

It’s a 1997 wrangler 4.0 5 speed, bought it in January, it had a hard start issue when I bought it, put a flagship one ecu in it. That fixed it at that time, this recently started. I have also purchased and installed a WranglerFix pcm, no change.

 

[Cooper Smith]

Check your ground straps. Bad grounds do really weird things, especially when both electronic ignition and fuel injection are involved.

 

[Hanks_Hotrods]

Check your ground straps. Bad grounds do really weird things, especially when both electronic ignition and fuel injection are involved.

I’ve done that a few times, taken them off, verified continuity, cleaned mounting points, and reinstalled

 

[hear]

I would verify the wiring at the crank & cam position sensor. Either one can ruin your day.

 

[RMETeeJay]

Cap/rotor/wires/spark plugs in good condition?

Wouldn't hurt to do a smoke test for vacuum leaks because sometimes they change with temperature.

 

[Hanks_Hotrods]

Cap/rotor/wires/spark plugs in good condition?

Wouldn't hurt to do a smoke test for vacuum leaks because sometimes they change with temperature.

Fuel trims aren’t crazy, cap/rotor/wires look okay ish. Tried different coil wire off my buddies jeep, no change.

 

[Hanks_Hotrods]

Update. Spent most of the weekend playing with it, back probed the ecu power, ground, 5vdc reference, no issues found. Ran new ground to ecu, no change. Removed the cluster, nothing interesting found. Replaced ignition switch, no change.

Now here’s something interesting, going to play with this alittle more. I supplied direct battery voltage to the ASD relay output, (to check for a corrupted circuit), and while driving down the road I’d kill the ignition, (again, ASD bypassed so the ecu shouldn’t be able to shut down). The jeep would act the same way. Reviewing the service manual, that would kill the fuel pump. So I checked the fuel pump connector, it was alittle loose feeling. I ziptied it together, drove the jeep a bit, seemed to help for a few miles then it went back to the same BS.

However, the gas gauge will wig out and sometimes read empty while I’m doing this, so I wonder if I have a fuel pressure problem after all? I did test that and the gauge read pressure, but it was a harbor freight oil pressure gauge that I used with some unions to my fuel pressure gauge hose…

Will check back in when I find something interesting

 

[hear]

If the gas gauge reads empty I would suspect a power/ground issue on the fuel level circuit. It’s distinct from the fuel pump circuit.

 

[Hanks_Hotrods]

Update, not fuel pump, not ASD,

Still doing it, gas gauge drops out when it does it sometimes. Closely inspected wiring, can’t find the issue.

Removed the airbag computer (airbag light has been on the whole time I’ve owned it)

Removed the cluster and drove around, both of these had no change.

 

[macleanflood]

Do you lose the PCM when it cuts out?

Like monitoring live data and it stops logging?

-Mac

 

[Hanks_Hotrods]

Do you lose the PCM when it cuts out?

Like monitoring live data and it stops logging?

-Mac

Yes. The scanner disconnects

 

[Hanks_Hotrods]

Do you lose the PCM when it cuts out?

Like monitoring live data and it stops logging?

-Mac

But 5vdc reference does not drop out, nor does switched 12vdc coming in to A2.

 

[RMETeeJay]

Have you inspected the plugs? When was the last tuneup done?

 

[macleanflood]

I'm guessing you need to really look hard at your wiring. Intermittent short to ground somewhere.

-Mac

 

[Hanks_Hotrods]

Have you inspected the plugs? When was the last tuneup done?

I’ve inspected them, and by the previous owner, but based on how it looks, less than 20k miles

 

[Hanks_Hotrods]

I'm guessing you need to really look hard at your wiring. Intermittent short to ground somewhere.

-Mac

Needle in a haystack.

 

[Hanks_Hotrods]

I'm guessing you need to really look hard at your wiring. Intermittent short to ground somewhere.

-Mac

Any great ideas on where to start looking first? I’ve sorta already been looking.

 

[macleanflood]

I'd start at the PCM connectors with the engine running and start wiggling harnesses and see if you can replicate that issue.

-Mac

 

[Hanks_Hotrods]

Update.

5VDC reference wire for the VSS rubbed on the tcase. Stroke of dumb luck found that. Fixed that and went on a long drive, no problems.

 

[Hanks_Hotrods]

Final update on this. That was definitely the issue. Wife’s been driving it to work and back a few days. Things working great.

I hope this helps someone in the future