ignition issue. HELP!!!

I have done a bunch of troubleshooting. Here is some history and steps ive done so far on my 99 cherokee.

around a month ago, my gauges would all drop out and check engine and air bag light would turn on. this would happen intermitenly like a broken wire or loose connection. off and on

Recently as im driving, my ignition to the engine would cut in and out. The only gauge that would drop out is the tach. even though im still rolling in gear it has no read out. intermitten as before with all the gauges

I assumed it was my key cylinder but i have tested that both of my ignition wires, both power wires, and acc. have power at all times. I test that my distriputer and coil dont have power when its not working.

That led me to believe it was the pcm. I have access to all data and verified the pcm has full power at all times.

any more ideas for troubleshooting?

4.0 inline 6

check for broken ground wires at the stud that holds the oil dipstick tube.

The gauges dropping out and the engine dropping out are two separate and unrelated issues.

The gauges have no effect on the engine or the PCM. The engine dropping out is probably a weak Crankshaft Position Sensor. The CPS test procedure has been posted many times. Test the CPS.

PCM failure is very highly unlikely and should only be considered after extensive diagnostic testing.

Tim_MN said:

The gauges dropping out and the engine dropping out are two separate and unrelated issues.

The gauges have no effect on the engine or the PCM. The engine dropping out is probably a weak Crankshaft Position Sensor. The CPS test procedure has been posted many times. Test the CPS.

PCM failure is very highly unlikely and should only be considered after extensive diagnostic testing.

Click to expand...

Tim_MN is right.

One other item that might cause issues is the ASD relay, but only for the ignition/tach (tach feed is from PCM).

Good luck.

Tim_MN said:

The gauges dropping out and the engine dropping out are two separate and unrelated issues.

The gauges have no effect on the engine or the PCM. The engine dropping out is probably a weak Crankshaft Position Sensor. The CPS test procedure has been posted many times. Test the CPS.

PCM failure is very highly unlikely and should only be considered after extensive diagnostic testing.

Click to expand...

bad cps. Thank you much guys.

Bring back an old thread.


1998 xj 4.0 automatic
Ignition switch removed from ign lock and starts with screwdriver.

Drive down the road and the gauges will quit, sometimes come right back on quick and somd times not.

Gonna try to go help him with his jeep but trying to read up on what to check.
Thanks for the help

01yellowxj said:

Bring back an old thread.


1998 xj 4.0 automatic
Ignition switch removed from ign lock and starts with screwdriver.

Drive down the road and the gauges will quit, sometimes come right back on quick and somd times not.

Gonna try to go help him with his jeep but trying to read up on what to check.
Thanks for the help

Click to expand...

May be a completely different problem with the gauges. There's a FSM for the one of the instr. cluster plugs.

I also have this problem with the gauges, doesn't occur often. Once in a while the gauges go out. Turning on then off a manually switched/powered oem aux. fan, (indirectly connected to OEM wiring) the gauges come right back on.

Cleaning the instrument cluster plugs did not cure my gauges problem.

Low voltage circuits (and their grounds) potentially are more susceptible of problems due from corrosion, electrolysis, poor voltages, etc.. Instrument cluster plug connectors, over long periods of time, tend to build up a black type of corrosion, from low voltage electrolysis, that's difficult to detect from visual inspection.

There's a repair/replacement service bulletin for one of the OEM instr. cluster plugs, which may have been originally the wrong size, perhaps the original factory OEM plug pins are slightly too thin potentially causing additional electrolysis.

You can try cleaning the plug connectors. Over time the OEM plug refereed to in the FSM may require replacement rather than only cleaning.

You would need to test and diagnose further to determine if the broken starter switch (part of the instr. cluster circuits) is effecting the gauges. A FSM as well as other aftermarket repair manuals, have circuit diagrams, some with diagnostic procedures.

There are circuit testing points from the OBD-II plug that is also part of the instr. cluster circuit.

Previous post I was referring to, meant to write "TSB" (techncial service bulletin) vs "FSM" (factor service manual).

http://www.jeepproblems.com/tsbs/Cherokee/1998/

Uncertain if there's only one TSB for this kind of problem.

http://www.jeepforum.com/forum/f12/need-tsb-08-15-99-pictures-160897/