Early 97 TJ check gauge light (but went away) - hard to start and voltage at 12V

[PattonD]

The daughter was driving our early 97 TJ, and the check gauge light came on; she looked and could not see why. When I went to start it, it took much longer than normal to start, and I saw the voltage gauge wasn't up to 14v per usual. The check gauge light did not come back on.

I was assuming I had an alternator issue, but I am seeing a few posts saying hard start plus not charging means it's the computers; what is my diagnostics process? I am confused between PCM and ECM, does it have one unit serving both functions? Is there a rebuilder that is better than the others? Is anything here one of the unique early 97 issues?

Thanks,
Patton

 

[JKP]

Your Jeep has a Powertrain Control Module, PCM.

The voltage regulator is in the PCM. I would have the alternator and battery tested first as auto parts stores will check that for free. Also, check the battery cables for corrosion and clean up the battery posts and connectors and the grounds.

If it turns out the regulator is bad, there are external ones that can be installed so that you don't have to replace the PCM.

If it turns out you need a PCM, Wrangler fix seems to be the way go.

 

[PattonD]

My battery charge has an alternator test, but how does it know if it is the alternator or voltage regulator in the PCM?

Due to the the sudden hard starting and the charging issue starting right after the check gauges light flashed on, I want to make sure the PCM is OK before throwing an alternator on it just to see.

 

[PattonD]

Only a year with the jeep sitting, while waiting got hit by a hail storm Time to get it running again.

I cleaned all of the connections, put in a new battery, fully charged, but I cant even get it to start much less check for the charging issue. Had a local mobile mechanic who is a former TJ owner and recommended by local jeep guys come by and see if he could figure out the issue and he thinks PCM as well. I mentioned that Wranglerfix asked to ensure to check the grounds, and he said the grounds are fine.

Anything else I need to look at on jeep before I send the PCM off for rebuild? Also, I see there are multiple levels of rebuilds, what is the practical difference? I see there is a flash update available, how do I know if I need one and what that could benefit?

 

[macleanflood]

Is the starter engaging and turning over the engine?

Do you have communication with the PCM via the ODB port and can you read live data?

-Mac

 

[PattonD]

Yes, starter is engaging and the ODB port scan is coming back with no errors.

I forgot to add, he tested the alternator for me, it checked out ok, that was the other reason we came back to the PCM as the issue due to the internal voltage regulator.

 

[macleanflood]

Will it bark off of you spray carb cleaner or starting fluid into the throttle body?

Try a spark plug tester and see if you have spark?

-Mac

 

[PattonD]

tech said no spark now, when this started, initially no spark, but then after cranking for 20ish seconds, it would start firing then crank

 

[macleanflood]

Do you get 800 rpm or so on the dash or does the RPM gauge not move when cranking?

-Mac

 

[PattonD]

No, only once it fires

 

[macleanflood]

Could be a bad Crank Position sensor or the wiring to said sensor.

No RPM on crank is the indicator.

-Mac

 

[PattonD]

Old thread, but I missed your comment (and still haven't fixed the jeep). Assuming the charging issue is the PCM, and the mechanic felt that was where to look, How do I tell the difference as to if this PCM or the crank position sensor is the issue. What is the test procedure for both?

 

[macleanflood]

You can send your PCM to @Wranglerfix for a diagnosis.

-Mac

 

[jonny jeep]

You can test the crank sensor with a multimeter. The 97 FSM says to measure the resitance between the B and C terminals. There are letters on the connector to show which is which. The resistance should on a 10K scale indicate open circuit. The FSM states to replace the sensor if low resistance is indicated (without saying exactly what low is).