I have a 1993 Jeep Grand Cherokee Laredo AWD. The car was having voltage issues, and so the previous owner installed a voltage regulator. Unfortunately, he installed the wrong one. He told me that he thought that could be the cause of the slow start and long crank. I got the car and used it like that for a while until I noticed that if I didn't hold the key long enough it would start in some weird way where it would move forward if put in the drive but would chock if I tried to accelerate. If I turned the car off and tried to crank again (this time long enough) it would then start just normal. Well, I brought the car to the shop and they installed a new voltage regulator and rewired the whole thing, the good news is it is charging correctly now, the bad news is that crank is still slow and if you don't hold the key long enough it will go into this weird mode again. Could it be a crank position sensor, throttle position sensor, camshaft position sensor, or some ignition problem? I am not finding much info on this and wanted to learn more about before through in new parts. Thanks!

 

Welcome to the forum.

There are two engines that were available on the '93 ZJ. It is best to ID the vehicle to permit others to help.

It is never good to modify the wiring, unless fully analyzed and engineered. The original configuration had the voltage regulator integrated in the alternator.

Assuming the engine is intact, to not cause excessive cranking load, then the starter should cause normal cranking speed.

The starter motor should get most of the battery voltage, causing normal cranking speed. It sounds like the starter is getting less voltage. I would start w/ CAREFULLY measuring the voltage on the starter motor during cranking. My speculation is that it should exceed 10VDC for normal cranking speed.

 

Well noted, it is the 4.0 straight 6 engine. The wiring was done to bypass the faulty voltage regulator on the ECU. The first time it was poorly done by the previous owner, I then have a professional shop redo the job. I will definitively take a look at the starter motor and maybe it will start a little better but I am not sure if the started would be the cause of the "limp mode" it goes into if it doesn't crank for long enough. Thanks for the time you've put to help me out.

 

The Powertrain Control Module (PCM) controls the generator output by bringing the field connection from battery voltage (no generator output) to ground (maximum generator output).

The generator has three wires (plus the fat red battery wire) for the voltage regulation. These are: black (ground); dark green / black (switched battery voltage for field) and dark green (field control voltage).

The Factory Service Manual (FSM) defines the battery voltage versus ambient temperature. The range is 13.87V to 15.0V for 20°F to 80°F. The operating vehicle should quickly bring the battery to this range. The idle battery should be 12.6VDC to indicate 100% charged.