blk93zj

Hey guys i have a 1993 zj limited with a 4.0 engine and i am having voltage problems.When i first start the jeep up in the morning the voltage is fine,the only problem is when i use any of the accy,s like the power windows,cigarette lighter anything that draws power the voltage on the dash guage drops dramatically but the jeep never stalls or anything the lights dim thats about it.I have already replaced the battery,altenator,battery cables put new ends on the cables,checked the grounds and the jeep already has a mopar reman ecm in it.I was wondering if anyone has any ideas?

Hymie

Using logic to solve your problem, work out which electrical paths are common to the high current paths that cause the problem (drop in vehicle voltage).

Favourite would have been the battery earthing connection (since every high current draw appears to cause the problem) – but you claim to have already eliminated this.

With a fully charged battery, do you suffer the problem without the engine running?
The answer to this question should eliminate the alternator (or identify it or its wiring as a possible culprit).

With the engine revving at over 1,500 and a heavy electrical load causing the lights to dim – what is the battery voltage (measured directly across the battery terminals)?

If you are certain that the battery earth (chassis connection) is good – then I would suspect a poor connection in the battery positive connection/path. I am not familiar with the zj – but many vehicles use pcb plug connections for power distribution. Your problem could be a poor connection in a multi-way plug connection – or even a pcb track making poor connection at a join.

If you can determine the high current paths, then check all connectors/connections in that path. Poor connections should be evident from charring/heat damage, resulting from the power dissipated at the poor connection.

Another possible culprit could be a relay (switched via the ignition), with bad contacts. Tracing the power distribution from the vehicle’s electrical schematics will identify possible relays. You might be able to swap relays (rather than having to buy a relay on a speculative fix).

blk93zj

Thanks Hymie,I tested the voltage with the jeep running and the voltage was good and i also checked the battery with the jeep off and the voltage was good i did not however try the accys with the jeep off. I am getting ready to get into it again and i wanted some feedback.The last time i worked on it was the end of summer and i got frustrated so i just let it go.Thanks again

Hymie

More thoughts on your volt drop problem:-

Measure the voltage at the lights (which are dimmed), with the high current load switched on – causing the light to dim. The voltage at the light should be 10V or less, to notice an appreciable dimming effect.

With the battery fully charged, at maybe 13V (or 14V with the engine running) - it is then a simple matter to determine whether the voltage drop is in the positive or negative supply line from the battery. With the lights dimmed, measure the voltage from the negative battery terminal to the 0V terminal of the dimmed light – and then measure the voltage from the positive battery terminal to the +V terminal of the dimmed light.

[Remember that the negative battery terminal is the zero volt reference point of the vehicle – and that the chassis (and 0V of the light), will be at a slightly positive voltage, versus the negative battery terminal]

Under normal conditions, both these voltages should be close to zero volts (with the full battery voltage across the light), but as a result of the resistance in the path (from one of the battery terminals) one of these voltages will be reading the difference between that battery terminal voltage and the light voltage (over 3V). You will then have determined which (+ or -) supply from the battery is giving you problems.

One possible quick route to locating the fault is to give the wiring loom and connectors a gentle wiggle, while observing the brightness of the dimmed lights.

Bubbasgoped

I had this problem when I bought my 98 ZJ 4.0. "MY" problem was with the ground off the battery. I up dated the ground on my battery (I am running a lot of audio stuff). I have three 4gauge wires off my battery two to the vehicle and two to the engine. That corrected my drops in voltage even with my additional items running off the battery.