Meinz

Hello, I'm new to this forum. Has anyone had good experience with purchasing a re-manufactured ECU? There's a couple of outfits on eBay that will send a "re-manufactured" ECU (around $200, exchange) for my 1996 Grand Cherokee and I'm wondering if they are reliable? Anyone have a good experience with a reliable source for a re-manufactured ECU?

The reason I'm looking for an ECU is, my battery charging system started acting up intermittently, then quit altogether. I understand that the ECU regulates the charging on my jeep; it does not use a standalone regulator. I did do the test to verify my alternator is functional and saw my voltage climb quickly from 12 to 15 volts at the battery, so I think the problem is the ECU.

Any insight or help would be appreciated.

Thanks

97grand4.0

Welcome to the forum.
I think you are getting way, way ahead of yourself changing the ecu,,,actually it's the pcm, hoping it will fix this based on what you are reporting. You state charging system acts up intermittently, ..how? Then you say the voltage goes from 12 to 15 when you start it up, well, that sounds pretty normal to me. So not even sure what the problem is, but if you can drive it, drive it over to adavance or autozone and ask for the free on vehicle charging system test. They have a microprocessor controlled, hand held, lcd readout that will paper print out the results of the starting and charging system in about 3 minutes.

Meinz

Thanks for your reply 97grand, although you misread what I wrote about the results of my alternator check. Right now the system does not charge the battery at all, and after starting the engine, it shows about 11 volts on the voltage meter for a few minutes, then the gauge goes to zero and the "check gauges" light comes on. The car runs fine otherwise, but the battery is slowly being drained.

After I figured out the system wasn't charging, I tested the alternator by removing the "field 2" wire at the alternator, then grounded the field 2 terminal using a jumper wire. I started the engine and using my digital voltmeter at the battery, I observed a steady climb from 12 to 15 volts, indicating the alternator itself is putting out charge voltage, but not when the field 2 wire is connected to the "PCM", which is supposed to regulate the charging.

That's why I suspect the PCM.

97grand4.0

Gotcha. Well couple things. There are 2 field wires, one is directly connected to ground via a jumper, the other comes from the pcm. Grounding the terminal that would otherwise be connected to the pcm will of course result in no voltage across the field and no output from the alternator.
That being said, its always agood idea to refresh that little black jumper wire connection where it bolts to the alt bracket. The nuts are so little, easy to get corrupted. If a bad ground there could do what you describe. Wire brush or sandpaper both the field terminals too.
Otherwise if that doesn't work it is tricky to test it on vehicle, but I would suggest remove and bring it in for a bench test. The very last thing you want to get into is a pcm swap. They have to be flashed for your vehicle mileage and VIN number by a dealer. Then the swap itself can cause problems with connectors, and if you somehow ended up with a wrong pcm you would repeat the whole process.
Have you checked with a code scanner to see if all your monitors have run? Because the batt temp sender under the battery can go bad and this is the only thing besides the pcm that give input to the charging system. If that sensor is bad you will have monitors not ready. just some thoughts hope it helps.

It sounds like you're not looking at the typical regulator problem here, you have more of a charging system failure.
I recall my stock alt failing, it was also intermittent as you describe except I don't recall the dash gauge going to 0..that suggests to me something else

Meinz

Thanks for your input 97grand. I just checked out the battery temp sensor and surprise...it's dead. No ohm reading between 9K and 12K, no ohms at all...just no continuity. Since that's only a $25 part, I'll change that out first. Hopefully, when the PCM sees input from the battery temp sensor again, it will allow charging to resume.

97grand4.0

No problem let us know how that works out. I.m not convinced that's your problem, I kind of think it's the alt. But do report back.

Meinz

Well you may be correct. Installed the new battery temp sensor and it did not change a thing. As it turns out the old one actually had a loose pin in the connector. It ohm'd out OK but only when I wiggled one of the connect pins, so I tossed it.

Thinking about what you said, I once again I tried the alternator test I mentioned earlier to rule it out completely, and this time the alternator did not put out a charge voltage as it had previously.

Now I'll replace it and hopefully that will take care of my charging issue. I wasn't really looking forward to replacing the PCM, but I guess the voltage rise from the previous alternator test led me to believe it might be the culprit and honestly, I'd never experienced an alternator that failed intermittently before. Mine either just quit or had the bearings go out.

Thanks again for your input 97grand.