volaticus

Short Version: I've been having problems starting. Got battery, starter, alternator tested at O'Reillys and Autozone. Replaced battery, alternator, and terminals. Still showing bad voltage regulator. Thoughts?

Long Version: So ol' faithful is quickly coming up on 300,000 miles, and she has started feeling a little more tired lately.

A month ago it began having problems starting. I would go to start it , and there would be a single click and then it would lose all power. I would go wiggle the battery terminals and cables, power would be restored, and then I would try again. I usually had to do this 10+ times before I would get it to turn over and start. I figured this meant it was the cables or terminals, so I cleaned the cables at the battery posts and replaced the terminals.

The problems starting persisted, but changed slightly. It was then turning over VERY slowly and usually needed me to pump the gas pedal to get it started. I would have to hold the gas pedal for a minute or two or it would stall out and die. I then went to O'Reillys and Autozone and had the systems tested. They both said I had a bad battery, bad diodes, and bad voltage regulator. I didn't believe the battery was bad (2 year old Optima Yellowtop), but I replaced it under warranty anyway. My starts were strong, but the testers said I had bad diodes and voltage regulator so I replaced the alternator with a new 90 amp unit. The tester is still saying I have a bad voltage regulator. My starts have still been strong, but this might just be because the battery hasn't been drained yet.

After a bit more research I saw some people mention that the voltage regulator is external to the alternator and instead in the ECU. Is this true? Did I replace a functioning alternator when I should have replaced the ECU instead? I have until tomorrow to go get my old core back and return this new alternator, so I'm just looking for some opinions or advice on how to tackle these electrical gremlins.

Thanks,
Matt

Larry's XJ

Didn't you have alternator tested ? Have you cleaned the grounds?

DFlintstone

Please fill out your info so at any post we can see what you have. I'm pretty sure the regulator is in the Alt till 90, then in the PCM 91 on. 87-90 have an ECU. Scanners for them are pretty rare, so I'm guessing you have something post 90, with the regulator in the puter". With a cheap $5 harbor freight digital volt meter you wanna see around 14 volts while it's running. Off, in the morning it should test around 12.7. I don't know where you are at with $, but maybe you should return it, then figure out what's actually wrong. You can always buy it back. Or if it's charging good, (mine idles 14.25 with everything on), if it's working now maybe call it done. Btw, the only diodes I'm aware of are in the alt. (OK there have got to be some in the puter, but that's not that)

s346k

I had the same issue with mine not starting. so I swapped obviously bad cables with the old, but decent, cables and ends I had laying around. I then started experiencing erratic charging. cleaned my grounds and that cleared up. then I had a low charge condition along with slow crank. I changed the battery temp sensor, which I believe is a 97+ only piece, and that restored everything back to normal.

as of late I began noticing the somewhat erratic charge and weak start. the cables etc are clearly in poor repair (again) at this point. I ordered a badass set of cables from xjwonders, which I have not installed yet.

these events have taken place over the last 3.5 year timespan.

97grand4.0

[QUOTE=volaticus;3275275]

"After a bit more research I saw some people mention that the voltage regulator is external to the alternator and instead in the ECU. Is this true?"

Yep, sure is true. Not likely you replaced the alternator in vein, though, if it was testing bad especially bad diodes, common in these alternators and the testers they use these days are very good and accurate.

So two things can also effect the charging rate, the regulator in the PCM, and the BATTERY TEMP SENSOR located in the bottom of the battery tray, this is also the AMBIENT temp sensor, so don't write it off as just a battery charging device, it also is critical to the pcm for sensing the ambient temp for the pcm to run a host of diagnostics and monitors for evap, 02 heaters, and others, and malfunctioning it can cause you to fail inspection for the above reasons. very obscure to troubleshoot so dont go stuffing a resistor in there (like I did, then failed inspection for 'monitors not ready' and spent $$ hunting it down) replace it if old or in doubt.