1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem

Topic: 1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED (Read 4619 times) previous topic - next topic

1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED

April 01, 2015, 10:08:24 PM

Jeez I hate intermittent issues; especially electrical ones......

Okay, I picked this car up a while back and all was well. Right before the neverending winter, I changed all the coolant hoses. It was IMMEDIATELY after that the amp light on the dash came on.... Out comes the voltmeter. The system is charging, just under 13 volts at idle.... I crack the throttle and it shoots up to 15.5. Well, that's not good.... Swap out the regulator as it's external. Same thing. I had left it at that point and then the snow hit. I had was starting it every 2 weeks while it sat unmoved. The battery ran low enough twice to where it needed a charge. I thought nothing of it.

I finally drove the car last week for the first time without any issue other than the amp light and the apparent overcharge.... Go to start it the next day, dead again. I swap out the relatively new battery for ANOTHER newish one I have that I had bench tested and is known good. I start hunting for electrical draws. Nothing. With the ignition on and all accessories off the car draws around .030 amps. Perfectly acceptable. I start her up, check voltage.....12.5 or so and goes to about 13 at 2000 RPM. Odd. Amp light STILL on..... I go in the car for a second and come back out only to find the voltage has jumped back up to 15+ when I rev it..... REALLY ODD!

I figure when I get around to it I'll pull the alternator and have the local parts store bench test it. In the meantime, I drive the car about 100 miles in the past week. Battery remains charged, car starts without issue, yet the amp light is STILL on. Fast forward to today. 14 mile drive, shut the car off for 10 minutes, and it will not restart. 10.3 Volts on the battery. I get a jump from a passer by and the low charging is back. 12.1 @ idle. 12.8 with the throttle cable pushed as far as it will go. I got the battery back up to 12.4 volts resting....

Obviously I have an issue. One thing I haven't checked yet is the alternators current output (amps) as I'm fairly certain you can't do that safely with your run of the mill hardware store multimeter( :hick: ) My gut tells me it is in fact the alternator and I'll know 100% for sure tomorrow. I'm not sure if I'm going stock replacement on this car or not. If I upgrade it'll be to the same setup I have on the Cougar.

Any thoughts concerning this or perhaps other things to look at are welcome.

1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED

Reply #1 – April 02, 2015, 11:29:31 AM

If you have a '86 or earlier T-Bird/Coug EVTM the Lincoln's charging system should be same as those with the external regulator(3.8 in '86)...

I'd check the wiring between alt and regulator(esp field & stator), either could cause problems... Also coolant is conductive if you got a load of it inside the alt it could have issues, dissembling and cleaning the brush holder assembly may fix that(I'd suspect wiring though)...

BTW the actual amperage output is really not important, as long as the voltage is maintained around 14v with all accessories on, it's charging enough... If amperage output is low but volt high, under heavy load(lights, wipers, blower, etc on), it discharges...

1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED

Reply #2 – April 02, 2015, 11:42:05 AM

No coolant spilled on the alternator when I swapped the hoses.
Pulled the alternator. Noticed the pulley was wobbling when I spun it by hand. Shaft is straight. I'm guessing someone dropped it.
Brought the alternator for a load test. Went to the Auto zone up the road. It passed.... At least on their tester... I'm changing the serp belt as well. It's not horrible, but it's showing signs of early wear so I might as well. Auto zone didn't have a Dayco belt, just their own brand. I figured I'd hit up the local Advance Auto Parts.

For the heck of it I brought the alternator and had them test it as well. Diode fail. A reman with a 2 yr warranty was $95. They'll have it this afternoon. Brand new was 279 and would take 3 days to come. I ordered the reman and a new belt. I have a feeling I'll still be chasing wires afterward, but hopefully not. Stay tuned...

1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED

Reply #3 – April 02, 2015, 01:27:10 PM

Hopefully the diode was the issue. Had this several times in both my Ford truck, and my Chevy.

Drive it all week long, park it friday night, get in it Sunday afternoon to head back to work, and deader than JFK.

Fuggin' diode. Good luck dude..

1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED

Reply #4 – April 02, 2015, 03:42:11 PM

Alternator swapped. No more red light! Voltage @ idle 14.2 Voltage @ 2000 RPM 14.6

AWW YEAH!!!!!

1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED

Reply #5 – April 02, 2015, 04:03:46 PM

Went through the same issue with my Mark VII. The alternator in my car passed THREE TIMES. I finally just replaced it out of frustration. Problem solved.

1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED

Reply #6 – April 02, 2015, 04:06:16 PM

Amazing what a little bitty part is capable of (not) doing..

That .gif kinda freaks me out. The last owl I was near was vicious and tried to bite the living piss out of it's handler. I should say "did" bite, and it looked like a MinPin on meth did the nipping. Hamburger on the dude forearm. Think mr. owl was having a really bad day, but I suppose the same could be said for the guy, too..

I'll stick to snakes and Boxers.

1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED

Reply #7 – April 02, 2015, 04:36:28 PM

The Autozone machine had generic hookups. The one at Advance had all sorts of different pigtails that were specific to whatever alternator was being tested.

1990 Lincoln Mark VII LSC -- Erratic AND intermittent charging system problem - FIXED

Reply #8 – April 03, 2015, 01:04:00 AM

Yep bad diodes sounds about right
When they go bad, the positive and negative terminals are basically being shorted and it kills your battery
I've actually had the same thing happen to me before I went 3g