I’m fighting an endless battle with my 1991 Mercury Capri over alternator belts and battery charging. I’ve tried every style, make and model of V-belts, including the NOS Ford type recommended by Capri enthusiasts online, and tensions from loose to as tight as I can get it, cleaned the pulleys, replaced the alternator… but I still get the same results: At first the alternator is charging the battery, but after a few minutes or maybe a half- hour of driving the alternator stops charging. Retensioning the belt always restores charging, but only for the next few minutes or half-hour again.
Arrggghhh! This is driving me nuts - I can’t figure it out. Do you have any thoughts on this?
Thank you…
Steve
How is the belt tension adjusted? At the alternator?
Tester
How is the belt tension adjusted? At the alternator?
The alternator is loosened from its top mounting bracket and pivoted on the lower mounting point to tighten or loosen the belt. I use a lever to apply pressure to it and retighten the upper bolt to lock it in place.
Steve
have you marked the bracket with a white marker to make sure it isn’t slipping?
it could be as simple s a stripped bolt/nut on the bracket.
is this end a nut on a long threaded bolt? possibly the nut has been replaced with a NON effective application nut. it is supposed to be a wide shoulder nut with serrations on the back to help grip the bracket.
The voltage regulator is probably quitting because it is getting hot(something is wrong with it).
Are you also tightening the pivot bolt for the alternator?
Tester
Can you actually see the belt slipping? When the charge light comes on, can you go look under the hood and see the belt turning, but not the alternator pulley? If that’s the case, it’ll usually be making a horrendus noise.
I’m thinking that retensioning the belt is a red-herring-- and that what’s actually making it work is some combination of turning the engine off, letting it sit for a while, or physically jostling the alternator. I would second Pleasedodgevan’s idea of checking the voltage regulator-- I think at this point FoMoCo cars still had the external regulator mounted on the fender-wall that don’t come with a rebuilt alternator. Either that or rebuilt alternators are known to go bad-- next time it does it, you might try (very carefully) measuring the voltage at the alternator connection while the motor’s running.
It does sound like a alternator/regulator. Is the regulator integrated in the alternator on your car? If not that would be a good chance. It is also possible it is the alternator, but you did replace it. It is still a possibility you may have gotten a bad one.
However let me throw in one more possibility. Are you sure the belt in properly aligned? That would include at all pulleys.
You are going to have to find out if your charging system has an external or internal voltage regulator. If it is an internal regulator and you have already changed out the alternator then you have a massive draw somewhere in the electrical system. When the alternator quits charging does the car die? If so, then you would have a massive voltage draw somewhere. Make sure the connections where the cables meet the battery are clean - not wire brushed, actually clean because you can wire brush the connections all day long and still have crude you can’t see or wire brush. Scrape the connections with a razor blade.
I’d also look for a bad cable connection - in fact I’d remove and clean all the cable connections from the battery and alternator. Also make sure your enging block has a good ground connection.
Excellent idea about the nut - my recollection is that it does not have the shoulder. Perhaps a toothed lock washer would be in order. Thanks… Steve
The Capri’s alternator was replaced in the course of my struggles, and it has the regulator built-in in this case. Could still be an issue, of course… Murphy is always available to invoke his law! Thanks. Steve
Are you also tightening the pivot bolt for the alternator?
No, I haven’t been - that’s a good idea! It is snug, and resists the motion as I adjust the tension, but not cranked-down. I should try that… thanks! Steve
see the belt turning, but not the alternator pulley?
The alternator is not dead-stopped in this condition, but it seems to be turning more slowly. I can leave the lock-down nut loose enough and apply leverage to tension the belt tighter with the engine running, and the charging will come back up as lean into the lever and tighten the belt - and go back down as I let it relax.
If that’s the case, it’ll usually be making a horrendus noise.
The noises produced during the slipping depends on the model of belt and the degree of looseness. I’ve become quite a connoisseur of squealing belt sounds working on this devil-car. Steve
'm thinking that retensioning the belt is a red-herring–
I would second Pleasedodgevan’s idea of checking the voltage regulator
Good thought, but I have replaced the alternator and regulator. The Capri was built in Australia and the alternator is Japanese and includes the regulator. I believe I recall it was made by Mitsubishi.
you might try (very carefully) measuring the voltage at the
alternator connection while the motor’s running.
It is the same at that at the battery posts under all circumstances (within a couple-tenths volt of that voltage at the battery). There is very low voltage-drop in the cables. Thanks… Steve
Steve
Are you sure the belt in properly aligned?
That would include at all pulleys.
I believe they are directly in line with each other - I’ll confirm that tonight. Thanks… Steve
When the alternator quits charging does the car die?
Not immediately, you can continue to drive on the battery. Eventually the voltage will sag down to the point where things will begin to malfunction, though. And sometimes by revving the engine a couple times the alternator will begin to charge, at least to some degree. Note that the belt noises will change or stop entirely when this happens. Thank you. Steve
I’d also look for a bad cable connection - in fact
I’d remove and clean all the cable connections
from the battery and alternator. Also make sure your
engine block has a good ground connection.
I’ve checked these points, confirming low resistance between each point, and watching the voltage drops from one end of the cables to the other. The voltage on the output terminal of the alternator is the same as that at the battery post under all circumstances (within a couple-tenths volt of that voltage at the battery). There is very low voltage-drop in the cables and connections. Thanks… Steve.
Interesting problem - and I can see you know your electronics enough to correctly look for bad connections by measuring voltage drop under load.
I think you need to start by ruling in or out the mechanical aspect of this problem - Is the tensioning of the belt not holding? Determine this by marking it as cappy208 suggested - or take a ruler and measure the disatance from the alternator pully to a fixed point that is in line with the direction the pully would move if it is slipping.
If you determine it’s NOT a mechanical slip of the tensioner - then I would try to rule out the next most likely failure point - the battery itself (I can theorize on what could be causing this - but I’ll save it for now)
If you can swap the battery with another one - that would be the easiest (I wouldn’t go buy a new one just yet) - if not - and IF you can reproduce the problem while stiiting at idle, do the following. Get a “donor car” (borrow a friends car) and disconnect a battery cable from it (just one will do). Next, connect it to your car with jumper cables as if you were going to jump start it. Let your car run and see if the problem happens - if not - disconnect the donor battery (without shutting off your car) and see if the problem happens.
This will rule in or out the battery as your cause.
I’m thinking it could be the battery because I have seen batteries have intermittent “opens”. If has such a problem it could be going open after it heats up from use - then while you are re-tensioning the alternater - it cools down and begins working again. It’s a long shot, but it seems you have exhausted all the “short shots”
These odd symptoms could be caused by the diode in the main wiring harness open and shorting. Check out Capri Article No. 90-22-10; which is, “Diode damage by incorrect battery charging”.
It might be Ford or Mercury Article No. 90-22-10; but, it definitely list Capri 1991 as the affected vehicle.
Get a copy of the Article from the Ford/Mercury/Capri dealer, or off the Web.
There are Capri enthusiasts?