Alternator blues...

driller

El Presidente
Staff member
One of the problems I have yet to completely resolve is the alternator curse on the '93.

The best and 1st aftermarket alternator I had was one from PA Performance. When I went to an underdrive crank pulley, I discovered the alternator was weak at idle. I immediately calculated the pulley size to overdrive the alternator back to stock speeds and it seemed to be fine for the longest time.

Then starting a couple years ago, I seemed to be 'over-revving' the alternator(s) and killing them. I noticed a pattern - it appeared to happen after a spirited drive or a dyno session when apparently the engine would hit the rev limiter.

The problem has compounded now after the head swap and raising the rev limiter to 7 grand. Since last fall, I have went through 3 alternators! :eek:

I've went back to a stock pulley but the voltage drops like a rock at idle. I thought maybe my old Odyssey battery was partly the cause but it always has tested good with a load tester. I've even swapped batteries with the '96 and that didn't help at all. The charging system on the '96 works just fine with the older Odyssey battery and the voltage still drops precariously at idle with the newer lead-acid battery in the '93.

I'm out of spare alternators and I am totally unsure which direction to go. :(

I am going to contact a local rebuilder of good rep and talk to him to see if he can rebuild one that will have good idle capabilities and be able to handle the higher rpms. I know there has to be a solution at either end but I am not sure if both high rpms and idle output can be attained.

If anyone has any pointers, I'm all ears. :eek:
 
Those alternators are so small, they can't get much of a regulator in those things can they?

Are there any companies that make heavy duty external regulators, that you could somehow wire in? That might at least help the higher RPM's?
 
I don't know if it's the regulator or the windings? I've never had an autopsy done on one, but I suspect I will soon.

Those MSD units look huge compared to the 4G Motorcrafts and I didn't see any brackets for the 4G. It may be worth an inquiry though.
 
I have a freshly rebuilt PA performance 200A unit available....

I have 2 of theirs that need rebuilt. :(

First one was a 160A that lasted the most and the second was a polished 130A. Both were good until I killed them hitting the rev limiter.

I actually forgot - I think I have a spare in the storage shed I bought from Jeremi a long time ago. But it's an OEM unit and I doubt it will like the high rpms either. That makes me breathe a bit easier but I still need to solve the problem(s).
 
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So, I got to thinking about this, and did some research.

I rev the **** out of my '98 Cobra, without alternator issues, and have since it was new. With underdrive pullies, BTW. And I've never even heard of anyone killing a stock alternator on a Cobra by over revving it.

Motorcraft lists the Cobra alternator as GLV-8356, and the Mark VIII alternator as GLV-8357.

However, every aftermarket listing I've looked at says that their alternators replace both the 8356 and 8357.

Maybe the 8356 is made for the higher redline?
 
I've had very similar issues with my alternator. The 94 went through 5 between october and november last year. I also blew up two fans in the process but I dont know if they were for similar reasons. I ended up putting a larger pulley on the alternator from the steeda kit, grounded the fan to the battery, and cleaned the engine ground strap and the main ground. I havnt lost any alternators yet this year so Im hoping it was a grounding issue. Just something you might check.
 
I have a MOTORCRAFT Part # GLV8357RM in The Mark. I also have a ATI 10% overdrive balancer, and rev beyond 7k with no problems with the alternator. There was nothing wrong with the original stock alternator with over 100k miles on it. I just replaced it with the new one when the new motor went in the car.

I think there might be something else involved that is cooking the alternator, JP.
 
I've been studying hard on this. After going back through the archives, I refreshed my memory and indeed do still believe it is an over-revving issue.

I found this old post of mine.

Pay attention class...

The stock crank pulley is 6.75" diameter.

The stock alternator pulley is 2.625" diameter.

That makes the ratio (D/d) 2.6:1.

At an idle speed of 700 rpm, that makes the alternator barely meet the 1,800 RPM minimum.

At a rev limit of 6,000 rpm, the alternator speed is just under the the max limit running at 15,428.6 RPM.

There is no room for error. What you gain on one end, you loose on the other.

I installed a 5.25" diameter Steeda underdrive crank pulley and it changed the ratio to 2.0:1 making the idle speed of the alternator 1,400 RPM, well below the recommended minimum.

I then install an overdrive pulley with a 1.875" diameter and raised the idle speed of the alternator to 1,960 RPM. OK, but now at the rev limit of 6,000 RPM the alternator is spinning at 16,800 RPM which is over the maximum recommended speed. A RPM spike of 6,500 - the alternator is now over 18,000 RPM. Too much of a good thing and after a while the alternator is toast.

Now take the same info and rev the car up to 7000 rpms.

Stock ratio of 2.6 x 7000 = 18,200 (2,200 rpms over speed but idle rpms are OK at 1,820).

Underdrive crank pulley with stock alternator pulley: Ratio of 2.0 x 7000 = 14,000 (OK, but not enough rpms to charge at idle with only 1,500 rpms).

Underdrive crank pulley with overdrive alternator pulley: Ratio of 2.8 x 7000 = 19,600 (3,600 rpms over speed but idle rpms are OK at 1,960).

If I want the top alternator speed of 16,000 with the engine at 7,000, I need a drive ratio of 2.3. That would make the alternator pulley diameter need to be 2.25" when paired with the Steeda crank pulley. I guess I could try that. At idle, that would put the alternator spinning at 1,610 rpms - still low but it may stand a chance. If I bump the engine idle to 800 rpms, the alternator should be OK idling at 1,840 rpms).

But there could be an underlying issue aggravating the charging system. The ground could very well be a questionable suspect. I will look into that.
 
What lets go at high rpm on these?

I've yet to have one diagnosed but I suspect the regulator.

This outfit is in eastern Tenn., you might want to talk to them.

I've considered them before. Would a high output alternator put out more at low speeds than a regular alternator? According to what I've looked at so far, they do.

I ended up putting a larger pulley on the alternator from the steeda kit, grounded the fan to the battery, and cleaned the engine ground strap and the main ground.

The fan is a big draw, so a direct ground on it sounds like a good move. Another heavy ground wire would be easier to install than accessing the factory ground.

Thanks for all the feedback. At least I have hope now. :)
 
Sounds like you need a alternator with a clutch to disengage for anything beyond 6k. =) I think there is a small supercharged Mercedes with a blower on a clutch to disengage when it isn't needed.
 
Years ago there used to be a setup that did something like that. You used a switch on the dash to turn the clutch on or off. Get out of the bleach box and turn switch off (Just use battery power the 1/4 mile), on the return road switch back on.
 
I have bought those, They are not even close, about a rib off. And I saw no way to install them with out removing the water cross over. Does this sound right? Also what alternators do we have anyway? A mitsubishi 4G?
 
No, it doesn't sound right.

I have had no issues with those pulleys as far as alignment.

The easiest way to R&R the pulley is to remove the alternator from the car.

Yes, we have the 4G alternator and I believe Mitsubishi was the manufacturer of the stock OEM units.

Check THIS out!
 
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