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Crown Vic alternator swap?

18K views 19 replies 5 participants last post by  WolfHunter984 
#1 ·
After installing under-drive pullies, my car has started to be hard to start if I leave it parked for a few days. Last night we put an ammeter on the battery and noticed that the alternator is only supplying a few amps at idle and the battery voltage is actually dropping as the car sits and idles. With some RPM, alternator starts sending higher amps to the battery and voltage starts to increase again.

Diagnosis: Stock alternator can't keep up when combined with under-drive pullies. Also, battery is 3 years old and may possibly be getting weak.

So I looked and stock alternators for these cars are $200+ facepalm2.gif Absolutely ridiculous.

So we had a thought.. there's an endless supply of alternators off of Crown Vics at the salvage yard, and I would assume that those had a higher amp output to drive all those sirens and lights. Can I swap a Crown Vic alternator onto a GT? Any specific model years I want to avoid?
 
#2 ·
I had some issues with my Underdrive Pullies as well. Did you use the supplied Alternator pulley? If so, I did as well, but ended up removing it and using the stock one and that helped my issues...

I now have a remanufactured Alternator from Oreillys with a lifetime warranty and it is working like a champ...

As far as the Crown Vic alternator...I can't say for sure...I do not see why they wouldn't be a direct fit. Although, with a higher amp alternator (depending on how many amps) you do need to upgrade a wire to handle the higher amps...not sure which one but I do know one of them needs to be upgraded. I believe anything 130amp and higher requires the wire upgrade.
 
#3 ·
Forgive my ignorance, but if you use the stock pulley, doesn't that defeat the idea of the under-drive setup and it's subsequent small power increase?

I have done a little research and it appears that in 2003 Ford switched to a clutched alternator on the Crown Vic. This allowed officers to accelerate hard over and over again and not put strain on components. Apparently they are controlled by the PCM, and under WOT the car will disengage the alternator so that the pulley will free-spin. Very interesting setup... they also put out 200 amps apparently. Wow.

Even if I get one of those and all included wiring from a salvage yard, I am not sure that would be compatible with a Mustang. The PCM control is what throws a wrench in this I assume.
 
#4 ·
In short, yes, underdrive pulley systems, unless they change the altenator pulley to offset the smaller crank pulley creates the low voltage situation....there is nothing wrong with your altenator or for that matter, even if you changed it, it it all likelihood would have the same result
 
#5 ·
My voltage went up with a stock alternator pulley. I datalogged both and the voltage is higher on the current stock pulley...different alternator so it could the alternator too.
 
#6 ·
Well I got a 200 amp non-clutched Crown Vic alternator and it doesn't fit. I had to upgrade the wiring and everything and then the alternator won't physically fit. The power connector hits the intake and won't allow the bolts to go into the upper bracket. Sigh....
 

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#7 ·
Did that come off a PI crown Vic?
 
#8 ·
2005 model I believe is what the tag from the salvage yard said.

So I guess I will have to finish the job when the sun comes back up. I'll probably end up putting my stock 105 amp unit back on and just put my stock pulley back on it. I refuse to pay $300 for a high output alternator. That's insane.
 
#9 · (Edited)
In general care should be taken using a part for one application in another. Ford uses many parts that are similar but do differ. Some differences in alternators include:
  • 2 wire verses 3 wire
  • case ground
  • location of terminals
  • case mounting
  • capacity

Here's what I do. Go to oreillyauto.com and look up the part in question. Once the part has been selected, click on the "compatibility" tab. This will give a list of other "applications" that the part will fit.

A couple of observations. I don't understand the logic of installing under drive pulleys and then being concerned when the alternator's output is barely keeping up at idle. Changing the alternator pulley to compensate only adds to the insanity.

Is it your intent to drive the car or sit in the parking lot looking at it? If you intent is to drive it, then the alternator will charge the battery during normal driving. If you intent is to set in a parking lot, then consider that most people report the alternator will still output enough to keep the battery from discharging.

Final thought. For the 7 years that I have owned my 2000 GT, it has had two alternators installed. Both came from a salvage yard and cost a big $35 each. The Mustang GT's alternator is so stupid easy the change that for me, changing a salvage yard alternator every 5 years isn't a big deal.
 
#10 ·
KWell my intent is to drive the car but even when you drive a car you're not constantly moving. We very commonly found ourselves in stop-and-go traffic during cruises and last year we even got into a traffic jam on the interstate and sat for an hour. So it is very important to have ample charging capacity while sitting as well. To make a long story short the 2005 Crown Victoria alternator was a very difficult project to get installed and then it did not work. There's something different about the wiring. Had a Master Mechanic check it out and still could not figure out what the deal is with it. So I ended up exchanging it and buying a brand new police interceptor alternator for a 2001 model. It is working fantastic but now my battery light is on in the dash and I don't know why. It is putting out more amperage and is charging the battery very well but for some reason the car will not shut off the battery light. I'm also getting a p1000 code.
 
#11 · (Edited)
but now my battery light is on in the dash and I don't know why. It is putting out more amperage and is charging the battery very well but for some reason the car will not shut off the battery light. I'm also getting a p1000 code.
The P1000 DTC code is common and isn't related to the alternator. P1000 will not cause the car to fail an inspection. Best to ignore the P1000 code.

IF the cluster battery warning light will not go out when the correct voltage has been confirmed, THEN:
  • Fuse F2.5 is blown
  • Fuse F1.20 is blown (unlikely as the alternator would not charge at all)
  • the main alternator's B+ fusible link has burned out.
  • the alternator's case is not grounded. Check the motor/frame ground.
  • There's a problem with the alternator's "I" sense circuit. The wire color is LG/RD
  • There's a problem in the cluster with the ballast resister.

Since you have modified a Crown Vic alternator to work in a Mustang my vote is that the LG/RD wire isn't actually connected.

The the key on, engine off, measure the voltage at the alternator LG/RD wire. Should be 12 volts.

Then with the key on, engine on measure the voltage at the LG/RD wire. Post the results.
 
#12 ·
The little green/red wire has been hooked up to have 12 volts on it. We spliced the 3 wire crown Vic connector into the mustang wiring. We upgraded the power wire. Voltage checks out ok at connections. Where is fuse F2.5 ? I'll check it, but at this point I'm thinking the crown Vic alternator must be wired differently internally or something. We just put yet another reman unit on and battery light still is on.

No alternator over 105 amps is available for Mustang at auto stores. That is why I'm trying to use a crown Vic one. Plus, CV is lots cheaper.
 
#13 · (Edited)
The little green/red wire has been hooked up to have 12 volts on it. We spliced the 3 wire crown Vic connector into the mustang wiring.
The post does not state exactly what the engine on voltage is on the LG/RD. The details matter. Use a meter that will give an accurate results. Hint. In a correctly working car, the voltage shouldn't be the same as battery voltage.

OBTW, the Mustang only uses 2 wires. The middle pin is not used. That may be the key to solving this.

1999-2004 BJB CJB fuse panel layout:
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271
 
#14 ·
Yeah we figured that the center wire on the Crown Vic connector is an aux wire for running some other type of accessories, so it's not needed on Mustang. So we spliced the wiring connector in so that the 12V hot wire is still providing 12V to the proper pin, and the keyed wire is still getting power when key is on to the proper pin. I will diagnose once again this afternoon and post results. Actually, I might just wire the Mustang two wire connector back on the car for kicks...but I don't anticipate change. I will also check the fuses. Got late last night at a big car show and didn't get a chance to check into it. Thanks.
 
#15 ·
Fuse 2.5 under the dash was OK. Hooked test machine up to car again and tested battery and alternator and both tested OK. Was seeing 13.8 volts with A/C off, and 13.2 volts with A/C on. It'll drop to 12.8 volts with A/C and headlights on. Just for kicks I installed the factory alternator connecter and wired it back to the original two wires it came from on the Mustang. That made no change in the status of the light on the dash. So the obvious issue is that 3rd pin on the Crown Vic alternator. Since the CV is wired slightly differently, the Mustang is looking for the current from a different source and it doesn't think the car is charging even though it is.

So now my choices appear to be:

A) Pay twice as much for a Mustang specific alternator of the same amp capacity so the light will go off.

B) Live with the charge light being on in the cluster.

Funny thing about it is that when the original factory alternator was not keeping up with demand and we were actually watching the battery voltage dropping as the car idled, the car did not throw the battery light on the dash. So apparently the cluster light doesn't do anything until it sees NO output, and by then you're screwed. So it's sort of a waste of time to have it.

Hmmm... decisions decisions...
 
#16 · (Edited)
Was seeing 13.8 volts with A/C off, and 13.2 volts with A/C on. It'll drop to 12.8 volts with A/C and headlights on.
The alternator is supposed to put out 6 volts LG/RD wire with the motor running. It's the presence of one half the normal voltage that turns off the dash battery warning light.

Pull fuse F2.5 and repeat the engine off and engine on voltage test of the LG/RD wire.

If the test shows zero for both engine on and off, then likely the alternator isn't sending the "I'm charging" 6 volt signal.

If the LG/RD wire shows 6 volts with the engine on/fuse pulled, this likely means there's a problem is upstream towards the cluster.
 
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#17 ·
OK I'll check it out tonight.

We took my old alternator to a local "old timer" shop who we've been dealing with for years. The guy has been rebuilding alternators for decades. He says the Crown Vic alternators have different regulators inside, which is my issue. He suggests finding an alternator off a Lincoln Mark VIII because those were also high-output, but they have the correct 2-pin connector and regulator. We have access to lots of this stuff from a friend who has a salvage yard, so it's worth a shot. :grin:

Thanks for the advice so far. I've been busy but I'll try to dig into this again tonight.
 
#18 ·
The wiring diagrams are not always totally complete. But on the diagrams that do show the value of the the ballast resister, the later model year Mustang uses a 490 Ohm where as the CV uses 390 Ohm.

Both sets of wiring diagrams indicate that both cars use one half voltage back feed signal to turn off the battery light. So the fact that you are seeing full battery voltage with the motor running indicates there's something wrong somewhere.

But honestly my understanding of the circuit leads me to believe that the reason there's a different ballast resister is because the bulbs used in the cluster are different. But I could be wrong.
 
#19 ·
Ok so I thought I'd wrap up this post for future reference in case somebody stumbles upon it later down the road.

To recap, the reason for trying to use a non-Mustang alternator was because A) All Mustang alternators are 105 amp output according to auto parts stores listings and a local reputable alternator rebuilder and B) Mustang alternators are excessively expensive. The Mustang alternator showed negative charging (could not keep battery charged with A/C and headlights on using under-drive pulleys). I needed more output.

What we discovered after more trouble shooting is that at some point we blew a fuse in the panel under the dash in the car, and the little green wire connected to the fuse box under the hood was also slightly loose and was making a poor connection. These things resulted in the battery warning light being lit on the cluster and no voltage at times to the connection on the alternator.

After replacing the fuse and crimping the connector on the underhood fuse box better, the Crown Victoria alternator started not only charging great but the warning light on the dash also went out. It's an alternator from a 2001 Crown Vic. We tried one from a 2005 Crown Vic and had fitment and wiring issues. We tried one from a late 90s Mark VIII and had fitment issues. But the same model year Crown Vic works great. Clamp-on amp tester shows a significantly higher output at idle now and my battery is no longer discharging while simulating sitting in traffic with A/C on and lights on.

Thanks for the advice and help along the way. I saved $100 by going with the CV alternator and the end result turned out like I wanted. wrenchin.gif
 
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