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I just completed my Cobra Mark IV with a donor 5.0 Coyote engine out of a 2016 Mustang GT. I purchased the Ford Performance ECU and wiring harness for the engine installation. After completion of the fuel system, electrical and instrumentation then engine started and ran perfectly. I noticed the output voltage with the engine running was 15.2 volts. I have been known for years that a perfect charging voltage is 13.6 to 14.2 for a typical 12 volt battery. I became more worried after the battery became fully charged but the voltage never varied from this over-voltage charging rate of 15.2. I replaced the alternator and same result 15.2. The voltage reading was confirmed using a Fluke meter that I trust. I am now tripping an 80 amp thermal overload I installed to protect the battery. The battery is getting warm to the touch, so things are definitely heading in the wrong direction! Can anybody help me figure out what is going on here I'm running out of ideas. Thanks , Carl Eldridge
 

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Seems odd that you are getting same results with two different alternators. Which alternator are your using? Are you certain that all your connections are tight? I am not familiar enough with alternator and the capacity of the voltage regulator to be certain. Could your pulley ratios be wrong? Spinning your alternator too fast?

Some more info here.

 

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What alternator are you using? The Ford Performance 5.0 Alternator M-8600-M50BALT recommended for a crate build? Or maybe something similar? From experience with two Coyote builds, I can confirm the alternator output is pretty high. In the upper 14's and maybe a little more in my experience. An 80 amp fuse is light. I haven't been able to confirm the exact output, but these 6G alternators are available with 130, 170, and 200-amp ratings. As already stated, check all your cable connections. Also maybe get the battery tested.
 

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I would try another battery if you have one that might fit to rule out the battery. I don't know squat about the Ford charging system and the ECM. My dodge van had charging problems, low alt output, and it turned out the be the ECM was bad. The ECM controls the alt field winding and that sets the output voltage. I wouldn't be surprised if a Ford is like that as well.
 

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Try calling Ford Performance Hotline....I've called these guys a couple of times (on water pump/chain case/pulley fitment issues) and they were very helpful. A couple of the techs have even done their own FF roadster builds. Doesn't have to be a Ford Performance part....anything Ford and they seem more than happy to assist.

 

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Seems odd that you are getting same results with two different alternators. Which alternator are your using? Are you certain that all your connections are tight? I am not familiar enough with alternator and the capacity of the voltage regulator to be certain. Could your pulley ratios be wrong? Spinning your alternator too fast?

Some more info here.

The Coyote engine is exactly the way it came out of the Donor Mustang. Only the Ford Performance ECU and wiring harness was added to eliminate all the anti skid, theft, seat belt, and a million other thing the factory ECU does. With the new Remy alternator in place I am now inclined to believe that the CPU controls the voltage. Does anybody know about this, or is the voltage solely controlled by the alternator internally?
 

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What alternator are you using? The Ford Performance 5.0 Alternator M-8600-M50BALT recommended for a crate build? Or maybe something similar? From experience with two Coyote builds, I can confirm the alternator output is pretty high. In the upper 14's and maybe a little more in my experience. An 80 amp fuse is light. I haven't been able to confirm the exact output, but these 6G alternators are available with 130, 170, and 200-amp ratings. As already stated, check all your cable connections. Also maybe get the battery tested.
All good suggestions, thanks. I have already replaced the Battery because the 80 amp overload tripped and was reset 3 times in a 10 minute ride. But what really pushed me to replace the battery was it's heating up to the touch. Very scary!! My Stock Remy is a 170 amp output which is way over sized when you consider it's only load is the CPU
and the radiator fan. All connections are tight and clean. The car only has 30 miles on it at this point. I will report back when the new battery is road tested and proved stable and cool charging. I am not against putting in the M50BALT if need be, but a few more questions need to be worked out.
 

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I would try another battery if you have one that might fit to rule out the battery. I don't know squat about the Ford charging system and the ECM. My dodge van had charging problems, low alt output, and it turned out the be the ECM was bad. The ECM controls the alt field winding and that sets the output voltage. I wouldn't be surprised if a Ford is like that as well.
Ahhh! you answered my question about the alternator taking it's Alt field voltage from the ECU. I suspected that! What that means is, I could replace the Alternator 10 times with the same result!! I did replace the battery and suspect that it is shorted internally which would explain the battery heating and overload tripping. The big question is, am I in the process of ruining another battery with the high voltage...That would be bad. I am going to call Ford Performance I hope they actually answer the phone.....!!
 

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Try calling Ford Performance Hotline....I've called these guys a couple of times (on water pump/chain case/pulley fitment issues) and they were very helpful. A couple of the techs have even done their own FF roadster builds. Doesn't have to be a Ford Performance part....anything Ford and they seem more than happy to assist.

Wow! you have no idea how glad I am to hear that. They would have the answer for sure. Thank you...Thanks you!
 

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All good suggestions, thanks. I have already replaced the Battery because the 80 amp overload tripped and was reset 3 times in a 10 minute ride. But what really pushed me to replace the battery was it's heating up to the touch. Very scary!! My Stock Remy is a 170 amp output which is way over sized when you consider it's only load is the CPU
and the radiator fan. All connections are tight and clean. The car only has 30 miles on it at this point. I will report back when the new battery is road tested and proved stable and cool charging. I am not against putting in the M50BALT if need be, but a few more questions need to be worked out.
I don't think the M50BALT alternator is the exact one used on a stock Coyote. But they're from the same family and I suspect act very similarly. As I said, I see similar voltages as you're describing with both my Coyote builds. And others have reported the same thing as well. So personally I'm not recommending replacing the alternator. I do think you need to replace that 80 amp breaker though. The fact that it's tripping is probably because your car is pulling more than that. Not necessarily because there's something wrong with the charging circuit. Yes, PCM and cooling fan. But whole bunch more on the engine (e.g. ignition, injectors, sensors), your fuel pump, the car's fuse panel and whatever's hooked to it like heater, lights, gauges, the list goes on.
 

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G'day Carl,

I have a gen 1 coyote and also have the same issue with reasonably high charging voltage at 14.8. as Paul said, I also believe that the ECM controls the charging output of the alternator. In my roadster I installed two fuses on the output cable from the alternator, 1 fuse is rated at 80 amps and feeds the battery, the other fuse is rated at 60 amps and feeds the PCM and all the other vehicle electrics. I have never had a problem with the battery fuse failing and I have even gone to the trouble of discharging the battery quite low to test that an extended high current charge into the battery from the alternator will not blow the fuse.
What I do suspect may be a problem is that DC resettable circuit breaker. I have experimented using these in my day job as an electrician. I have tested a number of brands ( as most seem to be copies of each other) and I can say without doubt that all of them are garbage. We found that they trip at wildly different currents and often that current becomes lower after the breaker has experienced a number of operations. They are pretty much a toy that should be thrown straight into the garbage. Maybe there is a reliable model out there but I haven't found it yet.

My suggestion is to use what the vehicle manufacturers use, Bussman is a good start.

I hope this can help you in some possible way.

Cheers Nigel in South Oz
 

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I have a Coyote Gen1 engine in mine and it puts out just over 15V. Been doing that since 2014. Never a problem. This is pretty normal as others have cited.
 

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I did not worry about my 15.2 volt alternator out put, until my Bussman 80 amp resettable overload started to trip on a regular basis. My actual load with the battery fully charged calculated out to about 16 amps. This was a warning sign that things were becoming dangerous, the energy been dumped into the battery was causing battery overheating. On Ford Performance"s advice, I pulled the three wire control plug from the ECU to the alternator. The result was a drop in output voltage to 13.8 which is "book value" for alternator output voltage. Now things are completely normal. I did have to replace the AMG battery as a precaution, the original could have been damaged by the overheating. Also the instructions from the maker of the AMG battery, Oddesey warns against charging at over 14.2 maximum.
 
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