BUSS AMG 250A/32v fuse keeps blowing upon starting (Gen 3 type 65 with Gen 2 coyote)

[Grkmf3]

Good evening everyone.
Hope all is well with everyone.

I'll be tackling this issue in the morning but wanted to see if anyone had any input that I might of not thought of and could be of use.

Here is the issue. (Long but detailed story):

I now have drove the Daytona for about 200 miles since I got it registered last week.
All was well with no issues until this morning when I arrived at work and reversed into the parking spot. As soon as I was about to release the clutch and go into neutral the entire car just shut off.

I turned the key off and back on and no power anywhere.
I ran a test light and located the main battery fuse was blown.

I went to autozone, bought four BUSS AMG 250A/32v fuse's (one to replace and the other three for backup).
I replaced it, pressed the start button and the car within 2 seconds of it cranking blew the fuse again.

Im now thinking that to blow a 250a fuse it can't be a short since it's not blowing when power is on but only when it tries to start.

I used the spare fuse and replaced it again but this time pulled the alternator cable off.
I tried starting it again and it cranked and within 2 seconds it stopped but didn't blow.
I tried starting it a 2nd time and once again within 2 seconds of cranking it blew the fuse.

At this point I'm thinking it's the starter so I re-connected the alternator cable.
I did pause to think if motor is the issue but since it's a brand new crate motor and is cranking over it can't be seized.

I replaced the fuse again and I decided to give the starter a couple whacks incase it was stuck
I pressed the start button and this time it cranked over for about 2-3 seconds and started up (big smile of relief on my face) only to hear a loud screech sound and back to motor just shutting off.
Gauges were still on at this point so I pressed the start button again and right away fuse blew.

Now I'm thinking a pulley must be seized so I checked them all (P/S, Alt, tensioner, idler, no A/C) and all were free spinning.

So in the morning I will grab my tools and jack with stands to go to my works parking lot and try to remove the starter to bench test it (Hopefully this is the issue) but before I go blow the last fuse and have to pay a shop to tow it and diagnose it (AAA wouldn't tow it to my house since I have no tow hook on it) I wanted to see if anyone else can give me an idea of what might be the issue or have any helpful hints to try.

Also the battery cable running from the trunk (moved battery back there vs FFR instructions of up front) is wrapped and hasn't been cut or rubbed through incase I get asked if the cable is still in good shape

Regards,
Dino
847-505-9364

[edwardb]

First, highly recommend stop burning up fuses and start diagnosing the problem. Sorry to state the obvious, but it's clearly not a defective fuse and whatever the problem is won't be fixed by continuing to change fuses. Could be doing damage somewhere. Second, need some clarification about the fuse you're describing. Are you talking about the 250 amp fuse that Ford provides with the Coyote control pack? It goes between the battery connection and the Coyote PDB. If wired that way, if blown the engine wouldn't run or start. But you should still have power in the rest of the car (gauges, lights, etc.) because the RF harness shouldn't be powered through that fuse. Is that what you're talking about and is that how you have it wired? Or something else?

Does it make a loud screech every time it stops? That's pretty concerning if it does. What has you oil pressure been doing? OK? Can you turn the motor over with a large socked and long handle? Typically on the harmonic balancer bolt.

[Grkmf3]

First, highly recommend stop burning up fuses and start diagnosing the problem. Sorry to state the obvious, but it's clearly not a defective fuse and whatever the problem is won't be fixed by continuing to change fuses. Could be doing damage somewhere. Second, need some clarification about the fuse you're describing. Are you talking about the 250 amp fuse that Ford provides with the Coyote control pack? It goes between the battery connection and the Coyote PDB. If wired that way, if blown the engine wouldn't run or start. But you should still have power in the rest of the car (gauges, lights, etc.) because the RF harness shouldn't be powered through that fuse. Is that what you're talking about and is that how you have it wired? Or something else?

Does it make a loud screech every time it stops? That's pretty concerning if it does. What has you oil pressure been doing? OK? Can you turn the motor over with a large socked and long handle? Typically on the harmonic balancer bolt.

Hi Edwardb,
I was hopping to jump on this early this morning but more important things came up that I had to take care of (trying to keep employees happy at work)

I agree with you and replacing fuses, I was just trying to eliminate the two obvious reasons

Yes its the 250a fuse that Ford provided but being that I bought the car almost complete I and not 100% sure how he tied it in and no paper work on his wiring.
When the fuse does blow it completely shuts all the power off to the entire car (nothing works) which goes to tell me its not wired how your saying.

As for the screech sound it does not do it ever time only once hence i wanted to check the pulley's

I tried turning it over by hand but can't really get a breaker bar in there to turn so my plan was to pull the the belt off and plugs out and then try

[acmikee]

try push starting the car

[edwardb]

If you're running the entire car through that 250 amp fuse -- starter and all -- there's a chance that's the problem. Even if it's not, I wouldn't leave it that way. Ford has that 250 amp fuse on the Coyote power distribution box (PDB) for a reason and it's not intended to run everything else. There are different types of fuses, and they blow at different rates. Could explain the delay, but obviously don't know for sure. No reason to start taking things apart on your engine IMO, including the plugs. Just get a wrench in there and make sure it will move. I'm able to turn my Coyote over with the belts and plugs in place. Just a little bit at a time. Just want to make sure it's not seized. I had an engine lose the mains and oil pressure some years ago. It made a terrible screech every time it shut down. Obviously was in bad shape at that point. Can't believe you're at that point but just reminded me. That's why I asked about what you're seeing with oil pressure. Also, you have the oil filter in the stock location versus a remote setup?

[Grkmf3]

I couldn't make it today so I'm having American Legends Hot Rods and Muscle Cars locally here pick it up tomorrow and just work on it.

I still think its the starter since oil pressure was normal the entire 40 min drive and even when it shut off plus the fact that the motor cranked over, started and ran for a couple seconds.

Thanks for the chat and I'll make sure to post the end result prior to listing it for sale here soon unfortunately (need to keep some money to keep business open and so employees have a job)