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Discussion Starter · #1 ·
Hi All,
I recently swapped the engine on my ST due to a broken rod (stock replacement longblock). The swap went beautifully, and the car ran great for over a week before I had an issue crop up. About a week ago the car cranked super slow and barely started. I drove it to work, parked it, tried restarting it without success. Came back out after work like 10 hours later and the car cranked super slow again but did start. Came home, connected another known good battery with jumper cables and had no improvement with the slow cranking. Put a battery charger on the car for a few hours, and it started right up. At that point I was thinking battery, but I was baffled why it didn't improve when I connected the second batter. Given that it seemed to be some kind of battery issue I cleaned the terminals and battery connections and put it back in. The car ran great for 5 days straight with no starting weirdness, no battery light, good voltage on my AP3, etc.

Tonight I went to start it again, and it again did the slow crank thing. Connected the spare battery and had no improvement. Also tried jumping it off my truck and also had zero improvement (it did not seem to be a battery issue as both times I got virtually no spark when I made the connection with the cables). After a few attempts to crank I saw a few puffs of smoke which I traced back to this ground area under the battery. The smoke was from this ~18 gauge white wire with violet stripe getting hot enough that it was melting after only 2-3 cranking attempts of maybe 5 seconds each. I'm confused what this wire is for and what it connects to, but it seems to be part of the piece that mounts to the negative battery cable terminal. From looking at a wiring diagram it seems to be some kind of a battery monitoring device but I could be mistaken.

I'm great with soldering so it's no big deal to splice in a new wire, but I'm trying to figure out if the damaged wire was the cause of the slow cranking or the effect. Unfortunately I suspect it's the latter, so just splicing a new wire will likely lead to the same result. It almost seems like maybe the car is trying to run the ground through this white/violet stripe wire during the cranking, but I'm not sure if that's even possible or what could be causing it.

Anyone have any ideas?

Other stuff to know about the car
  • The swapped engine was a OEM long block with stock turbo
  • Car is 93 Octane Strattified tuned, but it's the same tune I've been running for over a year
  • The battery is a brand spanking new Motorcraft battery, and was done as part of the engine swap
  • I've put ~600 miles on the new engine since the swap
  • After the issues today I had the battery tested at the auto parts store. It was confirmed good under load and was at 12.4V even after the failed starting attempts this afternoon

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The ground you have pictured is for the Electronic Power Steering. Some wiring from that ground eventually leads under the battery box and into the Pre Fuse Battery Junction Box. If you remove the airbox you'll see two harnesses terminating into a module vehicle forward of battery, the wire in question is the smaller one on vehicle RHS. The module attached to the ground wire is the Battery Monitoring System. If that module is broken it will produce a no crank situation, I believe.
 
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Discussion Starter · #4 ·
Those are all chassis grounds under the battery. Clean that paint and put them back together.
That's great advice as I've read before the these cars can be finicky about grounds. I'll try that and see if it changes anything.

The ground you have pictured is for the Electronic Power Steering. Some wiring from that ground eventually leads under the battery box and into the Pre Fuse Battery Junction Box. If you remove the airbox you'll see two harnesses terminating into a module vehicle forward of battery, the wire in question is the smaller one on vehicle RHS. The module attached to the ground wire is the Battery Monitoring System. If that module is broken it will produce a no crank situation, I believe.
This is very, very helpful and is crazy specific... I'm impressed! I don't know why I assumed this white/violet stripped wire ultimately connected to the battery monitoring system other than the color seemed to match. I'll try pulling the air box as well and see if I see anything that's suspect with the wiring/connections/etc. The car is stranded in the parking garage at my work so it makes tearing into it too much a bit of a challenge, especially since I'm already "that weird car guy"

Is it possible that the electric steering is somehow causing some kind of weird voltage drop when I crank the car? Just to see if it makes a change I'm tempting to pull the fuse/relay (haven't looked yet) and try cranking it just to see if that makes any change to the situation.

Again, the fact that this is intermittent and the car when maybe 30 starts with no issues, then 10 starts, then 5 starts has me baffled.
 

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You should do a draw test on the car.
Most Advance Auto should do this as long as they have a semi-intelligent tech who knows what they're doing.

You might be having an issue of an accessory drawing a bit of power and draining that battery as it sits.
If you have that it's just a matter of figuring what is drawing power and why.

I hope it works out.
Also Hey there from a neighbor slightly north.
 

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Discussion Starter · #6 ·
Just an update on this issue: After thinking about it some more I realized that @SIstomper was likely right and this was probably just a simple ground issue. It all fit with car's symptoms: the car would crank over slow but if it started it would run perfectly, the battery was charging just fine and no battery light on the dash was popping up. Plus I realized that the electric steering ground (thanks again @Loki C346 for identifying that wire) was probably frying because the starter had a weak ground so the car was trying to pull high power through that small ground instead.

If you recall my car was stranded at my work. After thinking this issue through I ran a jumper wire from the negative battery terminal straight to a ground by the starter, and the ST fired right up like nothing was ever wrong. I drove it home, put it up on ramps and right away found the issue. As SIstomper guessed it was just a loose ground, in this case being the ground that runs near the battery to the front of the engine on the transmission case. That ground was apparently just finger tight (a product of the recent engine swap). I took the bolt out, wire brushed both sides of the terminal, tightened it back up and the car started perfectly. After that I also replaced the electric steering ground wire so the car is as good as new.

Anyway, thank you very much to all for your help in sorting out this issue. I was baffled at the start, but as usual the peeps on this forum are an unbelievable wealth of info. Hopefully this thread will be useful to someone in the future if they're chasing down a similar issue.
 
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