Misfire on Startup & Constantly Dead Battery

[brandon_5.0h]

Afternoon all,

I've been having issues with the car in the past few months and was just wondering if anyone had any insight as to what's going on here. I believe it is all tied together in some way. So, on the dead battery front, the car is randomly dying. It has died as fast as sitting at the gas station pumping gas for 2 minutes, to not even being able to sit for a day without needing to jump. I am in cold weather (32F). The car has a new battery. Disclosure: I have a dashcam, sub, and radar detector installed. These have all been disconnected once at a time MULTIPLE times to ensure there is no draw but the same issue persists. As of recently, I believe there is a loose wire or ground somewhere in the harness that may be causing the other issues. The multiple misfires (on startup and cylinder 2) are also a hit-and-miss. I ran cleaner through it and have good 93 in it. The car also has new plugs, etc. However, this started happening when the car started dying constantly. With this, I've also noticed my taillights (left and right at random) decide to not work while the other does when the car turns on after jumping. I fix this by turning all lights off and then back on to auto in the cabin.

I am truly baffled by this car and would appreciate any and all feedback that hopefully, I have not thought of yet. Thanks in advance!

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[NGOT8R]

I just replaced the battery in my 2019 Bullitt, exactly one year ago and the new battery drains itself. I was keeping it on a slow-charge, but for the past 8 months, I haven’t bothered to do anything with it because the car wasn’t drivable. I’m close to being ready to put it back on the road, so my plan is to perform a charge, then remove the fill caps, add some distilled water and top off the charge again. I always felt like the Keep Alive Memory was the culprit in draining these batteries.

 

[NGOT8R]

i have jumped my car with one of those tablet sized batteries, drove around on the highway for 10 minutes, parked, turned off the car, and tried to refire immediately and it wouldn't even crank over. a trickle charge brought my battery back to health from being at 5.5V (sitting over winter)

Have you tried charging it up first and then topping it off with distilled water to get the electrolyte level back up, followed by a second charge? That is assuming you don’t have a sealed battery. When I bought my replacement battery they were out of sealed batteries, so I had to take what they had. I also carried a mini jump pack with me too up until I changed the battery.

 

[MiamiGT350]

When replacing the battery, you need to execute the BMS (battery management system) service. I think this thread is how to do it with no tools.

The service procedure can also be done via Forscan.

 

[NGOT8R]

When replacing the battery, you need to execute the BMS (battery management system) service. I think this thread is how to do it with no tools.

The service procedure can also be done via Forscan.

I didn’t even know there was such a thing. Thanks for posting this!

 

[MiamiGT350]

I suspect this isn't entirely what's going on, but it's something you should do.

I would start with checking the water levels in the battery (if it's not sealed), and use a wire brush across all the connections to make sure you have good solid connections on the battery.

You didn't mention the CCA on the battery, but you want something around 590 CCA: https://www.interstatebatteries.com/product-search-results/2018-ford-mustang-v850l

If needed, Autozone, Advanced Auto Parts, O'Reilly's etc should be able to test the battery for you.

 

[brandon_5.0h]

I have not performed the BMS reset. I will try that. I took a multi-meter to it and the battery read 11.3, just enough to not start it and reset "MyMode", guages, etc. It varies, however, as it has been 10.5 as well. When started, it shoots immediately back to 14.6-7. I have also read on KAM causing issues, but never considered it. I would tend to agree with the battery fill, but it is sealed and only a few months old. The CCA are 590, so that shouldn't be an issue either. I have a warranty on the battery from AutoZone, might swing by there.

Lund doesn't see anything wrong with the car via logs, so I'm not sure where to go on the misfire front. They said replace cam and crank sensor, but I heavily doubt it would be that, since it's constant only on startup and then dissipates afterwards.

 

[NGOT8R]

Crank sensor replacement is going to be a PITA to do with the intake manifold and/or tranny installed.

I just put a new crank sensor in my 2019 Bullitt, but I did it when the tranny was out of the car, so it was easy to do. Next time around it won’t be so easy, because I have the MMR Head Cooling Mod on the car, which means the passenger side billet insert for the head will need to be removed In order to replace the sensor.

 

[19gtMD]

I would absolutely check your battery again. Make sure you dont have a dead or a few dead cells. Maybe the new battery you had didnt have a good charge to begin with.

 

[brandon_5.0h]

Crank sensor replacement is going to be a PITA to do with the intake manifold and/or tranny installed.

I just put a new crank sensor in my 2019 Bullitt, but I did it when the tranny was out of the car, so it was easy to do. Next time around it won’t be so easy, because I have the MMR Head Cooling Mod on the car, which means the passenger side billet insert for the head will need to be removed In order to replace the sensor.

Why did you have to replace yours? I don't feel like blowing $300 on a sensor and the install more importantly for it to not matter at all.

 

[brandon_5.0h]

I would absolutely check your battery again. Make sure you dont have a dead or a few dead cells. Maybe the new battery you had didnt have a good charge to begin with.

This was previously my thought, but the chances of two batteries dying back to back - you'd have a better chance at winning the lottery, no?

 

[19gtMD]

Nope as stated. Some battery stores or auto part stores dont always charge their new batteries. I tend to test mine when i buy them. Honest it has happened to me on a motorcycle once

 

[KeyLime]

Pull the battery out of the car, charge it and let it sit on the shelf overnight. If the voltage is low the next day then you know there’s an internal short of other problem in the battery. If it’s still holding 12.5 volts then the problem is the car.

 

[19gtMD]

Pull the battery out of the car, charge it and let it sit on the shelf overnight. If the voltage is low the next day then you know there’s an internal short of other problem in the battery. If it’s still holding 12.5 volts then the problem is the car.

Also if the battery never gets up to 12.. Its an internal failure

 

[NGOT8R]

Why did you have to replace yours? I don't feel like blowing $300 on a sensor and the install more importantly for it to not matter at all.

I wasn’t having any trouble with y sensor that I know of, I only changed it because it was included with a rear seal plate kit that I purchased from MMR. I don’t think the sensors are that expensive by themselves though.

If you do decide to change yours, I suggest removing the intake manifold to access it, rather than removing the tranny, unless of course you’re do for a clutch.

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