Misfires
 

Has anyone ever experienced power draw that drains the battery within days and fuel cut/misfiring from a bad starter and alternator? The car has been acting up pretty bad recently and my starter just fried. In the process of figuring that out we discovered my alternator is on the way out the door as well. Any accessory, when my voltage got low enough, would trigger a misfire or lean out on me. It even got bad enough at one point to where the blinker and auto window up/down would trigger a misfire or fuel cut. I’m currently going through the car and all it’s fuses etc but I would like to hear your thoughts and opinions on whether a bad alternator and starter could be the root cause of this power draw that’s been haunting me. Thanks


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What is making you call it a low voltage condition? If your alternator is on it's way out, I'm curious if maybe it actually caused a voltage spike that blew your starter motor. If this is what happened, anything that's got a 12v line is in theory fair game. In the lab, we've ESD'd circuit boards that have failed in such a way that makes it hard to figure out what has happened. They would half-way work, but do all kinds of crazy ****. We had one case where a voltage spike killed a capacitor on a circuit board, but it failed closed (causing a short). This in turn caused it to destroy any other electronic hardware that it was plugged in to... almost like a hardware (as opposed to software) computer virus. I mention all of this to point out that transient voltage spikes can ruin things in very unexpected ways. Hopefully it can be diagnosed without spending money replacing many things.

I don’t think it’s all tied to low voltage but the symptoms significantly decreased when I threw in a new battery. I believe the low voltage is just a product of the starter and/or alternator slowly going bad over time. The cars creeping up on 90k, has been boosted for over 30k, as well as a bunch of accessories that require lots of power. I’ve been told that a bad starter solenoid can cause a power draw. I’m hoping that by replacing those two parts it’ll, ideally, solve the power draw mystery, or at least bring me back up to par so I can properly track down the issue.


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I am curious about your term "the starter fried". Did it smoke and need to be replaced, or have other symptoms?

As-far-as low voltage, it can be many things...Are any of the wires close to the hot components of your TT setup that could have melted? How low does the voltage get when you say "low voltage"? Is the voltage measured at the battery, or are you going from the voltmeter?

Electrical issues are undoubtedly the hardest to track down. Keep us posted as to any other symptoms or fixes...

The starter smoked, we did manage to get the car started after rocking it back and forth, but it is getting replaced. I’ll be ordering the starter and alternator this week.

The AAM Kit is super tight so there’s definitely a few things close. I haven’t dug that deep into yet. The only wire I can think of off the top of my head that run close are the 02 sensor wires and my AFR. I ceramic coated my down pipes and zip tied the wires as far away as I could without pulling too hard. I used a meter. The voltages measured 12.47 when it was off and around 13.1, give or take, while running. Which may not be an issue for regular cars but as I mentioned to the first guy I have A LOT of accessories that draw power. I have air compressors, head unit, amp, capacitor and a remote start system (left over from the previous owner which I’d like to rip out but can’t find it).

I’m really hoping that it’s not a melted wire or a short. Electrical issues are without a doubt the worst lol. I appreciate the input I will definitely update as I go along.


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The starter shouldn't be the problem. Alternator - maybe; but it sounds like it's charging the battery, so it's low on my list at this point. Since the battery is discharging, I suspect an intermittent short; possibly related to the turbo install. Check system voltage with a meter. A recording meter will help spot intermittent problems.

Edit: Didn't fully read previous post. You have low voltage, so the alternator jumps to the top of my list.

FWIW, on my gf's focus, the engine would rev close to stalling when idling and you turn on the AC. Couldnt figure it out til the starter gave out, and found a frayed battery cable.

Yea the alternator is barely charging the battery. It’s really only charging enough to keep the thing alive. Along with a new starter I’m replacing the alternator. If those solve my issues I’ll be super excited lol. If not, I’m just gonna have to do some more digging.


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This power draw has been haunting me for a really long time. But inly recently has it been bad enough to cause all the misfiring, leaning out etc issues. Before the starter went out I was just telling a friend of mine that whatever’s wrong with the car, I wish it would just break. Idc if its a little more money to replace if it’s broken but at least I know wtf was going on. It was driving me insane. And 3 days later the starter fried and here we are lol.


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Yeah, if your TT setup makes things a little tight in the engine bay, Id check the battery cables for frays or any oil/fluid leaks that may have sprayed into your starter or alternator.

You should want the problem to be that simple lol. It'd be awesome to crawl under the car and visually see a few melted wires that can be easily replaced in five minutes.

If I can visually see the wire then yea that would be the ideal situation lol. I was talking about if I have to track it down and run through the whole thing. That would suck lol


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Yeah lol, I was only thinking about it from the positive outcome

If issues decreased with a new battery, then there are several things to consider. Reading through the posts, it appears you are replacing the alternator, that's good. Based on the numbers you posted, 13.1 VDC is barely enough to keep the battery charged, much less run everything else. A good alternator puts out between 13.5 & 14.5 VDC. Check all your grounds, make sure they are all clean and secure. A bad ground will raise havoc in any electrical system. If you are running an amplifier and not running a 1 to 2 farad capacitor, you are killing your alternator. Just some thoughts... good luck.

I do have a capacitor for the sub/amp. I actually re-grounded them both straight to the frame a while back. They were originally installed with the ground from the amp going to the capacitor ground, then into the frame, so I gave them both a direct ground and that didn’t fix anything. If my battery still drains after replacing alternator and starter then I have to dive into all the grounds. Thanks for the input


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To see how many amps the system is pulling. You should put an amp clamp on the positive battery cable. And run the car for a while.

Update on my issue. Starter and alternator have been replaced. Car starts. Runs great at wide open throttle but still misfires and is only giving me mid to high 13’s for voltage. Found two codes, that don’t throw check engine lights, that lead to a sensor in the negative wire coming off the battery that apparently controls voltage to the alternator. I’ve never even heard of this. So that’s what I’m digging into next. These cars have too many sensors lol


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Ground..... it's always ground.... :bowrofl:

The alternator has to have power from the fuse box for field power, which also means, a ground back to the battery. You may have to run that wire(s) and check for burnt spots that might cause intermittent shorts. You're on the right track. :tup:

It's impossible to say that too many times!

And it's always the hardest problem to find (as you have discovered) Good luck; make sure to keep updating this thread.

Update on the misfiring and low voltage situation.

I did a deep scan on the car and found 2 codes related to the battery current sensor. I’ve never heard of this thing but it’s a sensor in the negative battery terminal wire that essentially communicates the load to the ECU and then the ECU tells the alternator how much voltage to pump out. Well my car is missing that sensor. I ordered a new one and am expecting it in any day now. After reading up on the sensor all the symptoms I’ve been having match up to everything that this sensor controls, even down to the power draw when the cars off. My only concern is I’ve had the car for 3 years and it’s been boosted for 30k miles, I’ve never taken this sensor out myself why did it wait until the last 8 months to get this bad a reveal itself?? Hoping this wire is my problem


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:icon14:

Just a guess but you may have been doing a small amount of damage each time you operated the car. A little damage here; a little damage there; then poof.

It’s possible. It really showed a few months after I upped my power levels and got the car re-tuned. I can see the sensor slowly going bad and then getting to this point but the thing is 100% missing lol. It’s a mystery I wish I didn’t have to solve haha


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I suspect that whoever did the original build, swapped out the battery ground cable because it either got smoked or it was a false attempt at saving weight. I've read way too many build threads where people put microscopic batteries in the car to 'save weight' and then wonder how come their battery cables get fried....:eek:

That’s almost what I’m thinking too. Originally AAM did the install at their shop. I swapped the engine about a year ago (not at AAM) and as we were going through everything we found a few corners that were cut and I wouldn’t be surprised if the sensor was giving them issues or if it got lost during the install and they just put it to the side. Regardless it’s being put back on when ever usps decides they want to give me my package and we’ll see what the voltage reads after. Fingers crossed!


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