Dead battery, now bad idle, and dying m42

[z6ne]

So my m42 318is was running fine until a couple days ago. It started first try after a couple cranks and idled fine.

But then I found my battery to be dead one day, so I jumped it with my dad's car, took it around the block, let it idle for like 20 minutes to charge the battery, turned it off, tried to crank it, and nada. Bad alternator? Starter? Battery drain somewhere?

So last night I jumped it with a friend's car, and it started up then started idling soooo rough at super low RPM. I kept my foot on the throttle for a couple minutes to warm it up, but when I let up to let it idle on its own, immediate bog down to near no RPM so I turned it off to keep it from dying.

Can you guys help me diagnose these problems?

P.O. Said he put in a new battery, plugs, and the head has been rebuilt, but I have learned from experience that what P.O. said can always be total bullshit :sad:

Help r3v, I wanna drive my car!

[Quadrajet]

Most alternators don't put out enough power till they are turning 2000rpms. Had the same problem with a battery, till I took it for a 30 minute drive at highway speeds.

The output of the Alternator should be like 13.5 volts with the headlights on when idling. You may also want to pull your voltage regulator/brush set and see if you need to replace due to short length brushes.

[E30_Pare]

Alternator is going out. Charge the battery & that should be a temporary bandaid until it drains again. If you got a multi meter there are ways to check for battery drain/bad alternator.

[kkamakasi]

Not to hijack this thread but...
Can a battery on its way out result in this symptom?

http://www.r3vlimited.com/board/showthread.php?t=293925

I thought it would be more of a vacuum leak...

[z6ne]

so would the bad alternator explain the poor idle? I jumped it again the other day and it ran even worse. Almost dieing like 3 times, and I pressed the accelerator, which only made revs go up if I pumped it slightly, even after that it wanted to die, so I turned it off :(

[oldmann]

Alternator runs all electrics while engine is running, battery handles starting.

Weak alternator makes battery carry the load until its dead too.

Fuel pump won't work right under low voltage, along with electronics, DME,
Injectors, sensors, So, yeah, weak alternator/battery will make it run like crap.

[z6ne]

Alternator runs all electrics while engine is running, battery handles starting.

Weak alternator makes battery carry the load until its dead too.

Fuel pump won't work right under low voltage, along with electronics, DME,
Injectors, sensors, So, yeah, weak alternator/battery will make it run like crap.

thanks man, I'm gonna start troubleshooting this week

[romeomike]

Consider replacing the voltage regulator/brush assembly first. I've done this to the two E30s I own and haven't had to install a new alternator so far.

[GillesBigCowboy]

There's a place that rebuilt my alternator in Marietta. They did a great job and I think it was like $100 +\- 20. I think it was like two initials in the name of it.

[z6ne]

There's a place that rebuilt my alternator in Marietta. They did a great job and I think it was like $100 +\- 20. I think it was like two initials in the name of it.

thanks, but that's more of a drive than I care to make, especially with a friend's pickup/e30 on a trailer :/

I'm about to check out Heritage Motorsports in cabbagetown, heard good stuff about em.

Jawja, hahaha

[Kozworth]

So my m42 318is was running fine until a couple days ago. It started first try after a couple cranks and idled fine.

But then I found my battery to be dead one day, so I jumped it with my dad's car, took it around the block, let it idle for like 20 minutes to charge the battery, turned it off, tried to crank it, and nada. Bad alternator? Starter? Battery drain somewhere?

So last night I jumped it with a friend's car, and it started up then started idling soooo rough at super low RPM. I kept my foot on the throttle for a couple minutes to warm it up, but when I let up to let it idle on its own, immediate bog down to near no RPM so I turned it off to keep it from dying.

Can you guys help me diagnose these problems?

P.O. Said he put in a new battery, plugs, and the head has been rebuilt, but I have learned from experience that what P.O. said can always be total bullshit :sad:

Help r3v, I wanna drive my car!

For the car to not charge, I would say alternator. There should be a way to test an alternator output with a dvom.

And for the idling, the m42 might have lost its adaptive strategy, which the pcm learns idle and fuel trim according to how the engine is worn and user driving style. With a disconnected battery, this memory could have been deleted, and you would just need to drive the car around for a little bit for the car to relearn.

Otherwise, look for any major intake leaks. Dipstick, filler cap, intake bellows, vacuum lines, etc. One might have rotted or disconnected without your knowledge.

[monty23psk]

With a multimeter you can see if the alternator is bad or not. With car one, if you get a little over 14 volts on the battery, it is charging You can also remove it and take it to place like autozone where they can test it for free. The same has to be done with the battery. You need to make sure you have a good battery and might have to charge it out of the car. If the the battery died, your ECU was reset and it could be a couple of minutes for everything to reprogram. This can be happening every time if you need to jump the car every time.

[z6ne]

thanks guys, been real busy and Heritage is closed until the 8th I think. Having trouble finding anywhere else around my area that's close/could tow the car

[z6ne]

Got my dad to help me out some, replaced alternator belt (one that was on was grossly too long and barely turning the alternator) and went ahead and did the power steering one too, was gonna do the AC compressor one as well, I bought the belt, but the hardware that attaches that extra smaller pulley was stripped so I'll have to deal with no AC in ATL summer, oh well. Also fixed one obvious air leak, and she's running again.

Idles kinda low RPMs when I first start it up, and the car vibrates a lot when idling, but once warm the idle RPMs go up somewhat, but still not perfect. The vibrations cease once the accelerator is pressed. More air leaks somewhere? What causes this?

[roguetoaster]

Glad you got it somewhat sorted.

The idle issue is most likely another vacuum leak, or an ICV issue (or less likely a coolant sensor/TPS/O2 sensor. If you want/are bothered by poor idle (and can live with high idle) you can set idle up by adjusting the throttle cable or the stop on the throttle body as a temporary fix. Simply adjust to a point where the car runs decently (I suggest no more than 1100rpm).