Alternator/Battery Issue

[laidback93]

Alright guys I’m stumped. My E30 would stall randomly, especially on cold start. Changed out my alternator as it wasn’t charging under load and she was running beautifully and idling perfect. However, the belt was loose and would squeal under load. Still it ran fine even tho I think the volts should have been higher IMO.

Yesterday my buddy installs a shorter belt and now no squeals. I go start it today (cold) and it does the same thing of barely starting and dying when you blip the throttle. I was like f&$! not again!

When it warms up it doesn’t die but it’s still not running like it did before we put the new belt in. I checked the tension and it seems fine. Exciter wire is working as well.

Could my battery have a bad cell because of the bad alternator? Not sure if that would cause my symptoms.

FYI - I bought a Bosch reman that is the valeo variant. The pulley appeared to be the same size as my original, yet we had to install a shorter belt as the original was loose with the new alternator. I heard it squeal for a second when I revved up the engine on cold start. It also was whining a bit on acceleration, but went away after a few minutes.

Today - I just went out and started her and she fired right up and there was no belt squeal or whining from the belt. I doubt it just fixed itself, but what do I know. Still the new set of numbers below doesn't seem perfect. The new alternator seems to be charging fine while idling, but not doing well under heavy load.

Voltage before with the old alternator:

Ignition off - 12.1v
Idle - 11.8v
2500rpm - 13.9v
Under heavy load - 12.1

Voltage after new alt and tighter belt:

Ignition off - 12.3v
Idle - 13.9
2500rpm - 13.92
Under heavy load - 12.0 (dipped below 12 for a moment)


UPDATE:

Pulled the battery and had it checked by Autozone. It passed.

Reinstall the battery and start her up. Perfect idle and the engine doesn't do the usual try to catch itself when you blip the throttle. I throw on the DMM and it's now showing almost 13v under heavy load.

What the heck!?!

Could the new tighter alternator belt be the culprit?

I'm at a total loss now. My E30 goes through more mood swings than I do.

[Vincenze]

I don't understand what's the problem.

When you start the car, the battery voltage is low, and the battery can't start the car. Correct?

12.3 V is pretty low. It should be closer to 12.5 V after driving for a while. Did you check how quickly the battery voltage goes down? Maybe, there is a parasitic draw.

[laidback93]

I don't understand what's the problem.

When you start the car, the battery voltage is low, and the battery can't start the car. Correct?

12.3 V is pretty low. It should be closer to 12.5 V after driving for a while. Did you check how quickly the battery voltage goes down? Maybe, there is a parasitic draw.

The car will start after cranking for a bit, but will die if you don't hold the throttle. It did this yesterday after putting on the new alt belt and made a squeal noise when I revved it. It also was whining a bit.

Today I start the car and the alternator wasn't making any noise, but it was still doing the thing where the engine revs drop too much before it catches itself. Didn't die today though.

Drove it around the block just now and retested, it was finally pumping almost 13v under heavy load. Battery is 12.5v with the car off.

I'm not understanding why there is such a variance between when I first start the car in the morning and then after driving. The charging system seems to be low when you start it for the first time of the day. Still wondering about the belt.

[Vincenze]

Why do you think it's a battery/alternator problem?

I would first check the fuel system. If the fuel pump doesn't provide enough fuel, then it's difficult to start a car, and it dies.

[Jaxx_]

how are the grounds?

[tomstin]

how are the grounds?

I was also thinking grounds as I read the OP. And, messing with the alternator it would be easy to move / disturb the main engine ground.

[laidback93]

Why do you think it's a battery/alternator problem?

I would first check the fuel system. If the fuel pump doesn't provide enough fuel, then it's difficult to start a car, and it dies.

Because the voltage seems to be all over the place and when they are in the high range the car runs beautifully.

But, I've suspected the fuel pump for quite some time now so that will be next to check.

FYI - ground straps in the engine bay are brand new CATuned replacements.

[Gregs///M]

Most likely you are experiencing a vacuum leak. Other items such as the TPS, coolant temp sensor, AFM, o2 sensor and DME condition can affect the car stalling. If you have a CEL, check the codes to see if any are reported. Considering you have a rebuilt Bosch alternator and charge appears to be working well, I would disregard the alternator as being the source of the stalling.

[laidback93]

Most likely you are experiencing a vacuum leak. Other items such as the TPS, coolant temp sensor, AFM, o2 sensor and DME condition can affect the car stalling. If you have a CEL, check the codes to see if any are reported. Considering you have a rebuilt Bosch alternator and charge appears to be working well, I would disregard the alternator as being the source of the stalling.

Hey Greg. I'd be shocked if it was a vacuum leak, but anything is possible. A used M20 was swapped into it this summer and my buddy went over everything. Hoses, belts, electrical connections. ICV, AFM, CTS, CPS and all ignition components have been replaced. TPS should be in spec. DME was swapped out of a low mileage vert. Pretty sure my original DME is fine. No CEL this time around.

Did a cold start today to get lunch and it ran perfect on initial start up. No stumble when revving.

It's totally random with the cold start issues. The only thing I thought about today was that disconnecting the battery to have it tested did something. Either by jostling the positive and negative battery cables or by resetting the DME.

We'll see what happens tomorrow. Fingers crossed.

[laidback93]

I uploaded a video of my M20 in action on a cold start.

Again, it doesn't always do it. I jumped in yesterday and it didn't stumble at all.

Question - is the alternator supposed to whine under load? Is that normal?

https://youtu.be/cuRI3w7bzvE

[McGyver]

The alternator shouldn't whine and the belts shouldn't squeal. Belt length and pulley diameter should not have any effect. The alternator should be spinning fast enough that the output is regulated by the voltage regulator. Your battery checked OK and your alternator is new, so it's not likely either of those. As Jaxx_ said, it could be that you messed up a ground wire when poking at stuff.

It sounds like you're having cold start issues. Use the Bentley to test all the sensors that Gregs///M mentioned.

Disconnecting the battery will reset the ECU, clearing fault codes and any adaptations.

[laidback93]

The alternator shouldn't whine and the belts shouldn't squeal. Belt length and pulley diameter should not have any effect. The alternator should be spinning fast enough that the output is regulated by the voltage regulator. Your battery checked OK and your alternator is new, so it's not likely either of those. As Jaxx_ said, it could be that you messed up a ground wire when poking at stuff.

It sounds like you're having cold start issues. Use the Bentley to test all the sensors that Gregs///M mentioned.

Disconnecting the battery will reset the ECU, clearing fault codes and any adaptations.

So I relented and drop her off at my local BMW indie shop. They readjusted the alternator belt and no more squeals. So that is good to go.

They found a small vacuum leak and fixed that. Didn't solve the cold start idle issue...

At this point all I can suspect is the used AFM and TPS we swapped from a low mileage vert. Or the fuel pump or o2 sensor. Those are the only things I can possibly think of.

I appreciate everyone's feedback in this thread. This has been an ongoing issue for years and have continued through a new M20 swap!