E30 Starter Wiring Help

[theserj]

Alright guys, so I have a 1988 325is M20

I just changed the starter, now the problem I am having is the entire power in the car shorts out after I turn the key to start the car.

I did not have this problem before changing the starter, so assuming something is wrong with the wiring?

I have already bench tested the starter, it works.

After I connect the battery, everything in the car works, all of the electricals seem fine. Even when I turn the car to "ON", everything still works.
As soon as I turn the key all the way to crank the engine, the entire power dies out.

This is how I wired my starter
Okay so I noticed that the car does not short out whenever I disconnect that small black terminal on the left (Its the bottom terminal on the car, the picture is just auto-rotated for upload purposes). Obviously it doesn't start either, but something tells me there is a shortage along this cable. How do I go about this?

Thank youIMG_0448.jpg

[Ceekers]

Alright guys, so I have a 1988 325is M20

I just changed the starter, now the problem I am having is the entire power in the car shorts out after I turn the key to start the car.

I did not have this problem before changing the starter, so assuming something is wrong with the wiring?

I have already bench tested the starter, it works.

After I connect the battery, everything in the car works, all of the electricals seem fine. Even when I turn the car to "ON", everything still works.
As soon as I turn the key all the way to crank the engine, the entire power dies out.

This is how I wired my starter
Okay so I noticed that the car does not short out whenever I disconnect that small black terminal on the left (Its the bottom terminal on the car, the picture is just auto-rotated for upload purposes). Obviously it doesn't start either, but something tells me there is a shortage along this cable. How do I go about this?


Thank youIMG_0448.jpg

I believe you have a separate problem that happened to show up. Check your engine ground; check all grounds its not grounding out so car goes dead as soon as you put the power to the starter. Engine ground located on the drivers side bottom connecting from the oil pan to the frame. Those typically corrode.

[theserj]

Alright you are definitely on to something here. I disconnected the cable from the engine and attempted to start the car, here is what happened;

The car does not short out, it just makes that solenoid clicking noise repeatedly. After inspecting my cable, it looks like I need a new one. Best place seems like my local BMW dealer, $25 and arrives Wednesday morning.

IMG_0452.jpg

Could this also be related to my alternator not charging my battery?

[richardodn]

Yes. That is the engine to chassis ground strap. Without it, the circuit can't be completed.

[theserj]

Alright so I got the cable a day early, swapped it and the car starts up. This cable seemed to solve my shorting out problem.

BUT, I just ran my voltmeter on my battery and here are the results:

12.6v with car off

13.5v with car on

12.5v with car on, HID low beams on, HID fogs on, Air compressor on, Fan on 4th setting, and flashers

Should it not need to be at least 14.2 with the car on?
Are there other ground cables I should replace to fix this?

[richardodn]

First two sound fine. With and without the full load, rev the car up to ~2000 RPM and measure voltage. What numbers are you getting then?

[theserj]

Okay so here are the results:

Car turned on - 13.21v

Revved at 2000rpm - 13.22v

Turned on Lights, AC, Fan Etc. - 12.47v

Revved at 2000rpm with everything on - 12.56v

So obviously the alternator is not charging the battery

Do you think it could be a bad battery ground terminal? Here is a picture of my ground

IMG_0256.jpg

[theserj]

I changed the battery cable cause it was rusted but still no charge. How do I go about testing the alternator since the battery is in the trunk? Do I need to use really long cables?

My check engine light also came on, but that could be related to something else

[richardodn]

Here's a thorough diagnostic procedure. However, I can venture a guess that you have a grounding issue somewhere. That could explain the things you're seeing. This procedure should point that out when measuring voltages using different ground points.


First we need to verify the charge path. Basically, this circuit consists of a heavy gauge circuit from the alternator (+ source) to the starter where it connects to the main battery cable and back to the battery + terminal. Return ground path is negative terminal to chassis, chassis to engine and engine to alternator. We do this by tracing voltage levels at various locations.

1. Start by making sure the battery is fully charged and connections are good. (About 12.5V.) Measure between the posts and not the clamps. Make sure the clamps are clean and snug. Make sure the negative cable where it attaches to the chassis is clean and snug. (This got me once.) Measure between the positive clamp and chassis ground but not where the negative cable connects. It should be almost the voltage across the posts.

2. IIRC, yours is a trunk mount battery. If not, I think there is no binding post on the firewall and you can skip this step. You have two hot wires coming from the positive terminal; a very thick one and a smaller one. These lead to a pair binding posts on the firewall. There are actually two posts here. The thick wire leads to the start/charge and general electrical. The other is for the engine management and injection system. I assume this was done to give injection a more dependable electrical feed. Measure between each post and chassis ground. You should have almost the same voltage you saw at the battery. If you don't go back and recheck all the battery cable connections.

3. With the ignition still off, check the voltage between the alternator charge (thicker) wire and ground. The charge wire connects to the same starter terminal as the heavy starter wire which in turn goes to the binding post/battery. Try it with ground on the chassis, then the engine and finally the alternator case. Any appreciable drop from the value we read at the binding post/battery indicates a connection or ground issue. We have already validated chassis ground so if the first measurement is low, check the starter connection. (Be sure to disconnect battery before messing with this.) If it drops when you ground to the engine, the main engine ground strap down by the motor mounts is suspect. If it drops when you use the alternator case, this is usually only an issue when the alternator has rubber isolation bushings at the mounts and the ground strap is bad or missing. It's also possible that all the brackets are loose.

At this point you have verified the charge path. Time to check the field path. This runs power to the ignition switch. In 86 the field circuit was from the ignition switch (start and run), to the cluster light and then to the field (D+) terminal. In 87 they added a resistor parallel to the light bulb so the field terminal would still get voltage even if the light burned out.

4. Disconnect the field (skinnier) wire from the alt. Turn the ignition on. Measure voltage between this wire and alternator, engine and chassis grounds. Once again they should all be about the same value. However it should be a bit below battery voltage due to the resistance in the lamp/resistor. If you don't see any voltage, the cluster light is burned out. Touch the wire to the alternator case. (Use a fused jumper if that makes you nervous.) The dash light should light. Try it again using engine and then chassis grounds. In all cases the light should light.

Now the field path is verified and I'm pretty confident the grounds are good.. Reconnect the field wire and start the car. Now we check the charge voltages.

5. Measure voltage from the alternator charge (thicker) terminal to the alternator case. (You can also use pin 14 on the diagnostic connector.) This should read at least 13 or so volts and rising up to 14V+ as you rev the engine to 2k RPM. Do this again using engine and then chassis as ground. Voltages should be approximately the same. Any drop indicates a ground issue.

6. Finally, go back and measure voltages at the battery posts. These should be very near what you saw directly off the alternator.

I know this is quite thorough, but it's likely to uncover the problem early on.

[theserj]

First and foremost, AMAZING write up. Thank you

So I went ahead and tested the battery on its own, 12.55v, healthy healthy.

Then I did the positive clamp to chassis ground, 12.52v.

I skipped the IIRC step.

Next, I connected the alternator charge wire and ground (strut mount nut), got 12.53v.

Then things got interesting with the engine. I connected the alternator charge wire and to this part of the engine right next to the starter. Not sure what its called but here is a pic. The voltage was varying from low 9's to mid 10's but was mainly steady around 9.8v.
IMG_0464.jpg



Then, I decided to connect the alternator charge wire and the engine hook where you lift it with a chain as shown, 12.52v.
FullSizeRender-1.jpg



I also decided to connect the alternator charge wire and this part under the manifold next to the starter, I got 12.52v. Isn't that weird that they are different?
FullSizeRender.jpg



Then I connected the alternator charge wire and the alternator case as shown, 12.51v.
IMG_0466.jpg



And just to be safe, I also connected to this part of the alternator as shown, 12.49v.
IMG_0467.jpg



Now onto step 4, I measured the voltage between the field wire and the alt, got 12.2v, seems normal with what you predicted.

Next, I measured the voltage between the field wire and the engine (engine hook where you lift the engine with a chain), got 12.18v.

Next, I measured the voltage between the field wire and the chassis ground (strut mount nut), got 12.18v.

Anyways, on to step 5, so i connected the alternator charge to the alternator case and turned on the car. It was varying from as low as 12.2v all the way up to 13.8v, it would mainly stay on the higher side above 13v. Revving the engine did not seem to affect it, it would just continue this cycle of alternating between 12.2v and 13.8v. No pattern I could see with the revving.

Then I connected the alternator charge to the chassis, this time it was varying from 12.2v to about 13.3v and revving did not affect it.

Then I connected the alternator charge to the engine, same exact diagnosis as the chassis, 12.2v to 13.3v and revving did nothing.

Could this be a bad alternator??

Step 6, the battery posts are now 12.62v.

Well that was fun haha

[yssolank]

Great write up. My alternator isn't charging my battery.

I followed all the steps.

I am not seeing any voltage accross +ve terminal binding post and engine block.

But I do see the voltage across +ve terminal binding post and oilpan where the main engine ground is and also voltage across the alternator case and also at the chassis ground.

Do you think the alternator mount is the problem and hence not able to charge the battery?

the voltage across alternator output and alternator case is 14.2 at 2k RPM but again nothing on the engine block. 12.6v across alternator output and engine oilpan and chassis ground.

Any ideas ?