4.8is no start, only one click.
 

Having a starting issue here car won't crank, it only click once when turning the key. I tried 2 brand new batteries so it's not a battery issue. I can hear the fuel pump working and everything and the car DOES and only start with a jump from the jumping terminals.

Today I got the starter replaced with a new one but that didn't fix it. Still the one click. Old starter did test good at the Auto zone. Battery terminals are measured at 12.7 volts, the grounds measured the same. There is significant power draws from the battery after a couple of tries.

Any ideas what else I should look into from here? EWS, DME? How do you properly diagnose those modules? Thanks!

The "click" symptom usually indicates a severe voltage drop when the battery is connected to the starter and a high current is drawn. This is normally caused by a bad battery with a high internal resistance but since you have eliminated this, I'd say you have a bad joint in the cable running from the battery to the starter solenoid. Or a bad starter solenoid, but I assume that was changed along with the starter (they are usually sold as a unit).

First thing to check would be the BST (battery safety terminal) - it may have come apart internally. Next check that any joints (X6404 & X7163) in the main positive lead that runs from the BST to the starter solenoid are clean and tight.

https://www.newtis.info/tisv2/a/en/e...-motor/bEud1CV

My guess? Bad BST....

Yes bst.

You can run a jumper cable from the battery to your B+ to determine if the battery cable is at fault. I read there is a connection at the B+ that can be the fault also.

Thanks much for the reply, I took your hint and did more testing. I jumped the car this morning and what I found was that the jumping terminals under the hood are getting above 14.5 volts from the alternator, however, the battery terminals in the trunk do not getting any charge from the alternator, voltage was 12.05 and dropping before I shut it down. That probably explains why I can jump the car but not be able to start it on its own. I'll take a better look at the BST and the cables as soon as I can.

Unfortunately I have ruled out the BST. It doesn't seem to be detonated and I do get voltage from it, I can also charge the battery from the jumping terminals under the hood so I think the BST should be fine. So the situation now is that I'm not getting a charge from the alternator, and no voltage to turn over the starter when turning the key.:dunno:

A voltage test does not rule out the BST - a voltage test requires near-zero amps - a crank requires over 200A.

Put a jumper cable from the battery+ to the jump terminal under the hood or the large + terminal in the trunk. If the car starts, the BST or cables are bad.

I don't think I have a jumping cable that long but I will definitely get I tested as soon as I can.

It seems like a bad connection at the B+ somebody on the forum recently had that exact problem.

Do you have the link or key words so I can search for it? Thanks!

Not sure which thread it was in but basically the B+ jump terminal under the hood was getting hot and was very corroded. The owner repalced the jump terminal with a new one, cleaned all the contacts and issue was solved.

It was also determined that on some cars the B+ from that battery actually connects to the alternator and the starter via this jump terminal, so it's electrical condition matters a lot.

Remeber to disconnect the battery B+ BEFORE goofing with the B+ jump terminal - or welding happens. :yikes:

Found it...

https://xoutpost.com/bmw-sav-forums/...ch-solved.html

Thanks much. My jumping B+ is connected to the alternator for sure cause it's getting alternator voltage, but I'm not sure if the battery cable is connected to the alternator via the jumping terminal. I'll do the jumping cable test first before anything else.

Another test you could try is a voltage drop test while cranking...

Using a multimeter, set to 20 volt range, connect the negaitve (black) lead to the B+ jump terminal and the positive lead (red) to the B+ battery terminal. Use any long wire to extend one of the leads - this wire wil carry almost zero current so it doesn't need to be a big wire.

Inital reading should be close to zero volts. Now crank the car and read the voltage that appears of the meter while cranking. Anything more than a volt or two indicates that the wiring from the battery to the jump terminal is faulty somewhere.

Good news! I did the jumping cable test and it fired right up, alternator is also charging the battery. so we can be confident now that the issue is narrowed down some where on the battery cable?

Great news! :thumbup:

Looking at this diagram there's not much left to check..

http://www.bimmerboard.com/members/q...%20Diagram.jpg

You're looking for any joint in the line from the battery B+ to the jump terminal. The BST is still the most likely culprit....

Awesome diagram, exactly the same layout as my car. I'll check everything tomorrow when there's light. Thanks!

The problem was discovered in the other thread because the B+ terminal got HOT from high resistance. There could also be a high resistance issue at the BST. Or just at the battery terminal itself classic post corrosion.


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Thanks so much for everyone's help. The issue is now resolved. It was indeed a bad connection on the B+ jumping terminal under the hood, the nut was very loose.
After a new battery and a starter I learned my lessons now to always diagnos the "small" things first.
Thanks again everyone!

Hooray! Glad it's sorted... :thumbup:

That's actually pretty cool that the bat cable takes that path. I have a precision 0.01 Ω resistor for measuring high current so it means i can get an exact measurement of the current to the starter from there


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You will notice that the diagram is incorrect. It shows the B+ is NOT in the current path to the starter. The reality is different than the diagram.

In reality the alternator and battery and possibly starter join up at the B+ terminal


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Depends on model year and engine - it's correct in some cases. ;-)

I've only every seen that diagram. Always the B+ out on the end not near current path. I haven't looked at mine but not sure which model might actually match the diagram.


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Given that diagram mentions a "water-cooled generator" I'm guessing it applies to the V8s. I'm also guessing that given the use of the term "generator" it wasn't drawn by an electrical engineer... ;)

The diagram certainly isn't correct, from a circuit path perspective - and the actual circuit diagrams (as shown in the TIS documents) don't seem to match what folk are finding in their cars either. And there does seem to be a bit of variation - e.g. my 3.0d has only a single cable at the jump terminal, running down to the starter motor (I think - I'll check more closely when I service it next week)., so no "hot jump terminal" for me.

Such fun... it's like our very own "Tower of Babel". :D

I've noticed it's Typical for BMW to refer to the alternator as generator. It's still a generator just internally generates ac voltage. We've just by convention stopped calling them generator when they switched to AC inside to initially be clear which type it was. They don't call the big wind farm units alternators.

So, I said I would look into this (at least on my own car) and confirm what was actually going on and lo and behold, what I had always assumed to be a single-ended terminal - the B+ jumper post - is ACTUALLY a bulkhead pass-through!! :rolleyes:

Peeling back the scuttle below the windscreen, I spotted the large battery lead coming up from the back of the car and connecting to the back of the B+ jumper post, via a large bulkhead-pass-though connection.

https://c1552172.ssl.cf0.rackcdn.com/601045_x800.webp

From there, a large lead runs down to the starter solenoid and then another runs from the starter solenoid to the alternator.

All this can be seen in the following parts diagram, with #6 being the passthrough terminal at the bulkhead. #9 Is presumably the lead to the starter and alternator on the M62/N62 cars (not used on M54/M57 cars): -

https://www.realoem.com/bmw/images/diag_2pke.png

So what is in my car doesn't match (exactly) the wiring diagram I posted earlier nor does it match the circuit diagrams in the TIS... :confused:

How YOUR car is actually wired may depend on where the starter is located - on my M57TU the starter is directly behind the alternator (left side of engine block) - same as the M54 but on the opposite side for the M62/N62engines, so the diagram above may be closer to what is in the V8 cars.

The important aspect to note is that, like many members have now discovered and in contradiction of most TIS wiring diagrams, the B+ jumper post is a VERY important connection point in the circuit from the battery to the starter and alternator - apparently in all E53 model variants.

Keep it tight and clean, boys and girls...