Intermittent starter failure

[rick8637]

Hi Guys,
Need a little help here. 91 850i auto. Sometimes i turn the key to start hear a clunk and all stops, turn key off and on again starts right up ! This senario happens maybe 1 in ten starts. Just today i went to start it and just a very slight click and then nothing. A few more trys and she started perfectly. Not sure where to start looking as the prob is so intermittent . Maybe pull or swap starter relay or unloader relay?? Any ideas would be appreciated!
Rick

[buildit]

Checked wires and connections on the starter?

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[rick8637]

Checked wires and connections on the starter?

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Yes, all seem OK

[buildit]

Battery connections?

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[cartoonz]

Fusible link cracked? That'll do that too.

[rick8637]

Battery connections?

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Yes Recent new batteries, did the same with old batteries . I may check starter connections again, they are difficult to access!

[buildit]

You could check the two ground posts on the front fenders as well

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[rjjablo]

1. Fusible Links in trunk are most likely it
2. Check and clean Ground from front of block to body
3, Go thru all the main power connections under the engine and inspect and clean, Unlikely

Starter is straightforward. Power comes from battery directly to block on the side of the body and then to the starter solenoid, solenoid gets signal AKA the click

You can jumper the starter relay which cuts out everything else if you want to test that

[rick8637]

I did check the grounds engine to body, They look like new. Fusible links??? where and how to test?

[rjjablo]

I did check the grounds engine to body, They look like new. Fusible links??? where and how to test?

Disconnect your batteries before you start fooling with them.

Two of them. In the trunk Right hand side in the front of the battery. I replaced mine with Audio Fuzes

https://www.bimmerforums.com/forum/s...-fuse-A-doosey!

[rick8637]

Disconnect your batteries before you start fooling with them.

Two of them. In the trunk Right hand side in the front of the battery. I replaced mine with Audio Fuzes

https://www.bimmerforums.com/forum/s...-fuse-A-doosey!

So Let me digest this, this Fuse is bad but only affects every 10th start? Since i started thread has been starting fine, baffled but thanks for the thought, I will dig it out and have a look

- - - Updated - - -

This is a bugger of a fault cause it rarely occurs. when it happens, I go to test something and it starts right up! I WILL find it

[rjjablo]

They will develop a Microcrack that you cannot see which gradually gets worse until it starts arcing across

Its one of those like the General Module you just do it problems go away.

[cartoonz]

So Let me digest this, this Fuse is bad but only affects every 10th start?

Yup. That is exactly what happens.

[rick8637]

Yup. That is exactly what happens.

So a 40 amp audio fuse is the best fix?. It sounds like a good idea to change this even if its not the starting issue

[rick8637]

Here is an 80amp fuse. Do yall thick this is a good replacement
Amazon.com: Carviya 4-8 Gauge AWG in-line Waterproof Fuse Holder with Two 80 80Amp AGU Type Fuses For Car Audio/Alarm/Amplifier/Compressors (80Amp, 1 Pack) : Automotive

[rick8637]

Now I searched and find there are 2 of those fuses on the right hand battery that should be changed. 1-50 amp and 1-80 amp . I will try find the proper amp rated fuses and replace these. Thanks for the tip!!A number of people have had issues almost like mine. I hope this is the fix.

[rick8637]

Now I searched and find there are 2 of those fuses on the right hand battery that should be changed. 1-50 amp and 1-80 amp . I will try find the proper amp rated fuses and replace these. Thanks for the tip!!A number of people have had issues almost like mine. I hope this is the fix.

Ok , I changed both fusible links as prescribed. They were both 80amp. The one in the black holder looked a bit suspect but I still have the same issue. I will check the ground wire again . Is there only one engine to body ground?

[Ericks2002]

Is it possible it’s the starter itself. Maybe the brushes are going bad?

[rjjablo]

I will check the ground wire again . Is there only one engine to body ground?

The only one that matters for starting is the Motor Mount to Body ground. I would take it off, make sure its flexible not crunch and measure it with Ohmmeter and inspect. You can also clean all the contacts under the hood where the various power cables attach for good measure.

[rick8637]

Possible I suppose .This is a replacement starter that has about 30K on it. 90% of the time it starts perfect and sounds strong.

[cartoonz]

Just FYI... those fusible links by the battery on your car should be 50A & 80A. They are not both 80

The ground wire is up next to the AC compressor. Runds from the frame rail to the top of the motor mount. They do corrode, so replace if it is suspect at all.

[rick8637]

Just FYI... those fusible links by the battery on your car should be 50A & 80A. They are not both 80

The ground wire is up next to the AC compressor. Runds from the frame rail to the top of the motor mount. They do corrode, so replace if it is suspect at all.

I was surprised they were both 80 amp too . I dont think this is the issue tho. I pulled the ground wire off and sanded and cleaned both connections, they did not look bad. After that I tried starting and... click then nothing. Next 5 starts were perfect and strong. Tricky issue but im gonna find it even if i have to pull the starter again( aarg). When I said the starter had 30K on it , that has been 15 years ago!! I dont drive it much and Sitting doesnt help !!

[rjjablo]

Pull the Starter Relay and use a jumper to directly engage the solenoid and see if the problem is the same. Takes the key and the ignition out of the equation

[rick8637]

Thanks rjjablo. With a little help . I have found there is a definite click (metalic ting) at the starter every time it fails. Key off key back on starts pretty consistently.Also I have noticed that it tends to fail when the car has been sitting and is completely cooled off and very rarely when hot. Im starting to think it is a flaky solenoid at the starter. I may try to remove the heat shield and check solenoid connection at the starter next?

[m6bigdog]

Thanks rjjablo. With a little help . I have found there is a definite click (metalic ting) at the starter every time it fails. Key off key back on starts pretty consistently.Also I have noticed that it tends to fail when the car has been sitting and is completely cooled off and very rarely when hot. Im starting to think it is a flaky solenoid at the starter. I may try to remove the heat shield and check solenoid connection at the starter next?

The starter has an external solenoid attached to the motor that engages the starter drive and high current contacts that connect the battery directly to the starter motor (no fused in the current path) after the drive is engaged into the flywheel gear.
The click you hear is the starter solenoid being energised from the key (start position).
There are several issues that typicality prevent the starter motor from running.
1-The voltage to the solenoid is insufficient to fully engage the solenoid (volt meter on the solenoid power terminal should verify).
2-The drive engagement is sticking, doesn't allow the drive to fully engage into the flywheel gear (prevents starter contact from make-up).
3-The starter contacts are degraded (burned up from repeated use over many engine start cycles) and the contacts make-up intermittently.

In any event, if the voltage to the starter solenoid meets specifications and the voltages at the battery cable and starter ground are good, then the starter must be removed to examine the drive engagement and starter high current contacts.
Replacing the starter is the best and most reliable option.
New solenoids are available or the original solenoid may be repairable?
Drive gear and engagement parts are available or can be lubricated, however if the problem is not fully/correctly repaired you will be pulling the starter again to replace more parts.