Starter isn't getting battery power intermittently.

[Offgrid]

This problem has been annoying me for weeks now, and I can't work out the cause of the failure.

The problem - The car starts easily most of the time. However, sometimes there is some hesitancy before the starter spins after turning the key. About every two days, the starter refuses to engage, and there is no power dip. If I connect a battery bank to the installed battery, and set it to boost, then the engine fires up instantly.

The equipment - The car is a 1990 740 estate with a manual B200E engine. I've tried 3 good batteries, which made no difference. The current one is a 2 year old Yuasa 5000 battery rated at 85 Ah. Charge level is 12.8 volts. The alternator kicks out 14.7 volts. The starter and solenoid look to be the original ones with surface rust and peeled paint.

What I've tried - I've connected the solenoid to the negative pole on the battery. I've cleaned all the obvious connection, and sprayed with switch cleaner. I've cleaned the battery terminals. I've banged the starter with a hammer. All of these actions seem to have no effect when the starter won't activate.

My thoughts. I suspected the ignition switch, but rejected that, as the engine fires when the battery is boosted. I doubt that all three apparently good batteries would cause the same problem. I can only assume that there is an extra resistance somewhere, and adding the booster pack overcomes this. I can't think where this would be, unless it is in the solenoid or the starter.

My next option is to remove the starter unit from the saloon, and try that in the estate. This would give me a chance to examine the starter and solenoid, and clean any internal connections. Has anybody got a better idea?

[john.wigley]

That sounds very like a dodgy earth (ground) to me, 'Offgrid'; have you checked the obvious?

Regards, John.

[Offgrid]

Originally Posted by john.wigley

That sounds very like a dodgy earth (ground) to me, 'Offgrid'; have you checked the obvious?

Regards, John.

That was my thought, and that is why I ran a jump lead from the solenoid to the negative post on the battery. I haven't tried connecting the starter to the battery though. That's an easy job, so maybe I should try that. Now I'll have to wait for it to fail again. Boosting the battery seems to fix the problem for anything between one hour and five days.

[loki_the_glt]

What about the engine to chassis earth strap - the braided one that runs from one of the cam-cover dome-headed bolts to the bulkhead? Easily, and often overlooked, but always a possible candidate for "culprit-ness"!

[Offgrid]

I haven't checked that, thanks for the suggestion. I'm of a mind to swop the starter with the one in the saloon. That would give me a chance to clean up this one, and remove the rust and debris. The earth strap probably needs cleaning as part of my general upgrade. I don't think it will be that though, as I ran a jump lead from the solenoid directly to the negative post on the battery.

[360beast]

There's a spade connector on the starter motor, take it off and clean it up as this is known to cause issues too, I've had a few people with no start faults including my own 940 and this was the culprit, I think it's a green wire and it sits on top of the starter motor.

[bob12]

I have had that little niggle a year or so ago on my 745. Just remove and cleaning up the + and - wire connectors at the solenoid and the starter motor should fix it. It doesn't harm freshing up the main engine ground.

Bob

[Offgrid]

It was silly of me not to clean the ignition connection on the solenoid. All the symptoms seem to indicate a fault in the ignition trigger. I'll remove the connector and clean the spade the next time it fails. I'll give it a spray with contact cleaner as well.

I should probably clean out the starter as well, but I think that is a job for Ron ( I'm sure you know Later Ron ).

[john.wigley]

Would that be the same Ron for whom my Dad always saved his last cigarette 70 odd years ago, 'Offgrid'? He also had a good friend called Nick, whom he would regularly pop out to see; Nick O'teen. J.

[Rversteeg]

I have heard of people who installed an auxiliary relay between starter motor and ignition key barrel, as the contacts in the ignition are not up to switching sufficient power to activate the starter motor relay. Boosting the voltage level with another battery will of course make it easier for the ignition contacts.
I have not read that you tried to put 12V power directly from the battery to the starter motor relay. Does this bring the starter motor to life?
By the way, Volvo installed a pink wiired service socket near the the left front wheel strut. This socket is directly connected to the starter motor relay, so applying 12V to it will bypass the ignition key.