Intermittent death - lots of potential causes checked

[Foeux]

Dear friends,

I hope you will be able.to help me solve a puzzle I have.

M895OTH - 945 ESTATE
2.3 non turbo

Problem: Sometimes unwilling to start with own battery. Always starts with extra jump (until today). 4 times now it has just shuddered to a stop. Still getting fuel but 'drains' battery to less than 5v almost instantaneously, resetting radio, not enough power to run hazards etc. However, either with a jump or some time being left, it will start again.

Today it was absolutely dead. Not even starting with a jump. Weak spark but not gone. Towed it to a garage, whereupon it started straight away (embarrassing). However, leave the ignition on, adjust electric seats then try to start again and it is dead as a doorbell again.

Buzzy noise coming from fusebox. Feeling inside, one relay right at the back ( with permanent live was buzzing really hard and fast. Could feel it. Despite this, with a multimeter, I could see the battery 'regaining charged. A volt every 30 seconds from 5v back to 12.

What have I done so far?

New batt (x2). Checked alternator. Ht leads new. Checked all earth straps.

It is at a garage atm

It is getting to be a real frustration, I inconvenienced several people today. Venerable and reliable the car is not being. I'd hate to be responsible for killing one but I've tolerated less from other cars and scrap value is high...

Any ideas much appreciated.

[TonyS9]

What is the voltage on the battery at idle or 1500 rpm?

Have you check the positive starter cable for wear+shorting on the bulkhead?

[Forrest]

Is the battery the right capacity for the car? Does it drain to 5V as soon as the battery is connected, with the key in position 2, or only when you try to start the engine? A battery drain on that scale is likely to be causing some heat somewhere.

The garage will hopefully have the equipment to test the battery, current drain and check that the battery is receiving a suitable charging voltage from the alternator.

Are you sure all the wires are connected correctly? For example, if you don't connect the exciter circuit/warning lamp to the alternator this will prevent the battery charging.

Perhaps most obviously, is the starter motor drawing an excessive current?

[Laird Scooby]

When you first turn the key to position 2 (without starting it) does the charge warning lamp (and a few others) come on and remain on until you start the car?

[Rversteeg]

If the engine is running normally, what voltage do you read across the battery terminals?
With only 5 V system voltage the engine will probabaly stop because the spark is be too weak or fuel pressure too low (electric fuel pump). Relays will also start to buzz. With a charging alternator however, it should normally not be possible for the system voltage to drop that low. Apperently for some reason during running the battery is not charged all the time and slowly drained until its voltage is too low for the engine to run. Either the alternator is not charging all the time or its charge does not always reach the battery.
The power seats are 30A fused, so apperently they take quite some power, so it could easily drain a slightly recovered battery again.
For the battery power to suddenly drop from 12 to 5V it would need a near short circuit, which you would no doubt notice. It is therefore more likely that you have an intermittent charging failure, draining the battery unnoticed during running. Are you sure the charging light in the instrument cluster is working?

The battery feed cable from the alternator runs via the starter motor. The crimped connection on the starter motor can give a high resistance. What is the voltage drop over this cable, measured between alternator and battery plus terminal?

[Foeux]

Originally Posted by TonyS9

What is the voltage on the battery at idle or 1500 rpm?

Have you check the positive starter cable for wear+shorting on the bulkhead?

Voltage at 1500 rpm is 13.82v

The cable appears in tact but have not removed or replaced yet.

[Foeux]

Originally Posted by Forrest

Is the battery the right capacity for the car? Does it drain to 5V as soon as the battery is connected, with the key in position 2, or only when you try to start the engine? A battery drain on that scale is likely to be causing some heat somewhere.

The garage will hopefully have the equipment to test the battery, current drain and check that the battery is receiving a suitable charging voltage from the alternator.

Are you sure all the wires are connected correctly? For example, if you don't connect the exciter circuit/warning lamp to the alternator this will prevent the battery charging.

Perhaps most obviously, is the starter motor drawing an excessive current?

Battery does not drain till key is in position 2. No heat or smoke anywhere. And this odd habit of 'healing' itself.

Batt reads 13.82v at 1500 rpm

Two people have said starter motor so will relay this to garage man.

Thanks for helping me.

[Foeux]

Originally Posted by Laird Scooby

When you first turn the key to position 2 (without starting it) does the charge warning lamp (and a few others) come on and remain on until you start the car?

Not hot car here to check but can see car today.

[Foeux]

Originally Posted by Rversteeg

If the engine is running normally, what voltage do you read across the battery terminals?
With only 5 V system voltage the engine will probabaly stop because the spark is be too weak or fuel pressure too low (electric fuel pump). Relays will also start to buzz. With a charging alternator however, it should normally not be possible for the system voltage to drop that low. Apperently for some reason during running the battery is not charged all the time and slowly drained until its voltage is too low for the engine to run. Either the alternator is not charging all the time or its charge does not always reach the battery.
The power seats are 30A fused, so apperently they take quite some power, so it could easily drain a slightly recovered battery again.
For the battery power to suddenly drop from 12 to 5V it would need a near short circuit, which you would no doubt notice. It is therefore more likely that you have an intermittent charging failure, draining the battery unnoticed during running. Are you sure the charging light in the instrument cluster is working?

The battery feed cable from the alternator runs via the starter motor. The crimped connection on the starter motor can give a high resistance. What is the voltage drop over this cable, measured between alternator and battery plus terminal?

The car will sometimes drain slowly if left. Sometimes start on the button after a week. A problem it has kept up with 3 different (2x new) batteries.

The car goes from running and charging battery to 5v in an instant with no smoke or fires.

In the time it took to tow the car 3 miles, it was suitably 'healed' to start under its own steam, an hour after being so flat it was dead.

Its almost as though the battery falsely shows 5v only to recover autonomously. Really confusing.

Today I will speak to garage man and make sure he is aware of the known High resistance fault on the starter cable.

Thanks so much for contributing to the discussion.

F

[Laird Scooby]

Originally Posted by Foeux

Voltage at 1500 rpm is 13.82v

The cable appears in tact but have not removed or replaced yet.

First, how exactly are you checking the voltage? I'm guessing you're using a DMM but are you going onto the battery terminal posts or the clamps on the ends of the battery cables? If one of those is broken or otherwise damaged/worn it may be breaking contact intermittnetly - ditto for the cables going into the clamps.

Also for the cables going to the chassis from the -ve terminal and also on the alternator from the machine case to earth - this strap has a habit of failing.

However, given all the clues so far, my money would be on the battery to starter earth cable and i'd guess it's frayed/broken/pulled out at the starter end where the cables goes onto the bellhousing. Ity could of course be the +ve lead on the starter with the same problems causing similar symptoms but all the sings point to an earth problem.

By the way, 13.82V @1500rpm is too low! Should be 14.4-14.0V depending whether the voltage regulator is cold or hot.