Guess The Fault...

[Spinal]

So I had a breakdown today... on the M25 none-the-less!

Luckily, it's not the W202, but the rally car, which I decided to take for a test drive...

As I went over the M3 flyover, I indicated right and noticed that every time the indicator came on, the rev-counter lost power and went to 0... uh-oh...

As I came off the flyover, I noticed that accelerating did... well... nothing! In fact, the car was slowly decelerating, so I decided to indicate left and go into the emergency lane... nope, no indicators either....

So I put on the hazard lights, which worked (albeit a too fast) and went onto the hard shoulder (engine still running happily).

Turned the engine off, then tried turning it on again... nope, no luck... allt he lights dimmed/went off and the engine barely turned over (so battery-related I thought)

40 minutes, and a call to the AA later, I was being brought home on a flatbed... once at home, I connected the rally car to the W202 and jump started it... no problems there...

Reversed onto the driveway, parked properly... revved the engine a few times (to the limiter) to make sure that it worked, and I noticed that the rev-counter wasn't moving....

Parked, tried starting the car again, no luck... so I pulled the battery and put it on charge...

My guess is either the battery is knackered, the ECU is throwing a fit or the alternator (which looks brand new) isn't doing it's duty...

Any diverging opinions?

M.

 

[Dieselman]

Wrong bulb in the indicator causing a short.?

 

[trapperjohn]

Could be on a winner with the alternator. Similar thing happened on my 124. Gradually all the different systems packed in on the day I bought it. Finally ground to a halt in the outside lane M6 north bound, standing traffic so no worries. Never had some many guys giving me a push onto the H.S. Long story short, recovered to 124 works, New Fuel Pump relay, new OVP relay and an alternator which Ian had about the place. Been sweet as a button ever since.

 

[Spinal]

Correct me if I'm wrong - but if it's the alternator the engine should cut out once the battery is drained... right?

Similarly, if it's the battery, the engine should work fine under the alternator's power, right?

So I'm thinking, I start the car, put a voltmeter to the terminals, and check to see if I'm getting the 14+ charging voltage. Next, I disconnect the battery and see if the engine cuts out. Finally, with the battery re-connected, I disconnect the alternator...

I'm thinking that one of the cells in the battery may have shorted, this in turn may be causing the alternator some issues... That said, I did start the car under it's own power before heading out, so that doesn't make sense...

There's a spaghetti of cables coming off the battery - very few of them seem "original" - many have inline glass fuses... I might disconnect a few and try to trace them to whatever they are powering, I think all those lines may be causing trouble...

I'll keep you updated

M.

 

[Ian_C]

""So I put on the hazard lights, which worked (albeit a too fast)""

Bad earth ? This will cause this....

Worth checking.

 

[Spinal]

Bad earth ? This will cause this....

Worth checking.

Bad earth of what? The battery or the alternator? Or am I missing the point all-together?

Sorry, not really clued up

M.

 

[DrNick]

Does sound ground related. When you tried to start it did all the dash lights come on normally and when you turned the key it all died? If so that sounds like a high resistance connection somewhere. Given that there are funnies going on with the indicators I'd be suspicious of ground connections. IS there an earthing strap from the engine to the bodywork or the battery - is it loose?

Check back from the battery ground connection and make sure that all the big connections are still good. I had an old Viva that was grounding itself through the throttle cable because the earth strap had failed. That gave all kinds of intermittent wierdness.

Large currents through a 'high' resistance (high just menaing higher than zero) will result in heating which could result in the connection going even higher resistance and stopping everything, and then it doesn't return to 'normal' until its cooled down a bit.

Worth checking the ground connections anyway - of course it could be in the battery itself - maybe a failing ground post?

 

[Spinal]

Update: Well; it's all on hold now while I wait for a new battery - the old one is pretty knackered.. after more than 48 hours on the "all singing all dancing" desulphating auto-charger, it's still not charged...

So I've ordered a new battery... at £50 it wasn't too bad... should be here tomorrow or Thursday...

Will then try to look for (again) the multimeter, if not, I'll just buy another!

M.

 

[Spinal]

Update:

So I got my battery yesterday and a nice new multimeter as I seem to have lost mine.

This is what I get (on a 3.0 V6 Petrol, MK2)
With Engine on, multimeter connected to:
+ Battery, - Battery : 12.1V
+ Battery, - Alternator : 12.1V
+ Alternator, - Battery : 16.0V
+ Alternator, - Alternator : 16.0V

Revving doesn't do much. Disconnecting the battery kills the engine.

This makes me think that the alternator is fine, and so is the battery (Well, it's new now ) but maybe I have a grounding issue? As in, shouldn't the alternator be able to keep the engine going without a battery? or am I mistaken?

That said, if it is grounding, why do I get the 16V charging voltage when I check the + alternator to the - battery? That sounds like I've got a circuit there...

Or maybe the 16V is too high? Could that be a problem?

Ideas? Should I just go for it, try it on Sunday at the Devil's pit and make sure I have the AA's number to hand?

M.

 

[stevesey]

Something odd there - a big voltage drop between alternator and battery on the + side so check all the connections there (grounding looks fine).

I'd suspect +ve side of alternator isn't actually connected to the battery (or is high impedance) thus when you disconnect the battery the engine dies. Also would explain the high voltage if the alternator is effectively unloaded.

HTH

 

[Spinal]

Is there an easy way to check that the + is connected to the battery? Can I just do a continuity test with the battery unplugged and engine off? (alternator pin -> battery clamp). Or is it (as I fear) a matter of tracing the cable and checking all the connections?

I am a bit concerned about the 16V though - from what I can see anything over 15V is "bad" for the battery... but then why can't I "read" more than 12V on the battery end?

m.

 

[stevesey]

Just do a resistance check between the alternator and battery + with the ignition off (no need to disconnect battery) - should be pretty close to 0 ohms.

If alternator is unloaded I wouldn't be suprised at 16V, but would expect that to reduce to a more normal 14.7 ish as soon as it trys to pass any current. Try measuring the alternator and battery volts with all the lights on and off - at idle the lights should drop the voltage a bit.

Alternative is that the regulator has gone - do the alternator volts rise with engine revs? (Careful though).

 

[Spinal]

I had a look through the workshop manual (which I was lucky enough to find on ebay - 2 boxes worth of official dealership binders ) and from the diagrams it seems like the connection from the alternator to the battery (on the +ive side) are quite direct...

So I decided to brave the dark, and with a flashlight in my mouth and the multimeter in my hands I went out...

Revving does nothing for the voltage on the alternator - but didn't check the battery... doh!

As for continuity, I'm getting zilch! I think you hit the nail on the head there; the +ive clamp is totally isolated from the +ive terminal of the alternator!

I guess tomorrow afternoon I'm going to have to take apart the wiring harness and look for a broken cable... or a loose connection... or a blown fuse... (here's hoping it's just a fuse!)

M.

 

[stevesey]

The alternator -> battery connection should be pretty easy to trace as it should be a reasonably chunky cable (say 5mm+). Check the connections at both ends first.

If the alternator end is a clamped connection it's worth undoing cleaning up and with some emery paper/wire brush and re-assembling anyway before you head south.

 

[Dieselman]

There won't be a fuse in circuit but there could be a relay.

I once had a car with a bad battery/alternator conection at the main supply junction. It cut the engine when the main beam + auxilary lights were switched on during a 250 mile night drive.

Nice easy fix though.

 

[Spinal]

So I traced the cables today... I say cables because there are 4 cables coming out of the alternator!

Two go towards ...something... (I didn't bother tracing them - not even sure they are +ive, they are very thin and come out of a plug, so I think maybe a monitor/sensor) the other two are the important ones... These two are light yellow...

One goes to the battery, and it's meant to charge the battery; the other goes to what appears to be the engine. Both are fused! What appears to goto the engine has a 60A fuse, and the one that goes to the battery has a 100A fuse.

I tested again for continuity, and at a higher (or lower, depeding on your point of view) setting, I did get some current going through.. but barely any, and with a very high resistance... so I guessed it was coming through the second wire through the engine.

Anyhow, long story short... the 100A fuse was blown I've also noticed a relay is missing a terminal, so something isn't right... but I'll deal with that next. The fuse isn't a regular blade fuse, it's a weird bolt-in thing... I popped by the local stealership and ordered two fuses (at roughly £4 each)... an extra one just in case... sadly, they wont be in stock until saturday...

To test it, I grabbed a 100A maxi-blade fuse from halfords (I really need to get a trade card), soldered two pieces of wire and clipped it in temporarily... Guess what? I get 14.5V across the battery with the engine running now

I'm very very pleased! I was worried I needed to replace the wiring loom, but this worked out alot easier!

I now need to replace that relay, but first I want to figure out what it's for... sadly the printing on the fusebox cover is totally worn out... Also, the ABS fuse is missing (but the one for the ABS computer isn't) so that needs looking into as well...

Sunday I have a greenlaning event, that will be the real test!

M.

 

[stevesey]

Unusuall to have a fuse in that circuit - but then it's not a shopping car.

One of the other wires will probably be the HRW feed - often wired directly to the alternator these days. Actually could that be the HRW relay you are talking about, does the HRW work? And does the one of the relay connections get energised when you flick the HRW switch?

 

[flango]

Hi Spinal

Fill me in on some details what type of car is it, is the car MSA log booked if so you presumably have a kill switch? Battery under the bonnet or in the boot? Reason I ask is I had a Chevette HS (Ex Dealer Team Vauxhall car) and had terrible electric problems with it, so did Tony Pond apparently who raced it in competition never got to the bottom of it and sold it on and got a Vauxhall Chevette HSR, consensus of opinion was it was the alternator, wiring, kill switch that was causing it.

 

[Spinal]

Unusuall to have a fuse in that circuit - but then it's not a shopping car.

One of the other wires will probably be the HRW feed - often wired directly to the alternator these days. Actually could that be the HRW relay you are talking about, does the HRW work? And does the one of the relay connections get energised when you flick the HRW switch?

HRW? As in the rear window? Really? I would have never guessed that consumed enough juice to be wired into the alternator directly!

As for having it... uhm... I think so, can't remember off the top of my head to be frank

The 100A fuse is "stock" for the car, at least having a look at this link:
http://www.pocuk.com/faq/enginebayfuses.htm

Flanaia; it's a Mistubishi Shogun MK2 (3.0l V6, with the 6G72 engine, the same that you can find in the GTO). I also believe that Mitsubishi used these in the Paris-Dakar rally... but don't quote me on that. The car is fairly stock, at the moment just some more lights, a larger battery, and some off-road tyres... but give me a few months and you wont recognise it

M.

I will post pics, don't worry