Bad ground/power connection

[mark e]

OK,

I thought maybe the other day I had an alternator problem, but it's now looking more like a bad ground somewhere ... symptons recently experinced under vibration include:

- Radio intermittently going off then coming back on straight away

- Entire dash lighting dimming

- Variable voltmeter readings whilst under static load

So, it's time (I reckon) to have a check of all major power connections. Other than at the battery, alternator and earth strap by the top engine mount, does anyone know of other significant points that may have come loose and cause the affects

(93 CS2.3T)

Thanks

[billj]

Or it could be a dodgy battery. A common failure mode these days is for a conductive sludge to build up which eventually shorts the plates. Before this becomes a solid failure, it can happen intermittently under vibration/braking. I had this happen on the Aero some time ago just as I was driving home from a battery shop who said it was fine and that there must have been some other reason it wouldn't start earlier that day.

Squire Furneaux diagnosed it properly next day (when I was booked in anyway) and fitted a nice new Saab battery (we all know Saab don't make batteries) at almost twice the price the battery shop would have charged!

[mark e]

Hmm... I hadn't suspected the battery to be honest because it's not that old- I'd say 18 months or so. But that sounds a more plausible reason for the volts dropping right down... I'll go have a peek...

[mark e]

Can't have a peek ... it's a sealed "maintenance free" jobbie... which I wouldn't expect to be giving up when under 2 years old, especially when it gets the best part of two hours running/charging every weekeday.

But you have got me wondering if it is faulty... I've got a pretty meaty amp (2 x 100W rms into 4 ohms or 30A rms) and on the bass kicks the headlamps dim, which suggests to me that the battery ain't acting as a very good capacitor like wot it orta. Cranking is OK strangely enuff...

[StephenA]

Cranking would indicate that the major connections to the engine are fine - any resistance at all on those links and you dont get a crank (0.12 of an ohm at 100amps swallows it all).

Check the feed for the non ignition circuits - if the problem was on the major line then power failures to the radio and dash would cause stalls in the engine as it would be like turning your car key on and off (I had a previous car do that).

[Nufis]

Originally posted by BillJ:
[qb](we all know Saab don't make batteries)[/qb][/b]

...and we all know 3/4 of SAABs electric system is BOSCH... Thus I have fitted BOSCH battery on mine, when Bären (or something like that)(was already fitted when I bought the car) gave up. Not a surprise, BOSCH has almost 1/3 more capacity in about the same or a bit less size, than its concurent. Oh yeah... price... almost 1/3 more for BOSCH than any other.

Best Reg
Dzintars 9000CS23T

[Paul D]

It does sound like a bad earth or other contact.

But another possibility is the Alternator fixings comming loose - causing the alternator belt to slip intermittently.

This caused the dash lights to dim and brighten and alternator voltage readout to fluctuate badly! Not so likely to cause noise on radio though - although could do if voltage switching from battery o/p to alternator o/p, etc.

I had this happen because a mechanic had failed to tighten the alternator fixing bolt sufficiently, which due to vibration caused an elongated hole in the mounting bracket and hence excess slack to occur with the alternator belt - intermittently!

[mark e]

Update... it's got worse! I hadn't been happy with the battery so I changed it for a Saab one. Apparently all was good... but the gremlins are back now. Here's what's been happening...

Yesterday, sitting at idle for a while with the A/C on, the engine suddenly cut out. Started again straight away with a check engine message that went out after a little while. Flashes are two short then one long.

Under hard acceleration (sometimes) the diplayed volts on the EDU drop to about 10, and the radio goes off, so I genuinely believe there's a loss of volts somewhere.

Sitting with engine idling, headlights on, if you turn the foglights on there's a very noticable brief dimming of the headlights. I haven't been able to repeat this with the engine off. The single rear foglight does not cause this.

Sometimes turning the indicator on is enough to momentarily turn the radio off.

Whenever the rear screen heater is on, radio reception goes hissy/crackley.

What I have checked so far:
- The main ground connection underneath the battery
- alternator charging current at idle (circa 30A when I put the new battery on)

Unfortunately, non of the above is 100% repeatable. My own theories are therefore:

a) possible bad ground connection to the main fuse/relay assembly behind the glovebox (my own favorite, as I'm clearly experiencing voltage dipping below the nominal battery terminal voltage

B) some sort of wierd alternator fault whereby it isn't happy under changing loads, and is managing to put a brief very low impednace across the circuit but this does sound a bit far fetched(I've checked the mountings and electrical connections to it)

Anyone got any other nuggets?

Thanks

[billj]

I'd favour a bad connection somewhere, but the intreresting thing is that you don't mention bad starting, so I wouldn't suspect either the positive battery terminal or either end of the ground connection. That leaves us with your other theory of the connection into the fusebox. I think it's not too hard to get to as you have a glove compartment (my Aero has a passenger airbag so the fusebox is underneath and a pig to get into the back of.

I can't honestly think how the alternator could cause problems like this. The battery alone should be capable of keeping the dash lights lit to full brightness.

Two flashes means MAP sensor, but I think you can probably ignore that as a side-effect in this case unless it happens again without the electrics dying first.

Sorry, that wasn't a lot of help, was it?

[mark e]

Nope, starting is fine and I've already checked (i.e. dismantled, cleaned, re-assembled) all the main connections near the battery

It seems like you're confirming what I suspected anyway- it's likely to get messy from here! (mind you it can't be as bad as my bolier exploits last night which included at one point a hose spurting off under 3 bar water pressure, spraying everywhere, and consequently tripping the RCD and all the lights going out... leaving me in total blackness, trying to get my thumb over the end of the offending pipe and find the hose to re-attach before I was ankle deep in foul, black, sludge ridden central heating water... )

[billj]

If the job turns out to be that bad, I'd trade the car in

[mark e]

Only 'cos you want to get your mits on her!! Gerroff she's mine!!

[cprsaab]

Have you checked the earth on the Gearbox for corrosion etc??

[mark e]

Spoke to my garage man... he recommended taking a look at the bulkead thru connector and cleaning the contacts. I'd forgotten about that fella , so I'll start there...