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Discussion Starter · #1 ·
Hi guys,

I had a gig last night, and afterwards the tardis started misbehaving itself! In three very odd ways... :-(

Firstly, when you put your fut on the brake pedal, the sidelights and dash lights (but only in the instrument binnacle) come on! The brake lights also work and the pictogram shows nothing out of the ordinary. When you put the lights on properly, ordinary behaviour resumes, but when you turn them off it goes odd again.

Any clues where to start looking?

Also, on my way home the boost randomly started topping out at about 1/4 of the way along the orange bar... it felt quite a bit slower, but when I opened the window I couldn't hear anything out of the ordinary, either on acceleration or over-run. The boost gauge still shows vaccum on over-run and a bit on idle too.

Any clues for that one?

And the last thing is, the temp gauge is usually very well behaved and sits bang on halfway, more or less stock still.

Last night it would get to halfway and then very quickly fall down about a cm (to about 8 o'clock). Like a very sharp needle movement (enough to catch your eye when driving). Then over the course of about 15 seconds climb back up to halfway and then drop again. It kept doing this all the way back, even after I stopped, switched off the ignition for a few mins, and kept going. As if that'd help! :)

Any clues where to start for that one? The fan wasn't coming on to coincide and push the needle down or anything, and I was doing a steady 65 on the M3, so it wasn't even like I was speeding up and slowing down.

I'll have a hunt for topics about boost problems as I know there are plenty, but the others are a bit odd!

Cheers - Jules
 

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The only common factor would seem to be the electrics - even the boost problem.

You could start with the easy stuff and check all the earth connections - including the little earth wire on the DI harness, which is very easy to pull off.

I'm sure other people will have more suggestions shortly.
 

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I there's been a post about the lighting problem earlier. I think it's been down to a rear brake/taillight bulb being fitted badly. When you brake the 12volts is sent across to the tail light and also the side lights. This can also get 12volts back through the ignition switch in cetain circumstances and pwer the ignition circuit so the engine won't shut down. I think you need the light switch on (night time etc) and your foot on the brake to do this. Don't forget that there are 4 bul at the back - two each side.

The other problems could be down to the temperature sender - either faulty itself or dirty / corroded connectors. If the temperature sender is faulty it will give the management system false readings which could result in the system cutting boost 'cos it thinks the engine is overheating or not warmed up.
 

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Discussion Starter · #4 ·
Thanks! That would make sense. I did just change the rear brake bulb yesterday morning, plus it was OK today but exhibited the same behaviour again today when I drove home this evening. Funnily enough the boost issue coincides with the lighting thing, so maybe there's something in that? Tomorrow I will experiment a little. I'd better read up on that thread about bad bulb fitting? There was only one way the bulb could fit and I'm not sure how you could do it badly? Never mind, I'm sure I'll find out :)

Cheers! Jules
 

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Someone once recommended changing BOTH bulbs at the same time to avoid the electronics sensing slightly different resistances.

I also seem to recall a query where the bulb had been fitted upside down which caused all sorts of funny things.

Saab electrics are strange things.......
 

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Changing all the bulbs for ones of the same make is recommended as a way to stop false brake light failure warnings coming up on SID. I don't think an odd will cause any other problems, like those described above.
 

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Discussion Starter · #7 ·
Thanks again for the input guys. Well, today I swapped my new bulb out for the old duff one, and drove in to work with my headlights on to try and simulate night time driving! Other than the obvious (i.e. the pictogram showed my brakelights were out) I had no problems. The boost was working fine
!

It seems very strange that the APC should be in some way hooked up to the lights, but then again I suppose it's all coming from the same battery.

Anyway, another gig tonight so we'll see what happens after dark! Maybe there's some strange combination of starting the car with my foot on the brake that's causing it to fail. We'll see!

Thanks again,

Jules
 

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Where did you get the new bulb from? Halfords bulbs seem to be the incorrect model - I had strange problems with mine after replacing the bulb (the engine would keep running until I turned the lights off).

The Saab dealer changed the bulb for a genuine Saab one and that fixed it.
 

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If the bulb was fawlty or the wrong sort, and you had the headlights on, it could mean that the brake light wire was seeing voltage too.

The APC will drop to base boost when the brakes are on.

Try driving with full boost in 4th, and just touch the brakes enough to light the lights and notice the drop in boost.

Andrew
 

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Might seem a silly question but the new bulb is identical to the old one, isn't it?
i.e same number of filaments, same number of contacts on the base, locating lugs in the same position?

It is possible - albeit difficult - to fit the bulb upside down, too.

I assume the contacts inside the bulb housing aren't corroded?
 
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