Last Chance for My '85 900

Hi

How have you tested?

Removed all plugs, take out fuel fuse crank engine?

If yes, please try once more ... and add a little engine oil through each plug hole (Don't know though what happens if you have a catalyst and oil goes down the exhaust pipe).

The added oil should show you if you have worn out rings/cylinders. If compression goes up then they are worn ...

Hope I am wrong! Do you loose coolant? If yes, compare also the plug on No. 3 with the others. Heads of that era, (definitely on an 1982/83 car ... crack on cylinder No.3. The crack is not repairable. This would explain why the engine does not work once it has warmed up ...

If it helps at all.

Regards Charles

The compression does come up slightly on three. I didn't test the other ones since they weren't critically low.

I lose only a tiny bit of coolant. There's no white "smoke" coming out of the exhaust and no sign of water in the oil.

Thanks, Charles.

-- Christian

Sounds like you need a warm up valve and an auxiliary air valve. Check the wiring to them and remove the aux air valve, place in freezer and see if it opens up.

OK looking for cheap solutions.

Take the rocker (head) cover off and check valve clearances. If it is the same head as I am thinking of ... there are metal shims which are used to adjust the gap (they can be ground down to the correct size etc)...

If the gap is too small the valves would stay open too long, hence low compression. Alternative is to have the head off and look at the condition of the valve seats.

When I had a cracked had ... I think the compression I got was less than the 90 you got but it is a long time ago to remember ... basically the car run on three cylinders.

Look for other problems if you can ;-)

I haven't had a warm-up valve for quite some time (wires were disconnected) but I didn't have problems until I disconnected the fuel from i tdue to leaking.

What does the auxiliary air valve do?

-- Christian

You need to buy a book on Bosch fuel injector system. I own an 85

900S. It has over 250000 miles and still runs perfect. I do all tune ups myself. It is very important that there be no vacuum leaks anywhere in the system. For instance if I fail to replace the oil filler cap correctly it will allow excess air into the system and make the engine run rough. Go over all the hoses carefully and make certain that they all seal, especially the large hose from the cam box to the intake plenum. You must plug any holes in intake air system if they are not connected to some other device.

The aux air is normally open and allow excess air into the intake to make the engine idle fast until it warms up. The temp sensor electrical resistance decreases with increasing coolant temperature and makes the aux air close down, thereby slowing the idle.

You need to get the warm up valve working also.

keep us posted on your saab. as another 1985 saab owner i am hoping for a happy outcome. rod

This is what I hear of Saabs. So, I hate to let mine go at only 167K.

I've gone over the vacuum lines several times. I found no leaks. There was a section that looked like it was close to cracking so I went ahead and replaced it.

If this were the problem, wouldn't it run poorly until warmed up? Mine runs well for the first 45 seconds (or so) and then goes quickly downhill.

I've had the elecrical portion of this disconnected for months and the car ran like a champ. I live in NM, USA, so winters are very mild. It doesn't make sense to me, but is there any way that removing its fuel line might have caused a problem?

-- Christian

Thanks, Rod. I do not want to let this car go. I'll keep everyone updated.

-- Christian

Get a copy of: How to Tune and Modify Bosch Fuel Injection by Ben Wilson ISBN 0-87938-570-7 published 1992. Barnes and Noble will order you a copy. Or try Amazon.com

Regarding your questions: The carburation on this car is extremely complicated. You need to understand it completely to make the car run well. It might be simpliar for you to take the car to a Saab dealer and make them tune it up.

It's easy to check the operation of these components - use the methods described in the Bentley manual. In my 1985 900i there is a break in the +12 v wire coming from the fuse/relay panel going to the warm-up reg and auxilliary air valve resulting in the at-start idle speed being really low (around 500 rpm), but as soon as the engine starts to warm up the idle speed comes up to the standard 850 to 900 rpm.

One of my future repairs is to fix that broken wire.

Apparently the 1985 cars are particularly prone to failed wiring which is something to do with the manufacturing of the wiring harnesses by a contract supplier to Saab. I'm not sure if it's a quality-control thing or simply using sub-standard wire.

Regards,

Craig.

How important is the cold-start injector? Does it have to be hooked up (wires & fuel line) for the car to run well? I live in a warm climate and don't have trouble w/ winter starts?

The wires in the '85 are terrible. The insulation seems to be made out of a substance about as durable as gelatin.

-- Christian

Unfortunately, I don't want to invest much more money into this vehicle and dealership garages aen't exactly cheap. The second problem is, the nearest dealerships are in Albuquerque & Santa Fe (180 miles each) so I'd have to haul the car.

-- Christian

Well you don't have to use it - all it does is inject pulses of fuel vapour to make starting easier and after about 10 seconds it shuts off when the thermo-time switch's bi-metallic strips heats up. So if the cold-start injector isn't working it just makes the engine harder to start when it's not already warmed up.

My white 900S has the thermo-time switch disconnected as it's got some sort of a wierd semi-short which holds the starter auxilliary relay engaged after letting go of the ignition key. I only had one spare brand-new thermo-time switch and that's already been used up on the turbo car I'm restoring so I need to get another one. 8-)

Yeah well I've only got one significant wiring faults in my 85 900i and that's with the +12 volt line to the warm-up reg and auxilliary air valve. So that engine runs really slow after starting but is fine after warming up. The wires to the AC high-temp cutout switch are also really bad - almost bare copper at the ends that join to the the female spade lugs which plug onto the thermo-switch itself. 8-) But that'll be simple to fix when I get some auto-rated wire of the right gauge, or just 'borrow' some out of the wiring harness in the 83 GLi that's my current 'donor' car.

Craig.

I've wondered if some of the problems I'm having are due to a wiring fault. I have one harness where every wire was bare copper. I taped the individual wires as best I could to prevent shorting but that didn't seem to help.

Not too sure how I would track something like that down unfortunately.

-- Christian

Best way is to use a schematic diagram of the wiring, and where you have suspect wires, work out where each wire connects to something, or joins into a connector, and do continuity checks, etc. That's how I worked out the wiring issue with the 85 900i.

It can be very tedious if you're tracing a lot of wires, but in general, all the wiring in the engine bay is going to degrade much faster than elsewhere, but if your car doesn't have an exhaust shield under the floor the wiring running down the centre can also cook (and in one recent case I saw on a forum site, short and start a fire!).

Also keep an eye on the rear light cluster wiring as that's a common place for water to get into the electrics.

Craig.

Thanks, Craig. I'll take a look and see what I can track down.

-- Christian