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Discussion Starter · #1 ·
Hello all!

I just purchased an 85 Saab 900 5 speed. Turbo off of ebay for the princely sum of $100 (something like 55-60 pounds). It has a bad radiator which I have temporarily fixed with stop leak. I have fixed a few other minor problems and thus far have spet another $10 on the car. (fluids and stopleak mostly)

What I have not been able to figure out is a power loss issue at low rpm. If you take off from a stop the car seems to have all the acceleration of my grandfathers electric wheelchair. (in other words slow as christmas) If you keep it floored or nearly so for 3 or 4 seconds the boost gauge begins to rise up into the yellow and the car will begin to make some someprisingly good power. If you take your foot off of the throttle for a couple of seconds when shifting gears the same is true for the next gear. If you manage the shift quickly it will lay rubber going from first to second. (it surprised both me and my semi terrified passenger, LOL)

Could this be related to a clogged catalytic converter, or maybe the vacum actuator on the turbo?

Any help in bringing this formerly unloved 900 back to it's former glory would be appreciated.

Bryan
 

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I'd get a tune-up and some extra maintenance items before beating your brain
. . .

sparkplugs
distributor rotor
distributor cap
sparkplug wires

Change the oil
Flush the coolant and change the thermostat

check the vacuum lines
check the timing

Then you can begin diagnosis
 

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Discussion Starter · #3 ·
I'd get a tune-up and some extra maintenance items before beating your brain
. . .

sparkplugs
distributor rotor
distributor cap
sparkplug wires

Change the oil
Flush the coolant and change the thermostat

check the vacuum lines
check the timing

Then you can begin diagnosis
Thanks for the tip, but I have already gone over most of the basics.
I guess I should have said that I am not a newb to cars, but this is the first Saab I have had the hood opened on. Frankly I figured it would be a nightmare to work on, but I have been pleasantly surprised. Thus far it has been easy.

As for the tune up and other basics

The sparkplugs are relatively new and have no fouling,

the Cap and rotor are relitively new as well.

I haven't checked all the plug wires yet, but I ohmed a couple of them out with an analog meter and they are reading about where they should. Once again they look to be much newer than 1985

Oil is still new enough to be clean, the sticker on the windshield says that the oil change is due next month or 2000 miles from now. (yes the speedo stopped but according to owner it died about 200 miles ago and a recent parking ticket found in the glovebox backs him up)

The radiator is rotten, so for now I have temporarily put some hillbilly stop leak in it. (black pepper works well in the short term and it won't clog up the heater core) I will take care of the coolant hoses and such when I replace the radiator.

I have checked and replaced any bad vacum lines I found that were marginal. It did have a rather large leak, unfortunately it was the brake booster, but that line is now plugged.

A friend has my timing light but, the car runs smooth and doesnt ping at all even under heavy acceleration up a steep grade with a lot of boost.


I still need to check the timing chain tension, but unless it is WAY to far gone the car could be sorted out first. (or at least I would think so)

In short the car is in decent shape and appears to have been taken decent care of until shortly before I got it.

I really don't want to toss a whole lot of money at it until I know what I have.

So back to my origional question

Could this be related to a clogged catalytic converter, or maybe the vacum actuator on the turbo?
 

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Could be either, but I'm betting that it will be something much more basic. I've driven a couple of Saabs that had a cylinder or two that weren't holding compression (bad head gasket), but sounded great. They weren't speedsters, let me tell you. Should have bought one of them, but I digress.

Check the ignition as suggested; you may not be getting enough spark.
 

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The boost won't cut in till about 2,700rpm so you may have a tuning issue prior to the turbo kicking in. Get the timing checked, could be retarded.
 

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Discussion Starter · #6 ·
Well I went ahead and plunked down $70 today on new plugs, wires, cap, and rotor just for the heck of it. I have checked the timing and it was a bit on the low side, but not by much. I checked the air filter which looked to be new so I reinstalled it.

Now the car runs EXACTLY like it did before I started.


Here is a better description of the symptoms.


When the car is cold and you start it up the idle will hunt, or rev up to 1200rpm or so then drop down almost to the point of stalling... stumble for a second or so then rev back up. It will do this for a minute or so before stabilising around 800rpm.

Once warm the car will idle smooth for a few seconds then stumble without losing to many rpms. In other words the idle doesnt drop and cause the stumble. I suspect it has something to do with fuel mixture or ignition. Since the ignition spark seems strong, when tested (nice long bright blue spark at the plug) I would beleive it to be fuel related.

When driving it alternates between running smooth for a few seconds and then losing some power and running roughly for a few seconds. If you keep it floored it will eventually smooth out a bit but will continue the smooth and strong/rough and weak cycle all the way up to the rev (or is it boost) limiter.

I looked in the service manual for the car but it doesnt show any way of getting codes out of the computer for anything pre 1988.

Any ideas on the problem?

What about leads on a cheap scan tool, or method of running the codes at home?
 

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Welcome to SaabCentral!

The hunting for idle sounds like a vacuum leak - that's a common problem. There are about a million miles (1.6 million Km) of vacuum hoses under the hood, and a leak in one of them can cause havoc with idle.

Not sure about a clogged cat - I'd look elsewhere first. If the AMM (Air Mass Meter) isn't working right, that will goof up the mixture, which will cause poor acceleration.

Does the '85 have APC? If so, and the Turbo guage doesn't move more than about 1/3 of the way into the yellow, you're on base boost, and that means the APC is not allowing full boost. That could be poor gas, an electrical or plumbing broblem, or a problem with the APC itself.

I don't think there are any codes to get out of the computer for a car that old since it doesn't really have a computer.

It sounds like the problems, while annoying and "interesting" to track down, aren't too bad for a $100 car. They can probably be found and remedied with effort but not too much cash layout.
 

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I'm still much of a newb at this but I thought I would put in my pennies worth to try to help. I had some bad idle and power loss and it took me months to sort out but I did thanks to the forum members. There were two main problems:

1/ Firstly the plug gap was to large and when running warm the spark did not always fire the cylinder. Warm starts were a nightmare and my wife was all set to sell the car (it was her car) :cry:

2/ I had several vacuume leaks so I replaced the pipes and I also noticed that, having read a posting in the forum,the idle screw on the throttle body had been over tightend and pushed through the casing causing quite a large leak.

I hpoe this helps. Although I have had many problems with my (wife's) 900T its a pleasure to drive it and I quite enjoy the challenge of keeping it running. I have a suspect drive shaft bearing problem at the moment so that will be my next challenge:eek:
 
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