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Discussion Starter · #1 ·
Hello again.

I posted a few issues a couple weeks back and didn't get much of a response.

I gave in and tuned it up, but it really didn't need it. The plugs that came out looked just like the perfect ones pictured in the back of every repair manual known to man. The wires, cap and rotor were fine as well, but I switched them out anyway.

The ignition timing is spot on now as well.

It turns out that the connector where the O2 sensor plugs in was full of crud and not making good connection. A little contact cleaner and an old toothbrush had it running much better.

I also pulled off the mass air sensor and there was a lot of crud in the screen. I cleaned it out, and that helped some as well.

By and far the biggest improvement came when I noticed that the car would die if I wiggled one of the wiring harnesses that comes across the intake, brake booster and over by the fuse box. It turns out that someone has repaired a burnt wire in there at some point in the past. The had spliced in a 6 inch piece of wire and had made sloppy connections. I repaired that and the car now runs respectably.


I still have a higher rpm, full throttle (or nearly so) cutout. It happens around 4500+ rpm and is usually at the higher end of the yellow on the boost gauge.

It is inconsistant in that it will run great foe a few minutes and then it will cut in and out when accelerating hard. I am running out of ideas.

Anyone out there with a good guess?
 

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I know you probably don't want to hear this but here it comes..................Its most lickly a vacuum leak. :D Something is opening up under boost and creating a leak would be my guess.

I would take all of the intercooler pipework out and reassmble it one peice at a time checking each for holes, splits or cracks, and make sure it is securely fastened back togeather.

Then I would replace all of the vacuum hoses. A fun task. :D

I had to do all of this on my 88 900t, it had a high rpm cutout as well.

It could also be the overboost cutout switch.
 

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Discussion Starter · #3 ·
Vacum leak? AAAARRRRGGGGHHH!!

Seriously, though I have reved it up a bit to get some boost and run my hands all around the pressure side of the turbo and the hoses going back to the throttle body. If there is a leak it is either a very small one or it is only opening up under alot of boost. This very well may be the case though.

As far as the overboost switch, where is it, and what would cause the car to get too much boost intermittantly?

One last thing, on level ground, in first gear, floored, about what rpm should my boost gauge hit the orange section?

One other last thing, what is the little switch on the side of the throttle body for? Mine doesnt seem to do anything. I have another microswitch that will fit, but havent checked the one on the car, nor popped the new on on yet.
 

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Good:

Check the information on the APC at http://www.900aero.com.

The APC dictates boost, cutoff, etc. There are adjustments. However, this is the LAST thing to try.
 

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Discussion Starter · #5 ·
I was under the impression that APC didn't come along until after 1985?



what is the little switch on the side of the throttle body for? Mine doesnt seem to do anything. I have another microswitch that will fit, but havent checked the one on the car, nor popped the new on on yet.
 

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Missing or coughing at full throttle going through the gears.

Hello: I have a similar situation in an 85 Non turbo Saab 900 ($50). I am not familiar with the fuel set up on the Turbo model. but perhaps my experience can help you to at least narrow it down. In my situation, I can get the car to sputter or not depending on how I finnesse the gas pedal. For example, carefully dialing in throttle will get me 70 mph in third gear with no sputtering and good accelleration.....if I am careful not to press the pedal all the way to the metal. If I try that by tromping the gas pedal, it will sputter around 3000 RPM. So I am inclined to think that your similar problem is not Turbo related but related to the fuel distributor not supplying enough fuel. or perhaps as the other contributor said, a vacuum leak. I will start looking for a vacuum leak in my system.
Hope this helps,
Rich 3Saabs.
 

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GoodSamaritan said:
I was under the impression that APC didn't come along until after 1985?
;oops: ;oops: ;oops: I didn't even look to see the year of your car. You are correct. Sorry for the confusion.;oops: ;oops: ;oops:
 

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GoodSamaritan said:
what is the little switch on the side of the throttle body for? Mine doesnt seem to do anything.
If it's squarish, black, and in line with the throttle shaft, it's the TPS (throttle position switch). It tells the ECU if you're on/off idle or at wide-open throttle.

Also, check out the overpressure switch, as suggested by Matt88S. This switch will kill power to the fuel pump if boost gets too high. See Bentley, page 234-8 for details and testing.
 

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overpressure switch is maybe a foot above the clutch pedal (or where it WOULD be if u drive auto), accessible through top or bottom of the dash--but ive heard bottom is easier. also, if this WAS your problem, your APC solenoid (mounted above radiator) would be clicking LIKE CRAZY, that is; if it is plugged in.
 

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GoodSamaritan said:
I was under the impression that APC didn't come along until after 1985?
Mine has it and its older than that. Easiest way to check is to look at your boost gauge and see if it says TURBO APC on it or not!
 
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