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Discussion Starter · #1 ·
When engine is warmed up it will begin to miss while accelerating hard above about 2200 rpm. As it misses, the tach bounces. Less throttle makes the missing stop. At freeway speed, 65 mph, it will be mostly OK until beginning slight acceleration. Pedal to the floor at 65 mph results in almost complete failure, that is, engine hardly runs at all, with tack bouncing all over. Dropping into 4th gear at 65 mph IS complete failure, no power at all, and tach is failed steady at 1500 rpm, even with foot off the gas. The problem occurs at corresponding lower speed in lower gears. For example at 25 mph, dropping into first gear makes the engine just quit until it slows down.

When engine and underhood temperature are cold there is no problem; the car runs fine. The problem first appears as the coolant temperature approaches normal. It is not really bad until well after reaching normal temperature, suggesting it is related to underhood temperature, not coolant temperature

This car is an early one with a single coil. Because I have had experience with a coil that failed like this, I replaced the coil with one from my shelf that has no internal resistance (same as standard Saab coil). There was no change in the problem.

I suspect a problem with the ignition amplifier because it affects the tach in harmony with the engine cutting out. Any comments or suggestions greatly appreciated.
 

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Sounds like a Crankshaft Position Sensor to me. Misfire after warming up, tachometer freaking out = Typical signs of CPS failure.

-Jim
 

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I agree on the CPS(crank position sensor).

Measure the Ohms (550 +/- 50 as I recall) cold, then hot.
http://www.saabcentral.com/forums/showthread.php?t=102007
This link goes into better detail..

I might also test the fuel pump, but a pressure/volume rig must be designed...maybe pressure would suffice....
Miles ?
The pump seems to be OK up to 150K miles or so..this varies.
 

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Discussion Starter · #6 ·
Thanks to Frank and Earthworm. Your suggestion that this might be the CPS was on target. I replaced the sensor, and the car will run through the rev range without missing a beat. It was somewhat difficult to find a parts supplier who could understand the difference between conventional distributor ignition (what I have) and the Direct ignition, however I did find the correct sensor at O'Riley Auto Parts. discountautoparts.com was very frustrating and sent the wrong sensor, and is dragging their feet about taking it back.

Unfortunately changing the CPS has introduced a new problem: The car is very difficult to start when cool or cold. I must crank for as long as 30 seconds before it fires. Hot starts are no problem. Warm starts are hard, but it will fire in 10 seconds or so.

Any ideas of what might be wrong now? This hard starting was not a problem before. Perhaps this new sensor is itself defective in some way. i would appreciate whatever advice offered.
 

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This may be a problem with the temperature sensor(on the inlet manifold) for the ECU..

Check it out..
Please let us know.
 

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Bill Vatter said:
Thanks to Frank and Earthworm. Your suggestion that this might be the CPS was on target. I replaced the sensor, and the car will run through the rev range without missing a beat. It was somewhat difficult to find a parts supplier who could understand the difference between conventional distributor ignition (what I have) and the Direct ignition, however I did find the correct sensor at O'Riley Auto Parts. discountautoparts.com was very frustrating and sent the wrong sensor, and is dragging their feet about taking it back.

Unfortunately changing the CPS has introduced a new problem: The car is very difficult to start when cool or cold. I must crank for as long as 30 seconds before it fires. Hot starts are no problem. Warm starts are hard, but it will fire in 10 seconds or so.

Any ideas of what might be wrong now? This hard starting was not a problem before. Perhaps this new sensor is itself defective in some way. i would appreciate whatever advice offered.
Could be the wrong sensor. Did it look exactly like the one you pulled out? Did it have a spacer on it?
 

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Discussion Starter · #9 ·
I checked all around the back and side of the engine for any connections inadvertantly undone or otherwise messed up. All looked OK. Based on Franks comment, I took the sensor back out and examined it very carefully. The new sensor was provided with an "O" ring not there on the original, and that was causing the tip of the sensor to be not quite as deeply inserted into the crankcase by perhaps .010 inch or so after the "O" ring was squished.

So I removed the "O" ring and put it back. Now the car starts instantly, so I conclude the sensor is very sensitive to the distance it is from the spinning crankshaft.

Car now OK, thanks much.

Bill
 

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The o-ring should be on both models. In my case, when I removed the sensor, the old o-ring stayed in the block. The original o-ring is green, you can just see it in the pic below.



So, if you put a new sensor in, with the new o-ring, and leave the old o-ring in place, the distance between the sensor tip and the aperture disk may be out of spec. In other words, two o-rings are one too many... :cheesy:

 

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Bill Vatter said:
So I removed the "O" ring and put it back. Now the car starts instantly, so I conclude the sensor is very sensitive to the distance it is from the spinning crankshaft.

Car now OK, thanks much.

Bill
Bingo! I noticed that the old spacer stayed in the block when I changed mine. Glad you found it.
 

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Discussion Starter · #12 ·
PMI,


What a supurb picture. How'd you get your camera in to snap that?

Not so easy to see on mine, but I think yes, I may have had an o-ring in there.

Anyway, the lesson for us is the tip of the sensor has to be in EXACTLY the correst spot, or it is going to be trouble. Anything that causes incorrect location is a problem.

Now I can go back to working on my 1924 Silver Ghost that has points, both in the distributor and in the magneto. (Two independent systems; two plugs per cylinder.) That stuff I can understand, even though there is a lot of it.
 

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Bill Vatter said:
Now I can go back to working on my 1924 Silver Ghost that has points, both in the distributor and in the magneto. (Two independent systems; two plugs per cylinder.) That stuff I can understand, even though there is a lot of it.
ok, I am jealous... :D

The pic was taken with the radiator fan removed (for more space to work, at least on the turbo where the downpipe is a bit awkwardly situated in front of the sensor)

For anyone else, here's the rest... CPS replacement (NG900 turbo)

The WIS actually has the tolerance on the distance of the CPS tip from the aperture disk. You can just see one of the holes (apertures) on the edge of the disk in the same pic.

Congrats on solving that, btw.
 
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