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Old 05-24-2020, 02:53 PM   #1
SLOTh_244
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Default 95 940 died on road, started right up

Guys

Was driving my 95 940 yesterday and the rpms dropped to zero, but the engine was still rotating. Pulled over and it started right back up. No CEL my tach had been sporadically jumpy once in awhile. My initial thought is that the coil might be starting to go out. Thoughts?
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Old 05-24-2020, 02:55 PM   #2
2manyturbos
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Crank position sensor or ignition module.
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Old 05-24-2020, 02:56 PM   #3
SLOTh_244
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So it pulls rpm from crank instead of coil like the 240s?
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Old 05-24-2020, 08:54 PM   #4
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IIRC, one way to see if it may be the ignition module aka power stage is to crank it and see if the tach needle moves.

If the engine cranks but the tach stays at Zero it could be the ignition module.

They wear out over time, and these bricks last a long time.
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Old 05-24-2020, 08:57 PM   #5
hessam69
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Fuel pump relay for a start
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Old 05-24-2020, 09:55 PM   #6
oldschoolvolvo
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Does it have Bosch Jetronic or Rex/Regina EMS?

On a Bosch system I’d suspect the ignition module aka powerstage. I had some similar symptoms and they were resolved by separating the powerstage from its heat sink, cleaning both halves thoroughly and reapplying some thermal paste between the two components. The powerstage generates heat during normal operation and if it cannot dissipate the heat properly it can cause issues.
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Old 05-24-2020, 10:53 PM   #7
SLOTh_244
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Quote:
Originally Posted by hessam69 View Post
Fuel pump relay for a start
I have had relay problems on other cars before, never had them start right back up without any cool down time. If the powerstage doesn't work I can try swapping the relay from my 91 in.

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Does it have Bosch Jetronic or Rex/Regina EMS?

On a Bosch system I’d suspect the ignition module aka powerstage. I had some similar symptoms and they were resolved by separating the powerstage from its heat sink, cleaning both halves thoroughly and reapplying some thermal paste between the two components. The powerstage generates heat during normal operation and if it cannot dissipate the heat properly it can cause issues.
Its Bosch. I've swapped in a spare ignition module, we'll see what that does. Its in the 90s here so i could totally understand it overheating.

I'll report in a day or two
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Old 05-25-2020, 09:09 AM   #8
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Originally Posted by SLOTh_244 View Post
So it pulls rpm from crank instead of coil like the 240s?
No, rpm comes from coil. But if crank sensor is dead, no ignition-> no spark.
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Old 05-26-2020, 09:52 PM   #9
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I'll keep testing, but took a drive on my spare power stage with no issues today. I cleaned the original powerstage and put arctic silver 5 thermal paste on it. I may test it too.
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Old 05-26-2020, 10:34 PM   #10
ZVOLV
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Wiggle test the crank sensor and see if it stalls.
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Old 06-03-2020, 05:54 PM   #11
SLOTh_244
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thanks for the help guys. Been driving for a week now and no issues with the car after swapping the powerstage.
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