Hi,

I am getting random stalls anywhere between 2 to 40 minutes apart.
Symptoms: At highway speed, the tach goes to 0, however the lights on the dash do not turn on until I put it into neutral as the tranny keep the engine turning. When trying to start right away the tach does not move, except for a little jump as the key goes to position II.

It will start and run perfectly after 2 to 5 minte rest until the next "fit".

The car is 1989 740 Turbo with BOSCH ignition , it has 200K miles on it.

I had identical symptoms at around 100K miles, the culprit was the Hall sensor in the distributor, so I figured this is the same thing, unfortunately it is not.

This is what I did so far, with absolutely no effect on the stalls, even though the car runs noticably better:

Attempt 1/ Replaced spark plugs, ignition wires, the distributor [ expecting the problem to be a rerun of the hall pickup problem] and also the fuel pump relay as it has about 80k miles on it.

Attempt 2/ Cleaned all contacts and connectors under the hood: connectors A,B,C and E, Igniton Module connector, Ignition coil, grounds....etc.

Attempt 3/ Swapped the Ignition Module - I had a used one from a parts car that I had at one time.

DEBUG I did so far: When car is running, I pulled out all relays, except for the fuel relay, the car keeps running. Pulling the fuel realy or the "radio relay" under the hood stops the engine - as expected. The "radio relay" is only a year old.
The connector and the wire to the hall pickup look OK - at least the section under the hood.
Pulling fuses 12 and 13 did not stop the engine.
Pulling the fuse for the intank fuel pump did not stall the engine.
Pulling fuse for the main fuel pump stalls the engine - as expected.
The fuel pump can be heard as the ignition key is turned just before it start to crank, whether the car starts or does not start.
I put an engine analyser in my car, so that next time it stalls someplace I can confirm my suspicion that I am not getting a spark. I do smell the fuel out of the exhaust when cranking and there is no start

Random events that may or may not be related:

a/ Stomping hard on the gas or brake pedal "appears to trigger" the engine to start after the stall, it also "appears that hitting the concsole at the hight where the relays are "may" effect a faster restart.
b/ Under the hood: Hitting the connectors/ignition module with a rubber handle of a screwdriver does not cause earlier start, however once the idling engine stopped when I hit the connector B [ driver side under the hood hinge] - however I could not repeat this. - Maybe the stars alligned for this one...

Unfortunately all of the events are so random, that I can not correlate what I did with what happens on the car. I wish that the car would just die, so I can follow the schematic and trace the problem.

The car was never in an accident, the dash was never taken out, so I do not expect pinched/broken wires.

I only had one problem with wiring, I had to replace a ground wire from the switches in the driver door going to the car chassis, as the wire between the door and the car broke.


Suggestions on what I should do next would be greatly appreciated. Thank you in advance.

 

could still be the same thing.

but... the tach going to zero indicates your ignition has stopped, maybe its he power module.

 

Hall Sensor.

 

Thank you for the suggestion, greatly appreciated.

There is a new Hall Sensor, as I replaced the distributor - no guarantee that the new sensor is not defective....

The last 3 things that I did were:
1/ clean again and relubricated the A,B,C and E connectors and the Ignition Module connector - for those of you that do not have the Volvo schematic, these are the harness connectors just under the hood hinges. I also took 2 pliers and push in on the wires on both sides of the connector to make sure that they are seated. At this time my bet is 90% chance of this being the problem.
2/ As the Ignition Power Module was very hot when the car was running, I cleaned the heatsink and the module, put on some Arctic Silver and I got an 6" L-bracket to which I mounted the Volvo heatsink and mounted it higher away from the battery. The L bracket becomes additional heatsink, the ignition module is now pretty much at ambient temparature.... I do not expect the heat to be a problem - this looks nice and keeps the electronics in the module cool and away from the battery acid.

So I drive the car, put on about 350 miles about 8 hours driving, the car runs realy nice - I was sure this was fixed.. Well no, it stalled again. And same thing in few seconds it starts and stops and start and runs like nothing is wrong.

So I started tapping things with the rubber handle of the screwdrier.. The moment I touched the connector under the driver side hood hinge the car stalled. This is second time this happened. So I am fairly sure that there is a poor connection ether in the connector or in the crimping of the pins to the wires.

I am going to connect the wires directly and take out the connector. As this solved my problem with the untilock brakes randomly kicking in then turning on the brake light.

 

I did not redo the wiring to get rid of the connectors... somehow I no longer feel that they are the problem.

I had another series of stalls today.
It started after I shut off the car for about 10 minutes. No amount of wiggling, reconnecting and tapping on the harness connectors made any difference.
Once it started it run 5 minues, then one more stall, then it run fine for about an hour.
I had all of my tools, unfortunately I did not have the schematics with me. so I was not able to confirm anything, other then having 12 V on both sides of the ignition coil and 12 V on 2 pins on the ignition module and about 0,2V on one of the other pins.
I was able to confirm that there is no spark.

I do not know if be chance, it started by me stomping on the gas padal and holding it down.. I do not see if and how this would have an effect, the throttle is mechanical.


I am starting to think that it is the new hall pickup in the distributor as Pierce and Lev stated. What are the chances that the hall pickup in a rebuild distributor that I put in would be defective?
Please let me know what you think I should do next.

 

I decided to look under the dash, as stompimg on the brake or the gas pedal helped to start the car.

There is a control module directly above the gas pedal. I could repeatedly stall the car by pushing on the connector. I cleaned/lubricated the connector, the car runs well now, lets hope is stays that way.

Again, thank you for suggestions.

 

I think thats the ICU. on LH2.4 cars they moved it over next to the ECU on the passenger side.

 

I checked the schematics, yes that is the ICU {Ignition Control Unit} as Pierce stated.
The root of the problem was that the metal latch holding the connector in place allowed close to 1/4 inch in/out play, as if they put in a wrong latch in the factory. After cleaning/lubricating the terminals, I used good old plastic cable ties to ensure that this no longer moves in and out.
Hopefully this helps someone else with same or similar problem/s as I think that I touched on must of the common under the hood things that can cause intermittent stalls when the ignition stops = tach goes to zero..

Oct 22 update: The ICU connector was it, the car is running realy well, no hickups of any sorts.