1993 940T Random Engine Shut Down

[amazon]

I'm 4,000 miles into a cross country trip 3,700 since these spontaneous shutdowns have been occurring. Without any warning, the engine loses power and stalls. After 10 -20 mins it starts up great and we continue on sometimes for 30 miles or so, sometimes for 130. A few days it has not happened at all. I now strongly suspect that it is a heat related wiring issue under the hood as it has occurred with greater frequency in the hot humid weather of Tennessee & North Carolina. I'm a one time quasi Volvo Mechanic so along the way I have installed a new main fuel pump & filter; crank position sensor; in-tank fuel pump; and fuel presure regulator. As of now we are always able to restart when adequate cooling takes place. Engine temperature has never been up and there is no coolant use, radiator and all hoses are new. It has never occurred in the cool of the day or evening. We are now in that ugly megalopolis stretching from DC to NY so this is potentially a serious safety issue.

This is the most difficult type scenario to diagnose as it can’t be predicted, or made to occur, and the engine won’t run long enough to stop & get the hood up and wiggle connections or wires. The only code that shows up occasionally is 1-2-1 which suggests a wiring problem related to the Air Mass Meter but again, that could be anywhere. A post I read said that a similar scenario was remedied by replacing the Fuel Pump Relay. So I did that but to no benefit. I even did the old coil replacement which dishonest shops always pull on uninformed customers, but again to no benefit, so I now have a back up FP Relay & Coil.

Before I spring for an AMM I’d sure like to have some ingenious diagnostic tips to learn if this is in fact what is causing the problem. It’s a lot of money to spend on a hunch. TD

[93Regina]

...spontaneous shutdowns...engine loses power and stalls...

Those two descriptions are opposed to each other...so, spontaneous shutdown is the correct assessment.

1. Key Switch contact shooting craps

2. Radio Suppressor Relay's contacts shooting craps

After it shuts down, check voltage on an injector when cranking.

[lummert]

Do you have a spare ignition power stage?

[amazon]

What is an ignition power stage?

[93Regina]

What is an ignition power stage?

Power Stage Amplifier Story

From mildly annoying to bad to worse: a no start nightmare

[lummert]

What is an ignition power stage?

Bosch name for an ignition module.

[mika]

I do not think I will understand the intricate details of the b230X setup as much as the white block engines. it amazes me that I learn something new every single day with the red blocks.