It was suggested earlier that you check the engine codes. Pierce sent you a link that explained how to do it. Did you try that?

Just because you switched the ECU and it started doesn't mean the ECU is bad. There are many items that fail intermittently before you get a hard failure. The only way to diagnose is like what Pierce said. Get a multimeter and wiring diagram and work your way from the pump back to the power source. Power to the pump is provided by a wire that runs from a relay to the pump. Check the at the pump first. No power? Then check on the output of the relay? Check power at input of the relay... and so on.

 

Does anyone have a good one that can be read? The only one I have found so far is from the our local library however the Chilton wiring book is so bad and the diagram is so smudged it is unreadable.

 

Just doing a google will yield lots of hits for wiring diagrams. I did it for your car and came up with this:

http://www.google.com/url?sa=t&rct=j...1uTRb1rhJ_F2Bg

 

except, a 1991 940SE is really a 960 turbo, its kind of a transition model, the I6 wasn't ready but the 760 was being discontinued. the 960's have major wiring differences from the 940's. the 940SE is reasonably similar to a 940T under the hood, but under the dash its completely different.

 

Yeah - but that PDF shows 940 and 940SE diagrams. They are different but both are there.

 

Thanks guys. I was reading the Diagram and if i'm correct it looks like the O2 Sensor is also wired into the fuel pump wiring system. Just using common sense here if that is true then would my brother running 87 octane in his turbo (Yea I Know no need to say it) would this cause the O2 Sensor to fail thus causing the shut down?

 

the O2 sensor is wired to the ECU (fuel injection computer), it uses it to fine tune the fuel-air mixture once the engine is warmed up. it really has nothing to do with the fuel pump.

the ECU also controls the fuel pumps, but all it looks at to turn the fuel pumps on is that the engine is turning (via the timing pulses passed from the ICU which gets them from the crank position sensor). moving engine== fuel pumps on. stopped engine == fuel pumps off 1-2 seconds later. its that simple.

 

Just Wanted to Update That the problems are fixed and the car is running beautiful again, Thanks to everyone for their help and especially Pierce..Could not have found the simplest problem without you

 

so what was it?

 

Well Pierce, The first problem is I completely over-thought the situation. Like you said a very simple robust system. What initially caused the problem was a crank position sensor. Why it was so hard is my Brother tried and tried to start the car draining the battery. (Hello?? If the car doesn't start in the first few tries You need to stop no matter how much you keep trying your efforts are futile) So he hooked up the battery charger (it was a old cheap kind) which has a bad surge thus frying the ECU..Thats when I came in..I didn't get all the facts till afterwards. Another helpful tip is if you must charge the battery please disconnect it and charge it completely. Do not trust Autozone to charge it completely for you. Im scrambling with all the info I was getting. so after the last post I just took a 2 week (get the heck away from it) vacation and then come back with a fresh mindset. Charged the battery fully for 2 days on a slow 2 amp charge. Cleaned all the wires that had contact with the battery, after installing the battery and reconnecting the wires I plugged in the ECU I turned the key and the second revolution the darn thing fired right up..Funny thing is my Dumb A** Brother was so frustrated he gave me the Pink and walked away so now I have a Beautiful sweet running '91 940SE Turbo 4 dr Sedan For Sale