Hi I'm new here and was hoping that one of you folks would have experienced this or at least help me figure it out. I am trying to figure out why there is no power to the 10 amp fuel pump fuse.Drove the car all day with no issues at all.. The next morning it just wont start. Found it wasn't getting fuel..I have replaced the tank pump thinking a shorted pump would disable the system, I have replaced the in tank Fuel Pump, Nothing. The fuel pump relay, Nothing, and pulled the under car fuel pump and checked it and its fine. I don't get it?? what could it be? I went to the library to get a wiring diagram and the Chilton's Mechanic wiring bible but it was so smudged I could not even read it..I am at you guys mercy, please help

 

fyi, a 940SE is actually a '960 Turbo' although it wasn't marketed as such. there's major electrical differences behind the dash between a 940SE and a regular 940. Although the engine compartment is pretty similar to a 91 740/940 turbo, the wiring is quite different.

those chilton books are pretty useless, you need the Volvo 'greenbook' wiring diagrams specific for the model/year car.

off the battery positive, there is a yellow-brown wire, that goes through pin 10 of the big block connector at the left A post, and to the fuse panel on the left end of the dashboard where it goes through fuse 31. one yellow-brown wire from that fuse goes to the fuel pump relay pin '30' where it provides the power for the ECU side of the fuel injection/pump relay as well as both coils.

the ignition key power goes to the ECU and when it sees the ignition is on, it powers the ECU half of the fuel relay... this provides power to the rest of the ECU, it powers the coil of the 'radio suppression relay' under the hood (which powers the fuel injectors).

When the ECU sees the engine is turning over, it turns on the other half of the fuel pump relay which powers the fuel pumps. the tank pump is on fuse 30 but the main pump is direct off the relay, this is all via 'pink' wires, starting at the 87/2 output of the fuel pump relay.

 

Pierce I could dang near kiss ya..Thanks so much..

 

I traced everything to the ECU and checked the small pink coming from it when cranking and got power from it..Where is the Radio Suppression relay? and what does it look like?

 

the 'radio' relay is under the hood. not sure exactly where on a 940SE, but I'd suspect the relay bracket on the left fender wall. it looks like a pretty ordinary relay. it provides power to the fuel injectors.

hey, look! its a 1991 940SE!!! (my son's old beater car, too many desert dirt roads)


I *think* its forward of the left side suspension tower, kinda down near the battery. its NOT that power module visible in the picture, I think thats the ignition power module.

 

I try again tomorrow..This is a major challenge for me..I build hot rods not volvos...lol..am I on the right track as far as the ECU? thats the right wire to check as car is cranking correct?

 

I don't think the starter wire goes to the ECU. oh, hah, it does, pin 30 of the ECU, lookatdat. afaik, the starter just tells the ECU to richen up the mixture a bit. what really counts is the timing pulses from the crank position sensor (CPS)

yellow-black wire from pin 20 of the ECU is the signal that tells the fuel pump relay to turn on the fuel pumps. it floats high when the fuel pumps are off, and the ECU grounds it to 0V to turn on the fuel pumps.

the timing input to the ECU is on pin 1, a yellow-grey wire, this comes from the ICU, and is a cleaned up version of the CPS (Crank Position Sensor) signal. pulses on this tell the ECU how fast the engine is turning so it knows when to inject fuel. also the fact that its turning over at all tells it to turn on the fuel pumps (about one second after the motor stops turning over, the ECU shuts off the fuel pumps).

btw, you might find this handy
http://www.volvoclub.org.uk/faq/Engi...eSymptoms.html
your car is LH2.4 (LH2.2 was used from 84-88, and on 89 turbos).

go through the 'no start' troubleshooter there. this is really one of the simplest fuel injection systems out there, very robust and reliable normally.

 

Well got it down to the ECU being the fault..Replaced ECU, Started right up ran fine. Next morning Took it off the jack went to start it...It did it again..Same thing..Something is frying the ECU..Any clues? Like I said before prior to all this it was running great and shut it off and the ECU goes bad? make absolutely no sense

 

Any other Ideas Pierce?

 

dunno, I've never had a ECU on a 2.4 system go bad.

that link on my previous post has a whole 'no start' troubleshooting sequence.

 

Have we ruled out the flywheel pickup (CPS) at this point? Do you see the tach move while cranking? I think it odd so see the computer fail. Also, by replacing the ECU, do you mean the fuel injection ECU of ignition? One other thing, are you getting any codes from the little on-board box? I don't know how versed you are on using that.

 

It fired right up as soon as I replaced the ECU. Then the next day after sitting overnight it stopped working again..Im not sure how to get any codes

 

OBD: Engine and OBD Diagnostic Codes
perform DTM1 on the ECU (pin 2), if you get code 1-1-1, the ECU processor is running so its not totally dead, and it thinks everything is OK. if you get any other code other than stone cold silence, then the ECU processor is running and the code says something which may or may not be pertinent.

 

Sometimes these pickups can fail intermittently. It still may not be the problem, but the ECU I think is fairly unlikely. And I hope it's not it. Which ECU did you replace?

 

what ECU number on it ? last 3 digits of the 0 280 000-937 number... a 1991 B230FT could be a 937, a 563, or a bunch more. do you have EGR? that requires an EGR specific ECU like a 933.

somewhat incomplete reference table: http://www.volvoclub.org.uk/faq/Engi...ReferenceChart

 

ECU Number 0 280 000 530.
Whats confusing me is the clues..in the beginning it was running great, then out of nowhere after siting overnight it wont start anymore..replaced just about everything and the moment I installed a new ECU it started right up, I started it 3 times and let it run for a bit during these times. Put it all back together and let it sit overnight again and the same problem came back..

 

huh. -530 isn't even on that list of ECU's, and its a lower number than even the LH 2.2 ECUs, and I'm pretty sure you have LH 2.4 in a 1991 940SE. are both your original and this replacement one -530 ?

 

Ooops...sorry meant 560

 

Anything?

 

if you've had two ECUs actually go bad, I'd have to suspect a short in the wiring harness.

I would not want to hazard a guess where this short is. its quite possible both ECUs are fine and the short is intermittent and stopping things from working.

I'd be in there with the wiring diagrams and a multimeter testing things, but I don't want to do that remotely.