Hi!
I have a problem with this volvo 940 1994 wagon turbo.
I bough it used and the owner told me that it had a problem but that it found out it was the fuel pump relay.
He changed it and solved the problem.
After i bough it i noticed a short circuit by the fire wall in the engine compartment.
While driving, the car stalled.
I start it, the engine runs, but when i put it in gear, it stopped.
I did this several times, i almost drained the battery.
I let it cool off and i wiggled the wires by the fire wall and the car started.
When i got home, my friend who is a mechanic, but not a volvo mechanic,
start looking at the wires and wiggling them, and the motor almost stop.
There are two bundled set of wires going from the driver side along the fire wall and then to the engine and other places. One is thicker, (have more wires in the bundle), than the other.
I separated them and the car run for a year.
Now the car runs for about 20 minuted and stops.
The next day, i started it and it runs for about another 20 minutes or so and then stop.
I talked to a mechanic that works on volvos and he said that i have to take it to his shop and that at that time, the short must be present or he can not check it.
This happened during the hot summers in california, both times.
Maybe the short circuit damage the fuel pump relay???
Should i replace the fuel pump relay and see what happens?
Or how can i check fort a short circuit when the problem is intermittent?
I will appreciate any help.
Thank you.
Hector.

 

if you have flakey wiring in that bundle, you probably should fix it first before chasing other problems.

its not clear to me that this is necessarily a short circuit, it could equally well be an intermittent open circuit.

there's a couple big 53 pin rectangular harness connectors on the left side of the firewall where all the engine stuff is connected to the interior stuff,also 2 or 3 8 pin connectors behind the left suspension tower with lots of important engine stuff going through them

 

Hi pierce!
What do you mean with "intermittent open circuit" ?
I am not too familiar with electricity.

also, why does the engine stops after 20 minutes or so?
the car is not moving, the engine is on but the car is parked on the drive way.

Thank you.
Hector.

 

intermittent as in, not all the time.

an open circuit is something like a broken wire or connection. its not making contact, so the electrons can't get through, but its not touching anything else, so electrons aren't going the wrong way.

a short circuit is where there is an insulation failure, and either a circuit is shorting to ground, or two circuits are shorting together, and the current is flowing in places it shouldn't be. a short of a wire thats carrying voltage to ground generally results in sparks or meltdown, or blowing fuses.

 

when it stops after idling 20 minutes when cold, does it just run fine then poof, its stopped just like it was shut off, or does it start to struggle and drift into non-running?

I just had a idea... you should check your crank position sensor connection and wire. this is a frequent source of failures, and could be temperature sensitive. the CPS itself rarely fails, but the insulation ont he wires can crumble from heat and oil. the CPS is stuck into the back of the engine, just above the flywheel, near the back left (intake side) corner of the head.

Crank Position Sensor

 

HI PIERCE!
THANK YOU FOR THE EXPLANATION OF "intermittent open circuit" .
WHEN THE CAR STOPS AFTER 20 MINUTES OR SO, IT DOES IT AS IF I TURN THE IGNITION OFF, WITH THE KEY.
IT DOES NOT STRUGGLES OR HESITATES, IT JUST SHUTS OFF.
ABOUT CHECKING THE CPS, IS THAT HARD TO DO?
IT SEEMS THAT IT IS NOT VERY MUCH ROOM BETWEEN THE BACK OF THE ENGINE AND THE FIRE WALL.
SHALL I TAKE IT TO A MECHANIC, WHERE HE CAN LIFT THE CAR?

THANK YOU.
HECTOR.

 

the CPS is on top of the flywheel. its to the left side (your right) of the distributor, and below it. yeah, its cramped back there.

I'm not saying the CPS *is* your problem, its just one of many things that might do this. without the signal from the CPS, there's no timing, so the fuel and spark shut off, the engine stops.

 

Hi pierce!
But the car run for a year, during cold weather, then it re appear in the summer. It is weird.
Any other ideas?
Thank you.
Hector.

 

someone who knows how to diagnose car problems and electrics is going to need to look at it.