Died while running – sudden loss of fuel?
 

Hi y'all!

I was just visiting some friends and while driving home and pulling over for a short stop the engine died just as I was coming to a halt. I think it was when a shifted to neutral (manual transmission). After that: won't start, cranks but nothing. I read the stickey and all belts turn and seem fine (the timing belt was done for a couple of years ago and has run maybe 20,000 miles since).

I can't say I'd notice anything out of ordinary and had plenty of fuel (refilled 60–70 miles ago). However I have the car as a summer car and it stands outside in the winter (in Finland, so it's proper winter with subzero temperatures). I left the tank with 3/4 of fuel. This season I have ran it for some 350 miles without problems.

Today, I was thinking about biking out to the countryside where it left me with a multimeter, some fresh fuel, a fuel filter (hasn't been changed during the five years I have owned the car – but I'm pretty sure the sole prior proprietor, my grandfather the cabbie, did proper maintenance), some wrenches. If this doesn't help I think I'll have towed to a nearby shop on Monday.

After studying the posts I was thinking about the following procedure: checking for air bubbles in the hose between filter and injection pump, checking hardline no. 1 if the system is primed, checking shut-off solenoid (clicking sound, voltage), priming and changing fuel filter. Does this seem as feasible course of action?

I was thinking that a clogged fuel filter might have done it, but after reading it seems that there should have been some warning signs and there were none. The only thing out of ordinary I noticed earlier on was abnormal fuel consumption (maybe 50% more) deeming from the fuel gauge readings. But after refueling and doing the math (13,7 US gal/~410 miles (52 litres/660 kms)) consumption doesn't seem out of ordinary. But I do think the fuel gauge behaved abnormally previously but not during this trip's 80 miles.

Thanks in advance and so happy that this forum exists!

A quick update
 

So I went there and tested it out today but couldn't get a positive result.

There were no air bubbles in the fuel hose to the IP and loosening the hardlines produced some drops of clear fuel. I filled the filter and screwed it on, cranked but alas! to no result. So as I had help I towed it to a nearby shop where the mechanic had worked on VW engines. I'll let you know what went amiss.

Welcome!

Sorry to hear of the trouble but hopefully the cause is something simple.

It think you are on the right track with troubleshooting so far. The things you mentioned checking are exactly where I would start also. Basically there are three things that could be causing this:
1) Air entered fuel system (a hose connection or the fuel filter loosened up) or a blockage occurred in the tank or something in the fuel supply caused aeration or restriction.
2) Loss of function of the fuel shutoff solenoid in the injection pump (solenoid failure or loss of voltage supply).
3) Base engine timing problem (slipped front or rear timing belt).

There could theoretically be a 4) loss of airflow due to blocked intake or exhaust, and a 5) sudden internal fuel injection pump failure, but those are both very unusual and unlikely compared to the first three.

Sounds like you will probably get the problem figured out in short order, but here are a couple of quick questions if it continues to be difficult to pinpoint:
- You said the engine was running completely normally right until it shut off. Maybe more fuel use but it might have just been the gauge. So, no other indications of trouble? Loss of power, harder starting etc?
- Did you check the fuel shutoff solenoid for voltage and clicking when actuated, as you mentioned planning to do? Something as simple as a blown fuse could deactivate that solenoid. The fact that you still saw a little dribble of fuel at the injectors doesn't necessarily mean the solenoid was opening, since a small amount of fuel still gets past it even when it's closed.

Fuel shutoff solenoid not functioning would be my first guess at the cause of the issue. On my '86 745 it used to blow fuse #13 occasionally and show this exact symptom, until I found a shorting wire to the A/C compressor that was on the same circuit.

If fuel is being delivered successfully to the injection pump but still not making it to the injectors even when that solenoid is confirmed to have +12v, you can also unscrew the solenoid and remove the plunger to determine whether the solenoid itself has failed.

Let us know what you find. :)

Thank you for the advice. There was no multimeter so I had to resort to sensory diagnostics, i.e. listening. And I thought I heard it click, then again as I never have listened to the solenoid I was not sure what to listen for.

Interesting with fuel supply at the end of the hardlines. There certainly wasn't any squirting just a trickle/moistening around where the injector/hardline connect, visible nonetheless. I sure do hope it's the solenoid replacing it didn't seem like a terrible hassle.

The supply of fuel(?) was really instantaneous.

Electrical malfunctions have not been completely unknown to the car: there was a jerry-rig solution in the dashboard (can't remember exactly to what end) which caused the generator to eventually fail 1,5 years ago. The only symptom at first was the tachometer loosing its reading from time to time. This was then fixed but I can't say with what solution and if that solution might cause short-circuiting.

I'll keep yo posted.

This might help:
Use a jumper wire long enough to clip to the solenoid connection and touch the other end to the battery positive. You should be able to hear the dull muted "thunk" of the solenoid, when you touch the wire to the battery positive, and again when you remove the wire. Compare that sound to what you hear (or not) when a helper turns the ignition key to the on and off positions (not start).

Problem solved
 

It was the solenoid. Fuse blown, such a rookie mistake not looking for it in the first place! But the ultimate reason for shorting out remains a mystery. I'll need to keep this in mind. Additionally, there were some leaky return lines and thus some air in the system. But this is now fixed. So, that's that. Thanks for the advice! So nice to that you guys were right on track from the beginning.

I'll keep rolling, a bit wiser :D

(Also note to self and others: if the pump works the injectors squirt, a little moist around the nut is probably just residual fuel leaking out.)

Good to hear it was something simple. :)

I don't know how many electrical differences may or may not exist between my 1986 US market 740 and your 1991 European market 940, but on my car, the exact same phenomenon of intermittently blowing fuse for injection pump power was caused by a chafed wire to the A/C compressor clutch. The wires were riding right on one of the A/C pipes, and had rubbed through in a spot and were shorting to the pipe. That circuit shared the same fuse as the IP/GP system and would pop the fuse and stall the engine when the wires shorted. It was hard for me to find because it would only happen intermittently when the engine moved a certain way, AND could only happen when the A/C clutch was being energized. But once I realized that it was only happening when the heater was running in the Defrost setting, I had a clue. ;)

You could start by checking that in case it's the same. Not sure what else is on that circuit in your car. Check all the wires around the injection pump too. All the emission control switches (on the throttle lever) and the altitude compensation solenoid in the bottom outer side of the injection pump are powered by the same main IP circuit as well. Same with the wiring to the EGR control solenoid, if your car has one. If any of those is disconnected and able to short to the IP case or engine, or if any has a chafed wire, then that will cause your issue. And finally, the glow plug control system also operates on this same circuit, so check the 4-wire harness going to the glow plug relay in the left hand side of the engine bay for any wires with bad/chafed insulation that could be shorting to each other or to ground somehow.


Agree on what you noted at the end. That is also something true that I have seen (and almost been tricked by a few times). If the solenoid is not opening, then fuel WILL still make it out to the injectors when you loosen the union nuts and crank the engine since a little bit of fuel does still make it past the solenoid plunger -- BUT it will only be a tiny amount, not nearly enough to start the engine. If the solenoid is working correctly and the pump is primed and turning, you should see big squirts of fuel out of the unions when cranking, not just a couple of drops. :) When you see the big squirts, then assuming the GP's are working and everything is in correct time, the engine will start.