Fuel relay

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Hello everyone I was out to day doing ok when my 1987 2.1 Dj died on me,I had to coast downhill because of traffic then tried to start it,but it wouldn't turn over got the RAC to take me home he told me one of the cylinders had had hydraulic meaning it had got full of petrol and wouldn't turn over. I took all the spark plugs out and drying out the XS petrol and it now turns out okay but The buzzing you normally hear for a few seconds when I turn it on to start,is continuous now I think it's the fuel pump relay that is buzzing anyone got any idea why doesn't switch off now because I think it's just over filling my cylinders with petrol.


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[autostart]

Hello everyone I was out to day doing ok when my 1987 2.1 Dj died on me,I had to coast downhill because of traffic then tried to start it,but it wouldn't turn over got the RAC to take me home he told me one of the cylinders had had hydraulic meaning it had got full of petrol and wouldn't turn over. I took all the spark plugs out and drying out the XS petrol and it now turns out okay but The buzzing you normally hear for a few seconds when I turn it on to start,is continuous now I think it's the fuel pump relay that is buzzing anyone got any idea why doesn't switch off now because I think it's just over filling my cylinders with petrol.

Apparently fuel is blowing by ALL the fuel injectors, as soon as the key is turned. The way the fuel system on the system works is, when the key is first turned one. the fuel pump starts for 2 seconds to pressurize the system. Now, even for those 2 seconds before cranking fuel blows past the injectors, and continues once you start cranking the engine. Whenever the fuel pump is running now, all the cylinders are getting gas, so essentially there is a continuous spray of gas into the cylinder. Any ideas please
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[syncroandy]

FP relay without the engine running sounds like a faulty ECU to me as it 'shouldn't do that'. Alternatively perhaps there's been some damage (eg. wear) to the loom causing a short to earth on the injectors 'cold side' and the FP relay trigger terminal, causing them to be 'on' all the time. Might be worth following the loom round the engine-bay and check there's no damage.

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Thanks for the reply went to my local VW place Mega bugs in Plumstead they checked the ECU for me working fine can't see no broken wires or fried ones i'm thinking it might be the fuel pressure regulator


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[ceetee25]

interesting. How did the garage test the ECU?
From the many tests I have done using voltmeter continuity it sounds like the safety cct for the pump which comes from the ECU is faulty and if its not functioning the pump will cont to run and fill up your sump with fuel as well as other places so thats an possible oil change in the offing.
So if they have electronically tested this bit thats good as the ECU functionality is difficult to test without proper diagnostic eq.

[Mr Bean]

I really haven't given much thought as to the finer details of the DJ fuel injection system. I just imagined the fuel injectors get a precicely timed (probably high current) pulse in the same way as the spark plugs get a precisely timed (albeit high voltage) pulse. Looking at my Bentley Manual I see both the wiring harness and the circuit diagram seems to show wires directly from the Fuel Control unit (I know this as the ECU if I have it right). This would indicate that the relevent business takes place within the ECU. The Bentley's does not seem to show a test for runaway fuel injectors!

If we are assuming that one or more of the injectors is putting out a continuous spray then either one or more injector is failed open or the FCU/ECU is commanding a continuous spray. Or as has been suggested that a loom wire is shorting over one or more of the injector wires bringing about the same result.

Based on my wide but but non-vehicle specific knowledge of electronic circuits the comparatively high current but short pulse required to operate an injector will probably be provided by a timed low current signal circuit which the drives a solid state device analogous to a relay which will handle the somewhat higher current required to operate the injector. Such devices have a tendency to fail in the switched on state and if this is the case then the ECU may be faulty although it must take some kind of crankshaft position sensor in a similar way to the ignition timing. So a faulty signal going into the ECU could be of interest.

I have to admit to being a fuel injection virgin so to speak but these are areas I would be looking into if my DJ had the same symptoms.

Hope this either helps or sparks off some more input.
CS

[ajsimmo]

Had one in that did this. Fitted my spare ECU and it ran perfectly. Yours may not be that.
Cannot be fuel pump relay, as that would just cause the pump to run, circulating fuel back to the tank via the FPR. If VW diagnostic procedure is followed, that would reveal an earth short in wiring loom to injectors.

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Well guys it was the ECU thanks for all your thoughts and suggestions.i didn't want to get one and find out it wasn't that,but after everyone pointing in that direction I took the plunge and bought a secondhand one. Thanks again


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