unofix Posted July 10, 2022 Share Posted July 10, 2022 I'm after some information about the engine compartment fusebox on the Focus Mk4 diesel. (Pictures posted below) According to the owners handbook the fuse for the diesel fuel pump is number '4B' 20Amp (although the diagram shows only '4A' which is for petrol.) Looking from the front of the car, plugged in to the top of the fusebox are two large multiway connectors. If I've worked this out correctly the connector on the left is the one which supplies the diesel fuel pump (and many other things). Can anyone [help please if you can @iantt] confirm the connector pin for the diesel pump ? is it perhaps pin 46 ? Is the wire colour for the pump Violet ? I would have expected removing fuse number 4 (20 Amp) to cause the diesel pump not to run (which might be true) and the car would eventually run out of fuel and stop, which doesn't happen !! Anyone know why the engine doesn't stop ? Quote Link to comment Share on other sites More sharing options...
iantt Posted July 10, 2022 Share Posted July 10, 2022 Yes, yes, yes, not sure. 1 Quote Link to comment Share on other sites More sharing options...
Tizer Posted July 10, 2022 Share Posted July 10, 2022 Could that one maybe for the Tank lift pump if your car has one and either the car still ran on the high pressure pump only or you did not leave it long enough. F4 on my Petrol car is also marked for the Fuel Pump but to kill the pressure in the fuel system you need to pull the one above F50, which is either 46 or 48, the number is a bit blurred in my online manual and there is nothing shown for it in the legend. And to confuse things further it is called F68 in a copy of the official manual that I have seen. 2 Quote Link to comment Share on other sites More sharing options...
TomsFocus Posted July 11, 2022 Share Posted July 11, 2022 I wonder how much 'syphon' effect there is on the HP pump in the later cars with a lift pump as well? If it'll keep pulling fuel once running, you should be able to idle for a while with all of the fuel in the filter...in fact, I reckon you could probably drive a mile or so from the filter capacity alone. (Estimate 100ml?) 1 Quote Link to comment Share on other sites More sharing options...
unofix Posted July 11, 2022 Author Share Posted July 11, 2022 28 minutes ago, TomsFocus said: I wonder how much 'syphon' effect there is on the HP pump in the later cars with a lift pump as well? If it'll keep pulling fuel once running, you should be able to idle for a while with all of the fuel in the filter...in fact, I reckon you could probably drive a mile or so from the filter capacity alone. (Estimate 100ml?) Well with the fuse removed the engine continued to run normal for just over 1 minute. Then the service spanner came on and the engine was limited to exactly 2000 RPM. I kept it running at about 1800 RPM for 10 minutes and concluded it was never going to stop. After switching off, replacing the fuse and restarting the engine the service spanner was no longer on and the car was back to full operation with no problems. A scan with FORScan showed a number of DTC's logged all related to fuel (or lack of it) but none were active and cleared without any issue. As you have probably already worked out, the purpose of the experiment was to see if disabling the fuel pump would be a possible way to immobilise the car. Answer seems to be it only slows it down, so maybe I could run after it if it gets stolen 🤣 4 Quote Link to comment Share on other sites More sharing options...
Tizer Posted July 11, 2022 Share Posted July 11, 2022 4 hours ago, unofix said: Well with the fuse removed the engine continued to run normal for just over 1 minute. Was that F4 or the other one?. I haven't tried to pull either on my Petrol car and I guess the difference with my car is it that it has a Returnless fuel system so will retain all its pressure at switch off. There must be another way of either killing the Injectors or the HP Pump on your car but it may not be a dedicated fuse. 4 hours ago, TomsFocus said: I wonder how much 'syphon' effect there is on the HP pump in the later cars with a lift pump as well? If it'll keep pulling fuel once running, you should be able to idle for a while with all of the fuel in the filter...in fact, I reckon you could probably drive a mile or so from the filter capacity alone. (Estimate 100ml?) I would have thought it would run almost normally if it was already running but would be difficult to start. 1 Quote Link to comment Share on other sites More sharing options...
unofix Posted July 11, 2022 Author Share Posted July 11, 2022 19 hours ago, Tizer said: F4 on my Petrol car is also marked for the Fuel Pump but to kill the pressure in the fuel system you need to pull the one above F50, which is either 46 or 48, the number is a bit blurred in my online manual and there is nothing shown for it in the legend. And to confuse things further it is called F68 in a copy of the official manual that I have seen. By God sir I think you have it !! I read your reply before but couldn't understand what you were meaning BUT having looked again I see what you were telling me. The Ford owners handbook has a picture of the fusebox which is just as poor quality as the one I posted above which has caused the problem. Fuse 4B which is for the petrol pump is NOT in the same location as the one marked 4A. As you were telling me the fuse I need to pull is the fuse above the one marked F50 and having looked very closely at the picture I can now see the fuse above F50 is in fact "4B" but due to the poor image quality it looks in the book to be "48" Need to recheck and see if I do have a fuse 4B, and if so what happens when I remove it. 2 Quote Link to comment Share on other sites More sharing options...
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