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S Max 1.8 TDCI fuel pressure drop during starting.


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(Follow on thread from my original one about not starting)

Car will not start, does one cough then nothing. Problem developed over a month when it slowly got harder to start then finally failed completely at fuel garage (engine warm at this point) and has not started since, despite lots of efforts. 

Fitted new glow plugs, no improvement, and run FORScan. Trace below shows fuel pressure for two consecutive attempts at starting, note pressure drop to zero occurs while still cranking.

Gave up and delivered to my usually trusted garage, they have dismissed air in fuel line and fitted new cam shaft position sensor, but no improvement and they now seem to be very short of ideas and I think would like to give up.

Any advice welcome, including anything else I can look at on FORScan since it is new to me.



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Many thanks rbitton782, no i have not checked the fuel pump and I have no idea how to check it.

Since this is a diesel, I imagine the pump is quite complex, my only experience of fuel pumps is the old diaphragm ones we used to have on petrol engines.

My feeling was that the pump must be mechanically driven and therefore must either rotate normally or not at all, hard to imagine it suddenly stopping. If it was worn, then could give low pressure but cannot see why pressure should suddenly go to zero.

The garage seem to think there is some sort electrical problem, I have no idea, but could there be some sort of dump valve which is activated by a signal from something?

Still not clear why garage have eliminated air in fuel pipes, whenever i change the fuel filter on this car, it will never start and  have to tow to garage for them to "bleed". Same garage that I am using now so must believe them on this point.

Certainly must not eliminate the pump, need to know more about its workings and how to test.

All information welcome and thanks again for your reply.




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Quoting direct from log book


  Variant QYWA1S

  Version EURO47CEA RG

Vin/Chassis/Frame No. WF0SXXGBWS6J06919

Engine No 6J06919

Cylinder Capacity (cc) 1753

Max. net power (kw) 92

Is there any way to test a fuel pump, other than replacing it and is there any logical process that a dodgy fuel pump could cause this characteristic of sudden pressure drop to zero.


Paul Longworth

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  • 2 weeks later...

Update - garage have concluded that the pump has failed and at a predicted cost of £1200, then advised scrapping, bill for their work £200.

Car now towed back to my house and deciding what to do. Only 140k and 11 years old so very reluctant to scrap. New pump on eBay about £400 but very concerned about how difficult to fit and not 100% sure it is the pump? There appears to be a pressure relieved valve on the pump with an electrical connection, could a fault be causing this to trip and drop the pressure.

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  • 1 month later...

Sorry for late update.

Major breakthrough, or so i thought. Unplugged electrical connection (1 of 2) on side of pump. Software then showed zero fuel pressure. Reconnected plug and engine started immediately, first time for two months. Turned engine off and then restarted ok with no hesitation. Went for 5 min drive, running ok, and turned engine off then restarted again with no problem. Left for 30 mins and tried to restart but no good. Tried pulling plug off and on many times but engine will not start again. With plug off then no pressure, with plug on then same as before, initial pressure thdn drops to zero during cranking as shown on earlier posted trace of fuel pressure.

Also purchased a priming pump and fitted transparent pipe after fuel pump, every time pipe is removed, air is sucked in but use of priming pump appears to remove air and fuel flows clean with no sign of air in transparent tubing.

Because I was able to start and run engine, albeit for a short time, then I feel the basic pump must be ok and therefore very reluctant to think of changing it.

Short of ideas but think next action will be the call AA man and tell a little lie, just in case he may come up with something, otherwise I will try and find a diesel specialist  and see how much they will charge. All very frustrating!!!!!



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Discussion with Diesel specialist in progress but just had a thought.

Error code indicates problem with cam sensor but not clear if this is simply because engine not rotating at the time and therefore no signal. Garage fitted new sensor and found no improvement so they replaced the old sensor.

It does seem funny that this fault keeps showing, it can be deleted but returns, I have a high level of trust in the garage, but I am just wondering if I should try this myself again? Could they have made an error or been supplied with a faulty sensor.

Any views?

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  • 4 weeks later...
  • 3 months later...
  • 3 months later...

Sorry for late reply.

Despite a pledge from the diesel specialist and transport cost of £80 they were unable to find the fault. Their conclusion was that the Engine management thingy was faulty and it would not be cost effective to continue any further and best to scrap.

The garage were very good explaining what they had done and that they felt unable to charge all the time they had spent on the job, I felt very frustrated but had faith in their explanations. They offered to arrange to scrap the car and pay me the balance, I think it went for £270 and they returned £80 to myself which paid for the original transport cost to the garage. End of car and end of story, would not want to get involved with any diesel cars again if I can help it.

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  • 3 years later...

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