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Old 23rd March 2020, 15:12   #1
Geoff130
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Default CDTI struggles over 2000 RPM

My CDTI has been running fine since changing the fuel pump relay (Intermittent starting) and unplugging the MAF sensor (wouldn't rev over 3000 RPM) Recently it's learned a new trick, somewhere around 2000 to 3000 RPM it feels like it's misfiring and won't rev any more. It's not always at the same point and sometimes it's not evident until really pushed. TOAF says the LP pressure is a little over 3 bar at idle and drops to 3 when revved, no ECU faults. Any ideas where to start looking. It may be a coincidence but this started after I topped up the tank with about 10 litres of fuel. I did check the receipt and it was definitely diesel.
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Old 25th March 2020, 18:34   #2
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Today just to be sure I checked the plenum was dry and it is, tried with and without the MAF but no difference and also disconnected and blanked off the control pipe to the EGR still the same.
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Old 26th March 2020, 19:16   #3
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A failing crank sensor has been known to cause a misfire at higher revs.--
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Old 26th March 2020, 20:15   #4
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I had virtually exactly those symptoms. For me it was one of the wires going to the injectors, get some one to hold it at set revs and have a good wiggle on all those wires going into the injectors. It was a break as the wire entered the plastic connector. I got a full new harness from a scrapper and that sorted it.
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Old 28th March 2020, 15:31   #5
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Thanks, as I've got a bit more time on my hands than usual i'll take the loom off from the ECU and check it all end to end.
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Old 25th April 2020, 12:04   #6
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I have now tried wiggling the injector harness as suggested with no effect but I did find the ECU end of the harness came off quite easily so re-seated it but still the same. I've also tried a new filter but no change. I've just checked the fuel flow and it's around 1.5 litres/min at the inlet to the filter. When driving it won't respond to the throttle over 2000 RPM then suddenly will shoot off at full power then die again. I have noticed with the ignition on but engine not started the under bonnet pump is running continuously, is that correct?
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Old 25th April 2020, 12:07   #7
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When I had the problem that the engine would not run over 2000rpm, it was a fault with the fuel rail pressure sensor.
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Old 25th April 2020, 12:21   #8
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The underbonnet pump runs until back pressure stops it. In other words when it has reached the set pressure. Yours evidently does not reach ‘working pressure’. Is your intank pump working?
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Old 25th April 2020, 13:14   #9
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The in tank pump sounds like it's continuously too. There's a tee after the filter, one leg goes to the high pressure pump the other seems to go back under the filter somewhere. Is that anything to do with the fuel cooler?
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Old 25th April 2020, 20:34   #10
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Quote:
Originally Posted by bl52krz View Post
The underbonnet pump runs until back pressure stops it. In other words when it has reached the set pressure. Yours evidently does not reach ‘working pressure’. Is your intank pump working?

Both pumps should run continuously all the time the engine is running, and if you turn the key to position II but don't start the engine they should run for around 30 seconds or a minute depending on which ECM is fitted, and then time out.


Quote:
Originally Posted by Geoff130 View Post
The in tank pump sounds like it's continuously too. There's a tee after the filter, one leg goes to the high pressure pump the other seems to go back under the filter somewhere. Is that anything to do with the fuel cooler?

No, the tee after the filter goes to a pressure relief valve and then back into the inlet side of the UBP to prevent over pressure in the LP circuit.

Bit more info in post #4 here:


https://the75andztclub.co.uk/forum/s...d.php?t=172055





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Last edited by Mike Noc; 25th April 2020 at 20:37..
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