2.0 HDi 90 - fuel temp sensor

[pauldoubleyou]

Hello everyone. My 307 HDi90 (of which the engine is in allsorts) is pretty lumpy and poorly running when its very cold. Im not on about starting issues - it will kick into life fine. I mean firstly it will run like it is on three cylinders for about 3 seconds when started, and when driving it is hesitating when not on boost, coulpled with jerks of acceleration when the pedal is held steady, almost like it is on boost and the wastegate is opening and it is dying off.

Any temperature over about 6 degrees and its fine. It also runs fine once the engine has hit about 70 degrees.

Just had a full service, turbo is fine, literally the only thing I havent changed is the fuel temp sensor (bear with me im getting to the point) - which on PP2000 is reporting at 90 degrees temperature when its 2 outside. MAF is fine (no change when unplugged) and the air intake volume is in the band through diagnostics.

Could this be the culprit? I dont want to disturb it if not as its integral to the fuel filter etc and Im sure it will snap something.

[ekjdm14]

Most possible, I would imagine.

While not having any direct experience with the way the HDi "brain" functions, I would imagine that when it thinks the fuel is hot (and thus less viscous) it would perhaps lessen the rail pressure &/or injector duration in order to correct the flow (I'm thinking hot thin diesel would move quicker through an open injector than cold, more viscous fuel).

Where I do have "kind of" experience, is with the Bosch fly-by wire pumps used on some VW TDi engines (and my old Nissan Largo too) where a common running/idling/stalling fault is caused by a fuel temp sensor out of range. In this case the sensor is integral to the pump, and told the ECU that the fuel was over 100c, and the fix I applied was to add a resistor in series to make it think the fuel was at a more "average" temperature.

I suppose you could try similar if you could unplug the sensor and substitute it with a resistor at a value that would tell the ECU the fuel was at, say, 10c and then see what the driveability is like when cold...

All the same, what's the mileage on the car? I believe the fuel filter should be changed at something like 40k anyway and many don't because of being that big complete assembly. Maybe would be worth just changing the whole thing while you're about it, then you at least know the filter is good for another few years as well.