Hello all,
Could someone suggest what the problem is please?
BACKGROUND:
I have a manual 2008 2.0 CRDI Premium with 125,000 miles on the odometer. For the last few months, it's had occassional difficulty in starting - cranks over but no start. I noticed that the fuel pump in the tank was silent when this happened.
Once running, it's smooth and powerful, never stalls, no visible smoke or odd smells from the exhaust. It had a new battery 6 months ago and all voltages are currently fine. Starter-motor sounds strong. Always filled with premium diesel and oil changed every 4,000 miles.
Always, I start the car by waiting for the glow-plug light to go out, the fuel pump normally whirs away for a couple of seconds before shutting off and the car is ready to start. Recently, the fuel pump couldn't be heard to "prime" when turning the key.
REPAIRS SO FAR:
No ECU faults showing using the Torque app with a bluetooth OBD2 reader/adapter.
Glow-plug light comes on and off as normal.
I noticed that I didn't hear the fuel pump priming when it suffered a no-start. The pump had been noisy and sounding "laboured" (changed to a lower pitch), so I guessed it was time for replacement.
First, I checked the battery and alternator voltages - all fine. Then I changed the fuel-filter (which was due anyway) and swapped out the fuel-pump relay with the one for the A/C which is identical. The fault persisted.
I couldn't source a new fuel-sender assembly with the pump included so I found a replacement pump only. This was used to replace the old pump in the old fuel sender mounted in the fuel tank. As I understand it, this provides pressure to the high-pressure fuel pump powered by the engine directly. The inside of the tank, the fuel sender and the sock-filter were totally clean. The new pump sounded healthier and quieter when working (constant pitch), but the same problem occured - it occasionally didn't prime when turning the key which then lead to a crank-no-start issue.
After reading up on this forum about immobiliser issues (dodgy antennae in the steering wheel and keyfob), I first checked the orange/key light - it stays illuminated and doesn't flash when turning the key. This suggests the immobiliser is happy and is not stopping the car from starting by blocking the fuel pump from being energised. I checked the keyfob battery voltage, which was at 3.0 Volts, so changed it out with a new one at 3.3 Volts. No difference.
I cleaned the fuel-sender unit connector and the two ECU connectors in the engine bay. No difference.
THOUGHTS:
It seems that the car is less likely to start when the car is cold - the fuel tank pump is silent - crank no start. Only after repeated cycling of the key does the fuel pump then come on, after which it starts promptly and without any stumbling/smoke - totally normal.
Sometimes, the pump comes on whilst waiting for the glow plug light to go out.
Rarely, the pump is heard to prime but the car then still won't start.
This problem is now getting more frequent - likely a third of the time when starting.
Could it be a problem further along, like a fuel pressure sensor or regulator? How could I diagnose that?
I found an old post on here about a similar issue with a burnt-out junction box under the dashboard which carries power from the fusebox/relay back to the pump. This required "significant dissassembly" to find. However, my car runs fine once started, so surely power delivery isn't the problem, as I can hear the fuel-sender pump humming all the time.
Obviously I'd like to avoid a big diagnostic bill and solve this myself - I'd be grateful for any suggestions.
Thanks in advance!
