LDV extended crank starting

LDV Maxus Engine code: R2516L VM39/40B 2.5CRD

I was called out to this vehicle, as it was causing the garage a lot of frustration.

The vehicle is a 2008 LDV Maxus and these vehicles present a lot of problems for the independent repairers, as most of the aftermarket diagnostic scan tools, do not have good or reliable coverage of them.  Also there is little or no service documentation availability.

The vehicle drives perfectly ok, once started, it just struggles to start especially from cold.

The garage had replaced the glow plugs and the relay to no avail.  They did manage to pull a code from the injection ECU, using a generic EOBD scan tool.  A P0335 crankshaft sensor malfunction.  They replaced the sensor and, whilst in the area, checked and cleaned the target wheel.  Still no change.  This was the time they called me.

I was able to communicate with the injection ECU and confirmed there were DTC’s for crankshaft sensor, amongst other codes.  However the interpretation of the codes present were not reliable.  I could see live data and selected PID’s for engine RPM, fuel rail pressure, and cam/crank synchronization.  I gave the engine a start command and was able to witness all PID’s reacting, including engine RPM and fuel rail pressure.  Unfortunately, I couldn’t rely on the cam/crank sync PID, as it displayed number codes instead of yes/no status.  It did however prove that the crankshaft sensor was working.

So I set up the scope to monitor some key information.  Crankshaft sensor signal, camshaft sensor signal, fuel rail pressure and battery current.  At this time I was particularly interested in the starter motor current, as this is easily overlooked and can cause just such symptoms.

Starter current
Starting current showing relative compression, cam/crank sync and fuel pressure

As you can see; this test has shown me the start up conditions.  It also allowed me to capture the cam/crank sync pattern, hopefully to research and verify.  The battery current checked for relative compressions and starter motor draw and as you can see proved fine.  The engine clearly failed to start.  I then took another capture, only this time replacing the battery current with injector no.1 current.  This showed me that the injectors were not being switched on, either because there was a fault with the voltage supply to them or because the ECU was inhibiting them.

Starter up sequence with injector no start
No start condition as illustrated with no injector operation

I had noted that the crankshaft sensor fault, which I had cleared previously, returned.  This made me suspicious of the valve timing, as the fuel drop off and no injector operation, is a fairly normal strategy for a cam/crank sync issue.

I checked my library files and found no entries of such a vehicle, so I looked on the Pico library.  ‘Result’!  There were two samples on file and they both matched each other, which gave me confidence in their accuracy.  They didn’t have an engine code against them but they did match my sample exactly!

That made me think; the valve timing appears to be correct, but the ECU keeps complaining of crankshaft sensor and that works.

I took another sample, during which time the engine started after a shorter crank time.  I captured the sample and compared the crankshaft signal to the known good library sample.

Starter up sequence with injector and start
Start sequence after long crank time

After I took a closer look at the library captures, concentrating on the crankshaft signal, I noticed my capture clearly had a lower amplitude to the sensor.  I checked how the library sample scope probes had been connected and noted they had used a common ground connection, as had I.  So I took a closer look at the sensor and noticed how it didn’t seem to sit flush in it’s mounting, even although it was tightened down securely.

I removed the sensor and inspected the mounting surface.  I attempted to clean it up and refit the sensor.  Unfortunately I don’t carry the necessary engineering tools and so was a little restricted in what I could achieve.  I found that the sensor appeared to sit flush if I rotated it away from it’s fixing position.  So I left it in the rotated position and re-captured a start sequence.

Starter up sequence with injector and start after fix
Crankshaft sensor refitted to create the improved output voltage

That did it!  Instant start and the crankshaft signal was much better with a stronger amplitude.

I left the garage with the job of perfecting the mounting surface.