TA DA !!! Been thinking about crank sensor and although I measured the a.c volts when the engine was running, I was concerned that a fault with this sensor may be 'masked' by the fact that when the engine cuts the revs drop (obviously) and the sensor output falls a bit. Other than testing the resistance (which was a bit higher than a known good one) I could only check the leads and connections which were fine.
Today - gave my knuckles a 'pain approaching' briefing and took out the crank sensor. This is a tricky, but possible job with the starter motor fitted. Rave and Haynes both say to remove the starter but I wasn't up for that. The sensor is under the bottom edge of the starter motor. A 5mm Allen key fits the securing bolt, but once in it won't turn because of the L shape of the Allen key. I found a spare and cut off the longest portion, fitted a 5mm 1/4 inch drive socket on the end, secured this with tape and used my 1/4 inch ratchet to remove the bolt. Unplug connector, remove sensor.
Fitted a known good sensor and took about 1 hour getting the bolt back in. I have a flexi-camera, without which I doubt I would have succeeded. There is an 'O' ring on the sensor and a collar on the sensor that needs to fit into a recess in the cylinder block so that it all sits flat and oil tight.

Now - the good news it that I took the car out, warmed it thoroughly and it happily revved to 5,000 rpm plus.
The slight uncertainty is that the old sensor was wearing a slightly squashed 'O' ring, suggesting that it had been trapped in between the sensor and the cylinder block. It may not have been sitting flat and at higher revs (higher frequency signal) the amplitude may have been dropping due to an increased spacing between the sensor and the toothed wheel. So the old sensor may be perfectly good. Guess what - I wasn't going to put it back to try it !

Now - all details of how we got to this are in the chain above, but there is a worthy lesson from this - the code reader was repeatedly showing P0235 - Boost Pressure Sensor failure. The big clue was the fuel pump relay dropping suggesting the the ECU thought that the engine had stopped. I am sure that this would have misled many garages in trying to resolve the fault. I am fortunate enough to have my old TD4 engine sitting on a stand and so all of this has cost me nothing but a few knuckles and some time, but I have learnt much about the engine in fault-finding this.

Many thanks to all for the input and ideas. It shows that a crank sensor fault can be hard to identify and being the hardest sensor to change it is probably ignored until last. Anyone with similar symptoms - I suggest checking that the sensor 'O' ring is flat and the sensor is sitting flat before buying a new one.

Happy ending at last.

Good to hear it's resolved.

If I need to short out relays for testing I tend to put a switch int series so I can apply or remove the short quickly when I want. Handy if driving when it's on a long cable into the car. As you say it can be a concern so this gives yer the opertuntiy to open the switch if something goes wrong when driving.

Glad it's sorted. I had a suspicion it was the CAS, when you said the rev counter dropped off at the moment the fault occurred, but it was just a suspicion.
Presumably the doner engine suffered the fault when it was in its last vehicle.

Not being a Freelander owner I don't follow Freelander posts but I wish everyone who asked for help on LRZ followed it up so well with the solution and 'SOLVED' in the title. Well done.

Thanks for feedback. Original car may well have had fault but there is a chance that the damaged seal and hence the air gap got tampered with as PO took off starter and gearbox to change clutch. A change that never happened!! Always important to conclude threads even if fault not found. Lost count of searches on here that have an Eastenders style cliff hanger ending!!

andyfreelandy said:

Thanks for feedback. Original car may well have had fault but there is a chance that the damaged seal and hence the air gap got tampered with as PO took off starter and gearbox to change clutch. A change that never happened!! Always important to conclude threads even if fault not found. Lost count of searches on here that have an Eastenders style cliff hanger ending!!

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Thanks for your story. I had the same issue on my td4 engine. The O ring on the crank sensor wasn’t pushed into the recess and wouldnt go in even with a lot of pushing and twisting or tightening the bolt, I had to swap to another o ring and added some grease and it would then push home. The previously limited 3000rpm engine then ran a lot higher, towards 4500rpm. I think the engine was a poorly built recon from what I can see. It was in a recent ebay ‘bargain’ purchase. It had pink paint blobs all over various parts and nuts which may be a sign of that. Unfortunately after a very brief bit of higher revving something else gave out! There was a bit of knocking and a cut in power. Then wouldnt start and sounds different like compression has gone on some cylinders, uneven turnover though. It must have been a right bodge recon engine build. I suspect timing chain or worse annoyingly.

THANK YOU FOR THIS!! Been struggling with the same problem for a few months now!! Sorted and happy now!Greetings and happy holidays from Nairobi Kenya!

And a Happy Christmas to you, too.

Arrrh, the benefits of a concluded thread with Solved in the title!!

Makes for peace for all!!!