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P38 "crank sensor" fault


Aragorn
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Got myself a P38 4.6 to replace my rather rusty Vauxhall Monterey. It was cheap, on ebay, with a fault described as a bad crank sensor. The guy made some weird comments about the crank sensor having failed because it had got oily from a leaky rear main seal.

The car starts, drives, everything seems fine. The seller claimed it would run for about 15mins before cutting out, i've seen similar symptoms before due to bad crank sensors, and the seller said it had shown up with a crank sensor fault on the Faultmate FCR. I've not actually seen the fault occur, as its not insured or MOT'd etc yet. But with everything pointing in the direction of the crank sensor, i ordered one and installed it.

I fitted the new one last night, but noticed that the one on it was already new(ish). The markings on it were identical to the one i'd bought, which isnt a genuine landrover part, and its significantly less oily than everything else in that area. Interestingly, there was no oil contamination on the old sensor itself.

Now i'm left wondering if theres infact some other issue going on. Hopefully get it insured and in for an MOT this week and i can see if the symptoms are cured. Maybe the guys just got unlucky and a cheap crappy aftermarket part has died on him. But it might well explain why someone who appears to have spent a LOT of money on this P38 over the last 5 years would throw in the towel and sell it to me for peanuts with such a seeminly minor fault. Are there any other common issues that could be causing it?

I will also add that when starting it, it feels somewhat lumpy. I'm not sure if its misfiring, its quite hard to tell on a V8 compared with a more typical 4 cylinder, but the car feels like it shakes if you lift the engine revs up past idle. Rev it up to say 3k and it smooths out. Again i'm not sure if this is just a function of not really having been driven much and just shunted around the drive etc. Maybe it just needs an italian tune up.

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The crank sensor (if it is the same as my 4.6 GEMS) will quite happily work in a puddle of oil as it is magnetic!

I'd pop the inspection cover off and turn the engine over, checking that all of the timing "pins" are there (including the gap) and that you haven't gained a gap.

The timing sensor is the only item on the ECU that the ECU can't use stored values as it uses the gap to determine TDC!

I have a lot of experience with this recently!!

Cheers

Peter

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Apologies, its a '94 GEMS engine, i should have said.

Yeh, i didnt recon the sensor would care about oil. I suspect hes been spun that line by the garage who have presumably replaced the crank sensor, and the problem has recurred, so they've tried to punt the blame by saying the oil leak has caused the new sensor to fail.

Good call on removing the cover, i'll have a go at that perhaps tomorrow evening. I'd imagine though, if a tooth was missing, it would simply not run at all, or run like ass, rather than running fine for a while then dying until it cooled down as he claimed it did?

Cheers

Kev

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No i dont.

The truck came with a Faultmate FCR (presumably because its useless to anyone else despite its price tag) which lets me read and clear fault codes, but not view any live data.

I do have a generic ELM327 device and i've heard those might be compatible with the engine at least, not tried hooking it up yet though.

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Cutting out may be a number of things, although I would be doubtful if it were the crank sensor. My problem was that the flex plate shattered and I hadn't realised that it had created a new gap in the timing pins! It wouldn't start or if it did, only briefly and ran like a bag of nails with back firing etc. In the end, rather than pull the box again and change the flywheel complete I fitted a new slotted disc at the front, behind the crank pulley and used a Ford sensor (supplied by a moderator of this forum). That started an ran sweetly.

However to stop totally could be ignition related, or maybe even mobiliser related. If it does it again see what (if anything) comes up on the speedo display.

Cheers

Peter

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TBH i've seen the crank sensor do exactly what he described was happening on a couple of other cars over the years. Most recently a friends corsa, stopped in town, wouldnt start, called recovery and when they turned up an hour later it fired right up, ran for about 10mins then died again. New crank sensor fitted and off it went.

Best guess is that the heat/expansion opens up a break internally within the sensor, and it reconnects again when it cools, a bit like a dry solder joint.

Got insurance sorted out, and MOT booked for tomorrow, so will see how it gets on!

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