Mk6 transit won’t start when engine warm

[marcrbarker]

Hey hang on a mo..

the CPS here is a Hall sensor,

This cranksensor we've been talking about can't be a Hall sensor. It's 2-pins.

And I've just looked up an example

1143723.jpg

"Inductive sensor" (I thought so)
Just a permanent magnet with coil solenoid. You know like they use on mopeds, scooters & chainsaws. It just makes a +ve & -ve voltage spike sgnal when a metal edge goes past it.
The problem with these is the tiny wire inside can detach when hot (prove it with Ohm meter test)
Other problem prone to is when covered in metal dust the signal output is lower than normal - which is no big deal when engine running because the metal edge goes past fast enough to induce the +/- pulse, but when the edge goes past slow (starting) there's not enough induction. I would had thought the PCM would throw a MIL warning light on instrument if that was to happen. And definately so if the wire inside detached.

[amlav]

Crankshaft sensor ? Pour some cold water on the crankshaft sensor when engine hot and won't start . It used to happen on older type Jeeps too . Make sure is the Crankshaft sensor ....not the camshaft sensor you pouring the water on to .

That sounds easy one to try. An empty dishwashing liquid bottle filled up with water ready to squirt the whole contents over the sensor.
As many have mentioned earlier the cranksensor has a tendency to collect metal dust - but it drops off again. (and from my experience if CPS ever do fail it when hot restart)

@amlav When this crank sensor problem happened with you, did you happen to notice any extra warning light on the instruments? Had you by chance also scanned (Forscan eg.) to see if there was also a stored DTC code ? (ie for crank sensor )

It did happend on earlier JEEP's 4x4 . (had one of those) .Usualy sensor had to be replaced . Those cars where not OBD2 compliant . Pouring water on cranks sensor was the way to confirm that fault.
Location of sensor is a bit dificult to reach but not to bad .
Did not happened on my MK6 Transit (yet ,,,)

[marcrbarker]

It did happend on earlier JEEP's 4x4

Ah OK non OBD2, though did the Jeep 4x4 have Check Engine light? Do you remember see any extra warning light on the instruments?
If I remeber rightly with crank sensor fault pre OBD there;s a "paperclip test" that did 1 flash/ 9 flash/ 1 flash/ 10 flash.... repeating sequence on the check engine light to indicate the cranksensor fault. Though having said that , with the "pour cold water test" you might not had gone there.

[Jim Archer]

Apologies, it's not a true Hall Effect sensor, but operates on the same principle. The coil is energised, and the reluctor ring causes the field to vary, and thus sends back to modified signal overlay - hope this makes sense.

Anything that disrupts the signal output will prevent the PCM seeing the signal it waits for. As said, it looks for a nice clear step, any significant contamination smears this and it won't fire. Quite often, a wee squirt of 'sniff' spins the crank fast enough to bump the signal above the 'miss' level.

Jim

[marcrbarker]

Apologies, it's not a true Hall Effect sensor, but operates on the same principle. The coil is energised, and the reluctor ring causes the field to vary, and thus sends back to modified signal overlay - hope this makes sense.
Anything that disrupts the signal output will prevent the PCM seeing the signal it waits for. As said, it looks for a nice clear step, any significant contamination smears this and it won't fire. Quite often, a wee squirt of 'sniff' spins the crank fast enough to bump the signal above the 'miss' level.
Jim

It's not that critical. It's like a cassette tape head, when it gets covered in oxide the sound's still there but it's getting gradually lower and more muffled.
With a clean sensor when engine's running there's up to 50x more signal (possibly more) than the minumum needed, at idle speed it'll be maybe 10x more, because inductive sensors give increasing output with faster RPM. The electronics in the PCM simply ignores that extra voltage.

When there's a contaminated sensor at normal RPM that's no big deal. There'll be more signal than the minimum needed. [Maybe the PCM later detects the signal is outside normal parameters and turns on th MIL check engine light (ignored by driver) before it got bad enough to affect starting]

But at cranking speed it's much lower output. Then one day these two factors (cranking speed+contamination) in combination is enough to reduce the output below the detection threshold. It's why bump starting or towstarting tends to work after cranking doesn't.

Just seems no one has ever yet given this any thought. Maybe there should be a "blinky" light for crank sensor like a computer hard disk light, so can see if the sensor is running or not.

[Jim Archer]

Cam-Crank sync is the Ford version of industrial 'blinky' light

It's usually a sure sign of a dicky sender if it starts fine cold.

Jim

[indacus]

Thanks again for all your information. I got the garage to change crank sensor last week and am sad to say the problem continues! Still won’t start when hot. Still no other warning lights. Occasionally it will start when hot (I keep checking once I’ve arrived if it will start hot) but it seems very random and most likely will not start until cool. Does anyone have any other ideas please?

[knobby1]

Thanks again for all your information. I got the garage to change crank sensor last week and am sad to say the problem continues! Still won’t start when hot. Still no other warning lights. Occasionally it will start when hot (I keep checking once I’ve arrived if it will start hot) but it seems very random and most likely will not start until cool. Does anyone have any other ideas please?

I still think it's a lazy starter....mine did this years ago when hot...replaced the starter and haven't had an issue since.

The brush pack wears along with the commutator and the starter will struggle..... it will still turn but not quite as fast as it needs to in order build up the required fuel pressure = failure to start.

Lord Knobrot

[Andyzot]

I’m experienced exactly the same, have you fixed it? My codes were faulty EGR and MAF which I’ve replaced, so I’m replacing the crank sensor next, then the starter motor, even though starter does seem fine

[knobby1]

I’m experienced exactly the same, have you fixed it? My codes were faulty EGR and MAF which I’ve replaced, so I’m replacing the crank sensor next, then the starter motor, even though starter does seem fine

EGR valve & MAF sensor won't stop it from starting.

My starter also sounded and seemed fine but would struggle to start until it was replaced....has been fine for the several years since.

Lord Knobrot

[Andyzot]

Thank you, I’ll replace over weekend probably. I replaced the MAF & EGR as they were showing codes anyway.

[knobby1]

Thank you, I’ll replace over weekend probably. I replaced the MAF & EGR as they were showing codes anyway.

MAF & MAP sensors rarely fail.....the MAF and MAP codes are usually caused by a duff EGR valve. I suspect there's thousands of MAF & MAP sensors laying around in people's garages and sheds with nothing wrong with them.

Lord Knobrot

[indacus]

No! Sadly still not fixed. Problem possibly seems more intermittent since changing crank sensor, ie. Will sometimes start hot with foot full on throttle. Also just cut out on me while driving this week, but then restarted as described. Is it seeming more like a fuel issue? Reason I don’t think it’s starter motor is because it really sounds like it has started, not just turning over, before cutout when you release key.

[Andyzot]

I agree totally, mine sounds like it’s fired up too.

I’ve changed the EGR, MAF and crank sensor, if anything mine is worse, smokes when cold and won’t start hot.
I keep following advice but it’s not really getting me anywhere, not that I don’t appreciate it, it’s just so frustrating.
I’m going to blank off the EGR over the next couple of days, see what that does, I’ll report back here so that it’s documented.

Good luck.

[knobby1]

I agree totally, mine sounds like it’s fired up too.

I’ve changed the EGR, MAF and crank sensor, if anything mine is worse, smokes when cold and won’t start hot.
I keep following advice but it’s not really getting me anywhere, not that I don’t appreciate it, it’s just so frustrating.
I’m going to blank off the EGR over the next couple of days, see what that does, I’ll report back here so that it’s documented.

Good luck.

What actual fault codes are you getting..??

Lord Knobrot