Please can someone help with a sta=range issue with a tdi?

Birchall

Dick Chown Award 2016
Hi,

I haven't come across this before but hopefully someone can help diagnose an issue with a tdi.


First symptom, The temperature was showing 70 rather than the usual 90. I know that sometimes the temperature on a tdi can drop a little in the cool weather but it might be relevant.

The engine suddenly dies and talks a while to fire up again, but if left it fires up ok.

So to me it is temperature related but I might be wrong.

It is not the temp sender I replaced that a couple of days ago (not with a cheap one, it was £21 and not one of the £7 ones!!!

The reason I changed oit was due to the temperature not reading anything even when fully warmed.

I would imagine that if the temperature drops too much it might be kicking into cold running and overfuel.

Is there anything else it could be?

Any ideas?

Steve B
 
It will be scanned tomorrow.

If it is temperature sender related it will not throw a code.

I am wondering if this is a symptom of a failing camshaft position sensor, I can't think of much else that can cause this. It runs sweet and strong normally.

Injector loom is the only other common fault, but I expected that to just cause a slight misfire?

Steve B
 
For it to die and start again later sound like a camshaft sensor or crank sensor something like that for it to just die like that

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Yes, that could be it, lets see what the scan comes up with.

I think my money is on a camshaft sensor and that would show up on the scan, I am pretty sure that the engine temperature dropping to 70 is not unheard of when the air is cool.

It may even be that in addition to the actual cause the temperature sender may also be a duff new one!! But it was a Meyle not a £7 one, but they fail too I suppose.

Cheers
Steve B
 
Yeah rare for a good make sensor to just fail unless takes reading from another sensor I know on the 1.6 fsi there's 2, is it taking temp from rad or the one near thermostat?

Not getting a wrong reading from air in the system? Has it got right amount of coolent plus water mix, just throwing ideas I'm at work and getting tired now lol

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Hi Steve,
Just wrote you a longish reply and the bl**dy forum as lost it :(

in short a measuring block shows the temp that the ECU is seeing, monitor this as the engine warms up, it should get to 90 deg or so and maintain this if the cabin heater is on cold
The fuelling maps are cut in / out via a control map this is engine temp dependent, the difference in fuelling between the 70 deg C map and the 90 Deg C map is not great enough to cause over fuelling to the extent that the engine will not start, but between -15 deg C and 90 Deg C it would certain be massively over fuelling and therefore would be likely to prevent starting / make starting very difficult

The Crank sensor is the most likely culprit as it fails when hot, but work fine when coldish, this also does not normally show up as a fault code.
The CAM sensor is also a possible cause, but I think the ECU will allow the engine to run with a failed CAM sensor as the crank sensor alone is enough for the ECU, but starting is more difficult as the ECU does not know if the crank is on a compression stroke (injection req'd) or an exhaust stroke (no injection required), the good bit is the CAM sensor normally throws a fault code :)

Cheers,
PS still got a 1.4 Black Petrol A2 here with your name on it :)
 
Hi Steve,
Just wrote you a longish reply and the bl**dy forum as lost it :(

in short a measuring block shows the temp that the ECU is seeing, monitor this as the engine warms up, it should get to 90 deg or so and maintain this if the cabin heater is on cold
The fuelling maps are cut in / out via a control map this is engine temp dependent, the difference in fuelling between the 70 deg C map and the 90 Deg C map is not great enough to cause over fuelling to the extent that the engine will not start, but between -15 deg C and 90 Deg C it would certain be massively over fuelling and therefore would be likely to prevent starting / make starting very difficult

The Crank sensor is the most likely culprit as it fails when hot, but work fine when coldish, this also does not normally show up as a fault code.
The CAM sensor is also a possible cause, but I think the ECU will allow the engine to run with a failed CAM sensor as the crank sensor alone is enough for the ECU, but starting is more difficult as the ECU does not know if the crank is on a compression stroke (injection req'd) or an exhaust stroke (no injection required), the good bit is the CAM sensor normally throws a fault code :)

Cheers,
PS still got a 1.4 Black Petrol A2 here with your name on it :)
Makes sense

Love the last bit like he's an a2 dealer lol

Steve is this the little Dolphin grey gem?

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Having slightly similar issues with my TDI90. Last week I fitted a new coolant thermostat and for the first time since i have owned the car (2 years) it is showing 90C. The problem, which I believe is related to the ECU receiving this 90C signal, is that it is now a pig to start when warm. Previously starting cold or warm has never been a problem other than a sluggish battery in winter. From researching various sites on the net it appears that, on the VAG 1.4TDI, when the ECU detects 90C it requires a starting cranking speed of 280rpm before it fuels the engine.
Having promised myself a new battery before next winter I am starting on that route before I start looking at Crankshaft sensor, camshaft sensor or Coolant sensor. Hope it is not necessary.
This seam to be a very common issue with VAG diesels which the main dealers have difficulty resolving.
Incidentally, the wrong thermostat 82C had been fitted at some time and the battery is the original, 13 years old.
Will keep you updated.
 
Having slightly similar issues with my TDI90. Last week I fitted a new coolant thermostat and for the first time since i have owned the car (2 years) it is showing 90C. The problem, which I believe is related to the ECU receiving this 90C signal, is that it is now a pig to start when warm. Previously starting cold or warm has never been a problem other than a sluggish battery in winter. From researching various sites on the net it appears that, on the VAG 1.4TDI, when the ECU detects 90C it requires a starting cranking speed of 280rpm before it fuels the engine.
Having promised myself a new battery before next winter I am starting on that route before I start looking at Crankshaft sensor, camshaft sensor or Coolant sensor. Hope it is not necessary.
This seam to be a very common issue with VAG diesels which the main dealers have difficulty resolving.
Incidentally, the wrong thermostat 82C had been fitted at some time and the battery is the original, 13 years old.
Will keep you updated.

New battery now fitted and I am happy to report that my TDI90 now regularly runs at 90C AND starts quite normally when the engine is hot.
 
Steve is this the little Dolphin grey gem?

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No, this is the 2003 TDI Sport I recently sold. But it is now going into the workshop for a new camshaft positioning sensor, new crank sensor and another new temperature sensor. The new owner wants us to do the cambelt etc plus a major service while we are doing the sensors, so this will be well sorted soon.

Steve B
 
No, this is the 2003 TDI Sport I recently sold. But it is now going into the workshop for a new camshaft positioning sensor, new crank sensor and another new temperature sensor. The new owner wants us to do the cambelt etc plus a major service while we are doing the sensors, so this will be well sorted soon.

Steve B
Nice so the problem will defo be sorted then? Have to post your findings and If this is a common problem on the tdi's

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