Warm starting problem on TDi75

Hi there. My 1.4tdi has similar intermittent warm start problem. Reading the above it disconnected the can sensor but engine would not start at all. Suspected tandem pump but measured fuel pressure at pump and was above the 3.5bar spec at idle and rose to maybe 4.5bar at faster engine speed. Needle was a blur because of pressure pulses. Anyway I'm wondering if its the cam sensor that will stop the engine starting rather than the crank sensor?
 
Cam sensor will not stop engine starting but it will take longer to start
Only time cam sensor would stop starting is if cam/crank timing is out. Eg belt skipped a tooth or two
Disconnect the cam sensor and try starting. It will take a few more cranks over as no cam sensor telling ecu which cylinder is on firing stroke but once the crank sensor as told the ecu information the ecu works out the firing sequence and engine will start and run fine

The disconnected cam sensor will put the mil light on and from memory will need a code reader to turn it off again


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Hi AndyP,
You have exactly described the restart problem I have with my TDI. Did you solve the problem by changing the cam sensor?
 
Crank sensors can become faulty when warm

Only when warm, never when hot or cold? I'm 99% convinced this is some type of fuel supply problem as there is no cloud of smoke after 15 seconds of cranking when it eventually starts.
 
Only when warm, never when hot or cold? I'm 99% convinced this is some type of fuel supply problem as there is no cloud of smoke after 15 seconds of cranking when it eventually starts.

Any way you can monitor fuel temps to check the sensor is not reading out of range.
Don't know the answer but it may be possible to disconnect the sensor to see if things improve as it's quite common for the output from other temp sensors are used as a back up

Cheers Spike
 
Any way you can monitor fuel temps to check the sensor is not reading out of range.
Don't know the answer but it may be possible to disconnect the sensor to see if things improve as it's quite common for the output from other temp sensors are used as a back up

Cheers Spike

That is something I hadn't considered, although I have replaced the fuel temp sensor. I'll have to check whether it can be done in Torque.
 
PROBLEM SOLVED. -- at least for me
With my newly purchased ODB cable I ran VCDS to check fault codes on my TDI and found an intermittent cam sensor fault, which was one of the suspected reasons for the starting problems with a warm engine. I changed the cam sensor and the problem has now disappeared.

I now have a theory what happened in my car :
Often after a short stop for shopping I had to crank the engine for two to four 5 sec periods before it started because of my broken cam sensor. This resulted in vapor bubbles in the fuel return pipe that normally would be no problems as the the return pipe goes to the fuel tank. But in this case the fuel pre heating valve placed at the fuel filter has not open yet and the return fuel with it’s bubbles is directed into the filter and creates a lock in the fuel supply. Then after driving for a minute or two the air lock in the fuel supply reaches the engine and result in a stop. After a number of cranks the engine can be started again and the hole thing repeats again if the preheating valve is not opened .
The preheating valve is opened when the temperature is reaching 30°C and directs the return fuel to the tank which ends the terminates the faulty behavior.
After changing the cam sensor I have no problems starting the car and the problem with air in the fuel pipe is avoided

/Freddie
 
PROBLEM SOLVED. -- at least for me
With my newly purchased ODB cable I ran VCDS to check fault codes on my TDI and found an intermittent cam sensor fault, which was one of the suspected reasons for the starting problems with a warm engine. I changed the cam sensor and the problem has now disappeared.

I now have a theory what happened in my car :
Often after a short stop for shopping I had to crank the engine for two to four 5 sec periods before it started because of my broken cam sensor. This resulted in vapor bubbles in the fuel return pipe that normally would be no problems as the the return pipe goes to the fuel tank. But in this case the fuel pre heating valve placed at the fuel filter has not open yet and the return fuel with it’s bubbles is directed into the filter and creates a lock in the fuel supply. Then after driving for a minute or two the air lock in the fuel supply reaches the engine and result in a stop. After a number of cranks the engine can be started again and the hole thing repeats again if the preheating valve is not opened .
The preheating valve is opened when the temperature is reaching 30°C and directs the return fuel to the tank which ends the terminates the faulty behavior.
After changing the cam sensor I have no problems starting the car and the problem with air in the fuel pipe is avoided

/Freddie

I like the theory, quite a lot, but I replaced my cam sensor (which didn't appear to be faulty anyway) and it made no difference unfortunately.
 
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