ML270cdi wont start when hot

[fastboysparky]

ML270 cdi. When cold everything is ok and it starts fine. After 5minutes driving it wont start again until cold. Any ideas please

 

[television]

Replace the crank shaft sensor is my view £47 from any Bosch service center

 

[fastboysparky]

Thanks television. Could you please give me explanation, car starts and runs all day with absolutely no problem at all, but if you stop for 5 mins then thats it 'dead'. As you crank the engine, sometimes it fires then stops otherwise it doesn't do nothing. i have tried cranking for long periods but still nothing. leave it an hour and its fine again.
I know you are the expert but surely if its the cps i would be experiencing problems hot or cold. Thanks

 

[television]

OK this is getting harder, the CPS always fails when the engine is hot due expansion breaking the wires, when cool they make contact again, and the car normally stops when hot. Your car runs all day,,so maybe not that,,will not be air otherwise it would be hard starting the engine.

They measure 1k ohm when good and open circuit when bad,,maybe you should have a fault code read out

 

[fastboysparky]

Ok, Thanks. i'll check the resistance tomorrow morning, take it for a run then check it again.

 

[Alex Crow]

television had it right first time. when hot the signal is too weak at cranking speed (200 rpm) but fine at idle (650rpm). go for the sensor.

 

[fastboysparky]

thanks guys, i've got it out and the reading is 680 ohms, a little weak, i'll get a replacement tomorrow.

 

[television]

£47 from Bosch or £87 from MB you takes your choice

 

[fastboysparky]

Hi new sensor MB part. Same fault. Any more ideas are welcome please.

 

[fastboysparky]

Update - Update

When you crank the engine their is only small amount of pressure in fuel rail.
Their is a small electrical valve in the fuel line before the pump at the front of the engine near the dipstick, there is a reading of 9v when the ignition is on but it does not stop the valve from being in an open condition.

 

[fastboysparky]

Update - Update - Update

The camshaft position sensor is to blame, it takes a reading only when the car is started then it could be unplugged 'theoretically'. The car heats up and runs fine but the sensor breaks down with heat. you stop the engine and when you come to restart it will not read.
I checked this by quickly removing the sensor and cooling it in the freezer, after 5mins i refitted it and the car started fine. I double checked this by reheating it and the car would not start again. I did this a few times just to make sure and it was the same every time. This is a 3 wire sensor so you can also check the resistance across the middle pin and the negative pin.
Hope this may solve a lot of problems for people it certainly has helped me.

 

[Alex Crow]

you said the rail pressure was low, how did you know? presumably you fixed this. fault code and live data assistance would have helped you here as failed cam sensors generally get logged by the ecu. diagnosing on here by symptoms alone is always best guess. glad you got it fixed - when you can make the symptoms repeatable as you said it gives confidence that you have found the problem!

 

[television]

Update - Update - Update

The camshaft position sensor is to blame, it takes a reading only when the car is started then it could be unplugged 'theoretically'. The car heats up and runs fine but the sensor breaks down with heat. you stop the engine and when you come to restart it will not read.
I checked this by quickly removing the sensor and cooling it in the freezer, after 5mins i refitted it and the car started fine. I double checked this by reheating it and the car would not start again. I did this a few times just to make sure and it was the same every time. This is a 3 wire sensor so you can also check the resistance across the middle pin and the negative pin.
Hope this may solve a lot of problems for people it certainly has helped me.

I have done quite extensive testing of these things, by heating, cooling and even freezing,,the design is very poor, or rather the construction. There are 3 materials used with very different values when heated. most of the ones that I have cut open, the fault was that there is no free play in the copper wires where they are fixed to the terminals. if the potting was not so deep, the end of the wires from the coil could be coiled, and would not beak off when hot and expanded.

No doubt if you make a product like this,,you have an income for life, so why should they improve things

 

[Noddy]

Hi, I have a simillar problem with my ML270 CDi (Y-reg) . It will normally start ok. But if I take it to the shops and then try to start the car when I'm done, it won't fire up.

If I leave it for 15-20 mins, it normally starts again. Have left it with a mechanic for a few days but sod's law...it starts everytime!

 

[television]

This could still be the CPS when you turn you engine off, the heat from within will through thermal runaway go to the outer edges of the casing,, just enough maybe to send the CPS open circuit for a while

 

[Alex Crow]

a likely cps fault. very often they do not fail while running, but fail on start up. it is because the cps signal is weaker at the 200rpm cranking speed than the 650rpm idling speed.

 

[turbopete]

air in the fuel! been trying to sort the exact same problem on my E300 Turbodiesel for about a year now, off and on!

 

[Noddy]

Left the car at the mechanic's yesterday. Just got back to me. ML finally conked out on him so he was able to diagnose the problem...
2 out of 6 diesel injectors need replacing. £300 each from dealer!
Also had to sort out the crank shaft sensor.

 

[kebo57]

Left the car at the mechanic's yesterday. Just got back to me. ML finally conked out on him so he was able to diagnose the problem...
2 out of 6 diesel injectors need replacing. £300 each from dealer!
Also had to sort out the crank shaft sensor.

Just had an injector replaced £110.00 all in, I also carry a crank shaft sensor on the motor its easy to swap over

Kevin

 

[television]

Just had an injector replaced £110.00 all in, I also carry a crank shaft sensor on the motor its easy to swap over

Kevin

Thats a good idea,,maybe I should carry suspension struts in mine and a new pump