W211 hot start problem

[alexmoon]

My W211 (2002) E270 CDi (92k) has developed an occasional hot starting problem. If engine is fully warmed up and I stop it for a few minutes sometimes it won't start again. Starter motor turns over very quickly but engine doesn't catch. If I leave it for a while then it starts again no problem. Might add it runs very smoothly and no fault codes appear on cluster. Your help much appreciated

 

[momomo]

CPS maybe. Crank position sensor. I say maybe because they genrally dont fail on the CDI engines, but it does sound exactly like a CPS fault. Not hard to change but can be a bit hard/tricky to get at.

Have you had it hooked up to STAR?

 

[alexmoon]

Thanks for prompt reply, Forgive my ignorance but is crankshaft sensor the same as a camshaft sensor?

 

[momomo]

Thats ok. They do sound similar. No they are not the same.

The crank position sensor is used to minitor the position/rotation speed of the crank shaft. The CPS is used with the similar camshaft sensor to monitor the relationship between the pistions and valves in the engine.

They are two separate sensors.

 

[alexmoon]

Not been hooked up to STAR yet. Will that defo confirm it's a CPS problem?
Will get my mechanic to order a CPS.

 

[momomo]

The CPS fault will not appear on the STAR machine. If you connect up STAR at the time when the car is not starting and if the CPS is at fault it will show then. But say you're car is fine at the time when hooked up it will not show this fault unfortunately. It doesn't get logged.

But other faults if any will show up when you connect it up and this will help to identify the problem if there is another issue causing your problem. Like i mentioned before this sounds exactly like a CPS fault.

 

[alexmoon]

Thanks for your help. Last question – why does it only happen when engine is hot?

 

[momomo]

Thanks for your help. Last question – why does it only happen when engine is hot?

Over time they become burnt or worn out. I believe this is because of the exposure to very high heat and general wear over a long period of time. So when it gets really hot, it stops working (stops transmitting the signal to the ecu which is needed for the ignition and other parts of the system) so the car wont start. When it cools down it begins to work again.

 

[alexmoon]

Momomo, It's a leaking injector. My man took engine cover off and injector nearest oil cap is blowing. He will change seal on Monday so hope this sorts it out.

 

[momomo]

Thats good news, make sure he recuts the seat where the injector and seal sit to make sure it doesn't leak again and its done properly.

Normally one leaky injector wont cause the symptoms you initially mentioned, about the hot start problem.

 

[alexmoon]

So I could have a leaky injector AND CPS problem? (Note: Hot start problem has only happened since I noticed whiff of oil-diesel from engine bay which I assume is leaking injector.)

 

[jaymanek]

I agree that I dont think the injector will be related...

 

[alexmoon]

Jaymanek, So what do you think it is?

 

[jaymanek]

i would also say CPS but needs to be checked as cannot remember every changing one on a diesel.

 

[momomo]

Alexmoon as i said earlier in the thread this does sound like a CPS failure but i have not heard of them failing on the diesels. What makes it hard is that the CPS will not throw up a code unless it it on the machine at the time when it is playing up and not starting.

Your mechanic has identified the leaky injector, this does not cause a hot start problem you are experiencing. It should be fixed anyhow. I would let him fix the leaky injector and then take the car for a good drive getting it hot and see if it starts up again after turning it off. If not then change the CPS.

There may be another issue, depends on how competent your mechanic is at diagnosing the problem. Your problem sound exactly like a CPS failure from your description of the problem hence our suggestions.

 

[alexmoon]

Thanks for that. Will do as you say and let you know.

 

[BlackC55]

It is very unlikely to be a CPS failure.

I bet it is and injector or two leaking off too much.

Easy to test with a leak off check

 

[momomo]

I bet it is and injector or two leaking off too much.

I dont know why i didn't even think of that.

Injector(s) leaking off too much do indeed cause starting issues! Sometimes a hot start problem or cold start problem. Its because the common rail cant build up enough pressure to start the car as the injector is leaking off.

Look at your fuel return pipes and see if there are bubbles and as Olly above get a leak off test done.

 

[peteubhi]

Hi guys i know this is an old thred but alexmoon did you get the problem sorted? I have the same problem, injector number 3 was leaking (tar build up) so had that replaced then injector number two was leaking so had that replaced, but still got hot start issues.
the mechanic said that the rest will also need replacing but i cannot dish out £150 for another 3 just yet....shall i change the CPS? any help would do as this is hurting my pocket..

 

[W210Virgin]

And what is the 'fix' for high leak off from an injector or 5