W211 hot start issues!?

[golf2]

Hi guys,

I have an issue with my 2003 OM648 E320 CDI. Recently I havent been using the car much and I went to start it up but it just cranked and didn't start. The battery didn't appear to be the issue as it was cranking over no problem but not starting. I thought i'd try jump starting it anyway and it fired sraight up. I put the battery on charge and the car started fine the new few times. After a couple of days I had the same crank but no start issue. I assumed the battery was weak so bought a brand new AGM 017 battery and the car started straight up. The following day I started the car up, drove for approx 1 hour and then stopped off at the shops. Upon returning to the car 20 mins later, it wouldn't start again! I tried several times but the engine just cranks over and over. I disconnected the battery and left it 5 mins but still no start. Around half an hour later I managed to get a jump start and it fired straight up. I checked the battery voltage and it's around 12.75v so no issues there with the new battery. I've got STAR so I've checked it on that and there are no fault codes. I've checked a few things like MAF function, fuel rail pressure, EGR function etc but all looks fine. I don't get any warning lights and the car drives perfectly once it's started. I drove it last night and once again it wouldn't start after sitting for around 30 mins. It eventually started after a few attempts. It started up fine this monring from cold but when I got to work I tried starting it up 30 mins later and it wouldn't start. Does anyone have any ideas? I'm thinking maybe cam or crank position sensor? I've also checked for fuel leaks but there's no sign of anything.

Thanks.

 

[mersum1es]

Has the car been remapped? Sometimes programmers disable fault codes to hide their inability to build up solid proof maps... anyway If no codes, you must read live data when NO start. What does fuel rail pressure reading is then? Another thing is to check if your crank and cam sensors sync. This should trigger a fault code but....

Edit usual hot start problems are CPS related...

 

[Abb]

Not sure if you would have fault codes if it was the crank position sensor, but the fact it turns and wont fire, but starts after it has cooled down, my money is the CPS.

 

[golf2]

Thanks for your replies.

The car was remapped in 2017 but this has now been removed and put back to stock.

I can't remember what the fuel rail pressure reading was but it was within the specified range. I will check if the crank and cam sensors sync, any idea how to check this?

I have just noticed when I first start the engine, I can hear a slight high pitched squeeky sound coming from the top of the engine near the injectors, after about 30 seconds it goes away. I was wondering if it could be an air leak in the fuel system but it always goes away after 30 seconds from starting.

Where the leak off pipes come off the top of the injectors, some of them have a brown residue around them, looks like a brown dust. Is this normal?

 

[Major774]

As it is temperature related... I would point to a failing CPS.

 

[golf2]

Thanks Major774.

I also just noticed this:

 

[golf2]

Bit of an update, I ran the engine start test through STAR and whilst cranking over it looks like the cam and crank aren't synchronising. I think I'll go ahead and order and crank sensor. Do you think it's worth also replacing the cam sensor? It's done 175k miles.
The fuel pressure is 364 bar at idle.

 

[AMGeed]

^ I'd replace the crank sensor first and see if that cures the fault.
.

 

[mersum1es]

You need to check fuel pressure when in cranks but not start.... of course its ok if engine runs.

But when you have already bought new sensor try it first.

 

[golf2]

Brand new Bosch crank sensor installed but problems remains, won't start when hot.

 

[Yex]

I had the same issue in my TVR Chimaera a few years ago. The car wouldn't start when hot as the cabling between the starter motor and the battery was not up to the job any more. After it was replaced with the correct spec cable I never had the issue again. Could it be that one of the cables in your starter set up is in a state of disrepair, or lose anywhere as you sound like you have exactly the same issue.

 

[golf2]

Thanks Yex, I will certainly inspect the wiring and check it looks in good condition.

I may also order a cam position sensor.

 

[golf2]

Hi chaps,

I've replaced both the crank and cam position sensors but it hasn't made a difference.

It starts fine when cold both just cranks with no start or occasionally will start after several attempts when the engine is hot.

I do have access to Star diagnostics but I don't know what I'm looking for. Does anyone have any suggestions as to what I could try next?

Thanks in advance.

 

[andym2]

Extreme cases of timing chain stretch could cause cam/crank sync issues. Possible given the mileage. Check using an oscilloscope.

 

[golf2]

Thanks Andy, I'm hoping it isn't the timing chain but I'll borrow an oscilloscope and do some tests.

Here is a video of the engine struggling to start using Star diagnostics. Is the rail pressure too low whilst cranking?

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[mersum1es]

refresh rate is so low its hard to say but yes it look like it keeps low... measure injector tank leaks.

You can also see live data about cam and crank sensor sync.

 

[golf2]

Thanks, is that a leak off test?

I've been trying to find the cam and crank sensor sync data in Star but haven't found it yet. I'll have another look.

 

[andym2]

The rail pressure while cranking looks a little on the low side to me. I think the 965 Sync status is the cam/crank so that seems ok. The battery voltage gets quite low, I guess that could be because it's been cranking for a while. If it's a fault in the high pressure fuel system be very careful fiddling with it though. The fuel pressures are ridiculously high (100bar is about 1500psi), you can get pressure retained even after it's switched off and the electrical connectors will have over 200v to fire the injectors so there's lots of scope to hurt yourself. The tiniest amount of dirt in the lines can trash the injectors so you have to be careful to keep everything really clean too.

 

[golf2]

Thanks for the information Andy, I won't mess about with the high pressure pump or fuel lines.
The battery was new a couple of months ago but where it's been sat for a while the voltage has dropped a bit. I'll put it back on trickle charge to top it up.
I think my next step will be a leak off test as everything else seems OK. The fuel filter is fairly new, cam and crank sync seems fine as far as I can tell. Can't see any physical signs of fuel leaks anywhere.
I disconnected the cam sensor deliberately to crank the engine over and check the rail pressure again. Does anyone know the minimum required pressure for the engine to fire? I can't seem to find a number other than the specified value in Star and I'm not sure if that's the specified value for when the engine is idling or cranking.

Here's the rail pressure when cranking with cam sensor disconnected:

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[mersum1es]

It is not enough. Out of memory I would say 250 bar required.

Leak off test you go...