W210 E320 cdi non start when hot

[jetboy]

Hi all, as in the title my old trusty (usually) steed will not start when the engine up to full operating water temp near 100'c.
I've replaced all o rings on fuel pipes, fuel filter and had the injectors reconditioned.
Local Indi's are less than helpful and buying a xentry seems impossible.
I've used a diagnostic that gives basic live data and I can see that there in no fuel rail pressure-hence no start when hot, backed up by a sniff of magic spray into the inlet and it starts so it's not a crank sensor but fuel pressure related.
Cold and warm starts are not an issue.
IS there something obvious that points to the problem and is there a way to check things like shut off valve, rail pressure sensor etc.
Thanking you in anticipation
Mark

 

[Dodipops]

Fuel temp sensor??

Fuel pressure regulator or rail pressure sensor.

Can also be the wiring that is breaking down under the temperature?

 

[jetboy]

It's there anyway to check them or is that the dredded xentry required ?

 

[Supernoodle]

I would say the clues are there. If all it takes to start is some easy start it's not a sensor, pressure control valve etc.

I'm guessing you have a mechanical low pressure pump? When hot there is air getting in and you can't pull sufficient fuel up. The easy start spins the low pressure pump up faster thereby overcoming that leak and pulling fuel up.

 

[mersum1es]

No fuel temp sensor in this age engine, aux pump worth to check. You can remove hose between hp and lp pump and pour fuel to can when someone crank the engine. LP pump failures are rare, but if pump is opened once, seals are probably not able to restore tightness anyway.

Yes, and obvious; do you see air bubbles running in clear fuel pipes? Is there bubbles when hot but not when cold?

When fuel filter is changed?

 

[jetboy]

I would say the clues are there. If all it takes to start is some easy start it's not a sensor, pressure control valve etc.

I'm guessing you have a mechanical low pressure pump? When hot there is air getting in and you can't pull sufficient fuel up. The easy start spins the low pressure pump up faster thereby overcoming that leak and pulling fuel up.

Yes has a lift pump

 

[jetboy]

No fuel temp sensor in this age engine, aux pump worth to check. You can remove hose between hp and lp pump and pour fuel to can when someone crank the engine. LP pump failures are rare, but if pump is opened once, seals are probably not able to restore tightness anyway.

Yes, and obvious; do you see air bubbles running in clear fuel pipes? Is there bubbles when hot but not when cold?

When fuel filter is changed?

I think you are right, no temp sensor that I could find on Google.
There are some sort bubbles in pipe from filter to lift pump when cold engine. I will observe the bubbles on hot engine.
Fuel filter recently changed and or silicone round to to ensure seal.

 

[Supernoodle]

Some bubbles is still too many.

This is the pump seal mentioned above.

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But if you have bubbles between filter and pump I guess your problem is upstream.

 

[jetboy]

Some bubbles is still too many.

This is the pump seal mentioned above.

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But if you have bubbles between filter and pump I guess your problem is upstream.

So his problem was with cold start and mine is hot start problem, not ruling it out tho-thankyou.
I might see if I can get a new o ring for it.
I did think whilst any air bubbles is not right that a few small ones would be ok in the pipe from filter.

 

[jetboy]

Thanks guys for you input.
I've had a good look over the engine checking wires and pipes etc and only really found the main fuel (hose) pipe from tank to be a little perished, bent it backwards and the splits were only superficial so that job can go on the wait list.
Although I'm chasing the hot start problem-air being in the pipe from filter to lift pump, should not be in there?
Tomorrow I'm going to use a washer pump to suck the fuel before the filter, that should tell me if it's a tank/supply issue-or just another silly idea

 

[jetboy]

As previously mentioned today I conducted a few tests, with no obvious evidence of how air is getting into the fuel system.
So first I put a washer pump on the fuel supply pipe, at fuel filter joint, so it's sucking from the tank, a few bubbles from when I disconnected the pipe, air did go into the pipe as the fuel ran back to the tank, then it ran clean and smooth-no air coming up to the filter after the surge of bubbles had cleared.
Second, then I pressurised the filter from the same joint, pushing it through the filter, which I noticed when I took the FF to LP pipe off to look inside, the filter didn't appear to be full-obviously as air is somehow getting in. I sprayed all over filter housing, pipes, joints, LP, SOV,HPP, etc with leak detector, only putting about 4psi in.
Nothing foamed suggesting a leak, although the rain was washing most of it off, if it was leaking I'd of thought I'd see it.
Obviously there was air in the pipe and I'd introduced more air by taking the o ringed (on FF) pipe off, it was moving along all the pipes-all the way to the SOV, I couldn't see what happened after that as the supply pipe to the HPP is non see through.
If the fuel can't get past the SOV, would you expect so see the air moving through all the pipes-up to the SOV ?
Well like I say, I'm not sure I've proven anything-other than you get wet when you work outside when it's raining.
So going forward, I was think about using a smoke detector into the fuel filter but as I think I'm chasing a vacuum leak rather than a pressure leak-if that would be worth it ?
Any tips for what/how to test further would be gratefully received and the next thing is to see if air in the FF to sov pipe when hot, moves when cranking and take off out of lift pump (to sov) pipe and see if it pumps while cranking ?
Thank you