Thoughts on deisel not starting when hot?

[tight fart]

A friends got a 2012 ish Chrysler voyager, starts and runs fine from cold but is a bu663r to start when hot. Any thoughts?

[GreenV8S]

Heat related electronic failure?

[melhookv12]

Petrol? Diesel ? Engine size? Fault codes ?

[LordLoveLength]

Suspect it isn’t getting fuel pressure high enough during hot cranking to allow the injectors to fire.
Probably a faulty injector - you need to do a leak off test during hot cranking.

Could be pump or pressure sensor also. Will it go off a bast of easystart?

[Tony1963]

One possibility is that some petrol was put in the tank recently, then when the driver realised what they were doing, they stopped and the tank was filled with diesel. Cold starts can be fine, but hot starts can take a fair number of turns to catch. Once started, all behaves as normal.

I’ve been in a few cars where the owner has done just this, and once the contaminated fuel has been run down to as low as possible, then the tank filled with diesel, no more hot start problems.

[gregpe]

internal injector leak. I've had the same with Accord dtci when cold no problem but when you stop on the garage to refuel no chance to start.

[tight fart]

Thanks, I'll pass the comments over.

[GreenV8S]

gregpe said:

internal injector leak. I've had the same with Accord dtci when cold no problem but when you stop on the garage to refuel no chance to start.

Do you mean it's leaking fuel into the cylinder?

[E-bmw]

gregpe said:

internal injector leak. I've had the same with Accord dtci when cold no problem but when you stop on the garage to refuel no chance to start.

Perhaps you can help my ignorance out here but, that makes no sense at all to me.

Hot scenario - Stop engine, fuel leaks out, try to start it won't.

as opposed to:

Cold scenario - Stop engine, more fuel leaks out, it starts.

Can't get my head round that.

[tight fart]

LordLoveLength said:

Suspect it isn’t getting fuel pressure high enough during hot cranking to allow the injectors to fire.
Probably a faulty injector - you need to do a leak off test during hot cranking.

Could be pump or pressure sensor also. Will it go off a bast of easystart?

It has always started eventually and the owner wouldn't have a clue about easystart.

I was curious as to whether these were symptoms of a regular fault.
It sounded to like lake of fuel pressure when hot but it does run normally when it does start.
It's a 2011 2777cc voyager diesel

[stevemiller]

It sounds like the cam sensor is starting to break down, the first symptoms is a hot start problem. The cam sensor typically is only used for the first crank to sync fuel compression. Therefore car cold the sensor works, car hot sensor fails to see the camshaft position. I had this problem and once a new cam sensor was fitted there was no hot start issue.

Regards Steve

[thetrickcyclist]

Maybe it needs some diesel instead

[LordLoveLength]

E-bmw said:

gregpe said:

internal injector leak. I've had the same with Accord dtci when cold no problem but when you stop on the garage to refuel no chance to start.

Perhaps you can help my ignorance out here but, that makes no sense at all to me.

Hot scenario - Stop engine, fuel leaks out, try to start it won't.

as opposed to:

Cold scenario - Stop engine, more fuel leaks out, it starts.

Can't get my head round that.

Fuel doesn’t leak out - it bypasses the injector internally and is returned to the tank.
When the injector is cold it doesn’t bypass (leak) as much.
Problem comes with low cranking speed on starter not generating enough fuel pressure from the mechanical pump to overcome the loss in the injector. The fuel just gets pumped back to the tank and the fuel rail pressure doesn’t get very high.
A high pressure is needed in the fuel rail before the injectors get energised.
When the car is running the engine drives the fuel pump enough to overcome the ‘leak’ - that’s why it’s worth a squirt of easy start or similar to get the engine running

[E-bmw]

LordLoveLength said:

E-bmw said:

gregpe said:

internal injector leak. I've had the same with Accord dtci when cold no problem but when you stop on the garage to refuel no chance to start.

Perhaps you can help my ignorance out here but, that makes no sense at all to me.

Hot scenario - Stop engine, fuel leaks out, try to start it won't.

as opposed to:

Cold scenario - Stop engine, more fuel leaks out, it starts.

Can't get my head round that.

Fuel doesn’t leak out - it bypasses the injector internally and is returned to the tank.
When the injector is cold it doesn’t bypass (leak) as much.
Problem comes with low cranking speed on starter not generating enough fuel pressure from the mechanical pump to overcome the loss in the injector. The fuel just gets pumped back to the tank and the fuel rail pressure doesn’t get very high.
A high pressure is needed in the fuel rail before the injectors get energised.
When the car is running the engine drives the fuel pump enough to overcome the ‘leak’ - that’s why it’s worth a squirt of easy start or similar to get the engine running

OK, so you are talking about fuel "drain back" that still makes zero sense because the longer the car is left the more of it drains back and the more it cools down at the same time, so still doesn't make sense because by the time it is cold (and in your estimation slowed draining back) it will have all leaked back if it is difficult to start when hot.

[LordLoveLength]

E-bmw said:

LordLoveLength said:

E-bmw said:

gregpe said:

internal injector leak. I've had the same with Accord dtci when cold no problem but when you stop on the garage to refuel no chance to start.

Perhaps you can help my ignorance out here but, that makes no sense at all to me.

Hot scenario - Stop engine, fuel leaks out, try to start it won't.

as opposed to:

Cold scenario - Stop engine, more fuel leaks out, it starts.

Can't get my head round that.

Fuel doesn’t leak out - it bypasses the injector internally and is returned to the tank.
When the injector is cold it doesn’t bypass (leak) as much.
Problem comes with low cranking speed on starter not generating enough fuel pressure from the mechanical pump to overcome the loss in the injector. The fuel just gets pumped back to the tank and the fuel rail pressure doesn’t get very high.
A high pressure is needed in the fuel rail before the injectors get energised.
When the car is running the engine drives the fuel pump enough to overcome the ‘leak’ - that’s why it’s worth a squirt of easy start or similar to get the engine running

OK, so you are talking about fuel "drain back" that still makes zero sense because the longer the car is left the more of it drains back and the more it cools down at the same time, so still doesn't make sense because by the time it is cold (and in your estimation slowed draining back) it will have all leaked back if it is difficult to start when hot.

No, not fuel drain-back, but fuel bypassing the injector when the engine is running (or trying to start)
You have an engine-driven fuel pump, pressurising (or trying to) a common fuel rail that all the injectors are connected to. Everything on this fuel rail needs to be fuel-tight to allow it to be pressurised.
Now, if one of the injectors isn't fuel-tight internally, the pump ends up pushing fuel back through the injector, to the leak off pipe which goes back to the tank. The rail pressure never gets a chance to build up enough to allow starting.
The problem is that the injector leaks internally more when it is hot - when it's cold and the injector doesn't leak as much, the starter can get enough pressure built up to allow starting.

If you've got a diagnostic tool that can graph live data, you can see the fuel rail pressure failing to build on hot engines. It's a simple test that tells a lot.

[E-bmw]

OK, makes a degree of sense now, I thank you for explaining it for me, not the most au-fait with diesels TBH.

[tight fart]

Well it's got worse and broke down completely, wouldn't start when cold.
He called the RAC and they diagnosed fuel pressure sensor.
It did start with a squirt of easy start.