Crank no start.

[mobotho]

Hi all, looking for some advice, and hopefully this may help others once concluded...I have posted on Ross-Tech forum and not had much help really, got trolled around a bit with more questions than answers that were already in post.

CGQB Engine, 3.0BiTDI Car was running OK...then died and won't restart.  Cranks but wont fire. Bellow is a list of tests done and results I have.  Just looking for something I may have missed/am not aware of.

I have no spike in fuel pressure when cranking the car. I have VCDS as my diagnostic tool. No fault codes. Fuel system always primed before any cranking.

I've checked low pressure fuel pump (LPFP) it's delivering 6 bar-but pretty sure that even if it was not functioning correctly there would be some increase in fuel pressure from the High pressure fuel pump (HPFP) based on the tests performed.

HPFP delivering nothing even after 30 seconds.

I blanked all injectors with ball bearings a) to rule out leaks b) to avoid contamination if the pump had collapsed.

I have blanked the left hand rail feed from the HP pump and the link from the right hand rail so that the Pressure regulating valve (N276) could not leak any pressure back to LP side. I cranked while reading live actual fuel pressure ready to kill the ignition as soon as I saw any increase (as I am aware this could be too much pressure in one rail as injectors were all still blanked) but still nothing.

I ran all tests with the N290 fuel metering valve (on the HPFP) in place but disconnected electronically as this defaults the system to full fuel delivery from LPFP. I also ran the test with it connected.

My system has two regulators and one sensor. Fuel metering (N290) on top of the HPFP,  Pressure regulating valve (PRV-N276) on the end of left hand rail,  ECU controls injectors etc  based on pressure sensor readings. PRV is open during ignition on engine off, then should close once the engine is cranked. I blanked this originally to eliminate ECU not telling it to close on cranking.

So the rail pressure control/regulation is done via the a combination of the LPFP, pulse width modulation (PWM)  of the fuel metering valve (N290), the mechanical action of the HPFP via crank rpm, and the Pressure regulating Valve (N276)- the pressure sensor monitors and sends data to ECU that runs the show...

So there is fuel to the HPFP, leaking injectors have been ruled out, PRV taken out of the equation, and still no pressure.

Unless the pump has snapped its cam, or the chain, given the injectors tested 100% the pump has either collapsed and not sent shavings anywhere or I'm thinking the HPFP has a stuck valve not allowing the LP fuel to the High pressure side be compressed and make its way out.

A garage would have thrown a new HPFP at this 3 months ago so I'm fetching it out at least for another bench test as there's nothing else to test unless someone has any ideas.

Thanks for reading!

[cliffcoggin]

If you have proved to yourself that the pump is not making pressure, your only choices are to renew it or repair it. I don't know if the pump is gear or piston or some other type, but why can it not be worn to the point of not sealing the moving parts?

[mobotho]

Hi @cliffcoggin its a chain driven twin piston cp4.2 (Fig 1.) so dual cam that gives 4 compressions per rotation, can produce up to 2700 bar or zero 😒🤣

At 150,000 if it had worn I would expect to see a lot more failures of these on vehicles up round the 130K+ mile mark that were non catastrophic and it seems very rare.

They are fitted to earlier 3.0 BiTDI Audi's, Ford Power strokes (6.7 V8 Diesel) and Jeeps and RAM's some BMW high performance diesels. They seem to either grenade themselves-the roller underneath the pistons rotates 90° and then the rotating cam lobe gets a nice U carved into it (See Fig 2.) The shrapnel goes through to HP side, to the injectors so they're fubar, and back through the LP to the fuel tank, them through the LP pump to the filter, or fuel starvation/water or misfuelling=zero lubrication and a similar ending just a bit less aggressive.

 

Fig 1.

 

Orange is HP fuel out, and as you say, no reason why (and I believe from research it happens), that something cant stick shut and stop the HP fuel from exiting.

I've tried using a Birmingham screwdriver with a soft drift while cranking to shock the top (recommended method from a diesel specialist) to see if I get any pressure but nothing and I'm not prepared to hit any harder.

 

Fig 2.

 

I'm looking for someone to say "ah yeah I had one of these fail, it wasn't catastrophic it was the..."

I've found a guy in the States who had one fail on a Ford with very similar to my symptoms, was running but had some issues (mine was throwing P0087 at full throttle but could make 2700 Bar), came back to it and it wouldn't start...

He had a new HPFP that wouldn't make pressure right out the box! Eventually managed to get them to replace that one under warranty, got one with a test certificate and that sorted it.

I've got a final couple of things to double check and its surgery time...

I will update anon.

 

 

[mobotho]

FIXED...

Sorry for slow response but been busy...

It was the High pressure fuel pump as I suspected this time. Swapped it out and and hey presto it started. PF Jones did the best price (UK) on a new unit, I used Darkside developments for PRV (pressure regulating valve) but any good diesel specialist should be able to get you a Bosch OEM part.

P0087 (low fuel rail pressure) at full throttle was fixed by swapping the PRV (N276). So it turns out these newer valves will only take one fitting...If removed and refitted they will trigger P0087 at full throttle, ask me how I know 😒...I borrowed a known working valve (from a friend🫤) when mine wouldn't start and when refitted to donor car it caused the same P0087 I had been experiencing since the original injector failure prior to the pump failing on mine.

The high pressure pump suffered a non catastrophic failure, the valves/adjusters (see diagram in earlier posts) had stuck shut while it was running, seems impossible but that was the issue. I removed and stripped the pump down, once cleaned I managed to get them free and fuel flowing but since it would only be a matter of time for them to either stick again or the pump grenade (150K miles) I opted for a new unit. 

Any questions on CR diesel 3.0 TDI Audi's I'd like to think I can help since I checked just about everything...

[Steve Q]

4 hours ago, mobotho said:

FIXED...

Sorry for slow response but been busy...

It was the High pressure fuel pump as I suspected this time. Swapped it out and and hey presto it started. PF Jones did the best price (UK) on a new unit, I used Darkside developments for PRV (pressure regulating valve) but any good diesel specialist should be able to get you a Bosch OEM part.

P0087 (low fuel rail pressure) at full throttle was fixed by swapping the PRV (N276). So it turns out these newer valves will only take one fitting...If removed and refitted they will trigger P0087 at full throttle, ask me how I know 😒...I borrowed a known working valve (from a friend🫤) when mine wouldn't start and when refitted to donor car it caused the same P0087 I had been experiencing since the original injector failure prior to the pump failing on mine.

The high pressure pump suffered a non catastrophic failure, the valves/adjusters (see diagram in earlier posts) had stuck shut while it was running, seems impossible but that was the issue. I removed and stripped the pump down, once cleaned I managed to get them free and fuel flowing but since it would only be a matter of time for them to either stick again or the pump grenade (150K miles) I opted for a new unit. 

Any questions on CR diesel 3.0 TDI Audi's I'd like to think I can help since I checked just about everything...

Glad you got sorted. High pressure pump failure seems to becoming common on audis.