SOLVED -- Compression testing a diesel engine

[Rioja Cupra]

Is there a fuel cutoff solenoid on a PD160 Cupra?
I need to make sure the engine does not fire during a compression test.

 

[rafletcher]

There will be, yes, because that’s how diesels are stopped.

 

[Rioja Cupra]

There will be, yes, because that’s how diesels are stopped.

Yes, but do you know where it is and how to ensure it is closed when cranking the engine?

 

[Rich.T]

Unplug the harness to the pump?

 

[Yellow fr]

Or you could unplug the crack sensor


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[Seriously?]

Or you could unplug the crack sensor


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Best Spell Check epic fail of the Year Cheers mate, made me laugh on a Monday morning, which ain't easy !

 

[Rioja Cupra]

Thank you chaps, a couple of options there.
Will probably go for the high pressure pump, mainly because I can see that connector.
I would hate to bugger up the tester.

 

[Rich.T]

Take all 4 glow plugs out?

 

[Rioja Cupra]

Take all 4 glow plugs out?

I'll need to have the injector port and the glow-plug port obstructed or there won't be any compression. to measure.
However it may be worth cranking it without any glow-plugs as you suggest to flush out any fuel that may be lurking.

The intention is to use the glow-plug port for the compression tester, due to it being easy to access on a PD.

 

[Rioja Cupra]

Thank you chaps, a couple of options there.
Will probably go for the high pressure pump, mainly because I can see that connector.
I would hate to bugger up the tester.

The high pressure pump electrical connector is utterly inaccessible without stripping the cooling system.
Edit:
That connector may be something to do with fuel cooling.

 

[rafletcher]

Daft question, but is it separately fused?

 

[Rioja Cupra]

Daft question, but is it separately fused?

Thank you for your suggestion.

I just found this.
https://www.myarchive.us/richc/VW_TDI_with_PumpeDuse.pdf
It is mechanically driven.

I suppose the solenoids on the injectors are shut down to stop the engine.

I'm glad that I curse at that connector for longer than I did.

I could unplug the harness into the cylinder head (If it is a plug) and see if the engine will still crank over, either it will or it won't. I can't see how it will break anything apart from creating a host of fault codes.

 

[Rich.T]

If you're not worried about fault codes, unplug the cam sensor.
Wire goes into the back of the cambelt cover on the front of the engine.
That'll stop it starting.

 

[Rioja Cupra]

If you're not worried about fault codes, unplug the cam sensor.
Wire goes into the back of the cambelt cover on the front of the engine.
That'll stop it starting.

Fault codes are easy to clear, however finding and disconnecting sensors on this car is a nightmare.
So, the left end of the engine looking from the front. I guess it is 1/2 to 2/3 of the way down the engine towards front of the car, from the pdf I linked to earlier?

 

[Rich.T]

If memory serves, the plug for it is next to the dipstick. So follow the wire from the plug and it should disappear behind the belt cover roughly at the height of the lower edge of the top pulley.

 

[Rich.T]

Its a light colour connector and black wire.

 

[Rioja Cupra]

If memory serves, the plug for it is next to the dipstick. So follow the wire from the plug and it should disappear behind the belt cover roughly at the height of the lower edge of the top pulley.
View attachment 24121 View attachment 24122 View attachment 24123

Thank you Rich, that is a great help.
I will have a look in the morning.
James

 

[Rioja Cupra]

Thank you Rich, that is a great help.
I will have a look in the morning.
James

Mine is hidden behind o globe shaped object making this even more fun in the dark..
There are two connectors, one above the other, parallel to the engine block.
The top one's cable heads off to the left, the bottom one down, into the unknown depths below.
I'll try with the top one disconnected and VCDS scan it before cranking and after.

 

[Rioja Cupra]

Mine is hidden behind o globe shaped object making this even more fun in the dark..
There are two connectors, one above the other, parallel to the engine block.
The top one's cable heads off to the left, the bottom one down, into the unknown depths below.
I'll try with the top one disconnected and VCDS scan it before cranking and after.

Well that was indeed the correct connector, however after reading that PD document I remembered that the engine will run without the camshaft sensor but will take more revolutions to start using the crankshaft sensor for control.

Well what the hell, I tried it.
VCDS before.
Disconnect camshaft sensor.
Start engine, yes it did run,
VCDS to confirm it was the correct sensor. It was.

Now I need to find where the crankshaft sensor connector is because that will stop it for sure....Famous last words.

Edit:
Found it.
It was the bottom of the two connectors near the dipstick tube.
No fault code, however the engine turns over without starting.

Edit the edit:
Cranked it a bit longer to see if the engine RPM block on VCDS showed anything and the glowplug light started flashing together with another warning.
VCDS ran again. resulted in an error code for the crankshaft.
On to the actual compression test, when the battery has had its top-up charge.

 

[Rioja Cupra]

How effective is it?

I was going to start a new thread regarding the results, but I may as well continue the saga here.

#1 and #2 were at about 30 Bar which is correct for a BUK engine in good condition. #2 and #4 are lower at about 20 Bar, which is low.
I was going to drip some oil in the bore to see if it is the rings or the valves, however I chickened out due to the risk of the engine firing. I had this happen once many years ago, and it nearly destroyed the tester.

Next step is to try a leak test, both when cold and then when hot.

If leaking is reduced when hot, the next step would be a leak test when cold with some oil in the bores.