Citroen C5 MK3 THP 1.6 Compression Testing

[Brian C5]

Looking for some help please. I want to carry out a compression test on my 2012 Citroen C5 MK3 1.6 petrol THP (Prince engine) as I am having trouble with number 3 cylinder not firing even after changing the coil and spark plug. The cylinder already has a lot of petrol in it so I want to stop the fuel pump from running by removing a fuse before conducting a compression test.
Checked the handbook but cannot find anything listed to stop fuel pump running.
Any help/advice would be appreciated.

Thanks in advance.

Brian

[Hell Razor5543]

I would do a BSi reset, and (while the battery is disconnected) do the compression test.

viewtopic.php?t=61997

[Brian C5]

Thanks for the info.

[xantia_v6]

I am fairly sure that the ECU will not trigger the injector if it detects that the ignition coils are disconnected.

I also remind you that the cylinders are numbered from the gearbox end.

[Brian C5]

Thanks for the prompt reply I will let you know how I get on with the compression test. Unfortunatley my compression tester only works on 12mm plugs so I have ordered a reducer that takes it down to 10mm. When this arrives I can crack on with it.

[wheeler]

I would do a BSi reset, and (while the battery is disconnected) do the compression test.

viewtopic.php?t=61997

How would you do a compression test with the battery disconnected?

The easiest way to stop the fuel pump is just to unplug it. Lift up the back seats, pop the access panel off & unplug it. I would unplug it while the engine is running, the engine will run for a few seconds before cutting out this means the fuel line pressure will have dropped to. If you dont de pressurise the fuel line it will still inject fuel into the cylinders even with the fuel pump disabled.

[Hell Razor5543]

Couldn't you (using a long spanner) turn the engine over manually? A mechanic I use will, after replacing the timing belt, etc. on a car, turn the engine over twice manually before using the starter, in case he made a mistake with the timing.

[wheeler]

You need to turn the engine quite a bit faster than you could by hand to build up decent compression.
I’d say turning the engine by hand after timing belt replacement is more to check that the timing hasn’t jumped & that there is no valve to piston contact/engine lock up. Yes you can feel a bit of compression when turning by hand but its not enough.

[Brian C5]

Thanks for all your comments.

Today I carried out the compression test hoping no fuel would still be injected as all coils were removed and the ecu would detect this so not to pump any petrol. The reason I am doing the test as number 3 cylinder is not firing even though coil and sparkplug were changed and it is swimming in petrol. Before doing the test I dried the petrol from number three cylinder using a long thin bladed screwdriver with a rag rolled around it.

The resuts were :- number 1. 150psi number 2, 160psi number 3. 230 psi number4. 150 psi. Number 3 reading of 230 psi is not a misprint as I think this cylinder is was starting to hrydraulic due to the amount of petrol still going into it. Petrol was spraying/spurting out the the plug hole in large amounts whist I was testing the other cylinders.

My question is do you think the fuel injector in this cylinder is faulty and has failed fully open causing large amounts of petrol to fill the cylinder??
looking for some help as I am struggling to diagnose this problem.

The only fault code generated by this fault has been "P1339 Combustion Misfiring Injector No 3"

Thanks in advance

[wheeler]

I would do what I said above. Start the engine then unplug the fuel pump whilst the engine is still running & wait for it to cut out. Repeat the test with the fuel pump left disconnected. This way you know the fuel line will be de pressurised & it wont inject more fuel even if the injectors are being triggered.

[xantia_v6]

A faulty injector seems like a good theory. With a diagnostic tool you should be able to see how quickly the rail pressure drops after cranking the engine. Alternately, if you dry out the cylinder, then crank the engine to pressurise the fuel rail, you may be able to detect unwanted fuel being injected.

[Brian C5]

Thanks for all of your advice. Not sure if my dianostic tool would be good enough to test for rail pressure drops but I will look into it. I will redo the test by disconnected pump and run engine until sytem is dry.

If I decide to remove the injector how do you test it for faults?

Thanks

[xantia_v6]

You don't want to remove an injector unless really necessary, as you should then replace the Teflon seals on all the injectors which requires a special sizing tool and the seals are not cheap. Not to mention access to the injectors

I would go down the path of diagnosing the injector in-situ.

[Brian C5]

Thanks for the tip about the seals etc. I will now go down the road with a scanner now.

[Brian C5]

Looking for more help/advice please.

Decided to do the compression test again as my old compression tester failed. Purchased a new one today and conducted the test again with fuel pump disconnected to prevent more petrol getting into the engine. When I got the results I couldn't believe how different they were compared to my old gauge. So much so I tested my old Laguna to ensure the the gauge was operating correctly (which it is).

The test was done three times and the figures are all very low on all cylinders :- No1 105psi No2 90psi No3 105 No4 105.

The car has covered 48K and has the oil changed every 8k with reommended Elf oil and genuine oil filter.

My question is could these low figures be caused by the valve timing slipping due to timing chain stretch which is a common fault with the THP 1.6 Prince engine (as fitted to the Mini cooper S R56 N14).

PS I did not get any fault codes relating to timing issues or strange noises from a cold starts prior to this problem which can be an indication of timing chain issues.

Thanks