A bit of help on in cylinder pressure

Post discussions on projects you are working on
Post Reply
Yamukela
Newbie
Posts: 0
Joined: Fri Jun 07, 2024 9:27 am

A bit of help on in cylinder pressure

Post by Yamukela »

I did an in cylinder pressure test on a Ford Figo TDci (diesel) 2008 F6J6 engine. The engine is out of the car with all ancillaries removed except for the starter motor and fuel pump. The intake box, E.G.R system are all removed. The injectors and glow plugs are still in. I modified an old glow plug to measure pressures.

When I crank the engine I get a nice waveform except for a bump at the bottom plateau (red circle). This is when the piston has reached BDC (180°), and starts to move towards the cylinder head reducing the volume of the cylinder, but since the exhaust valve is now open, the gas charge escapes into the exhaust. So the plateau represents the time during which the piston is pushing exhaust gas out and during this time the pressure in the cylinder should be nearly equal to the atmospheric pressure.

But as you can see on the attachment there is a bit of a bump (4.1psi). If the exhaust valve is open at this point what can cause this bump?

Another thing I picked up is that the plateau does not dip again before compression starts (purple circle). I do not know if it should dip on cranking only cause there is no vacuum created because of throttle closing.

Also, the Ford manual states that the difference between the cylinder pressures should not be more than 5 bar but says nothing about what the pressure should be. #1, #2 and #3 pressures (158psi) are almost exactly the same, however #4 is 192 psi. I cannot find a reliable source which tells me what the in cylinder pressures should be.
Attachments
20240607114547.png

Martyn
Site Admin
Site Admin
Posts: 4549
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

Re: A bit of help on in cylinder pressure

Post by Martyn »

You may wish to repost this in our Specialist Automotive Forum https://www.picoauto.com/support/index.php
Martyn
Technical Support Manager

Yamukela
Newbie
Posts: 0
Joined: Fri Jun 07, 2024 9:27 am

Re: A bit of help on in cylinder pressure

Post by Yamukela »

Will do thank you :D

Post Reply