Compression Testing our Engines?

[JTaylor2005]

Hi All,

Has anyone ever managed to compression test one of these engines? I am intrigued to know how well each cylinder is doing and because I fancy just playing about. Can you get glow plug adapters or something like that? 

How do you stop the engine firing up when doing a pressure test? Remove the injector plugs etc? 

Thanks

[bashbarnard]

Pretty much ban on with what youre saying. Glow plug adapter and disconnect the injectors. I don't know what the compression should be off the top of my head though.

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[pug306driver]

did I read it on hear, don't attempt to start/run the engine with an injector wire disconnected, fries the ecu ??

I am sure an "adaptor" could be made from an old heater plug for a compression tester/test ?

[JTaylor2005]

I believe that is attempting to run it with just one or two removed. It uses the reverse pulse of a closing injector to help charge the capacitor for the next injector to fire. (Apparently)

[bashbarnard]

Old f*cking wives tail that. I've never had an issue and I've been doing it since I've been in the trade [emoji23]

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[Poodle]

I've heard the same rumour and seen loads of mechanics do it regularly without a single issue.

[Ruan]

Old f*cking wives tail that. I've never had an issue and I've been doing it since I've been in the trade [emoji23]

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It's f*cking not an old wives tale. Stop telling anyone it is, go plug in Peugeot planet into any Piezo system and note the FIRST thing it says. NEVER remove an injector plug when the engine is running.

Solenoid injectors you'll usually knock out two cylinders, and are likely to damage the injector driver. They are driven with 80VDC and charged by pulsing the coil of the other injector it's paired with, which if active is likely to draw a pretty big arc and send the current through the roof and destroy the driver. You've just been lucky you've never hit it when the injector is on.

Piezo systems like the Siemens 8v HDis etc, if you remove the injector plug when it's running and catch it with it on, it cannot turn off. Go read about how Piezo systems work and you'll understand why, if the electric field is removed with the injector in it's open state, it will hold the injector open and not close, emptying the entire contents of the rail through that injector.

You've only ever been lucky doing it to not unplug it when it's active. Seen what happens when it's been done on both, usually destroys the piezo injector and ecu, solenoid units usually just kills the driver in the ECU. Yes, it's unlikely you hit it, but the chance isn't worth it.

[Piggy]

Just unplug the cam sensor?!?

Lol

Won't inject then.

[bashbarnard]

Not on about when it's running man. I'm on about having them disconnected to compression test [emoji16]

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[Ruan]

As above, unplug cam sensor, no chance of any issues then and it's 1 plug vs 4!

[JTaylor2005]

Never even thought about that! Good shout!

[Poodle]

There must be a lot of extremely lucky mechanics out there then eh. I'm not disputing the theory, just the reality. And I agree with you entirely that it's not best practice, but then how often do you replace high-pressure fuel lines after loosening/removing them?

[bashbarnard]

I'll have you know I reolace high pressure fuel lines every time they get loosed and removed ?
I also replace the cat/dpff everyone a turbo blows and in no way whatsoever drive it down the road smokey

[Ruan]

There must be a lot of extremely lucky mechanics out there then eh. I'm not disputing the theory, just the reality. And I agree with you entirely that it's not best practice, but then how often do you replace high-pressure fuel lines after loosening/removing them?

Yup, there is... But then when you consider at idle, the injectors will generally be open for around ~270uS, that's 0.00027 seconds every 720*CA = 0.141 Seconds @ 850rpm per injector - it's very unlucky to hit it, but if you do hit it, it's new ECU and injector times.

But saying that, I've seen damage done on both types of ECU from doing it, so it's not _THAT_ unlucky.

[Uberderv]

To stop it running you can unplug all of the injectors **before** you turn the engine over but never whilst it's running. I usually do this after an oil change to circulate the new oil before starting.

[Ruan]

To stop it running you can unplug all of the injectors **before** you turn the engine over but never whilst it's running. I usually do this after an oil change to circulate the new oil before starting.

Yep you can do that, or just unplug the cam sensor, much easier 4 plugs vs 1!

[Uberderv]

Yep you can do that, or just unplug the cam sensor, much easier 4 plugs vs 1!

 And that Sir is what I shall do from now on