Compression testing

Argenta · Post by **Argenta** » Tue Jan 10, 2023 2:26 am

Hiya, whats usually throwing up low comp figures on 1 cyl..?
These are my current ones:
1. 12
2. 10
3. 12
4. 12
5. 12
6. 12 bar.

Hmm…? If it was headgasket I suppose I’d seen lower on two cylinders?

Chippie · Post by **Chippie** » Tue Jan 10, 2023 8:28 am

One low cylinder could still be head gasket leaking into oil/water passages, although I’d probably expect a greater drop in compression, it could be a scored bore or burnt valve, only my best guess I’m afraid.

GuidoK · Post by **GuidoK** » Tue Jan 10, 2023 10:50 am

This is not a good way to diagnose the headgasket because it usually takes much much more pressure to leak past a weak spot in the headgasket (remember, this is compression, not the pressures that take place during combustion, that's ~5-10 times as high)

What are you trying to achieve with these numbers?

If you want to know where and if cyl2 leaks (substantially), then you have to do a leakdown test and maybe some other tricks.

Rockhopper · Post by **Rockhopper** » Tue Jan 10, 2023 2:00 pm

Squirt some oil in and do it again. If it stays the same then it’s valves, if it goes up then it’s rings or bores. Most likely.

Argenta · Post by **Argenta** » Tue Jan 10, 2023 3:06 pm

Yeah, I actually forgot the oil-squinting this time, gonna do that first, then check valve clearance, then leakdown test.
Something is definately up with cyl.2

Thanx all for now!

Argenta · Post by **Argenta** » Mon Mar 13, 2023 10:15 am

Update on this: Compression results was a result of faulty tester actually.
So, did a leakdown test (very even results 72-73psi) refurbished injectors, cleaned tick-over valve (forgot its english name), new plugs, coils, 2nd air pump functions controlled... To no avail!!

As long as the secondary air pump is on (50-60seconds in this weather) the idle is pretty lumpy. After that - even Steven.

Does anyone have any ideas..?

My only idea left is new engine mounts. However there's no vibration/noise i.e. engine touching anything.

beanie · Post by **beanie** » Mon Mar 13, 2023 12:44 pm

I had an occasionally rough cold start and it turned out to be the air shut off valve attached to the plenum.

Worth a check as it doesn’t take long to remove. If you shake it you should feel something moving inside. It might be gummed up so give it a clean by spraying some carb cleaner in there and shaking, let it sit, shake again etc.

Argenta · Post by **Argenta** » Mon Mar 13, 2023 1:48 pm

Thanx!
Must be the one I meant, this one under the plenum? I've just cleaned it this saturday to no avail...
As with ITB's which in all fairness were'nt that dirty.

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beanie · Post by **beanie** » Mon Mar 13, 2023 2:04 pm

If that’s under the plenum I assume it’s the ISV? The one I meant is a small plastic one-I think it’s to do with the brake servo.

I don’t have the standard s54 part number but the csl one is 11617833647. Have a google and you’ll see what I mean. It comes off somewhere on the back right as you look at the engine from the front.

Edit-this is the csl version, I can’t remember if the valve is the same across all s54 and it’s just the pipes that change. That’s probably the case but it will serve as a reference.

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No guarantee it will work but I spent ages chasing a really rough cold start that would immediately disappear after the warm up sequence and it turned out to be that.

Argenta · Post by **Argenta** » Mon Mar 13, 2023 2:58 pm

Oh right, the one on the side! I'll check it out, thank you very much!

Wow if that little bugger is to blame..

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