O Compression

[Flybynight 0]

First time poster here so go easy on me. I've tried a search with no luck. So here goes. Daughter's 06 cdi is in the shop with starting problems (as in very hard to start) Mech. says o compression. I find that hard to believe since she drove it there. It's been getting harder to start, sometimes if she plugged it in overnight it was better. Always starts once up and running. Anyway they checked the glow plugs and changed the fuel filter (very pricey filter). Still wont start any where else we should be looking. If it is low compression what about a rebuild?I forgot to mention the car is at the dealer's.so many questions and few answers.ThanksDon

[bilgladstone 13]

You're right, it cannot be zero compression; if the dealership told you that, they are numbskulls. Where you should be looking is for another shop that has a clue. They have already charged you for an expensive and completely unnecessary fuel filter replacement. Cut you losses and take the car somewhere else before these guys take any more of your hard earned cash.Bil

[Flybynight 0]

Since it's already there I thought I might have another direction to send them in. Either that or I have it towed to another shop. More money gone! Just got off the phone with the mech. He says that only 1 cylinder has normal compression and the other 2 are low. He's suggesting doing an engine flush. He thinks that maybe there is a carbon build up and this would loosen it and restore the compression? Does that make any sense to anyone? He did get the car running and took it out for a drive. HDon

Edited September 19, 2012 by smart142

[bilgladstone 13]

Is this a Mercedes/smart shop? What does the code reader say? That would give your guy a hint in what direction to go.B

[Flybynight 0]

no codes coming up. not sure if there would be for low compression. Does it seem resonable to do an engine flush to restore compression?

[bilgladstone 13]

Engine flush could help I have had good DIY success with Seafoam but professionals likely use something else.Bil

[Flybynight 0]

Well i'll give it a try and let you know how it turns out.

[MikeT 744]

Inspect the length of the cam gear teeth through the oil filler cap. If they are not prominent, It could be that the valves are doing weird stuff (e.g. not closing fully) due to the gear dissolving and collateral damage. That requires at least a partial rebuild. It could also be caused by crud building up on the valve stems. Seafoam etc could help if this is the case.

[Flybynight 0]

Well we've done the engine flush and added super concentrated fuel additive, driven the hell out of her and still hard to start with low compression. I've been behind her when she's driven away and no oil burnt exshaust. So don't know what to do next :suicide_anim:Mike T: I had a look at the time chain gear though the oil cap and it looks fine. thanks

Edited September 28, 2012 by Flybynight

[bilgladstone 13]

Next? A leak-down test would be a helpful diagnostic. It's basically a "reverse compression test", where 100psi compressed air is fed, with a suitable adapter, to the suspect cylinder through the glow plug hole. An experienced mechanic can then listen at the exhaust, the intake and the crankcase and tell you whether the leak is intake or exhaust valve, or piston ring, or maybe even a head gasket.

B

[tolsen 630]

What are the compression readings? Have you confirmed glow plugs are working?

[mig2006 0]

valves are likely shot. had identical symptoms on 50 kilometer 2006 cdi. 2 cylinders no comp when it finally refused to start all together.rebuild shop said had never seen valves worn/damaged like that & only thing he could think of to cause it was car being left to idle in winter & never warming up enuf to get proper combustion? i saw the tear down & cannot believe the car ran as long as it did.never used a drop of oil!cost $2800 to do valves/rings/gaskets etc. pistons were fine. seems to run way it should & even starts in winter. still annoyed about the guy i bought it from as he knew there was a problem but i was stupid/trusting

[ray4406 0]

a leak down will tell you hwere the compression pressure is leaking but they have to know how to do the test properly each piston tested must be brought up to top dead center on compression stroke and stay there when the air is applied.

[Silver 8]

Browse: "Eric the car guy how to perform a leak down test" on you tube to get a good idea of what it is.

[ray4406 0]

i have heard of other cdi's with valve seats falling out I have started to think how is this possible on some cars not all first thing to come to mind is have these cars with the cylinder head trouble ever been over heated and i mean ever? Or low on coolant where the gauge might even read cold?

[AHZELA 12]

Head scratcher.