Mysterious compression test

[Patrick66]

Hi - I've just taken delivery of a 1.8 Turbo tourer. Before delivery it had new cambelt, head gasket and engine rebuild. During the first few days of using it I got jerking when I accelerated hard so took it in and a misfire was diagnosed. the mechanic subsequently did a compression test and found around 80 psi on all 4 cylinders rising to 150 after oil injection. Plus misfire codes on the diagnostic. So looking like something wrong with the piston rings?

So I took it back to the dealers and they could find nothing - no codes and a nice 160-170 on all 4 cylinders during a compression test. And it drives fine. So I don't really have any grounds to demand a refund (not that I don't like the car). Has anyone ever heard of a misfire and compression problem suddenly coming right with no intervention or could the original diagnosis have just been false codes.

Cheers
Patrick

[T-Cut]

Piston rings need an oil film to perform correctly. Nothing you report seems especially worrying, to me anyway. There are lots of other causes of misfiring under acceleration. My first suggestion would be to check the fuel filter security. I'm not saying this is the cause, but it's on the list and near the top imo.

Search for FFS and FOC for more info on this particular problem.

TC

[3disco]

Hi - I've just taken delivery of a 1.8 Turbo tourer. Before delivery it had new cambelt, head gasket and engine rebuild. During the first few days of using it I got jerking when I accelerated hard so took it in and a misfire was diagnosed. the mechanic subsequently did a compression test and found around 80 psi on all 4 cylinders rising to 150 after oil injection. Plus misfire codes on the diagnostic. So looking like something wrong with the piston rings?

So I took it back to the dealers and they could find nothing - no codes and a nice 160-170 on all 4 cylinders during a compression test. And it drives fine. So I don't really have any grounds to demand a refund (not that I don't like the car). Has anyone ever heard of a misfire and compression problem suddenly coming right with no intervention or could the original diagnosis have just been false codes.

Cheers
Patrick
the car would not run with only 80psi so would suggest he had a faulty compression tester!

[Lovel]

Hi - I've just taken delivery of a 1.8 Turbo tourer. Before delivery it had new cambelt, head gasket and engine rebuild. During the first few days of using it I got jerking when I accelerated hard so took it in and a misfire was diagnosed. the mechanic subsequently did a compression test and found around 80 psi on all 4 cylinders rising to 150 after oil injection. Plus misfire codes on the diagnostic. So looking like something wrong with the piston rings?

So I took it back to the dealers and they could find nothing - no codes and a nice 160-170 on all 4 cylinders during a compression test. And it drives fine. So I don't really have any grounds to demand a refund (not that I don't like the car). Has anyone ever heard of a misfire and compression problem suddenly coming right with no intervention or could the original diagnosis have just been false codes.

Cheers
Patrick

My experience of some of the vehicles that have had elastomer bead failure of the head gasket, especially the ones that have not had regular oil changes and have been allowed to run with the elastomer bead gone for some time, where the oil eventaully turns into a gravy like substance. I believe the tappets get contaminated with said gravy to such an extent that the tappet does not function as it should, leading to lower than normal cylinder compression pressure and excessive noise with excess tappet to valve clearance and also the opening and closing times of the valves are altered hence rough running initially. Eventually as you run the engine the new oil gets around the system and any remaining water or oil residue gets squeezed out over time leaving the tappet with nice clean viscous and non compressable oil. Of course the best way to get rid of contaminated tappet fluid is to squeeze it out when you overhaul the head, however because of the time involved and cost, I'm would think that most folks may not carry out this technique, you would not believe the amount a gunge that can come out of a tappet!

In a healthy k series engine, if you check your engine cold with full throttle and all plugs removed you will find the pressures in each cylinder varying quite widely and realtively low.
On a hot engine on full throttle and all plugs removed you will find that the pressure are very consitent and can be in the region of 190psi or even more see attached table for info.

Pressures also dependant upon starter motor speed, battery charge

1.6 k series, engine hot, with throttle held fully open
Miles Cyl 1 cyl 2 cyl 3 cyl 4 PSI
60165 198 195 198 198
63703 200 200 200 200
78369 208 208 208 205 new gauge
89242 195 195 198 192
97235 225 220 220 222
1.6 k series engine cold
Miles cyl 1 cyl 2 cyl 3 cyl 4 PSI
60165 165 172 176 198

[Patrick66]

Thanks for all your v useful info guys. I'll see how it goes, I believe there is a Rover specialist nearby (Herefordshire) so I'll maybe take it in again for a check over and to look at the fuel filter issue.

Cheers
Patrick