This all took place a couple of weeks ago, but I haven't posted here until now because it winds me up too much to think about it!
For a while now (many, many months) my car had a bit of a slight, intermittent misfire and lack of power when cold. It had this mentioned when it went for a service, but no fault was found. It must have been like this for over 12000 miles, because it went for another service, then it went for a failed EGR valve (again). When we went to pick it up after EGR replacement the misfire was there, so we got a tech to look at it, and they kept it for a few more days.
They did compression tests (wet and dry) and the compression was low on both, on cylinders 3 & 4. Both tests being low usually means either faulty valve(s) or busted (rather than slightly worn) piston rings as far as I'm aware.
Apparently the valves were freed, but I was warned that this may not cure the root of the problem, and if it returned, the head would have to come off, which would be in the region of £600-800. Sure enough a week later the problem returned, and it seems to be worse than before. If the piston rings were cracked I believe the misfire would be there all the time, rather than intermittently.
So here's what I'm thinking:
1. I assume that the valves were probably freed by removing the camcover and just getting access to the cam end of the valve. If so I might have a go at this myself, except the Multijet has the air filter assembly on top the engine. I assume it's fairly straightforward to remove this and get the camcover off?
2. Why would valves stick? I don't know if it's the inlet or exhaust valves which are sticking. The three things I can think of are that the back of the valve is contaminated (on the exhaust valve, but no way to see this without taking the head off), the valve stem isn't well lubricated (possibly due to poor oil flow), or the valve is bent or damaged (would this give an intermittent misfire though?).
3. Why would you get two this happening on two adjacent cylinders? I'm not sure how the oil gets to the valves and cams to lubricate them, but I wonder if there could be something impeding the oil flow up that end. Alternatively it could just be bad luck.
4. If it can't be sorted properly without the head off, I might take it to Motormech in Birmingham, where I had the head off my Coupe 20VT and a new valve for about £300. If I end up doing that it might be worth rebuilding the top end.... on a car with 75k miles.
So what do you all think?
For a while now (many, many months) my car had a bit of a slight, intermittent misfire and lack of power when cold. It had this mentioned when it went for a service, but no fault was found. It must have been like this for over 12000 miles, because it went for another service, then it went for a failed EGR valve (again). When we went to pick it up after EGR replacement the misfire was there, so we got a tech to look at it, and they kept it for a few more days.
They did compression tests (wet and dry) and the compression was low on both, on cylinders 3 & 4. Both tests being low usually means either faulty valve(s) or busted (rather than slightly worn) piston rings as far as I'm aware.
Apparently the valves were freed, but I was warned that this may not cure the root of the problem, and if it returned, the head would have to come off, which would be in the region of £600-800. Sure enough a week later the problem returned, and it seems to be worse than before. If the piston rings were cracked I believe the misfire would be there all the time, rather than intermittently.
So here's what I'm thinking:
1. I assume that the valves were probably freed by removing the camcover and just getting access to the cam end of the valve. If so I might have a go at this myself, except the Multijet has the air filter assembly on top the engine. I assume it's fairly straightforward to remove this and get the camcover off?
2. Why would valves stick? I don't know if it's the inlet or exhaust valves which are sticking. The three things I can think of are that the back of the valve is contaminated (on the exhaust valve, but no way to see this without taking the head off), the valve stem isn't well lubricated (possibly due to poor oil flow), or the valve is bent or damaged (would this give an intermittent misfire though?).
3. Why would you get two this happening on two adjacent cylinders? I'm not sure how the oil gets to the valves and cams to lubricate them, but I wonder if there could be something impeding the oil flow up that end. Alternatively it could just be bad luck.
4. If it can't be sorted properly without the head off, I might take it to Motormech in Birmingham, where I had the head off my Coupe 20VT and a new valve for about £300. If I end up doing that it might be worth rebuilding the top end.... on a car with 75k miles.
So what do you all think?
