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[Matchless]

My project 2.5 estate has been on the road for a couple of months now but is not well, it lacks bottom-end performance and is drinking fuel. I have worked through a diagnostic process and reached a conclusion as to what I think is wrong with it and should find out if I am right in the next day or so...weather permitting.

I thought I would post up the symptoms and the results of my tests to see if anyone comes to the same conclusion but if I am right then I suspect there will be others suffering with the same fault.

A bit of history: It was bought as a runner but "makes a rattling noise". The cambelt tensioner had failed and the passenger bank timing was 2 teeth out. A new cambelt kit had it idling smoothly but it wouldnt rev over 2500, this was fixed by a new fuel filter. It passed the MoT and I started using it which is when I realised there was something wrong.

Symptoms:

Revs freely to 6750 but lacks torque and bottom-end 'grunt'.
No hint of a missfire or un-even running.
Fuel consumption is 22mpg at best on commute (my Elite used to manage 27 on the same run).
Air mass meter OK and coolant temp sensor OK.
looking back at the MoT emission test:
      lambda slightly high
      CO at top limit
      HC slightly raised
Manifold vacuum low at 17.5" Checked all the breather seals, vacuum pipes etc and eventually changed the manifold and bridge gaskets...no improvement.
EGR valve blanked off...no improvement.
HT leads, plugs coil etc checked.
Compression test shows drivers side 15 bar, passenger side lower at 13 bar.
Back to the vacuum gauge, when I hold the rear multi-ram open by hand the gauge oscillates rapidly between 21" and 14".

So what do you think is wrong and how do you account for all the symptoms?....

[Auto Addict]

As they say in the trade.........



































































F*@k knows

[JamesV6CDX]

I reckon since the timing belt slipped and the passenger bank was that far out -

A small amount of cylinder head damage has happened, eg a small amount of damage so the valves to they don't QUITE seat (hence open and close) properly, hence the lower compression on that bank.

Therefore the cylinders on that side can't burn the fuel quite as efficiently, which is what's resulting in the poor performance and excessive consumption.

Head off time!

[STMO123]

Bent valve/s on the passenger bank :-/

[STMO123]

Bent valves on the passenger bank :-/

That's what I just said, in a roudabout way  

So you did James, so you did

[TheBoy]

No idea and moment, head still spinning to think clearly. I do not think its bent valves though.

If you need Tech2, just shout....

[JamesV6CDX]

No idea and moment, head still spinning to think clearly. I do not think its bent valves though.

If you need Tech2, just shout....

Tech2 won't resolve a 2 bar difference in compression between banks- that's 29.1Psi!

There is a valve issue...

[Markjay]

No idea and moment, head still spinning to think clearly. I do not think its bent valves though.

If you need Tech2, just shout....

My previous 'Meega had a tensioner failure with jumped tooth (or teeth - don't know by how much because Vx sorted it), and no valve damage occurred.

I don't think that the difference between 13 and 15 is symptomatic of bent valve, I would expect far lower figures on the leaking side.

Piston/Valve damage is likely to get worst with RPM (though admittedly not always), low-end performance problem would typically be something else (vacuum leak / sensor problems etc)

I know I am not being helpful, but so far Matchless all you technical posts were spot-on so it seems that you know your Omegas well and I suspect that you did a fair bit of diagnosing already and the answer isn't going to be a easy one...

[Markjay]

...(though admittedly not always)...

 

[TheBoy]

Piston/Valve damage is likely to get worst with RPM

Can't agree..

My Veccy, with a hole in the valve, missed like a b!tch at low revs, but was fine at higher revs...

I still think there's a valve seating issue

You had valve damage, you had very low compression. If valve damage occured due to slipped belt, I would suspect very low compression.


Got this inkling about a slightly coked up head...   ...but that doesn't happen nowadays  :-/

[TheBoy]

  ...but that doesn't happen nowadays  :-/

You should have seen what came off the Veccy.. and not just in pot no 3 !!

Difference being is that that crappy little engine had done 200k!

[TheBoy]

Can we stop going off on a tangent on this thread, and stick to original post...

[Dave-C]

My project 2.5 estate has been on the road for a couple of months now but is not well, it lacks bottom-end performance and is drinking fuel. I have worked through a diagnostic process and reached a conclusion as to what I think is wrong with it and should find out if I am right in the next day or so...weather permitting.

I thought I would post up the symptoms and the results of my tests to see if anyone comes to the same conclusion but if I am right then I suspect there will be others suffering with the same fault.

A bit of history: It was bought as a runner but "makes a rattling noise". The cambelt tensioner had failed and the passenger bank timing was 2 teeth out. A new cambelt kit had it idling smoothly but it wouldnt rev over 2500, this was fixed by a new fuel filter. It passed the MoT and I started using it which is when I realised there was something wrong.

Symptoms:

Revs freely to 6750 but lacks torque and bottom-end 'grunt'.
No hint of a missfire or un-even running.
Fuel consumption is 22mpg at best on commute (my Elite used to manage 27 on the same run).
Air mass meter OK and coolant temp sensor OK.
looking back at the MoT emission test:
      lambda slightly high
      CO at top limit
      HC slightly raised
Manifold vacuum low at 17.5" Checked all the breather seals, vacuum pipes etc and eventually changed the manifold and bridge gaskets...no improvement.
EGR valve blanked off...no improvement.
HT leads, plugs coil etc checked.
Compression test shows drivers side 15 bar, passenger side lower at 13 bar.
Back to the vacuum gauge, when I hold the rear multi-ram open by hand the gauge oscillates rapidly between 21" and 14".

So what do you think is wrong and how do you account for all the symptoms?....

Assuming that this car had run like this for a short while, is there any logic to this theory?  Cam timing out causing unburnt fuel to flood cat and cause blockage....   I'm not totally sold on an induction or compressing situation, but, a back pressure problem....  been there with a similar prob with a Cossie 24v.... must say that the 15bar - 13 bar difference may constitute a damaged valve.....  shall be watching this one closely........

DC

DC

[Matchless]

Right.....my theory was that there had been minor valve - piston contact when the tensioner failed and that the exhaust valves on one bank were not sealing. I based this mainly on the poor compression figures and the MoT emission results, if the exhaust valves were leaking then fuel / air mix would enter the exhaust during the compression stroke. The lambda sensor would 'see' the oxygen in the air and return a high lambda value which is interpreted as 'go rich' so more fuel is injected which ruins the fuel consumption (would have expected a lambda sensor fault code though as the O2 level would not reduce). The unburnt fuel leaking past the valve would reach the catalyst and burn there but there is insufficient oxygen to burn fully so the tailpipe CO level would be high (as seen at MoT).

Makes sense to you?

[TheBoy]

Right.....my theory was that there had been minor valve - piston contact when the tensioner failed and that the exhaust valves on one bank were not sealing. I based this mainly on the poor compression figures and the MoT emission results, if the exhaust valves were leaking then fuel / air mix would enter the exhaust during the compression stroke. The lambda sensor would 'see' the oxygen in the air and return a high lambda value which is interpreted as 'go rich' so more fuel is injected which ruins the fuel consumption (would have expected a lambda sensor fault code though as the O2 level would not reduce). The unburnt fuel leaking past the valve would reach the catalyst and burn there but there is insufficient oxygen to burn fully so the tailpipe CO level would be high (as seen at MoT).

Makes sense to you?

Can't argue with your logic (or your expertise ), but would have though any valve damage would have resulted in significantly lower compression...