Annoying idle problem - 940 LPT

[Laird Scooby]

Originally Posted by TonyS9

Higher RPMs are always lower mpg, even when the engine feels more relaxed. Engine friction is the dominant force. You do need a very light throttle to avoid engine vibration at those rpms though. Lower speed is also a consistent benefit.

Be interesting to prove it one way or another. Best economy i ever got from my 827 Sterling was 43mpg cruising at between 80-90mph, did the same trip the previous day in similar conditions at between 70-80 and only returned 40mpg.

[Cylinder 8]

I've just got the car back from having a smoke test done, apparently there are no vacuum leaks. I'm pretty much stumped now.

Fuel pressure?
Ignition amplifier?
Radio suppression relay?
Corroded earths?

That's all I can think of but I'm not convinced any of those things would give the symptoms I have.

[Laird Scooby]

Originally Posted by Cylinder 8

I've just got the car back from having a smoke test done, apparently there are no vacuum leaks. I'm pretty much stumped now.

Fuel pressure?
Ignition amplifier?
Radio suppression relay?
Corroded earths?

That's all I can think of but I'm not convinced any of those things would give the symptoms I have.

I doubt any of those would give the symptoms you've got, have you added the 2L of meths to less than 1/4 tank of fuel yet? Given everything else, it's pointing to something you've not yet checked and that's one of the few things and should be near the top to eliminate the obvious.

[TonyS9]

Tested my compression and its low on Cyl1, probably burnt valves from running 15psi without checking O2 early on. Next job to tackle!

1-130psi
2,3,4- 160psi

[Laird Scooby]

Originally Posted by TonyS9

Tested my compression and its low on Cyl1, probably burnt valves from running 15psi without checking O2 early on. Next job to tackle!

1-130psi
2,3,4- 160psi

Could also be the beginnings of HGF Tony, possibly the gap between the combustion chamber and the water jacket near the thermostat, they seem to like to go there for some reason.
Burned valves would also be a consideration but as the head has to come off either way............

[TonyS9]

Originally Posted by Laird Scooby

Could also be the beginnings of HGF Tony, possibly the gap between the combustion chamber and the water jacket near the thermostat, they seem to like to go there for some reason.
Burned valves would also be a consideration but as the head has to come off either way............

This is the 360, head was rebuilt, valves ground in, skimmed, plug threads cleaned, new bolts etc only a few years ago. Been only doing track days and drag racing in it mainly so <1000 miles. I had thought it was impossible to burn the valves on B230FT but I ran a variable fuel pressure regulator as a bodge to up the power without monitoring the O2.

I did the valves in the 1980 340 years back and it made a hude difference, I've done many red blocks since then and while the valve seats were not smooth, grinding made little difference.

Still it will be good to get that compression back, she did feel a bit sluggish and starting badly. I had tested it before but my old gauge was not sealing properly. Very hard to get the right extension so you can tighen them down properly, but the latest gauge has a push on rubber seal which was effective.

Will find out soon if its HG or valves.

[baggy798]

Just bypass the idle valve and be done with it.