[mark e]

The woes of Bubbles, chapter n...

Over the weekend, I conducted a compression test- pulled fuel pump fuse, removed DI, did test including teaspoon of oil etc...

Put it all back together and... misfire under anything more than 0.5bar of boost.

Have tried a test DI on it tonight... still misfiring... have dumped the damn thing at garage as I am out of patience with it . Plugs are only a couple of days old.

So, I'm now puzzling over possible causes for the misfire... any offers...??

 

[wrighar]

Iffy Crank angle sensor?
DI unit.

Stuck.

 

[sgould]

Can't remember the rest of the saga, but if the compression is OK and the ignition is OK, you only have fuel left - sticking injector?.

Or the crankshaft position sensor?

Cosmic Blue 9-5 has cured (fingers crossed) his stalling and poor starting etc by changing this. I'm probably about to do the same. Have a look at bottom of page 1 on this thread

 

[mark e]

Hmmm... crank position sensor... that's the only part that hasn't been changed recently... it might also explain the pinking I had?

I did wonder about an injector problem but start up idle is OK...

Compression test was OK but not brilliant; all within "good" range but a variation of 26psi/1.8bar.

(I still think there's possibly a head problem )

 

[mark e]

Consensus from my local specialist is that it is a head problem... it's a refurbished head that appears in a previous life to have had the thread stripped from the spark plug holes. Steel sleeves have been fitted, which the plugs then screw in to, but they have worked loose on #2 & #3. As a result, they are a) not sealing properly and B) not conducting heat away properly from the spark plugs, which would explain why there's evidence of the plugs overheating. And they haven't ruled out the possibility of a crack either. It needs a pressure test to confirm this... so it's going back ot the suppliers.

 

[johncc]

I'm curious, because of similar(ish) symptoms. Would you say this means:

1) That there are head/valve problems that a compression test just won't detect.
2) That you were doing the compression test wrong.
3) That the variation between cylinders should be very low ... e.g. 10 psi, else there may be a problem.

Love to know your thoughts on it.

 

[mark e]

John,

1) Maybe
2) No
3) Yes, there should ideally be less than 10 psi or so variation between cylinders- I had over 26psi