misfire ?

[weston_masive]

hello all first of all thanks again to anyone who helped me with my push rod tube seal question.
yesterday i attempted the push rod tube seal with the supervision of a mate (lol) completed it and fired my bus into life, I stood there with a great big grin on my face until my mate said "you got a misfire".
well my heart sank yet again so close but yet so far i have been through hell with this bus and after nearly 2 years of work one of the last jobs to get done so we can go away for half term now this,
Any way i have spent this morning looking. I done a compression check all around 130 psi so I went round one by one removing a lead no3 made no difference to it running. I took the plugs out and they are all black and dry . I new plugs in new leads, rota, dizzy cap still no difference .
So to sum it up i have spark and compression and seems to be over fueling too? (plugs being black)
Any help gratefully appreciated

[California Dreamin]

I still think you are in the right area......Definately have good compression ...check
Known good plug lead and cap....check
New distributor cap.....check
New plug......check

Now double check....swap over leads and plugs and see if the 'dead' cylinder changes to another.

Martin

[weston_masive]

tried that im wondering if vlave clearance could cause a misfire? or incorrect set up? the engine had new valves and rings etc and it aint moved since i didnt even pick up on the misfire so i dont even know how long it was there

[California Dreamin]

tried that im wondering if vlave clearance could cause a misfire? or incorrect set up? the engine had new valves and rings etc and it aint moved since i didnt even pick up on the misfire so i dont even know how long it was there

I'm wondering if vlave clearance could cause a misfire Yes if the valves were not properly closing but this would have given you a 'low compression' on that cylinder which you say is the same as the others.

It isn't rocket science....
You have compression
You have a spark
You have fuel
3 cylinders are functioning correctly so that rules out carburettor/pump & general ignition issues.

I suppose you could have a massive air leak on that one cylinder.....loose manifold bolts..hole/crack but this is clutching at straws.

Martin

[BOXY]

WHS^^^
Try swapping the plug and lead with one of the working cylinders and see if the fault moves.

Do worry about the plug colour. If the engine is only running for a minute or two the choke will still be on so the mixture will be rich. Plug colour is only useful if you've done a plug chop.

[weston_masive]

swapped leads stays with no3 its also runs on lpg so tryed switching it to lpg and it also makes no difference to no3

[BOXY]

Did you swap the plug?

[jim potter]

id chuck a set of plugs in it .. are these the plugs from before the rebuild ???

i had a old vr6 turbo , that when it fouled it plugs , when i orig built they needed changing , as i xouldnt get them back into life .

only what 2.50 a plug and ten minutes to change.

double check all the leads ..

then if you have checked everything mentioned above, is start looking at air leaks or injector plugs if its a injection model

[Footprint]

Swap the plugs around - if the misfire moves with it you'll have confirmed the problem.

[weston_masive]

put 2 sets of brand new plugs in bosh and then some silver lpg type ones

[BOXY]

If the compression is good, the plug is good, & the lead is good the next cheapest thing to check / replace is the dizzie cap. Check the contact for no.3 to see if it's loose or the socket for the HT lead is knackered. When you say "misfire", what do you mean?

I took the plugs out and they are all black and dry

If the plug isn't firing it'll be wet when you take it out. If its not wet then the plug is firing and your "misfire" could be an exhaust leak letting the engine "pop".

[weston_masive]

thanks for all the input.
Just to make it clear :
Swapped plugs for new and swapped them in different cylinders
same with leads
new dizzy cap
new rotor arm
still wont run on no3 cylinder the plug is firing its just if you pull no3 lead off it makes no difference to the running of the engine

[Ian Hulley]

No.3 compression is definately the same as the others ? Plug fires when out and is wet with fuel so therefore not firing under compression ...

[weston_masive]

no3 compression is a shade under 130 psi,with the plug out its got a good spark, the plug wasnt wet when i took it out just really black (same as all the others) but when you stand by the bus it smells like its running really rich

[Ian Hulley]

The only thing I can think of is if the valve rocker(s) are wrongly adjusted ... it's allowing the cylinder to compress (which it would if the valve(s) wasn't under load the spring(s) would shut the valve) but not opening the valve(s) to allow the cylinder to run properly.

Ian