High compression causing a cylinder not to run?

[skud52]

Hi guys, got a 2.0 16v on r1 carbs and had no troubles up till now, the engine has been fitted into my new shell and is only running on 3 cylinders, #4 isnt firing, checked spark and that seams ok, tip a bit of fuel down and it fires however ive had the carbs apart snd nothing seams wrong,

Did a compression test and found that #4 was considerable higher than the rest, so is it possible that this is why it isnt firing, and that tipping fuel in is making a richer mixture for it to run rather than the carb not feeding the cylinder at all?

Not sure whether tho have the head off or is there anything you guys can suggest??

Cheers, Ben

[Royston]

What is the pressure you are getting under test psi/bar?

The higher the compression pressure, the harder it is for the spark to ingite the fuel, could be a lead breaking down (if in distributor) coil pack, or lack of fuel, especially as you are on separate carb per cylinder

If you crank with no spark, do all the plugs get wet?

Seems strange that one is high, I would say 3 are low

Are you testing with the throttle butterfly open or closed

As a comparison, I did a test on a Rover K series 1.4 and got 150 psi across all cylinders at the weekend, they are @ 10:1CR

[skud52]

1-3 were around 110 and #4 was 190. We thought it was possible that its a case that 3 are low but it seams a bit high for as far as im aware a standard engine.

Test was done with butterflys closed, how would this affect the results?

Ill try cranking with no spark add get back to you on that, also would it be worth doin a wet test?

Cheers, ben

[Royston]

Is the plug oiled on no4?, if there was oil present, could increase sealing/pressure 190psi sounds high, 110 also sounds low ish but should run

Closed butterfly iirc creates vacuum in inlet side, don't think it really matters, but open gives freeflow on inlet side

if you can feed fuel to the no4 carb and it runs ok, would identify fuelling (or easy start, short squirts only)

[skud52]

#4 plug wasnt covered in oil and ive looded down bore with a torch and it seams fairly normal. Im rather reluctant to take the head off but its looking like i have no choice, although im doubtfull as ti whether this will solve the problem

Cheers, ben

[Stuart]

190 does seem a little high for a std engine with the butterflies closed. I'd definitely check for oil on plug 4.

How long has the engine stood between resells?

[skud52]

Engines been stood for 6-8 months i would have guessed, 1 thing thats worrying me a little the more i think about it is that i fitted some arp rob bolts but surely if #4 wasnt fitted tight the bottom end would knock?

[ocdstigy]

Im no sure if it's worth mentioning but the readings my mate gets on a similar setup is 125 on cylinder 2/3/4 and 1 is reading 155,i will update when he finds the problem.

[skud52]

Im no sure if it's worth mentioning but the readings my mate gets on a similar setup is 125 on cylinder 2/3/4 and 1 is reading 155,i will update when he finds the problem.

Yea cheers, that would be great!

[ocdstigy]

Ok i have spoke to him on the phone,he has put it down to a worn piston ring........

[skud52]

Surely thats not causing a higher compression tho? Also is it not running on the high compression cylinder like mine?

Cheers ben

[Stuart]

if its a worn oil control ring then you would get a higher compression test on the deaded one as its leaking oil up to seal the bores better.

[skud52]

Ok but is this like to cause it not to fire?

[Royston]

Higher the compression, the more difficult it becomes to light the fuel

[skud52]

Hence why if i tip some extra down then it fires into life? Would richening the mixture screw on that carb give me an indication as to whether its a compression problem or a straight lack of fuel?

[ocdstigy]

He explained to me the ring is worn not sealing the cylinder and causing the problem,however your car may be different,im no mechanic so couldnt comment im afraid,just thought i would post what my mate has told me about his,cheers.