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cylinder not firing
notshy - February 23rd, 2011 at 09:21 PM

G'day Guys!

New to the formum...but hoping you can help me out? I have a 1500 bug that has started to run rough. We haven't had it very long so we went through and put new plugs, leads, points and condenser on and still no joy. The mech at work said it sounded as if it was electrical. It does start but pulling the back left lead off does not affect it when running, pointing to that port being the prob. Plenty of spark, compression about 100. It did come good for a couple of days at the beginning of all the dramas after I played with the leads but it only lasted a couple of days before it did it again. I'm starting to run out of ideas, any of yours would be greatly appreciated!!

65standard - February 23rd, 2011 at 10:13 PM

The back left lead is No.4 cylinder. Forward left is No. 3, Rear right is No.2 and forward right is No.1

When you pulled the plug off, what did it look like? Was it oily? If so, you could have shot rings in that cylinder.

Have you checked your valve clearances? They could be too large, opening too late and closing too early. it's possible to have them out in one cylinder, making it run rough. The clearances should be .006" to .008" depending on who you talk to.

Hope this helps.

vw54 - February 24th, 2011 at 06:37 AM

have you checked the tappets

Big Al - February 24th, 2011 at 08:24 AM

I had a similar problem with my VW after fixing an engine fire in that I put the leads on incorrectly. For some reason my engine has been tuned to fire off no.3 rather than no1 so the leads on the distributer are different from the book? I managed to start the car but it ran very rough.

Also check that your dizzy hasn't moved ( timing).

Joel - February 24th, 2011 at 08:56 AM

That compression is a tad on the low side, not badly but certainly not factory fresh engine.

waveman1500 - February 24th, 2011 at 07:33 PM

Quote:
Originally posted by Joel
That compression is a tad on the low side, not badly but certainly not factory fresh engine.


This is true, but 100psi is still enough to have it run nicely and fire on all four. Have you looked at the distributor cap, rotor button and maybe even the points cam inside the distributor? Sometimes the points cams can round off with neglect if they're never oiled.

Also look for other faults, is the exhaust blocked? Intake manifold? Do the valves go up and down properly when you turn the engine over by hand?

Oh, and the cylinder numbering that 65standard gives is only correct if you refer to the rearward end of the car as the 'back' cylinder and the cylinder closest to the driver as the 'front'. Because you work on the engine from the back of the car and reach into the engine bay, I tend to call #3 and #1 (up against the firewall) the 'back' cylinders, and the ones closest to the engine lid the 'front' (#4 and #2).

ratty 63 - February 25th, 2011 at 09:34 AM

Might be a long shot - but have you flooded the engine recently?

I have found that once the spark plugs have been soaked in fuel they don't recover any more. Not sure why - never used to be a problem... perhaps it's the new fuel or a change in the materials they use in the plugs....

It's also not impossible to have an internal short in a spark plug, even when they are brand new.

Before you get too involved in removing parts for testing it might be worth changing the plugs (particularly the plug in the cylinder that isn't firing) to check....


R :)

notshy - February 25th, 2011 at 11:01 AM

Thanks for the tips guys, it's given me a few things to look at. My mate has a few parts eg dissy, rotor button that I might try and fault find with. I did swap all the plugs around to see if it was the 1 dodgey plug, but not the case. The plugs just appear all the same ...just a bit black.

notshy - April 29th, 2011 at 08:09 AM

Well I've been away for a while and not really much the wiser but the bug did come good after a new plug and a good hard drive out on the open road to clean it out! Thanks again!