Jump to content

L20b missing cylinder help

Recommended Posts

Hello i have a 73 620 pickup with a 76 l20b. When i got the truck the head was cracked. Took me about a year to find a head for it. I finally find one its a w58 l20 round head. Spend a good fifteen hours cleaning everything up takin my time putting it all together. Finally get it timed im running the cam in the number 2 postion. Truck will fire instantly everytime you turn the key but will only hit 3 cylinders. Ive checked my valve clearance warm and cold. Ive checked my firing order even bought new plugs thinking one may have fouled and still nothing. Im at my wits end. Willing to try anything just have ran out of ideas. Any help tips or advice would be greatly appericated.

Link to comment
  • Replies 10
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Guest Rick-rat

Check your plug wires, maybe one is not letting spark through. Pull the wires one at a time when running so you can tell which cylinder is not firing. Have you done a compression check?

Link to comment

I can hear and feel that its missing a cylinder. I just cant figure out why. Ill admit im still by all means a mechinac in training, this just now has to be my daily driver and ive ran out of ideas. But now i can atleast see which ones missing. Ive read several places that timing should be 12 degrees BTDC. Mine is currently roughly 10 degrees is that enough to be throwing it this far off? It will run wth the distributor centered but do to the miss will occasionally try to de at lights and stop signs but if i turn the distributor almost all the way to the right it raises the idle so it doesnt try to die but makes the truck shake quite a bit.

Link to comment

Hearing and feeling isn't enough. A crack in the exhaust manifold will make the exhaust sound weird but it's nothing.


Check for spark on all 4 plug wires.

Check compression on all 4.


If you have both then it's fine.

Link to comment

Timing at 12* if you have the electronic ignitions. 



5* for your points dizzy. Reference a service manual to be certain. 


As datsunaholic mentioned previously... the 5 degree is probably for the dual points dizzy that has a built in retard set of points. The retard is 6-7 degrees removed from the 5 this brings it close to 12. The retard is solely for emissions and I would get rid of the second points and run full and proper advance.

Link to comment
  • 2 weeks later...

Do what hainz said by pulling plug wires to determine what cylinder is missing. Then pull that plug and hold the threads to the block to ground it and look to see if the plug is sparking (engine running, or starter turning). If spark is present then your problem is in the engine. If no spark, problem is in the dizzy. I'm expecting no spark, and the dizzy cap, or plug wire is bad. But it could easily be a valve not opening or closing right. Considering you did head work, this becomes even more likely. Pull the valve cover, wrench the crank through two rotations and look for obvious problems.


Still though, I bet you just have a bad plug wire, or you installed spark plugs without properly gaping the plug tips. Yeah, I bet that's it actually. Gap your plugs right, set advance, adjust points, adjust dwell, set advance again. Then tune carb and post video.



Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.