need help: misfire on idle
 

hi, I have a carrera 3.0 (1977) and have misfires on idle every now and then ..

config: stock, new spark plugs, new spark cables, distributor new, vacuum lines new, filters new, new harness, new coil ..

any idea?

One cylinder could be too lean. Dirty injector not opening. Depnding on miles I would replace them all.

also check intake bolts.
take a look at the plugs and see if one stands out from the others.


what plugs are you using.

Oh yea! I just started having that with my 1977 2.7L this morning. All my ignition components are new from about two months ago. It's really irritating.

I'm about to pull the plugs and figure out which cylinder is the culprit.

I was also thinking it's an injector...

+1 check the plugs for lean situation.

Make sure the boots for the wires are fully seated into both plugs and dizzy. If you did not hear or feel the "click/s" it is not on. Any back fires?

I was on the freeway and got horrible back fires from my cylinder, pulled over and found #2 was not fully seated on the plug.

While your checking,pull the fuel pump fuse/disable, pull each wire one at a time, place a new plug on the wire, ground it, have a helper crank engine and check for proper purple/blue spark on each or use an old plug and check for spark, it will probably be orange in color.

Please post pics of the plugs

Were these done by you or your mechanic?

Mine is only happening at idle right now and seems to go away at higher rpm. Either way my injectors are original, so I ordered 6 when I walked in the door this morning.

I dislike the idea of driving home with a lean cylinder, even if it's intermittent.

Pull your injectors and check their spray pattern. You might have one or two that are not atomizing as they should.

Joe

injectors usually show up at idle because they are spraying such a small amount of fuel. also because of the small amount of fuel needed at idle the fuel distributor can be the cause.
once above idle a "bad" injector can be fine. also at cruise, a little on the lean side does not hurt anything. very lean at WOT is a concern.

on my 930 when I was having issues I tested fuel flow at what would be idle, took about 20 minutes of fuel flow to get enough fuel to compare, cruise and of course WOT. I ended up getting 6 injectors.

^ That makes sense. On cold start it didn't misfire because it was receiving more fuel, then on warm idle it misfires pretty bad, at cruise it went away again.

Either way, 41 year old injectors are due for replacement :)

+1 ^

My 77 had a dead cylinder from a bad injector. Replaced that and it was running ok but still had that not so smooth idle. Added some Techron fuel injection cleaner and took it for a long drive. Much better idle. Continued with Techron treated fuel for the next 500 miles. Now the idle is smooth and the engine has more power. Point is, CIS injected Cars are prone to clogged injectors. Regular use of fuel injection cleaners in the fuel and Italian tune ups are a must.

injectors are a wear item.

Replaced my injectors, runs like a dream.