f-head misfire at idle......still

Ok, so for those of you following/responding to my posts, you are pretty clear on the saga of getting my jeep running satisfactorily. Now I need help with the one little problem that will not go away, and has always been there: The misfire at idle....(those of you that have helped me previously, and know all that I have been through can skip the rest of this post now...)

The jeep continues to have a misfire type condition at idle, only really noticeable at the exhaust pipe. It revs great, and runs great with even a little throttle. Has some hesitation when I initially apply the throttle. Still misses at idle though.....Any help would be wonderful, and graciously accepted.....

So far I have replaced: cap, rotor, wires, points (gapped to .020), plugs (came gapped at .035, but I didn't think that .005 extra gap would cause any trouble), PCV valve.
I have also: Cleaned the carb (spray on carb cleaner), changed the oil, set timing to 5* advance (should I maybe try to advance it more?) , checked for vacuum leaks with the carb cleaner method, and endlessly fiddled with the idle mixture.
I will be doing a compression check in the next couple of days....

 

sorry, thats what I meant....I disconnected and plugged the vacuum advance line when I timed it....

 

Just a thought, When you installed the new rotor and points did you happen to notice if the distributor shaft bushing was still good and that the reluctor was not excessively loose on the shaft, I have seen reluctors loose enough on the distributor shaft to almost close up a set of points when wiggled back and forth. Are the flyweights, flyweight pivot posts and springs still tight and serviceable.

 

I will go experiment with the timing a bit more, and do the compression test. I just wasn't sure if I should stray too far from the stock specs....how far is safe for the timing?

I haven't torn apart the distributor to inspect the weights and springs, but the shaft doesn't seem to have much play, (other than a little gear lash).

 

I'll check it out, and oil it up if needed. Thanks alot.....and stay tuned for compression test results.......(insert suspense here)

 

Ok.....so.......Compression reads like this:
1-110, 2-100, 3-104, 4-96......New problem as well....the #4 plug had a nice coating of oil on it....I have been checking the plugs pretty regularly, and this is a new developement....What can I do? (this jeep is my daily driver, and I have to leave for work in 1/2 hour, what kind of danger am I facing?) Any ideas on what I should check next?

 

No danger - clean the plugs, put them back, drive it. Could be that the #4 cylinder is a little more worn than the others, and is the first to oil foul. Once it fouls, the misfire will make unburnt oil build up. Might switch to a hotter plug. A longer, hotter spark would help too, but I'm not sure what's practical on a F134 - maybe Pertronix with a MSD box? How old is the coil? What's the color of the spark?

Compression readings aren't bad - mean is 103, +/- 10% is 113/93. In-spec for a used engine. Not sure what normal is for that engine, but I'd guess 100-120 nominal. Valves are most likely ok. Rings may be worn, but if so, the wear is even (good!). You might have some oil coming in through a valve guide - that won't show up on the compression test. Any smoke?

Redo your compression test (just to be thorough) and repeat after adding about a teaspoon full of oil through the spark plug holes. This will indicate how worn the rings are.

 

Will do tonight after I get off work (re check/oil in plug holes..).....I have only once or twice (a few weeks ago actually) had a small puff of blue smoke. None in quite a while though....
Thanks alot for the piece of mind....Gotta go.

 

Does anyone have any suggestions for plugs that I should try? It seems to skip less now, (I still don't know where the oil is coming from, but I will check it out tomorrow.) Anyway, best plugs that I can pick up? And, should I add gap to the points maybe, to try and get a longer/hotter spark?

 

Check the coil. What color is the spark?

I'd just replace it. Carrying a spare coil is a good idea anyway, even if it doesn't help.

With a Champion plug, you increase the number to get a hotter plug. Not sure about other brands, but they are probably the same.

 

Couldn't find anything about hotter plugs, but I got the right kind in it now.(non resistor/gapped at .030).....It turns out however that the #4 cylinder isn't igniting.....I hooked up an old plug and cranked it....the spark was weak looking and orange, or maybe yellow, something like that......So is it possible that the coil is on its way out, and since #4 has the weakest compression that its just not able to ignite where as the others are? (I pulled the plug wire while it was idling and there was no change, all others dropped rpm)
(also turns out that the plugs I had not only had a gap of .035, but were the resistor type as well...fixed that)
Any suggestions?
What would be the best/cheap coil?
Will the $20.00 duralast work, or should I go aftermarket?

 

plug wires are all new......and it shows the same rpm on the timing light as all the others.....also, checked wire from coil, and it has an orange spark.....

 

I've had no probs with $20 coils (before and after the MSD box).

BTW, is there some concensus about resistor vs non-resistor plugs? Mine had resistor when I got it and seems fine ... but maybe it could be better with non-resistor (?)