one cylinder not firing - stumped

[MichaelP]

About a week ago, after being stuck in a 20 minute, slooooow line of traffic, our 1600 was suddenly running on 3 cylinders. I chalked it up to blowby (bottom end needs a rebuild this winter) and figured an Italian tune up would cure it.

But no. I've cleaned and regapped the plugs, which, aside from some carbon build-up were ok. I swapped in a known good set of wires and tried another set of points. Checked timing. Another Italian tune up and it still runs on 3 cylinders.

I'm stumped. Stuck valve? Before I do a compression test, is there something obvious I'm missing? FWIW, the head has a few thousand miles on a rebuild.

[Guest Anonymous]

Try adjusting the valves and that should help.

cheers

[TobyB]

Do a leakdown test to eliminate the valves...

then check the valve train! Also, figure out which one it is

(by wire removal)

and swap things around, like plugs and wires. Plugs do short, caps crack, etc...

t

[Guest Anonymous]

rings can also occasionally stick while it id running , rev it up and slowly pour Marvells Mystery oil in through the carb. that should clear the stuck rings at least, it worked for mine!

[Beaner7102]

With the engine running, pull one plug lead at a time to identify which plug it is. Then swap out the dead plug with a NEW one (best to replace all of them). Beaner7102

[peteinjp]

(nt)

[MichaelP]

Yup, brand new cap + wires. I'll try swapping the plugs around tomorrow, though it seems strange one would suddenly short as they have a few thousand miles on them. I can check compression but I don't have equipment for a leakdown.

Hoping it's not a munched ring. Thanks for the suggestions.

[winstontj]

About a week ago, after being stuck in a 20 minute, slooooow line of traffic, our 1600 was suddenly running on 3 cylinders. I chalked it up to blowby (bottom end needs a rebuild this winter) and figured an Italian tune up would cure it.

But no. I've cleaned and regapped the plugs, which, aside from some carbon build-up were ok. I swapped in a known good set of wires and tried another set of points. Checked timing. Another Italian tune up and it still runs on 3 cylinders.

I'm stumped. Stuck valve? Before I do a compression test, is there something obvious I'm missing? FWIW, the head has a few thousand miles on a rebuild.

If you're really running on only 3 cylinders you'll be able to tell exactly what one it is from your plugs. The one that's black, sooted and crappy will be the telltale sign. Do everything that others said and also think about heat/plugs. What plugs are you running? I had a #1 cylinder problem. Not sure why... changed out wires, cap, rotor, points, condensor, coil, plugs, adjusted valves... well everything. In the end running standard plugs in #'s 2,3 & 4 and one hotter in #1 yielded even plugs across the board. Idling is still a little rough, fuel consumption is down about 1.5mpg since the problem started but all in all it seems that the plug swap treated the symptoms - although it did not solve the problem. I believe I have either a bad ring, valve or valve seal.

If your ignition is fine then take a look at plugs to diagnose and fix the problem. You may be able to avoid or postpone a rebuild if it goes in your favour.

HTH,

TJW

[Biscuit3]

Could be a blown head gasket. Karl had the same not too long ago. You'd want either a stuck or burnt valve, or a blown heady, either way, here's hoping it's neither.

[c.d.iesel]

1. adjust the valves - COLD

2. and change the oil and filter & re-Italian Tune-up

[MichaelP]

The more I think about it, a stuck intake valve might be the problem, as the motor sounds fine off throttle/on the overrun.

The question is, if it is a stuck intake valve, is there anything that can be done while adjusting valves?

[oh2fly]

Confirm which cylinder is the problem by removing one plug wire at a time while idling. Use caution! Then, while checking the valve clearance, if the problem was a tight valve, you will see it because you can not get any feeler gauge in there. Wait until the engine is completely cold and set all the valves to .oo6 thou and then see how it idles.

[BillWilliams]

(nt)