intermittant miss on #3+7

[BobbyK]

Replaced cap, rotor and wires.

Wires separators used and routed away from anything hot.

Put the timing light on each plug wire and all are good except #3+7.
They intermittently will not fire.
Old wires did the same thing with the new cap.
Haven't checked the plugs yet.

Bad cap?

All pins on cap have continuity.Meaning no resistance from where the rotor contacts to where the plug wire boot attaches to.

Any ideas?

[milled]

I think those are the cylnders wich always run alittle leaner than others, try different heat range plugs mabe.

[Bus Ted Knuckle]

I'd try new plugs.

[Huck]

Is this an HEI or points system? Either you have spark coming down the wire or you don't which has nothing to do with the plugs. I have installed new defective distributor caps, rotors, points, condensers, plugs, plug wires so anything is possible. Caps don't tend to wear out very quickly and plug wires if good take years to go bad. Try swapping spark plug wires with other cylinders to get spark to 3&7. No spark coming out of the cap---bad cap or problem with distributor. Should be a pretty easy problem to find if you back up into the process. Huck

[JMac11]

Check compression on these adjacent cylinders if you can. Do it with both plugs out. I had a similar problem with a 1/3 skip. was a bad head gasket between the cylinders. Idled ok for an old motor but skipped under any load. Check #1 had 60# compression, left out the plug to check 3 had 0#. Rechecked 1 with #3 plug out 0# again. Never any water oil issues.

BTW I think the engine was a cheapo reman.

[68gmsee]

I agree with changing the plugs. I had a miss on mine while idling and it turned out to be a bad spark plug. They weren't old, just had one that was defective. Changed them all to a different brand.

[BobbyK]

I'm running A/C Delco R45TS's, gapped at .045
Thinking they are prob. pretty fouled.
I'll go and take a few pic's.

[BobbyK]

Pulled all the plugs...pretty fouled.

My TPI was running VERY poorly(rich) turned out 4 of the 8 injectors were bad.
Anyway,threw a intake a carb on and this is where we stand.

Here's the pic's of the plugs.

[70rs/ss]

Change the plugs! They are fouled and are probably miss firing.

[70rs/ss]

Try a heat range higher maybe and adjust the carb you are running fat (rich) as well. Are you running an hei, if so 45 thous is OK, if not the gap is to big for a points.

[dukes69]

does it have spark at the plug all the time?

[BobbyK]

Are you running an hei,

Yup,HEI

does it have spark at the plug all the time?

Intermittent
With the timing light on the #3+7 it does fire but with noticeable gaps in the strobe of the light.

Try a heat range higher maybe and adjust the carb you are running fat (rich) as well.

Suggestion on a heat range?
I just got the carb on this week.Haven't even tried to adjust it yet.Still set at what the previous owner had it set at.

I want to resolve the spark issue 1st.

Thanks though.

[dukes69]

if you dont have spark going to the two spark plugs in question, why would you need to change plugs. i might have read this post wrong. i would think the problem is before the plugs. just my 2 cents.

[BobbyK]

Didn't check at the spark plug for spark there.
Just put the timing light pickup near the end of the plug wire.

I allready have a set of new plugs.I'll install and see what happens.
I'll update when I do.

[BobbyK]

FIXED...New plugs...runs like a champ.