80 model 350 has good compression and spark but is not firing on #2

[cluke78]

hey guys hope you can help. i have a 80 model 350 in my c10. it starts up good but has a dead miss on number 2. i ran a comp test on all the cylinders and number 2 has the highest  at 165 the rest are between 150 and 155. i change plugs and nothing happened. the truck has a bad shake at idle but worst when i try to drive it. can anybody help

[bd]

Welcome to the site from Central California!!

Describe how the old spark plugs look (e.g., color, deposits, wear, damage).

What's the compression on cylinder 3?

Pull the #2 and #3 spark plug wires off the cap.  Any green or black discoloration up inside the wires?  Do the same thing at the spark plug end of the wires.  Any discoloration up inside the boots?  If you have an ohmmeter, measure the resistance of the #2 and #3 plug wires end-to-end and post the results.  Remove the distributor cap, flip it over and look for carbon tracking, especially around the #2 and #3 posts.

[cluke78]

i just put brand new plugs in last night  and gaped them to .45 the wires are about a month old with less than maybe 2 hours running time on them. now i did use a rotor out of another dist. so i will check that tonight and see if it has any build up on it. but i did notice that the fire coming out of the spark plug was a redish orange color and i think its supposed to be blue right?. just don't make since to me how i can have fire and compression and have a dead miss

[bd]

While diagnosing, bear in mind that cylinders #2 and #3 are running mates, so symptoms on the #2 cylinder can originate from #3. 

Does the engine backfire or pop back?  Did you verify the firing order of the plug wires at the distributor cap?

Reddish spark color indicates lower energy level than blue.  Blue to blue-white is ideal.  Measure the ignition supply voltage to the distributor on the 12-gauge pink/black wire.  Verify that it's ~14 volts with the engine running.

Do you have a vacuum gauge?

[cluke78]

ok i will check the number 3 cylinder thank you. yes i checked the firing order and its right and no i dont have a vacuum gauge, could the number 3 cylinder cylinder mess up the number 2 firing issue? and i did notice that my dist. has nouches cut in the housing and he cap has the twist and lock hold downs on it. does the hold downs have to be in the nouches for the cap to seat. could that cause the low voltage? it seems to be seated fine but just throwing out things i can think of. thank you all for your help

[bd]

The cap will fully seat down onto the distributor only one way.  There's a 1/4" notch in the wall of the distributor housing that mates with a tab on the bottom side of the cap.  The hold-downs lock into relief pockets beneath the housing.  Correct cap orientation should be obvious once you see the single tab and notch.

As I stated, it's 'possible' that a problem in the #3 cylinder could mimic issues with #2.  So, it's prudent to take a look at both cylinders until you identify the actual failure. 

Considering what you've posted thus far, the two possible scenarios that come to mind are an ignition problem and improper valve opening.  So, check the voltage available to the distributor on the pink/black wire. 

How comfortable are you with removing the valve covers?

Have you owned the vehicle long enough to establish a history?  How long has it been missing?

[cluke78]

the truck had a 305 in it. i got a 350 motor and put it inand it has all ways had a miss in it. could the valves be to tight and not letting the valves close? and i have the valve covers off right now and all the valves are moving fine to me but they could be to tight

[Captkaos]

Are they moving equally as far as up and down?

[bd]

Are they moving equally as far as up and down?

I agree.  Do all the rockers move the same amount?

the truck had a 305 in it. i got a 350 motor and put it inand it has all ways had a miss in it. could the valves be to tight and not letting the valves close? and i have the valve covers off right now and all the valves are moving fine to me but they could be to tight

If the valves are too tight, you would more likely have low compression in one or more cylinders, because one or more valves wouldn't close completely.  Still, since you have the covers off, run the engine at idle and one-rocker-at-a-time, back the adjustment off until it just starts to clatter.  Then tighten the adjustment until the clatter just stops.  Now, slowly tighten the rocker nut an additional 1/2 turn.  Adjust all the rockers in turn, one-at-a-time.  Tighten the valves slowly so you don't stall the engine.

FYI - If you have never done a running engine valve adjustment, it will make a mess!  There are static methods of setting the valves, but I think a running valve adjustment is the best approach under the circumstances.

How long ago did you install the motor?  And, did you replace the wires to stop the miss, or were the wires replaced as part of the engine swap?

Have you checked the supply voltage to the distributor, yet?

[Engineer]

If you have compression, and spark, I'm leaning toward a flat cam lobe.

Check to make sure your valves are opening all the way on your dead/weak cylinder.

[cluke78]

yes i have changed the wires and plugs. and the valves look like they are opening and closeing at the same rate. what is a way i can check to see if the rockers are to tight. someone told me that i should be able to turn the push rod with my fingers? if thats the case they are to tight becuase i can not turn the rod

[454Man]

What you can do is bump the rocker nut back off once our twice on that cylinder.if it is the rockers the truck will run better with each bump back. I've done it with great results, but I knew the problem was the rockers being too tight

[bd]

...what is a way i can check to see if the rockers are to tight. someone told me that i should be able to turn the push rod with my fingers? if thats the case they are to tight becuase i can not turn the rod

When the lifters are on the base circle of the cam that's generally true, but not guaranteed.  Why not just adjust them, then you'll know they're set correctly and you can move forward?

[cluke78]

i think i might have found the problem i backed off the rocker arm nut a little and fireed her up and it seems to run better. i can ive it gas without the motor shaking. but my question is do i really need the egr valve on this truck because its really getting in the way when tring to remove the valve cover

[454Man]

Good to hear you may have found the problem, though I will say its probably a good time to adjust  the valves since one or two were off.