Missing on one cylinder - 351C

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I'm a bit of a hack when it comes to this stuff and can deal with basics, but could use some help before digging into this. 

I have a 351C 4V in my '72 fastback project. The engine has always run rougher than seems right, but I chocked that up to carb tuning etc as we've been focused on converting to manual trans and other items. After a basic tune up (plugs, wires, cap and rotor), the car runs better, but still not quite right and seems like it's missing at least at low RPM. The car is running a Mallory Hyfire VI-A ignition and distributor. 

I finally broke out my IR temp gun and measured the temp of the headers at each cylinder and my #1 cylinder is cold. It is getting spark and if I pull the plug it's of course nasty / fouled and covered with gas. Swapped it out with a new one and same thing. That cylinder just seems dead. 

I probably won't get to this for a few days, but could use some guidance on debugging it. I'm thinking my first stop should be a compression check, but beyond that I really don't have a game plan. I'd appreciate any recommendations on where to go with this and how to debug it. 

Thanks

 

Heardatbeat

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I am not super experienced at diagnostics but it would be a good idea to do a compression test. Also check what gap and spark plug is in there and double check to make sure it is the correct heat range and gap. It would be the easiest and least expensive place to start. My '71 was running funky when I bought mine and it turned out to be a completely wrong heat range and gap spark plug. Just my 2 cents. I am sure someone with more experience will help out more than I ever could.

 
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I'm a bit of a hack when it comes to this stuff and can deal with basics, but could use some help before digging into this. 

I have a 351C 4V in my '72 fastback project. The engine has always run rougher than seems right, but I chocked that up to carb tuning etc as we've been focused on converting to manual trans and other items. After a basic tune up (plugs, wires, cap and rotor), the car runs better, but still not quite right and seems like it's missing at least at low RPM. The car is running a Mallory Hyfire VI-A ignition and distributor. 

I finally broke out my IR temp gun and measured the temp of the headers at each cylinder and my #1 cylinder is cold. It is getting spark and if I pull the plug it's of course nasty / fouled and covered with gas. Swapped it out with a new one and same thing. That cylinder just seems dead. 

I probably won't get to this for a few days, but could use some guidance on debugging it. I'm thinking my first stop should be a compression check, but beyond that I really don't have a game plan. I'd appreciate any recommendations on where to go with this and how to debug it. 

Thanks
Yes a compression check is the next logical step. Because it is relatively easy you might consider pulling the valve cover to look at the valves for that cylinder while someone cranks it over for you. Could be a bent pushrod or a bent or sticky valve. If no or low compression and the valvetrain looks ok you will have to dig deeper. Possible blown head gasket or broken ring?

 

Hemikiller

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As others said, a wire swap, compression test are good ideas.

Check your plug gap too. .035' - 0.86mm.

Another bad guy I can think of, if you have spark and compression is not crazy low.

If the car ran fine before but stayed a long while without running is a lifter that is stuck in its compression state.

 

midlife

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I'd also throw a timing light on spark plug #1, and see if it is firing. If it ain't, then the problem is either in the wire, the plug, or the distributor. It's a good way to determine valve train or electrical.

 
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Thanks for all the feedback on this. As usual you guys are all very helpful.

Finally took the advice given here a number of times and ordered a vacuum gauge. May or may not help here, but something I need to have. If I can break away from work this weekend, I'll do the compression test, try swapping the plug wires and if needed get into the value cover. When I am using a timing light, I am using that on #1 so it is getting spark at least that far, but that's about it. Love if would be something simple like that.

I've never saw the car run before I bought it as was basically in a field with little background info. I was told that it ran like a bat out of hell from people who knew the previous owner, but no detail other than it ran great and was fast. Since I've had it, it has run like this. Better now since tuning it up, but still missing the whole time.

 
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Due to inflation, here's my nickels worth on a compression check.

I take all the plugs out, but make sure the plug sockets are cleaned out first, no dirt or other crap. You know that already I'm sure. Disconnect the HT lead and ground it.

I use a bump start button, very cheap and saves either having to run around and crank it each time or have someone else crank it for you.

Start at #1 and write down the highest reading, then move on. All reading ought to be within about 10%, but the closer the better.

 
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Had a few minutes to try a few things today. 

First, tried swapping wires as suggested with no change. Pulled the plug and was able to see a spark at the plug when I turned over the engine. 

Did a compression check of that side of the engine (didn't have time to do more). All cylinders came in at 150-155. 

Pulled off the valve cover for the first time and everything looks OK to me. One thing I hadn't noticed before is the rocker on the very end is hitting the valve cover. It did that enough to crack the cover. Somehow I never noticed that before. The same thing is happening on the other side in the rear cylinder. So needless to say, need to get some new covers. The cylinder is still cold running with the covers off. 

Video of valve train 

Pretty good exhaust leak if you hear some popping or tapping in that video. 

Also didn't know there were rollers in there. Sure wish I know more about the history of this engine. I know it's been built a bit, but I have zero info on what might have been done. 

Any more thought's based on this?

Thanks

 

EvilPuppetMaster

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Had a few minutes to try a few things today. 

First, tried swapping wires as suggested with no change. Pulled the plug and was able to see a spark at the plug when I turned over the engine. 

Did a compression check of that side of the engine (didn't have time to do more). All cylinders came in at 150-155. 

Pulled off the valve cover for the first time and everything looks OK to me. One thing I hadn't noticed before is the rocker on the very end is hitting the valve cover. It did that enough to crack the cover. Somehow I never noticed that before. The same thing is happening on the other side in the rear cylinder. So needless to say, need to get some new covers. The cylinder is still cold running with the covers off. 

Video of valve train 

Pretty good exhaust leak if you hear some popping or tapping in that video. 

Also didn't know there were rollers in there. Sure wish I know more about the history of this engine. I know it's been built a bit, but I have zero info on what might have been done. 

Any more thought's based on this?

Thanks
I had an issue like that that I was chasing for months.

It was an internal leak between heads and intake manifold.

Tighten your intake manifold bolts to 25 ft-lbs and try again

Alex

 

SVO2SCJ

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You have a mechanical valve train - if you LOOK you see that the forward spring DOESN'T compress when actuated by the lobe/pushrod. I would remove THAT ROCKER only, inspect the pushrod to straightness, (glass) RAP the valve with a rubber mallet (on the head) incase stuck (doubt it seeing the others) and reinstall setting cold valve lash at .027 to start.

It just looks like you aren't getting fuel into that /those cylinders. Hense the BLACK plug. (you have spark but no fuel to burn)

Mark

P.S. HITTING valve cover (or anything that shows interference) is a tell tale sign that there is a problem. Once you get this done change that OIL ! (likely much of the unburn gas is in the pan) You will be fine - seems like you have been wrenching on this (and posting thanks). AND you are getting better.learning what we learn 40+ years ago!

 

Hemikiller

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You have a mechanical valve train - if you LOOK you see that the forward spring DOESN'T compress when actuated by the lobe/pushrod.     I would remove THAT ROCKER only, inspect the pushrod to straightness, (glass) RAP the valve with a rubber mallet (on the head) incase stuck (doubt it seeing the others) and reinstall setting cold valve lash at .027 to start.

It just looks like you aren't getting fuel into that /those cylinders.  Hense the BLACK plug.  (you have spark but no fuel to burn)  

Mark

P.S.  HITTING valve cover (or anything that shows interference)  is a tell tale sign that there is a problem.    Once you get this done change that OIL !   (likely much of the unburn gas is in the pan)   You will be fine - seems like you have been wrenching on this (and posting thanks).  AND you are getting better.learning what we learn 40+ years ago!
I'm going to agree with Mark here, watched the video four or five times. It looks like the #1 intake rocker is not actually depressing the valve very far, which would explain some of the popping/tapping noises. Best case, the poly-lock came loose and just needs to be adjusted.

 

SVO2SCJ

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You have a mechanical valve train - if you LOOK you see that the forward spring DOESN'T compress when actuated by the lobe/pushrod.     I would remove THAT ROCKER only, inspect the pushrod to straightness, (glass) RAP the valve with a rubber mallet (on the head) incase stuck (doubt it seeing the others) and reinstall setting cold valve lash at .027 to start.

It just looks like you aren't getting fuel into that /those cylinders.  Hense the BLACK plug.  (you have spark but no fuel to burn)  

Mark

P.S.  HITTING valve cover (or anything that shows interference)  is a tell tale sign that there is a problem.    Once you get this done change that OIL !   (likely much of the unburn gas is in the pan)   You will be fine - seems like you have been wrenching on this (and posting thanks).  AND you are getting better.learning what we learn 40+ years ago!
I'm going to agree with Mark here, watched the video four or five times. It looks like the #1 intake rocker is not actually depressing the valve very far, which would explain some of the popping/tapping noises. Best case, the poly-lock came loose and just needs to be adjusted.
WAIT "two people" agree !! We need to take this to Facebook (so we get 1100 different replies) ! LOL

Mark

P.S. Nicest thing here is WE are all supporting similar interests and though different degrees of ability MANY put time and effort into posts to help! We could make all post/questions better. If you have more info, baseline /change , PRIOR WORK done and PHOTOS etc etc it would go a long way to diagnosing

 

Hemikiller

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You have a mechanical valve train - if you LOOK you see that the forward spring DOESN'T compress when actuated by the lobe/pushrod.     I would remove THAT ROCKER only, inspect the pushrod to straightness, (glass) RAP the valve with a rubber mallet (on the head) incase stuck (doubt it seeing the others) and reinstall setting cold valve lash at .027 to start.

It just looks like you aren't getting fuel into that /those cylinders.  Hense the BLACK plug.  (you have spark but no fuel to burn)  

Mark

P.S.  HITTING valve cover (or anything that shows interference)  is a tell tale sign that there is a problem.    Once you get this done change that OIL !   (likely much of the unburn gas is in the pan)   You will be fine - seems like you have been wrenching on this (and posting thanks).  AND you are getting better.learning what we learn 40+ years ago!
I'm going to agree with Mark here, watched the video four or five times. It looks like the #1 intake rocker is not actually depressing the valve very far, which would explain some of the popping/tapping noises. Best case, the poly-lock came loose and just needs to be adjusted.
WAIT "two people" agree !!    We need to take this to Facebook (so we get 1100 different replies) !  LOL  

Mark

P.S.  Nicest thing here is WE are all supporting similar interests and though different degrees of ability MANY put time and effort into posts to help!    We could make all post/questions better.  If you have more info, baseline /change , PRIOR WORK done and PHOTOS  etc etc it would go a long way to diagnosing
So true. I posted this before about the FB car forums....

On an up note, looks like the OP has a nice set of heads, with closed chamber 4Vs, screw in studs and guideplates...  ::thumb::

------

FB groups is like a free car show, where they let anyone in, and the conversations typically follow the path of:

5 posts saying they had the exact same car back in the day and wish they hadn't sold it, but it was a different year, a different color, a straight six and in the end, you find out it was really an AMC Pacer. 

23 posts with out of focus pictures of their car and no input toward the OT. 

3 posts so badly mis-spelled you don't have a clue what they are trying to get across

4 posts calling out the badly mis-spelled posts

15 posts calling the 4 responders "grammar/spelling nazis"

3 posts with incorrect information

6 posts calling out the bad info

3 posts from the bad info posters, saying "that's how it was cuz I bought it off the dealer's lot like that"

1 post that is actually OT and answers the OP.

-----

 
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Thanks again for all the comments.

I think spring not going down may have been more about the angle of the camera. Here's another short clip just turning it over where you can see more of the movement. 

Another Angle.

To me it looks like it's got good movement. 

I think the valve cover hitting on both sides in the same spot is because they reworked the heads and needed to switch to taller covers. Both sides are hitting in the same spot 

https://lh3.googleusercontent.com/unkYBiqekXxZbz1JBiriZn4PpyDwlOvvfZdcLaW5nLNnHATDa35dOPGxKSHxwz2dW9mpTcjpi1t_H9tTnZbx9N2_WkKJ7eYSmoU3dalNoJcipjhxSGb_cieniWFV_i3CaCHccgIy6oU=w962-h721-no[/img]

The oil is pretty new, but like you mentioned, I think there is a ton of gas getting into right now. So yes, once I get this sorted, that will be changed again.

I used to wrench a lot when I was a kid and thought this would all come back to me faster. Hell, I worked at Super Shops (old guys will know this) for years and could tell you every part # you'd need to build a complete small block Chevy, mild to wild from memory and was wrenching every weekend for me and friends. Take 30 years off the old stuff and it's like starting over. I understand the concepts, but taking time to get back in the groove. 

Thanks for the help!

 
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Just because you're getting spark with the spark plug removed and grounded does not mean that the plug is firing under load. We had a combination spark plug cleaner and tester. It tested the plug firing when subjected to air pressure. A plug could show a nice blue spark with zero pressure and not fire at all when it had 120 psi on it. I would try swapping that plug with another one, and see if the problem follows the spark plug. Being dirty and wet just makes the problem worse.

 
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Just because you're getting spark with the spark plug removed and grounded does not mean that the plug is firing under load. We had a combination spark plug cleaner and tester. It tested the plug firing when subjected to air pressure. A plug could show a nice blue spark with zero pressure and not fire at all when it had 120 psi on it. I would try swapping that plug with another one, and see if the problem follows the spark plug. Being dirty and wet just makes the problem worse.
Agreed and I was thinking the same thing as everything else looks like it ought to at least be doing something. Should have swapped it the other day. I'll probably pick up a new set on the way home tonight for good measure. 

Thanks

 

boilermaster

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Dude,

Was confused about the fact that all the cylinders on the side you checked showed good compression.

That should have not been the case if the intake was not opening and closing fully.

No air in= not much compression, glad that has been sorted.

Can you tell us if you have a solid cam and lifters or hydraulics with adjustable rocker gear ?

If indeed you have a hydraulic cam/lifters perhaps the rocker cover has bled the lifter down ?

The fact that you are not seeing any heat in that cylinder DOES suggest a real problem.

Any chance what so ever that you have 2 wires crossed ?

Other things that come to mind would be, valve preload excessive (if you have hydraulics) or valves too tight (solids)

wouldn't hurt to check the heat of the remaining cylinders and sort the valve lash, regaurdless of what valvetrain you have recheck that firing order.

Boilermaster

 
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