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Missing on one cylinder - 351C
#1
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
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#2
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.

If you ain't learning, you ain't living. 
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#3
(03-21-2019, 12:26 PM)TheDude Wrote: 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?

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#4
Compression test for certain, but first swap the plug wire with another cylinder. If the problem follows, it is the plug wire.

Put a vacuum gage on the engine, the best $15 diagnostic tool that exists.

https://www.crankshaftcoalition.com/wiki..._diagnosis

http://www.wallaceracing.com/vacuum-guage-reading.htm


[+] 1 user Likes Hemikiller's post
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#5
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.

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
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#6
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.

Let me check your shorts!
http://midlifeharness.com

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#7
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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#8
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.

I learn something new every day!
[+] 1 user Likes Stanglover's post
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#9
The spreadsheet in this thread can simplify the calculations for your compression test.
https://www.7173mustangs.com/thread-comp...#pid115411

If I had to guess, I would guess you had a stuck valve that bent a pushrod, due to sitting in a field for some time.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
[+] 1 user Likes Don C's post
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#10
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
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