Engine Miss or Camshaft
Thread Starter
Instructor
Joined: Jul 2002
Posts: 125
Likes: 1
From: Fort Walton Beach Fl
Engine Miss or Camshaft
How can a novice tell the difference between an engine miss or loping camshaft without knowing any history other than it has been opened up, probably rebuilt at some point. Small block 350. TIA
Drifting
Joined: Aug 2013
Posts: 1,263
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From: perth Aus w.a
2020 Corvette of the Year Finalist (stock)
C3 of Year Winner (stock) 2019
You could give it a compression test(and leak down test) to eliminate valves and rings ,and ohm test your spark plug leads ,plus new plugs .Always start with the simple things first 
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
I had a car that developed a miss while on a trip. I was convinced that it had lost a lobe on the cam. Turned out to be a bad plug wire.
Thread Starter
Instructor
Joined: Jul 2002
Posts: 125
Likes: 1
From: Fort Walton Beach Fl
A little update-Changed plugs twice, wires , cap, and rotor. Carb was sent off and rebuilt by a professional. Sounds like time for a compression and leak down test. The needle on the vacuum gauge is not steady but hovers around latent timing?? I guess now verify TDC, valve lash(solid lifters), and compression/leak down. What would be the logical order or does it matter? Thanks everyone for the guidance.
Last edited by Bigb69; Aug 31, 2019 at 06:19 AM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
If it is a lobe on the cam, you will hear it clacking almost immediately. And it wears down from that point at a very fast rate. It is doubtful that is what is going on with your engine as a lobe wearing off sporadically is very rare.
Check your ignition first. Then go to compression checks as stated above.
Jebby
Check your ignition first. Then go to compression checks as stated above.
Jebby
Thread Starter
Instructor
Joined: Jul 2002
Posts: 125
Likes: 1
From: Fort Walton Beach Fl
It seems to be present while cold and hot, idle and light acceleration. I think it may still be there under WOT, just harder for me to detect it. The vacuum gauge will stay around 13 in and fluctuate 1 to 2 in.
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Dr. Detroit
Joined: Mar 2012
Posts: 10,097
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From: New Braunfels Texas
Race Director
Joined: Jul 2015
Posts: 13,082
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From: SW Florida.
Pull valve covers. Crank starter. Watch rockers. Bad lobe or pushrod will be obvious. If all 16 move the same amount, probably cam is fine. Check timing chain. If #1 exh is just closing and #1 intake just opening as tdc mark sez tdc, chain is in time. Now readjust lifters. Now get back to your ignition or fuel or vacuum issue.
Thread Starter
Instructor
Joined: Jul 2002
Posts: 125
Likes: 1
From: Fort Walton Beach Fl
My description was lacking. Not that I suspected a bad lobe on the cam but is it a more aggressive than stock camshaft with a lope, or misfire. I think it's probably time to pull the valve covers and have a look.
Safety Car
Joined: Nov 2008
Posts: 3,717
Likes: 551
From: Seattle Washington
Pull a spark plug wire. You will now hear what it sounds like with a miss. Go around pulling one wire at a time and see if one doesn't change the sound. If none of them change the sound and it sounds the best if they are all hooked up these is probably nothing wrong. If a cam Lobe has gone bad there will be slack in that Cylinders valve train and it will be making a ticking sound. A much different sound than a miss.
