Spark plug readings


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By Nat Santamaria - 13 Years Ago
Hey guys.

57 Tbird with a 312/Fordomatic

I checked my plugs yesterday and found that the first 4 plugs from the front of the car (2 on each bank from the front) were dry and had a nice tan colour indicating a nice clean burn. The next one each side were somewhat lighter the porcelain almost pure white and the last 1 on each bank closest to the firewall were extremely white with a bit of ashy crusty deposit on them. Is the result of needing to adjust valves? Can this also be the cause of my engine vibration at around 1200-1400 rpm range. It does it in park or neutral and also when I am driving it.



Thanks
By Ted - 13 Years Ago

First impression is that you have a leaking intake manifold gasket.  It would be prudent to check for a vacuum leak either at the intake ports or possibly at the vacuum port at the back of the manifold assuming you have a ECZ-B intake.  Using a non-dampened vacuum gauge while running the engine may also help to determine exactly what is going on.  Running a wrench over the intake manifold bolts may be an easy solution if you find them on the loose side.

By Nat Santamaria - 13 Years Ago
Hi Ted.

The vacuum reading is a steady needle at 19 inches. The car idles smoothly and quietly.





Thanks
By pegleg - 13 Years Ago
Still check for loose bolts. A vacuum leak is a very logical explanation. Also make sure that the vacuum port at the rear of the manifold is hooked to something THAT doesn't LEAK.
By Nat Santamaria - 13 Years Ago
Ok I will check them. there are 8 correct. Do you know the torque setting and is there any pattern to tighening.
By brokengate - 13 Years Ago
Intake manifold torque 23-28 ft/lbs as listed here with other info http://www.secondchancegarage.com/public/414.cfm I have never seen a listed pattern for an intake manifold on a y-block, if I remember right there are a couple bolts I couldn't fit the torque wrench and used the calibrated hand. 
By pegleg - 13 Years Ago
I would start in the center and work toward the ends, side to side. Similar to what you'd do for a head. When you're done let it idle and spray each port with either around the gasket (others will have other ideas here, but this works for me) If the idle changes at any point, you have located a leak. BE CAREFUL, either is very flammable. w00t
By pasngas - 13 Years Ago
i agree to spraying around manifold intake ports and carb base gasket to check for vacuum leaks but i use carb cleaner and works fine little less flamable
By Nat Santamaria - 13 Years Ago
Hey guys.

I tightened up the intake to 25 lb torque. Some of the bolts were off by a few pounds. It seems to have fixed the problem. the spark plugs on each bank closest to the firewall have a better colour to them. They are not a hot white but a have a tan colour to them. They are only slightly whiter than the rest.

Many thanks