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Original Message
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| A couple more things |
| By mcj67 - 01/24/2001 10:23:33 PM; IP 12.78.136.226 |
Hello Schu, Do you have a book called How to rebuild your big block Ford, by Steve Christ? This is a very good book on FE engines, and it is highly recomended by many forum regulars.
You said you checked the carb surfaces with carb. cleaner, how about the intake manifold surfaces?
Also I would check the compression on all the cylinders.
(this is how it is done in Steves book )
Compression testing should be done with engine warm to give the most-accurate indication of engine condition. Run engine to bring it up to operating temperature then remove all the spark plugs, next disable the ignition system by removing the points-to-coil lead. next block the throttle wide open, and make sure the choke is open. Install the tester in number one sparkplug hole. Crank the engine over at least three times and record the highest reading. Check the rest of the cylinders the same way and compare the readings. The lowest reading should be at least 75%of the highest.
Vacume testing (also from Steves book )
First test should be done with the engine running. Hook the vacume gage to a fitting on the intake manifold and start enging. At idle the reading should be about 16"-18", (Hg) inches. Altitude, ignition timing, and cam design all can affect manifold vacume. It will be less at high altitudes and on engines with a high-overlap-performance-camshaft. A reading of 15" Hg or less indicates either incorrect ignition timing or a worn engine. Set the timing and recheck vacume. If the needle floats-moves slowly back and forth-the mixture is probably over-rich. Turn the idle-mixture screws in or increase engine speed to 2,000-2,500 rpm to see if this corrects the problem. If the reading is low 12" Hg or less the engine may have a blown head gasket or an air leak. Next, accelerate the engine rapidly and then release the throttle. When the engine is accelerating,the reading should drop but remain steady. If the reading fluctuates, the valve springs may be weak. When you release the throttle, the reading should jump to about 5"Hg above the reading at idle and then settleback to the original idle reading. If the reading does not go that high, the pistons and rings are not sealing well.
If you get a normal reading that soon drops back to zero when you first start the engine, suspect a plugged exhaust system.
( cranking vacume test)
With a helping hand or a remote starter switch crank the engine over. The vacume gage needle should remain fairly steady while the engine is being cranked. If the needle fluctuates, one of the cylinders is not doing its share.The cause of this could be, incorrect valve adjustment, a worn camshaft lobe,collapsed lifter, a leaky valve,worn cylinder bore or piston rings, a hole in the piston or a leaky head gasket.
If your car has a tach or you have one you can hook up you can do a power balance test,(good test to locate a problem cylinder)
Idle engine at 1,000 rpm, pull the plug wire off one cylinder and allow engine rpm to stabilize, then note the rpm drop, reinstall plug wire. Do the same to all eight cylinders. The ones with the most drop in rpm are the stronger cylinders, and the ones with the least drop in rpm are the weakest cylinders.
( Induced Firing )
If rpm rises when one cylinder is disabled that plug wire may be connected to the wrong sparkplug. If wiring is correct, the sparkplug was probably being fired by induced current.
Induced Current or Inductance occurs when the magnetic field around one wire induces a current in an adjacent wire. This causes two sparkplugs to fire simultameously. In most cases this causes no problems, because there is insufficient air fuel mixture to burn in the other cylinder. Problems arise when the firing is induced in a cylinder where there is enough compressed air-fuel mixture to burn. The two wires usually involved where this becomes a problem are #7 and #8. These cylinders normally fire in order, #7followed by #8. If the two wires are running close to one another, #8 cylinder will fire 90 degrees too soon. This is hard on the engine as it tries to turn the crankshaft backwards. for this reason be sure #7 and #8 sparkplug wires don't run next to each other for any distance..
Again this is a good book for trouble shooting and rebuilding
Good Luck Mike Jones |
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