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Help! F250 390 1968

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#1 abailon2014


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Posted 28 December 2014 - 04:52 PM

My truck cranks for a long time before starting. Takes up to 3 tries to start it up. Did a complete tune up as well. After start up, it runs well.

#2 miesk5


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Posted 30 December 2014 - 08:48 AM

yo a,

This is by 1972hiboy;
"I would recomend you get a in-line spark tester that will light up when it gets a signal and keep the plug firing without the risk of shocking yourself. While its running watch the spark for consistency then if the spark becomes irratic and weak and the engine starts to sputter well then you know its ignition. That will at least get you going in the right direction SIMPLY. Other testing opinions pending result of that test right there.."

Google, diy spark tester using good spark plug. connects between the plug wire and plug. It also goes between coil and coil wire then Distributor cap and plug wire. You can see if you have spark or not

other comments;
" you should get a strong blue spark. A weak or orange spark indicated a bad coil or weak or dirty points...
pull a plug wire and make sure you are getting a spark to ground when trying to start the engine. Just trying to figure if it is gas or electrical" A bad condenser can affect spark

"... Engine off, pump gas pedal and see if it is squirting fuel down in the carb. IF not, pull off the filter and see if it is pumping fuel through it..."

Check vacuum hose(s); "...

All distributors are equipped with both vacuum and centrifugal advance units. Vacuum advance governs the ignition timing (spark advance) at low engine speeds (rpm) or low engine loading. The centrifugal advance, in combination with the vacuum advance, controls the ignition timing at higher engine speeds or heavy engine loading to provide the correct ignition timing for maximum engine performance. A dual-diaphragm advance is used on some engines to provide additional ignition timing retardation during engine idle operation.

The distributor vacuum control valve advances the spark timing under conditions of prolonged idling, thus preventing overheating. The deceleration valve provides advanced timing on deceleration. The distributor modulator prevents spark advance below a set vehicle speed on either acceleration or deceleration..."

Trouble Checks
1.Check for the existence and approximate quality of spark by pulling the high-tension wire out of the distributor cap. With ignition switch on and the loose end of this wire held about 1/4 in. from the engine block, crank the engine. This should produce a good, strong spark.

2.Reconnect the high-tension coil wire to the distributor cap and make a similar test at the spark plugs. A good spark at the plugs indicates the trouble to be other than ignition output failure.

3.If the spark is weak or non-existent, remove the cover from the mounting plate and connect a dwell meter to the tachometer block. Hook up the red lead to the terminal in the red area and the black lead to black.

4.With ignition on, crank engine and note meter reading. A dwell angle of less than 45° (for an eight lobe cam) indicates that the transistor is working properly.

78 Breaker point type distributor circuit.gif
Breaker point type distributor circuit

5.A dwell meter reading of zero indicates that the breaker points are dirty or not closing and should be replaced or adjusted.

A dwell meter reading of 45° (8 lobe cam) indicates the following:

◾Ignition system is not being supplied with current.

◾Breaker points are not opening.

◾Transistor is defective.

1.Disconnect the bullet connector from the distributor lead and again crank the engine. A meter reading of zero indicates trouble in the breaker points. A meter reading of 45° (eight lobe cam) indicates power source or transistor trouble. To determine which, connect a voltmeter, or test light to the red/green lead terminal of the ballast resistor and crank the engine. A reading of 45° or steady light indicates transistor failure. Replace the transistor amplifier assembly. Absence of any indication shows an open circuit between the battery and the transistor.

2.A weak spark in Steps 1 or 2 indicates a weak ignition coil. Turn ignition off, replace coil, then repeat Step 1. Do not attempt to test coil, because its low impedance will cause inaccurate readings.

78 Breaker point type schematic circuit.jpg
Breaker point type schematic circuit

3.To jump the ignition switch from under the hood, disconnect the ballast resistor-to-ignition switch wire (red with green chaser) at the ballast resistor. Then, connect a jumper from the positive battery terminal to the vacated ballast resistor blade terminal. If the resistor is not open, the ignition system will now be supplied with current. Check this provision before going further.

4.The only locations from which to get troubleshooting information are the tachometer block terminals, the ballast resistor terminals and the distributor primary bullet connector. By connecting a voltmeter and an ammeter at these points, with a well charged battery and the brown wire disconnected from the cold start relay, cranking amperages and voltages may be obtained that should correspond with the following chart.

Do not pierce insulation material to obtain meter readings.
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