wont start
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Freshman User
Joined: Oct 2012
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wont start
was driving my 78 f150 351m today and it just died no power, found the wire coming off the starter solenoid with fuseable link broke, repaired and now cranks but wont start, checked and no spark, replaced coil and still no spark, where should i look next? what test's should i perform?
Senior User
Joined: Oct 2012
Posts: 197
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From: Dublin CA
Do you have 12 volts to the plus side of coil? Start there.
If thats good, have someone crank it while you have a test light on the neg side of coil to ground. The light should pulse on and off while cranking. If not, chances are you have bad pick up coil assembly in the distributor. Dont forget to make sure the distributor is turning, and the tang on top of the rotor is in good shape. Check to see if you have spark coming off the coil wire by holding it about a quarter inch from the block. Nice blue spark.
If thats good, have someone crank it while you have a test light on the neg side of coil to ground. The light should pulse on and off while cranking. If not, chances are you have bad pick up coil assembly in the distributor. Dont forget to make sure the distributor is turning, and the tang on top of the rotor is in good shape. Check to see if you have spark coming off the coil wire by holding it about a quarter inch from the block. Nice blue spark.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
You should only have 6 to 7 volts to the coil with the key in RUN on Duraspark II ignition. The only time you will see full voltage to the coil is with the key in START, but because the starter is cranking, the actual voltage at the coil is still below 12 volts.
The test you mentioned is a good start. A bad ignition module (or no power to a good module) can also cause the same behavior.
The test you mentioned is a good start. A bad ignition module (or no power to a good module) can also cause the same behavior.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 787
From: Simi Valley, CA
You should only have 6 to 7 volts to the coil with the key in RUN on Duraspark II ignition. The only time you will see full voltage to the coil is with the key in START, but because the starter is cranking, the actual voltage at the coil is still below 12 volts.
The test you mentioned is a good start. A bad ignition module (or no power to a good module) can also cause the same behavior.
The test you mentioned is a good start. A bad ignition module (or no power to a good module) can also cause the same behavior.
1) Module overheats, engine dies. Module cools down, engine restarts almost at once.
2) Module overheats, engine dies. Module cools down, engine restarts in an hour...or so.
3) Sooner or later, usually sooner, the module overheats, BURNS OUT. Now the engine will not restart.
Engine heat is the mortal enemy of these modules, which are mounted on the left fender inner apron.
If replacing the little charmer, use some washers to space it further away form the apron. The more airflow the better.
Since the module fails when it overheats: Taking it to an autoparts store to be tested: It will test OK unless it has burned out.
There are three possible modules used on 1976/79 FoMoCo vehicles. Modules have a colored plastic square above where the wires feed out. The most common module has a blue plastic square.
1U2Z-12A199-AA (replaced D6AZ-12A199-A & D9VZ-12A199-A) .. Ignition Module-blue plastic square (Motorcraft DY-893).
D4PZ-12A112-A .. Stator aka magnetic pickup coil, mounts inside dizzy (Motorcraft DU-1A). Similar symptoms apply to this little charmer.
Applications: All 1974/79 FoMoCo V8's except 1979 LTD/Mercury Grand Marquis 351W with EEC.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Note that cranking voltage is not 12 volts either, for the reasons I stated above.
If it's good, then move on to the test that nine inch described. This can help pinpoint why you're not getting spark. Based on those results there are some more tests to try too.
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Freshman User
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Voltage to the coil tested good, didn't have a test light for the negative side so used a dvom set to continuity while someone cranked and it stayed open the whole time so I replaced the module same thing, tried to replace pickup coil but couldn't get the star gear "armature" off the distributor I will get a puller to do that tomorrow, if it still doesn't start the only thing left would be the ground wire right? Could I splice in a new wire temporarily to get the truck home?
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
so I replaced the module same thing, tried to replace pickup coil but couldn't get the star gear "armature" off the distributor I will get a puller to do that tomorrow, if it still doesn't start the only thing left would be the ground wire right? Could I splice in a new wire temporarily to get the truck home?
1) Disconnect the distributor. Measure the resistance between the ORANGE and PURPLE wires coming from the distributor. The resistance should be between 400 and 700 ohms.
2) There should be no continuity between either ORANGE or PURPLE and BLACK.
3) Measure the continuity between the BLACK wire coming from the distributor and ground on the engine (with the distributor installed). It should be a short.
4) Disconnect the 2-wire connector at the ignition module. Measure the voltage on the TRUCK side of the connector. The RED with BLUE stripe wire should have 12 volts in START. The WHITE wire should have 12 volts in RUN.
Note: before people try to correct me on #4, the colors are swapped between what actually comes from the truck and what goes to the module. Coming from the truck, RED with BLUE stripe is hot-in-START and WHITE is hot-in-RUN. However on most replacement modules (even Motorcraft brand), RED is hot-in-RUN and WHITE is hot-in-START on the module.
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Freshman User
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OK all here's an update i replaced the Pickup coil and have spark now, then I have no fuel, find the previous owner did away with mechanical pump and put an electric online pump in, replaced it and have fuel now if I push the pedal to the floor and crank it will start for a second and shut right off even if I play with the throttle, also I replaced all the plugs so the entire ignition except for base down distributor Is new, any ideas?
