1977 F-150 351M, 2wd, 4bbl

Truck started dieing for no reason. Would start an intermittent miss (didn't matter if idle or under load), then just die as if the key was shut off. No sputtering, just instant shut down. After sitting a long while, it would fire off again. It had been running fairly well up to this point.

I replaced the distributor/cap/rotor & ignition control box. It wouldn't fire. Pulled coil wire to see if it was sparking, and only when the key was let off did it spark. So I would crank=nothing, let off key=it would spark.

I replaced the ignition key switch, and coil just to be sure. Same thing. While cranking, no spark...right when I let off key, it would spark.

Any ideas?

 

The module is not switching on its own. You get the single "spark" when letting off the key because you're collapsing the coil.

Disconnect the distributor, and measure the resistance between the ORANGE and PURPLE wires coming from the truck. It should be between 400 and 700 ohms. Neither should have continuity against the BLACK wire. Report your results; to be clear, your next post must contain a resistance measurement, or I can't help you.

 

You replaced the entire distributor or just the cap and rotor on the distributor?

 

I don't have a meter, but will find a loaner. Thanks for the instructions, will get some measurements soon.

Replaced the entire distributor.

 

So I got the meter (thank you for the additional help, fmc400), but as I am a novice wrench turner, I've hit another speedbump. I decided to post here because I've seen a few other posts dealing with similar issues, might help someone else.

I went to get a resistance reading at the distributor between orange & purple wires. The connection at the distributor had only black/orange/black w/blue stripe on the truck side. It looked like this:



I tried to get a measurement between any of these wires through the connector, but nothing. I'm sure I was doing it wrong. I traced this back to the harnesses coming through firewall. The only visible purple & orange wires I found were at the ignition control box on the ignition box side of the connection. It looks like this:



I noticed the wires on the truck side of this connection that coincided with the purple & orange were black w/blue stripe & orange, like I saw at the distributor.

Am I trying to get a reading at the right place? If so, to get a resistance measurement, do I insert probes from meter into the connector? Or am I just way off base here?

I'm sure my lack of knowledge is frustrating, but all my friends who work on cars say to install a push button ignition switch to bypass this, but that seems kinda half-as*, and doesn't really fix anything. Any help is much appreciated.

 

Bump.

Tried getting a resistance measurement, but not sure if I'm doing it right. Stuck probes into connector, nothing. If anyone can help a rookie out on how to get the reading mentioned in above posts, I'd really appreciate it. Thanks.

 

Sorry for the delay; I thought I had responded, but now I remember having it in front of me then getting distracted and wandering off.

I made a typographical error in my previous post and I apologize. The distributor resistance measurement needs to be made on the distributor side of the connector (MALE terminals). The connector in your first picture has FEMALE terminals and is coming from the truck. Hopefully I didn't make you waste too much time wracking your brain.

Here's a picture of the distributor by itself, if that's helpful. You can see the connector coming off the distributor which is what you're interested in.

 

No worries. Only cuss words uttered were directed at getting that connector apart.

Resistance measurement is 653.

No measurement when either are measured against the black wire.

 

Those observations are good, and rule out the pickup module. Next, check power going to the ignition module. Unplug the two-terminal connector and measure the voltages at the connector coming from the TRUCK. You may have to gently insert a paperclip into the female connectors, since most meter probes are too fat to go inside.

Disconnect the 'S' terminal of the starter solenoid to keep the engine from turning over. Back on the TRUCK side of the module connector, the RED with BLUE stripe wire coming from the TRUCK (typically goes to a WHITE wire on the module) should have 12 volts with the key in START. The WHITE wire coming from the TRUCK (typically goes to a RED wire on the module) should have 12 volts with the key in RUN.

 

crazy i just had the same thing happen to me. Truck was running fine until i made it home and then it died, hard to start back, and now wont start at all. I purchased a new coil and ignition module, put them on and nothing. I figured the coil was kicking the bucket because it looked like the first one put on the truck. I guess I will check for spark, because i know i have fuel and air.

 

So to get a voltage reading (getting measurement on truck side of 2 terminal connector that goes to ignition module):

Does battery charge affect this? Last time I tried to start it, I ran the battery down. Not dead, but you could here it dieing down. Do I need to charge it back up, or does this not matter for this measurement?

How do I check this? Set meter on 750 ACV? If I am checking to see if I get 12V in START on the red w/blue stripe wire on truck side, where do I put the second probe? Does it matter which probe (red or black) goes where?

Also, when checking to see if I get 12V in RUN on the white wire on truck side, where does the second probe go?

Ah yes. My inexperience is shining. Thanks again for walking me through this.

 

As long as the battery isn't completely gone, it's fine. You can measure the voltage across the battery posts; whatever you read there is what you should see for your two measurements.

In all cases, set the meter to read DC VOLTS. Sometimes this is shown as a small straight line with 3 small lines underneath. This is different from AC VOLTS, which may be represented by a squiggly line (sine wave). Do not set the meter to read any sort of AC voltage.

If your meter has a "range" setting, something like 2/20/200/2000 etc, set it to "20". If not, your meter auto ranges (and is a nicer model).

In both cases (START and RUN), the RED probe goes to the terminal in question; the BLACK probe goes to clean, unpainted metal on the engine (GROUND). It doesn't hurt for them to be swapped; you'll simply see a negative number.

There should only be one "port" on your meter for the BLACK proble (ground or common). There is likely more than one port for the RED probe - one for AMPs and one for VOLTS/OHMs. Connect to whatever one is labelled as VOLTS. Make sure you have a good connection to both GROUND and the terminal of interest.

 

Thanks for the crash course, I really appreciate it.


First thing I did was get a reading at the battery. Measurement was a steady 12.9V

I then tested the truck side (female) of the two terminal connector going to the ignition control box.

First wire was Blue-ish on truck side, but it coincided with the red wire on the ignition box side. With the key in RUN, it read a steady 12.4V

I then disconnected the starter from the solenoid. I tested the red w/blue stripe wire on the truck side, which coincided with the white wire on ignition box side. With my buddy holding the key in START, it read a steady 11.65V

Thanks again for helping me out.

 

Nice work so far. You're getting power to the module, and the pickup module is good. If the module is new (and presumably good), there's not too much else that can go wrong.

Maybe it's time for a sanity check. You seem to not be getting spark as seen at the plugs (secondary side), but you should make sure whether it's there on the primary side. Hook everything back up, and connect a test light from the negative terminal of the coil (possibly labelled TACH TEST) to clean, unpainted metal on the engine block (GROUND). Keep the coil connected. Crank the engine over with the key, and the test light should BLINK.

If your meter is an older-style analog meter with a needle, you can instead set it to VOLTS just as you did with your previous measurements, and look for the needle bouncing back and forth, which means the same thing as the test light flashing.

 

SO last night I busted the lead off my $5 Harbor Freight meter. I invested in a fancier model from the parts store. It has a selection on the dial for "RPM x10" where you select 4, 6, or 8 cyl. Is this what I want, or do I need to get an actual thing called a test light?