Had a tough morning this morning......

Driving to work in my 74 f100 and was doing 65 on the express way as usual and all the sudden the truck sputtered a couple times and i think a saw a backfire/explosion from under my truck out of the driver side of the truck. The truck stalled and as luck may have it there was a rest stop directly in front of me. I coasted into the rest stop and parked the truck. I tried starting it and she turned over but would not fire. I got out and checked the connections in the engine and looked for something to jump out at me but did not find anything. Unfortunately i left my tools at home this morning so i did not have a meter or anything. Had to call my wife to pick me up and drop me off a work (she was not happy).

Anyway the truck has the factory duraspark electronic ignition and i was wondering if anyone had any ideas. I was thinking this or ignition module (this truck is fairly new to me... a month) and i am not sure if it even has a electronic ignition. Sorry i do not have any details yet but just wanted to touch base and vent a little.

I believe i am getting gas in the carb but it was very dark this morning.....i smelled gas. I am going to check this as soon as i get out of work...put gas in the carb and see if i get the same scenario.

Thanks for reading

Rich

 

The 74 model trucks did not come with the Duraspark electronic ignition from the factory (at least the one I had didn't). Electronic ignition began in 75 I believe.

It's possible that at some point an electronic ignition might have been swapped in. If so, the symptoms described COULD be ignition module, magnetic pickup in the distributor, or coil.

Also, the stock timing set had nylon gears from the factory. If the engine has the original timing set, it could have jumped time or had one of the gears fail. The distributor drive gear roll pin could have sheared as well.

Just some things to check.

 

That almost sounds like it sheared the roll pin on the distributor - exactly like firstonraceday suggested. Pull the distributor cap off, crank the motor and see if the rotor turns.

 

Yeah, the longer I typed on my original post, the more I thought the distributor roll pin might have sheared.

One thing I may have been mistaken on though, I know for sure the 351M/400 engines had nylon gears in the factory timing set, not sure about the FE's.

 

that was the first thing that i thought too that the distributor gear had a problem

 

Thanks for the quick replies. I will take the distributer cap off and see if the rotor is turning.

thanks again...

 

Update....

Got off work and grabbed some tools and went to pick up my truck. I took the distributor cap off and turned it over and the rotor did turn every time. I then measured the voltage at the i terminal on the starter relay (got 8 volts) and also 8 volts on the coil.

I tested and am getting gas in the carb when i throttle the gas.

I then just tried to start it for the hell of it and it started right up and drove me home.

I was thinking on the way home and wanted to give a little more info....yesterday on the way home the truck stalled when i was coming to a stop doing approx 20mph. i was coasting and put it in neutral and tried starting it again while driving....heard a click but nothing happened. dead...would not turn over and had absolutely no power, no lights, no radio, hazards etc. I looked at my fuses and all were good. i then popped the hood and played around and the negative battery cable was a little loose so i took it off and tightened it up. got back in the truck and she fired right back up. i did not think anything of this today...i just assumed my battery cable was loose. might be nothing but just wanted to give this info in case it matters.

I have done some research on this website and many people say the ignition module goes bad likes this. will die and then start up (maybe this happened yesterday).. and then will die and take a while or hours to start (maybe today)...and then die all together. I looked in my manual and it gives you about a dozen resistor checks to complete on this thing and then many users state you can not test this (can take it to a shop and get it test but they advise that this really does not work because they usually fail when they get hot).

any advise or other tests to complete.....should i just replace this module. i would really like to verify this as i would like to be certain

thanks


fyi..according to my shop manual the 74 did have a breakerless pick up coil system.

 

Both the ignition module, and the pickup module inside the distributor are known for causing heat-related problems. They get hot, the truck shuts off, and it starts right up after it cools off a bit. However, when they begin to fail, they usually just cut the motor off immediately. Very rarely does an ignition module cause a backfire. However, it's still possible. If you literally saw the backfire come out from underneath the truck, you know for sure that combustion occured while a valve was open. If this were me, I'd scribe the timing mark on the balancer with white-out, and watch it with a timing light while the motor is running and make sure it's not jumping to make sure you don't have any slop in your timing chain. Since it's intermittent, and runs fine otherwise, my guess would be the problem is isolated to the ignition module or the magnetic pickup. However, as I said before, it's very rare for either of these items to cause a problem other than cutting the motor completely, so I'd tend to doubt that's the problem.

Regardless of what the shop manual said, do you have points or breakerless? I've heard of some 74's having points. I've seen this problem happen when the condensor loses ground on a points system. When that happens, the condensor can't filter the points and they arc, which causes backfires. So, first verify you actually have breakerless (ignore the book). Then check the timing.

 

Well learn something new every day, I didn't think they came along until 75.

Could be the module or pickup in the distributor. You're correct, once the module starts failing, it will show up first when it gets hot. One day, it will fail entirely. Most parts stores will test the module, but if the module is cool a failure might not show up. The module type is determined by the color of the grommet where the wiring goes in. NumberDummy can give specifics on this.

If you're going to replace the module, get a Motorcraft unit (available through Rock Auto). The cheapos from most parts stores are generally not good quality. When mounted on the fender, there should be a space between the unit and fender to allow air flow behind to help cool it.

On edit: FMC400 beat me to it...

 

I have a 79 so i'm not sure this will apply, but i had the same thing happen to me. The only differance is the engine would also die if I hit a bump in the road. I had a mechanic look at. When the dust cleared he had replaced just about everything ignition wise. The problem persisted. He finally told me he couldn't fix it and wanted to convert the system back to points!! I ended up taking it to a guy that worked at a Ford dealership (friend of a friend). He fixed it in like 5 mins. It was the starter solenoid, I think that's the correct term. The positive battery cable is directly attacted to it. It was a 20 dollar part.

 

That is another thing to look at if the trucks dies again. I would have someone try turning it overand while they do that tap the solenoid and see what that does.

 

Rock Auto has a Standard Motor Products brand module for $52...
the LX-200 and it's a dangged good one! :)

The LX-200 is for:
'73 Lincoln only
'74 -everything that had Dura Spark-
'75 F-series only

That's not to say that some '74 stuff didn't have points. ;)
Seems like Bill the ND said something like: mid-year '74 for pickups.

The way to test to see if it's the module is to put in a new one and the
problem goes away. No kidding, that's Ford's instructions -after- you first
test the electrical system for problems using a volt and ohm meter so the
new module won't be damaged tho.

My original module went belly up in '79 and I bought a $109 Standard Motor
Products "Blue Streak" and I recently installed a new LX-200 from Rock Auto
and carry the old Blue Streak as a spare. Never needed a spare even the
Motorcraft just messed around, it never really quit and left me stranded.

At least you've got a meter! :)
YeeeHaaaw! :)

Check your resistances and voltages the instructions that come with the
module tell you to before installing it and you'll be fine. If it's something else
you'll find out soon enough but at least it won't be the module for sure. ;)

Alvin in AZ
ps- my pickup's never broke down and left me stranded anywhere, ever.
pps- yours did once so far but if you'd've had more time it might've restarted.
ppps- Don's idea sounds like a good one to try, at least it'll be quick and cheap! :)

 

My distributor is the breakerless one. Sorry i should have clarified that.

I felt the engine die and was checking the gauges, speed, etc. and believe i felt and saw a backfire but who knows for sure, i was trying to look at 5 different things when it died. I will check the timing just to verify, it can not hurt anything. Will it jump many times or will i need to watch for a while (1o minutes or??), just wondering.

I will also tap the solenoid when turning it over and see what happens.

After that it sounds like the recommendation is to replace the module and the pickup.

Thanks.

I will update later after i complete the tests above.

 

have had the same problem on my 76.. 360 and did get the backfire once. ran ok until it got hot and would restart in a few minutes. timeing ok and gets gas. the modual looks original so a replacement is coming.

 

I have no idea how many times (or the percentage of times) I've hunted
trouble and checked stuff (Like Don's suggestion) figuring "this prob'ly doesn't
have anything to do with the trouble but it's easy to be sure and you won't
-know- until you check it out" and either found it to be the problem :) or
found more than one thing wrong.

Sometimes when the trouble clears up you, you just go through checking
everything and anything that's not "perfect" you do something about and
somewhere along the line you fix "it" or the two or three things that added
up to failure.

Alvin in AZ (retired RR signal maintainer)