Hey all, my 77 F100 SC will be steadly cruising along , then all of a sudden, it'll almost die (like when your fuel filter is clogged), come back, then do it a couple more times before dying completely. After a while, I can start it back up and limp a few more miles using only idle speed. Next morning, starts up fine...might be good for a couple of days, then does it again.
BTW, my stereo, lights, etc are not affected -only the engine dies.


First time I thought it was the fuel filter, so I replaced it (still does it)
-old filter was clean
-good fuel pressure in the line
-carb was rebuilt a few months ago with no problems

Second time I thought "ok, then it's the Ignition Module", replaced it with a good unit, was good for 2 days, then I was right back on the side of the road!
-ignition coil is also new



I've had fuel filters and Ignition modules go out me, the symptoms are exactly the same, but no luck this time. I suspect it's still an electrical problem. Engine runs fine otherwise. Help. Please.

dizzy pickup module?

 

Stator or frayed wiring in the distributor?

 

wires can be bad anywhere from the ignition to the distributor...a downside of duraspark. I've never owned a 77-79 that didn't have probs with ignition (latest issue was the wires went bad at a connection so had to be spliced to bypass). SO, if it is ignition, you will need to either test and find the problem or replace the system with something like an HEI distributor that takes a single hot lead from the switch...I've done both. The original system is ok once you fix the bugs and learn how to quickly diagnose...and it automatically retards the timing a bit for easier starts. Still not sure how i'll go on my new rebuild...the duraspark is spliced together and I have a couple hei units in the garage....but with increased compression I like the idea of the auto retard......?? I wish the duraspark had been either designed or built better. Make sure the box is either made to create a space between it and the firewall for cooling or use washers. Many times the symptom include intermittant operation ie runs fine then no spark then ok then bad again etc.

 

I actually do suspect the distributor somewhat. Few months back, I had to replace the Vac Advance on the dist. (Had some trouble getting the right one...had to be adjustable since my EGR's disconnected -EGR ping) Anyway, thinking about just replacing the whole dizzy this time (thinking bad elecs inside)...If there's another way, or a few more simple checks I can do before replacing the D, by all means let me know.
Had some charging sys/alt problems recently (replaced alt, reg., and coil) but prime suspect was the wiring harness from solenoid to reg/alt. Been having a hard time fining a replacement....found one I thought would work, but when I got back, found that it was missing a few plugs. So, I still have this questionable section of wiring harness (just secured it as best I could till I could find the right one). I really do think this is an electrical problem in combination with ambient temp in the engine compartment(though none of my acc. are affected when the engine dies, save for the guage to lean towards the D). I don't want to stray from the stock ignition components though.
Since the prob is intermittent, I cant just whip out a meter and start testing circuits anytime I want. I'd rather just replace components that could be suspect.

 

This used to happen to my dads truck all the time, I think he replaced the starter solenoid or something.

 

It could be a sticky Needle Valve. The next time that it happens tap on the fuel bowl with the handle of a screwdriver or similar. If it runs good again, then it is the needle valve or float.

 

I'll try the needle-valve idea next time it happens. About that... could I also unscrew the top and just see if the float bowl is dry, or better yet, just give the throttle a good pull and see if the acc. pump shoots some gas down the carb? If it is the needle valve, then I shouldn't have gas getting into the barrels, right?

I didn't think that a bad starter solenoid would cause an engine cruising happily down the road to die like that.

I'd like to know what components can cause a running engine to die, without affecting any accessories (unless they only use battery power...for example, when my alt goes out, I know the engine runs off the batt until it runs out of charge, but even in that instance, my headlights dim significantly and I notice the major "drain" on my dash gauge)

I know these things can cause the running engine to die:
-ignition module
-ignition switch
-clogged fuel filter
-outta gas!

Help me out with this list....anything

I'm thinking about using the Chilton's test procedure to check for a bad stator(pickup) in the dizzy before changing it completely.

 

Yes, you can unscrew the top of the carburetor to inspect the bowl. You can even do it while running. I do this to set the wet float level.

The accelerator pump should shoot two healthy jets from the venturi when you give it a push.

Engines can die from a faulty accessory...but you need to know this: HOW DID IT DIE? Did it die like you took the key out while the electrical items were still going? Or did it stumble, hesitate, lose power abruptly, then die a slow death??

 

Sounds like some sort of electrical issue to me. Wires and electronic components will heat up and expand creating an open circuit and when they cool, close again and work fine until subjected too heat. I had a similar problem w/ my '67 Mustang and it ended up being a $2.00 condenser.

 

theres a small magnet thing in the dizzy, its what triggers the spark i believe, anyway when they go bad the quit working when they get hot, acting exactly like a bad module, but wait a while then it will be fine for a bit then do it again, we went through the same thing with a farm truck and we ended up going through the electrics before figuring it out.

 

Ignition depends on a few things:

Air
Fuel
Compression
Spark

We can assume that your motor is always getting air and compression. That leaves fuel and spark.
If you check your accelerator pump the next time is dies and you are getting fuel, then concentrate on spark.

You can check the spark with a suitable tool or a handy screwdriver.

 

Allrighty...I just finished up the stator (mag pickup) test as described in the chilton book. Here's what I got:

-Put the ohmmeter b/n Orange and Purple - resistance was about 650 (spec was 400-800)
-b/n Black and gd, while vac adv. active, I got 0.5 (spec was 0)
-b/n Og and gd, I got 0. (spec was >70,000)
-b/n Pr and gd, I got 0. (spec was >70,000)

(it's possible that the last two readings are not right if i was meant to measure b/n connector side and gd, rather than stator side and gd, which is what i did)

Jermafenser, this is exactly what happens: I'm cruising down the interstate in the summer sun, I lose all engine power briefly (as if I turned off the switch... i have had my ignition switch go bad on me before -very similar, except my accesories still work). it lasts only a sec. or two, then kicks back in, full power, few minutes later, it'll happen again, but might last a few more seconds. by this time, i'm already starting to get off the road because It now starts to happen much more frequently, and no longer returns to full power. finally it dies completely and wont start back up, if I'm lucky, I'm already stopped on the side of the road at this point. if not, i just drift as far as I can. heh! Sure, it's very similar to many fuel delivery probs, but I've pretty much checked that all out, and it seems to be ok. I rebuilt the carb a several months ago, been running like a champ. Fuel pressures good, fuel filter's new, and I'm sure it's not vapor lock.
I think it's electrical.
It's related to ambient engine compartment temp somehow. it'll be completely fine in the morning (when it's still dark and cool out) or after it's been sitting. After sitting on the side of the road for about 20 min, I can start it right back up and get going (at least until it kicks out on me again) and it will not start at all until I've waited.

Prime suspect right now is the dizzy pickup module.

 

If it dies like that, then it really sounds like an ignition problem. Oftentimes, it's the ignition module that went bad. Hot, no go. Cold, like new. What have you replaced on the ignition system lately?

If shopping for a new module, make sure you buy a Motorcraft one. The aftermarket units don't hold up well. If the distributor wires are broken or frayed, it will cause similar issues as well. If the pickup module and stator is good, I'd look at the wires and the module as stated above.

 

if you carry a can of starting fluid you, the next time it quits you can give it a shot of spray and determine if it's a fuel problem or not. if it fires on the spray right after it quits, fuel problem.

"Fuel pressures good, fuel filter's new, and I'm sure it's not vapor lock."

have you watched a F/P gauge as the engine quits? have you checked the accelerator pump shot after it quits? this can still be tricky because the accel pump may have some fuel in it as the bowl is dry.

 

As I said, I already replaced the ignition module. That was the 2nd thing I replaced (The first being the fuel filter)