1987 460, 4180 carburator, Duraspark ignition.

It was running fine when I put it away 10 days ago and it started right up today. However, after a short run it began acting up; missing and popping (back firing) out the carb.

I swapped out the duraspark ignition module but that didn't change anything.

Distributor was replaced about 3,000 miles ago and I also replaced the duraspark ignition module about 1,000 miles ago, after another episode of cutting out, but that time it would just shut down once it hit 2,500 RPMs.

Now I'm beginning to wonder if these ignition problems are all related to the new distributor? Perhaps the new pick up inside the distributor is bad?

Anyway, was supposed to go camping tomorrow but now I'm scratching my head. Any advice would be greatly appreciated.

 

Did you replace the coil ?

 

Coil was replaced 6,000 miles ago in January 2014 with a Napa IC21. The old one was leaking.

 

Have the module tested any decent parts store can do it.
The new ones suck.

 

When you say module do you mean the blue grommet ignition module or the pickup inside the distributor?

Last night cold start and initial run up was fine but it started acting up once it reached operating temperature.

The first thing I did was swap out the ignition module with a new one but there was no change in the problem.

 

The DSII pickup inside the distributor should read between 450-950 ohms across the orange and purple wires of the distributor connector.
While you're at it check the black wire to ground as you work the distributor advance with your hand.
This is the only ground in the whole Duraspark ignition system.

 

Thank you Ard and Roadrash.

To eliminate a possible fuel delivery problem I changed out the big canister fuel filter on the frame rail and took if for a ride.

It ran fine cold but as soon as it warmed up the missing and popping returned so I'm thinking the problem is heat related.

I'm no expert with an ohm meter and I haven't checked the resistance values of the new distributor pickup yet but acting on Roadrash's initial suggestion I did check the coil resistance both cold and hot:

Cold: + to - terminals = .003 on 2k setting and center terminal 9.43 @ 20k setting.

Hot: + to - terminals = .001 on 2k setting and center terminal 11.79 @ 20k setting.

The fact that the coil resistance values change hot versus cold, plus the fact that the problem manifests only at operating temperature, makes me think the coil is defective and as soon as it cools back down I'll change it out.

 

Winner, winner, chicken dinner! Replaced coil and put 20 hard miles on it. No problems.

Except what kind of engineer would design a coil mounting bracket with an 11/32" nut? Really! LOL.

Time to pack up and go camping. thanks again guys!

 

Why would it fail in 6,000 miles?

Is there a resistor wire in the run circuit?

 

D7AZ-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-213).

49" long / Color coded red with green stripes / 1.30 - 1.40 ohms resistance / #16 gauge wire.

1980/89 F100/350, Bronco & Econoline.

 

Since the wiring is completely stock I'm guessing it has the correct resistor wire in the circuit but if I wanted to verify how would I do that? Motor running and check for 8 +/- volts at + terminal of coil?

As to why the coil failed after such a short time, I've been told NAPA parts aren't what they used to be, cheap China crap as Number Genius would say, which is too bad since back in the 80's and 90's I used to consider them top end.

But it's been a brutally hot summer here in the Pacific Nothwest with many days in the 100's. Combine that with a big 460 in a small van chassis engine compartment and you literally have an oven torture chamber for baking electrical components. I've been seriously considering adding a hood scoop to improve engine compartment air flow.

The other problem is the coil is mounted horizontally on my truck and not vertically as recommended by the manufacturer. Today's oil filled coils just weren't made to lay on their sides like the epoxy filled OEM coils.

Anyway, it's a good story. Fortunately I have the receipt for the old one and Napa at least has a good return policy.

 

Recently, a "new" NAPA store opened locally. The last one closed 10+ years ago. Upon my initial visit, I met and spoke with a really nice and knowledgeable NAPA employee [something like 30+ years experience with NAPA]. I asked about quality and he answered saying that NAPA has taken on a lower priced line of products to compete with the "box" stores, and instructed me to always ask for the "good stuff" [i.e. Echlin, Belden, etc.].

 

Check the resistance between the coil primary feed and the red (run) wire going to your module.
Check this against the white wire in the same plug, which should be zero Ohms, or close to it.....

Bill gave the values needed to figure it out

 

I have returned from camping and there is more to this story. Ard asks an important question but first the back story.

The distributor was replaced in April at 98,915 miles. Then in late June at 100,417 miles I replaced the ignition module after it suddenly began cutting out at 2,500 RPM, and when I say cutting out I mean BAM! Ignition dropped out and would catch again at 1,000 RPM...new module cured the problem and I was on my way.

Through August I noticed it wasn't starting as well as it used to and then on 8/26 at 101,241 miles, the ignition started breaking up and cutting out under moderate to heavy throttle. This was resolved by replacing the coil and I departed for a camping trip. However, 70 miles out from home I could feel a miss at highway cruise (2,500 RPM) and could see the tach bouncing accordingly but I continued on to my destination.

Two days later on the return trip it ran great cold but as soon as it got warm and I was cruising down the highway it started missing again. Imagine my dread as I approached the big city and stop and go traffic, surely there was no way I would make it through.

Miraculously however I idled through the city gridlock but once back on the highway at speed I could feel the ignition miss getting worse until suddenly, a mere 10 miles from home, the tach dropped to zero and I coasted to a stop, dead on the side of I-5.

 

The camper rocked as the big rigs whizzed past and I took stock of the situation.

I had another ignition module I could try but since I'd just replaced it that didn't make any sense.

I also had a new distributor pick up I could try but that didn't make any sense either. Every bad distributor pick-up story I've read here has always been "gets hot, completely quits" never read about one causing a miss...and besides, I really didn't feel like tearing into the dizzy on the side of the freeway.

Then I looked at my extra coil, an OEM coil I scrounged from the junk yard for my spare parts kit, and figured "sure, why not".

I didn't bother pulling the old coil out, I just stuffed the junk yard coil in loose beside the dizzy and transferred over the horseshoe and coil wire, hit the key and VarOOM! baby fired right up! I didnt waste any time, I slammed down the hood and got the heck out of there.

Once back up to speed on the highway the tach swung wildly between 3,000 and 1,000 RPM and I'm thinking to myself "that was short, here we go again" but this time it wasn't missing. Ignition was rock solid. When I exited the freeway the tach dropped to zero and I looked for a place to pull over, until realizing, HEY it's still running! And as I made my way home the tach fixed itself and returned to normal.

And so after all that, here's what I think...

The cheap aftermarket tach, which is attached directly to the coil signal wire, is failing and shorting out my ignition. Since everything else is new it's the only thing that makes sense.

The fact that the problem primarily occurs at 2,500 rpm, typical highway cruising speed, makes me think I just plum wore the tach out at that particular spot. Looking back, it didn't seem to cut out much at higher or lower RPM.

And now back to Ard's question. Do you suppose constantly shorting out the coil like that could cause it to fail prematurely?