My Mustang is missing!

I've been chasing this problem for about six months and I still can't solve it. Under full throttle on a grade in third gear at around 3,500 rpm the engine begins to miss. As the acceleration continues the miss becomes more prominent. I had a local mechanic try to diagnose my problem. He put it on an oscilloscope and found nothing, so he changed my wires and charged me $322. The car still misses. In fact, it's getting more pronounced. With my cutouts closed you can only feel the hesitation, but with them open you can hear it missing plain as day. I have a Pertronix Ignitor ignition that has been in the car for about 19 years and a Pertronix Flamethrower coil. When I first noticed the miss, I changed the plugs expecting to find at least one that was fouled, but they all looked nice and tan in color and the gaps were still pretty good after 50K miles of use. Any suggestions as to what to do next? I want to drive this car to Reno for Hot August Nights in early August and I want to get this miss behind me by then. There's a whole lot of high speed grade climbing between here and Reno.

fuel starvation by higher rpm ?

Can you go back to points and see if the miss is still there?

Are you sure it is a miss and not pinging?

I would also check your total timing.

If your Mustang is missing, where was the last place you saw it? Did you file a police report?

does the miss happen all the time at 3500 and up, or does it come and go? one thing to consider is that the pertronix module is failing, probably due to heat load(electronics tend to do that on occasion).

Just to be clear the miss only happens when on a grade? Flat land WOT, same gear, same rpm no miss? I ask because ignition isn't really aware of the angle at which you are traveling. I'd be looking at your carb. Float level, etc.

B67FSTB said:

fuel starvation by higher rpm ?

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Ya know, in one of my more lucid moments it crossed my mind that I hadn't changed the fuel filter since I installed the Road Demon about twelve years ago. That just might be my problem. I'll replace it and then, if it doesn't clear up, I'll buy some points and a condenser.

Put points in if you can and report back.

Midlife said:

If your Mustang is missing, where was the last place you saw it? Did you file a police report?

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Oh, it's in the garage, but it was missing on the grade near here. I wonder if I will ever find it (the miss). The cops up here are a bunch of Girl Scouts. Probably no help, but I'll stop one and ask about my missing Mustang. Thanks for the suggestion!

3175375 said:

Put points in if you can and report back.

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I think I probably can if I can find my feeler gauges. It's still only a couple of screws and bumping the ignition until you get to a lobe on the distributor shaft, right? Just checking since I haven't had to fool with points in about two decades.

I'm betting on either failing Pertronix or lean misfire.

Even though the ignition doesn't care about load, a weak spark will fire at low load, but may not be enough to ignite the mix at higher load.

And even though the car runs ok at 3500 on flat ground, it may not be richening the mix enough under load to account for the high cylinder pressure you're exposing it to. Or maybe it's leaning out due to fuel starvation.

RagTop said:

I think I probably can if I can find my feeler gauges. It's still only a couple of screws and bumping the ignition until you get to a lobe on the distributor shaft, right? Just checking since I haven't had to fool with points in about two decades.

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its been about that amount of time since i have had to deal with points, but i had gotten to the point where i could eyeball the proper point gap. no feeler gauges needed.

RagTop said:

I think I probably can if I can find my feeler gauges. It's still only a couple of screws and bumping the ignition until you get to a lobe on the distributor shaft, right? Just checking since I haven't had to fool with points in about two decades.

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Just get you a match book cover. Wait can you find match book any more?

Horseplay said:

Just to be clear the miss only happens when on a grade? Flat land WOT, same gear, same rpm no miss? I ask because ignition isn't really aware of the angle at which you are traveling. I'd be looking at your carb. Float level, etc.

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This is pointing in the direction I would look to first. The rear float level is most likely too low.
Causing the lean condition.

I just changed out the fuel filter and that was no joy. I'll have a look at the sight windows on the carb bowls. The Demon has really big ones. Then I'll have to consider either switching back to points or buying another Ignitor. I wonder if a competent mechanic could find this problem using a proper set of electronic tools? Years ago I had a '74 Pinto (yeah, I know) that would just quit running while it was on the road. Very embarrassing and very dangerous. Anyway, I took it to a mechanic and the guy diagnosed it as a fuel problem. I suggested it might be the coil, but he said it tested fine. He rebuilt the damn near new 1V, replaced the fuel pump, replaced the fuel line and pulled and boiled out the gas tank. It kept quitting on me. I told him to replace the coil and he finally did. The car never quit again and I went back for the labor costs for all the other work he had done.

If you can't find a matchbook cover, fold a business card in half. I would rotate the engine pulling on the belts or by putting a ratchet on the flywheel

I bought a new Flamethrower coil yesterday and was going to put it in today. At $40 it was worth a try. When I went to disconnect the wires from my existing Flamethrower the red wire from the Igniter slipped out of the crimped eyelet. I decided to clean up the existing unit, re-crimp a new eyelet on the + distributor wire and try it out. The car runs much smoother but still starts to break up in the 3,800 rpm range under WOT and climbing any shallow grade. My tachometer seems to have come back to life. I was also getting some really strange clacking noises from the engine Wednesday night, so I decided to remove the shroud today. This one was just as warped as the last one, but it was OK when I installed it on Monday. Looks like they keep sagging from heat. Gotta wonder what these "Ford Tooling" guys are making these shrouds out of. This one had sagged enough to contact the fan blades again both on the top and bottom. The fan tore a piece out of the lower shroud about 2"x 3/4". I'm running without a shroud today in 100* heat and the car is maintaining its temperature nicely with the overdrive pulley and the 5 bladed fan. I still need to run down that stupid miss before August 10 when I leave for Hot August Nights in Reno. Any suggestions as to what type of diagnostics I should try to isolate the cause?

Can you richen up the power circuit and see if that makes a difference? What kind of carb do you have?

Pertronix have been known to fail and do so in odd ways (certain RPM ranges, etc). An Ignitor module is not too expensive and the newer versions have more benefits/features as well. As long as you are spending money ...