I am having a issues with my ford FE 390. It will start just fine on the first crank but after a half hour of idling it will flat out die, no sputtering or backfiring. Then it will become very difficult to start and will not stay running. This is a new problem, this setup has been working just fine for the past year and a half. Setup is the same besides a new alternator installed 2 months ago. I am using a msd 6al box, Mallory unilite distributor, with a Mallory voltage protection box, an allstar ignition coil, optima battery, and a powermaster 3G ford 120amp one wire alternator. Things I have already tested are as follows. Battery is good reading 12.6v at no load. All msd box wiring has been triple checked connections and power all in order. The allstar ignition coil was a replacement for a suspect Mallory canister style coil but both have now been tested and fall with .7 ohms of resistance. The msd box has been tested by me by grounding the white wire and checking spark at the option coil plug, which tested well. All Fuel lines are cool, and a plenum spacer is used on the carb. Not vapor lock. Now I'm trying to test the Mallory module but it when I block the eye and test the negative terminal of the ignition coil the reading is ZERO volts. Is this because of the MSD box I cannot read voltage on the coil?If so how do I test the module ? Thanks for any info Sent from my iPhone using The H.A.M.B. mobile app
So with some research I found do***entation of how the test is supposed to be performed. At the top of the picture it stats that if using a CD box like my msd I must rewire the ignition system to test the module. I unplugged my msd box. Wired everything like the diagram shows except the 12V from the ignition, I just took 12V directly from the battery. But now when I perform the test I only get 2.5v from the negative coil when the module eye is blocked or not. Is that the sign I need that the module is at fault or since I never have 12V at the negative side of the coil indicate other faulty wiring? Sent from my iPhone using The H.A.M.B. mobile app
I don't have any suggestions for trouble shooting, but under what cir***stances do you idle the engine for half an hour?
Ebbsspeed one day my truck died on me on the side of the road, I couldn't get it started up again for an hour until everything cooled down then I just limbed it home. Now starting it up when the motor is cool is no problem but letting it idle at 800rpm for a half hour heats up something that then kills the engine. Sent from my iPhone using The H.A.M.B. mobile app
From what you describe with the voltage always staying at 2.5 volts, seems to me your issue is #3b in the Unilite testing procedure. There should definitely be a change when you block the optical sensor. If it is doing this when you test it hot, let it cool off and redo the test.
Thanks Ebbsspeed I'll have to try again tomorrow when the engine is cool, I'll post what I find. Sent from my iPhone using The H.A.M.B. mobile app
As I recall MSD, in their installation instructions for a 6AL, state that no test instrument is to be attached to the + or the - on the coil because it could cause damage to the red box. Just saying. If you are going to continue checking out the system it might be best to take a look at the fine print in the literature that came with the MSD. My guess is that you have a coil failure....an intermittent failure is a specialty of ignition coils. When you drive the car long enough, or allow it to idle long enough, the coil finally gets to full temperature and starts shorting between the primary and secondary winding inside the coil. When the coil is cooler it still has some life in it and supplies spark to the plugs until it again gets hot or the little 'carbon trail' inside the coil gets to be a big carbon trail and is then the easiest path for the spark 100% of the time. Testing a bad but cold coil and finding it to be 'good' is common.
If I understand correctly (and I haven't done much real research so I may not) the MSD 6AL is a CDI type ignition, capacitive discharg ignition, they charge a capacitor to a few hundred volts and almost instantly discharges it thrugh the ignition coil when it's time t make a spark - the coil works as a transformer and transforms the quick jolt to a ~100 times higher voltage at the high tension lead. A conventional 12V ignition runs 12V through the coil for some time (as long as the points are closed in a points type ignition) to build up a magnetic field in the coil, and gets the spark when the voltage to the coil is cut (the points open, or something electronically equivalent) so the magneic field collapses. This is two very diffrent methods, and a conventional voltage meter would most likely not be quick enough to detect the very short pulses the coil gets in a CDI type system. A oscilloscope would be able to show them, but most people don't have one and probably couldn't use it anyway... Since heat seems to be your issue (or rather, whats making the faulty ignition stop working) you can use that to search for the faulty device. Run the car until it dies, then quick cool the ignition components one by one using cold water, a bag of ice or whatever. If the ignition is back in action after a few minutes of cooling instead of waiting half an hour, you have found the component that stops working when hot. Didn't help cooling one component? Move on to the next, try again!
This was my first thought, but in the original post he said he'd replaced a suspected bad Mallory coil with the allstar coil, so I didn't mention it. I suppose you could have a pair exhibiting the same failure, but probably not likely.
I've tried the Mallory coil, all star coil and a third accel coil I had laying around all tested for resistance hot and cold and fell within spec. Sent from my iPhone using The H.A.M.B. mobile app
Now I have wired the coil without the MSD box like the Mallory diagram i posted earlier. But now the 12v from the ignition switch is the correct voltage when disconnected from the coil. (It's only 11.75 but it's the same as the battery. I accidentally drained it last night leaving the key on) But then when I connect it to the coil it drops to 3.95v. What am I doing wrong? Sent from my iPhone using The H.A.M.B. mobile app
Mallory says to use a coil with less then 1ohms of resistance when using a CD ignition, which all my coils read around .7 ohms Sent from my iPhone using The H.A.M.B. mobile app
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