Ford - This is driving me nuts

The module on these can do some pretty wonky things.. When the problem occurs, connect your test light to the coil negative terminal... Key on, the light should be lit... cranking, the light should flash...

This is one of the classic Dura Spark module failure modes. The other is loss of spark when the engine is warm, then spark after cooldown. It's possible that the cause is somewhere else, but my money is on the module.

Your description of your problem could lead to one of several different causes. Apparently you do not have the proper skills or training to analyze the problem. Why keep changing parts? Take your truck to a competent technician and have him do that for you and correct the problem, WBMA. ;)

mike hunt

Put a volt meter across the battery, if the voltage during cranking drops below 10.5 volts, the ignition module (Duraspark) will shut off.

The first thing that comes to my mind is a dirty or loose plug on the side of the starter relay/solenoid. I have had to replace more than one of those plugs when they got stretched or corroded. The one on my Jeep is currently soldered to the wire from the key that triggers the solenoid. Sometimes they can be cleaned and carefully squeezed to tighten them. This connection powers the coil and ignition module when the key is in start.

One test is to take a jumper wire from the battery plus to the coil plus and see if it starts consistently that way. Note: It will not shut down until you remove the jumper.

If it still hic ups, then I suspect the connection on the ignition module or the module itself as being bad. 'Usually' when the module dies, it dies, but not always.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

snipped-for-privacy@UNLISTED.com wrote:

It looks like almost everyone pointed to the module. I am going to go check the battery voltage and connections first. However, if the module is bad, do I specifically need one for this year and the 400 engine, or can I use one from another Ford year and/or engine? I know a guy with about 20 junked Fords in his back 40. There's a good chance he has something that may work, but just how many varieties are them?

Thanks Mark

Worn brushes in a starter can have those same exact symptoms. You can change the brushes, without changing the starter. Polishing the comm while it's apart will give you added starting power. With a polished comm, that sucker will crank faster than you have ever heard it crank. (been there, done that).

You can confirm by tapping on the starter with a wrench or small hammer while someone is twisting the key.

Hopefully you had already checked for loose connections.

Mike, the engine will crank but not start when hot. It's in about the middle of the OP.

There are a few flavors of Dura Spark modules, 4 if I remember correctly, it's been a long time. They were usually identified by the color of the grommet where the wires enter the box. Match up the connectors and the grommet color and you are good to go. Failures were common on these modules so used modules are a real coin toss, especially on parts this old. I remember seeing guys with 3 bad ones screwed to the inner fender, they would switch the connectors around as they quit working. A quick search of Autozone shows a Wells brand (yeech) for $19.99. A quality module can likely be had for ~$30.

of the OP.

True, but heat from the manifolds still affects the solenoid connection on the fender which gives the symptoms he described. Him saying it tries to start when he drops the key back to run implies something in the 'start' circuit for the ignition is bad.

The module or the connection on the module can be suspect easily too, but if it is only a loose push on plug thing, it is a cheap easy fix. Mine acted like that when hot, then all the time. That solenoid connection is now soldered to the connected trigger wire from the key switch because I didn't have a spare plug when it finally died.

Using the jumper wire to power the coil like I described is an easy test. If it doesn't start right up, look at the module.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

I have personally seen 4 of the Wells ones come dead in the box....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

of the OP.

Oh, ok, I see what you're after. A problem in the starter bypass circuit. I forgot about that one. Did Dura Spark have that circuit to the starter relay? I don't really remember.

Yep. Good stuff alright.

Yes it did.

everyone seems to be mentioning the module in this case. I too had a ford,

77 to be exact, with a 400 and it did the exact same thing. After replacing every ignition component, and having it do the same thing, the culprit turned out to be a faulty ignition switch. I do have to agree with the others, it sounds more like a module, but if that doesn't work, you may want to try a new switch, and not the lock and tumbler part, some parts techs at a few of these part houses don't realize there are generally two parts to these assembleys. good luck

middle of the OP.

I plan to do the test as you said. I replaced the solenoid yesterday and cleaned all the contacts. However, I was thinking there could be a problem with the ignition switch, so your test will tell. Of course this problem is intermittent, so I have to wait till it starts screwing up again.

Thanks for the tip

Mark

What circuit are you referring to? I got a wiring diagram from AutoZone, but I am not sure what you mean.....

From what I see, there is a resistor inline from the RUN position, and a direct connection in the START position. I dont see any other circuits.

Mark

Why would the starter brushes make the engine not fire? The starter is cranking the engine properly, I just am not getting a spark (at times, since the problem is intermittant).

Yes, I checked connections on the starter, replaced solenoid, battery terminal cleaned, checked module plug connectors, and ignition coil terminals. Since I got a spare coil, I intend to substitute that too.

Thanks Mark

Hmmmm, alot cheaper that I thought. I had to replace one on an Olds once and that cost over $80, and was just a little thing that went in the distributor.

Having a basic understanding of electronics, what is inside them anyhow? I know they must have some sort of SCR or Triac and a trigger device (IC). A few capacitors and resistors...... Right? All they really do is provide a pulse to replace points, and its picked up from that magnet rotor in the dist. They cant be all that complicated. Kind of makes me wonder what that box is so big.

Mark