My 1985 3.7L S6 (Custom 100) only cranks once per day. It cranks and idles smooth, then it dies, not to restart until the next day. When driving it, it will run longer, but sometimes it will not get gas when pressing gas pedal and sometimes it will backfire.

It has a new fuel filter and fuel pump. It has a new ignition coil, voltage regulator (ecu), starter, distributor cap, plug wires, plugs, and battery. Battery has a good ground. Ballast resistor seems to test for correct resistance.

I found a bad ground wire at the ignition coil which i spliced. i haven't soldered and shrink tubed it yet. I've replaced some worn air hoses coming off the air filter and fuel hoses (near the fuel filter and fuel pump).

I've ran it for about 3 years with no problems except replacing the starter, steering box, battery, and a couple of tune ups. I cleaned up the fuel system with 3 cans of sea foam, octane boost (to burn through the crude), and other cleaner. I've taken apart, cleaned, and inspected the carb.

It doesn't seem to get spark from the ignition coil but the ignition coil was replaced when the problem started. The original problem was that it would run until it got warm, would quit, and not restart until it cooled down after about 30 minutes. I parked it after I couldn't get it started again. At that time I had cleaned and inspected the carb and replaced the distributor cap, plug wires, plugs, and voltage regulator. After sitting, I replaced the fuel filter, fuel pump, some fuel hoses at the fuel filter and fuel pump, cleaned the carb, and added octane boost and fuel cleaner to the tank. I also replaced the battery and replaced the ground terminal (again). It would crank, but only once per day. Later I found the bad wire to the ignition coil and spliced it. Still same problem.

The distributor is a single pick-up. which is different from what the book says it should be. I guess I should add that I had disconnected the fuse for the dome light and horn. I previously had the dome light burn out. I also had the horn to start going off for no reason so i disconnected the 20 amp fuse for it. Not sure if that short has anything to do with anything.

 

What is the resistance of the pick-up coil both before you first start it and after it quits and won't restart. Should be 150-900 ohms. Have you set the air gap at .006 inch using a nonmagnetic (brass) feeler gage? Do you have a good ground from the control module to the engine? Have you run checks on the control module while it won't restart?

 

when you say control module, do you mean the computer under the fender or the voltage regulator on the firewall? i don't suspect the computer since problems with a computer usually exhibit the problem of random stalling, made worse with abrupt changes in ambient temperature or vibration, due to cold solder joints. i'm not sure if it would exhibit problems differently with this non-standardized computer.

not sure what you mean by the air gap. in the distributor? the book says it shouldn't need adjustment. seems to idle really smooth when it does run so i don't suspect a timing issue.

i was going to run through the tests in the haynes book for the ignition system so i don't fry anything and to make sure i'm testing things the right way.

i just checked for spark at the ignition coil. it doesn't seem to give spark when turning it over after it dies.

i was going to check for resistance when my nephew is available to run through the tests. he is staying with my mother where my truck died and has a meter. i had my tools out to bring them, but i forgot to bring them.

is the pick-up coil the same as the ignition coil?

i hate to buy another ignition coil without making sure it is the problem. i suspect a short somewhere in the wiring or the resistance ballast on the fender near the battery. i do get voltage at the voltage regulator (ecu) on the firewall which i tested with a simple light bulb voltage tester. autozone tested it and said the battery and starter were good and the voltage regulator was bad. i swapped out the fairly new voltage regulator with a brand new one and returned it on the spot saying their machine lied that it wasn't the voltage regulator.

my dad suspects the carb or distributor, but he doesn't want to work on it.

i think i was suppose to put this thread in the parent forum. this forum is suppose to be non-technical.

 

The ECU (Electronic Control Unit) is another name for the ECM (Electronic Control Module). The voltage regulator and the ECU are not the same thing. The voltage regulator has 2 pins while the ECU has 5 pins of which only 4 are used in your application.

The pick-up coil is not the same as the ignition coil. The pick-up coil is inside the distributer and the wires that stick out of the distributer are a part of the pick-up coil. The pick-up coil replaced the ignition points.

The air gap is between the reluctor (the six pointed star on the distributer shaft) and the magnetic pick-up on the pick-up coil. Most times once the air gap is set it doesn't move again and doesn't need to be adjusted for routine maintenance. You are not doing routine maintenance, you are having a problem and you need to check everything that effects the running of the engine to find the problem.

The carb has nothing to do with a loss of spark but I agree with your dad about suspecting the distributer until the test is run on the pick-up coil to rule it in or out as the problem. I also suspect the ECU until the proper tests rule it good or bad.

You are correct that this is not really the right place for technical help, but as usual help will be rendered where ever it is needed as it has been in the past.

 

so does the truck have a lean burn computer behind the battery or does it have a 4 or 5 pin ecu on the firewall or fender?

 

ok, i thought you were talking about the distributor. pick-up coil does sound like part of a single pick-up distributor. i'll include it in the tests. i'll have to locate a feeler gauge. my nephew's friend probably has one.

yes, it has an obd-1 computer, which i call a pcm after working on jeeps, under the fender behind the battery, with what i believe are a couple of 16-pin connectors. the voltage regulator (autozone calls it a voltage regulator), a 5" square with an odd triangular 3-pin connector, is attached to the firewall. i think the haynes book also calls it an ecu. i've seen the ecm term before too, which leads to the confusion. there is a small 3"x2"x2" thing near the battery with 5 wires connected to it, with one of those being a fairly heavy gauge red wire. i've heard it call a resistance ballister, which i believe makes sure it delivers the right amps with my basic knowledge of amps, ohms, and resistors. the wires look a little rough going into it, but my dad checked the voltage on it, and we've sprayed the connectors with electronics cleaner and taped up the wires.

i don't get any kind of stalling when playing with the wires near all those components.

 

the voltage regulator and ecu are 2 different things and both would be bolt to the firewall if you had them. since you have the lean burn system you will not have a ecu bolted to the firewall. most people that have the lean burn system usually convert to the 4 or 5 pin ecu system when they start having problems with the dumb computer. some people will also even go as far as doing the gm hei setup.
heres what a 4pin ecu setup looks like

 

I was going to sell the truck. I had a guy name Bruce call on it who has several dodge trucks and restores them. He mentioned he knew what was wrong with it and that he had a way to bypass the computer, but he sounded like he had a few when he called. I couldn't even say a word. He never showed up to look at it. I'm guessing this is what he was talking about, going with the ecu system. I decided against selling it since I wasn't raising enough money selling stuff to buy something else that was running.

If it is the computer, I would be tempted to go with the ecu system, but I wouldn't be sure everything i would need to do. i'm guessing it is cheaper than buying a new computer if the problem is the computer and would disable a lot of unnecessary components. it would reduce optimal performance, but there would less points of failure where performance would be reduced anyway.

any threads on how to do this?

 

if you can find the parts you need at a junk yard you might be able to get what you need for almost nothing. the 2nd most expensive parts it the plug that plugs into the ecu. you can get a ecu and ballast resister for less than $30 but the plug is about $50. you will also eventually want a distributor with a vacuum advance but you could drive it without it but it may not run as great and could get a bit worse gas mileage. as far as wiring goes it is about as simple as the picture above. the only tricky part would be finding a line that is only live when the ignition is on.

 

i started running the tests. 12.5 volts at the battery. no spark from the spark plugs. 11.8 volts at the positive and negative terminal of the ignition coil with the ignition in the start position. no spark from the ignition coil wire that goes to the distributor. no spark either after disconnecting the spark control computer (10 pin connector going into the computer). so far, the tests indicate bad ignition coil, but i replaced it first when this problem started. i did splice the negative wire going to the negative coil because it was breaking at the terminal. not sure if that problem caused the coil to go bad. i'm going to try going through the rest of the tests.