Ignition system wiring

[ridegnu]

This is a follow up of an old post I had in drivetrain which can be found here: http://www.jeep-cj.com/forums/f2/new-85-cj-wont-idle-20241/


And is now an electrical problem. The PO drove this vehicle fine for years before I got it, so the wiring cannot be that far off, I cause myself an initial headache using a schematic from a four cylinder. In haste I replaced starter relay, coil, distributor, spark plugs, ignition module.

THen after hours of no spark I towed it to the mecahnic


First he found out the wiring diagram I got from the internet turned out to be for a inline four cylinder not a six. He said he changed over a few wires, bypass the Motor Control Unit between the Ignition control module and the distributor because apparently the MCU would not allow the distributor to fire, and got it running.


That’s when the 1.35 Ohm sensitive resistance wire which was running from the ignition switch to the positive side of the coil started melting. He tore it out and moved it to a different location which was now from the positive side of the ignition coil to the starter relay, as it appeared on his all data wiring schematic.


He seemed more frazzled about all the colorful wires more then I was. Anyways with wiring changed to suit the schematic for the six cylinder now the ohm sensitive wire running from the starter relay to the ignition coil is getting warm when the key is in the run position.


The mechanic said the coil is receiving 12v on the run position when it should be receiving six. He also said he tested the new ohm sensitive wire after he cut the melted section out and moved it. Although after cutting over 70% of a resistance sensitive wire you think it would loose some of its resistance capabilities.


Unfortunately I did not have a voltmeter with me and could not confirm anything he said. The only conclusion I came to is that the ohm sensitive wire seemed to get warm but eventually reached a certain temperature and remained there with the engine off key in run position.

Im not sure why this wire keep getting hot, and I never had a chance to ask him why he left the MCU disconnected if he already bypassed it in the ignition system.


So I’m wondering if running the motor with the MCU disconnected will hurt it, and why this ohm sensitive wiring could be getting hot. I know I need to test the voltage at coil again.

 

[gert]

The ohm sensitive wire is a resistor so yes it will get warm as it is try to limit the current that is going thru it. I also tossed the "MCU" (feed back computer)on my Jeep as soon as I got it because it is useless it doubles all the wiring under your hood for nothing. Is your jeep running now? I seem to remember having to go back and re wire my ignition because i removed the feed back computer

 

[ridegnu]

He said the jeep was running, but the wire getting that hot was no good (seemed fine to me). He didn't seem to think cutting the length in half would affect it's resistance, i'm going to take my multimeter and confirm that this morning.

Other then that when I left it friday night it would fire and run poorly and didn't seem to have any other problems.

Well off to the shop for now to have a looksie.

 

[ridegnu]

So I must of drove to 8 different stores after listening to 7 different people not admit that they did not fully understand what they were talking about.

I didn't find any resistor wire, which I believe is made out of platinum. I did find somebody who worked on 60's Volkswagens and they said they used are BorgWarner VR1 resistor in order to drop the 12V to 6V for the wiper motors.

So I ordered two of those (he said it took two to drop the voltage) and im going ot give those a try today.

 

[Torxhead]

Another option is by using a standard wire such as a 16 ga. and adding a diode, this will stop the backfeeding which is the reason for the resistor wire. If you want to try that route I can get a part # for you. I do have a wiring diagram for my '86 in my "Images" in this forum, but it would have to be blown up to see. That resistance wire comes from the alternator on my schematic. The mcu disconnect wiring is probably the "Nutter By-pass", which can be found on the net

 

[Hedgehog]

If I rememer correctly Resistance wire gets hotter as it gets shorter.

 

[ridegnu]

If I rememer correctly Resistance wire gets hotter as it gets shorter.

That sounds about right.

To begin with I had about 75% of my coil wire left and my resistance was 1.1 Ohms (spec. 1.35). With key on engine off (KOEO); ignition coil + terminal = 7.4v. About a 20% drop in resistance and a 20% increase in voltage.

I removed the resistor wire and replaced with a single wire in same position from the starter relay to the ignition coil + = 12v KOEO. Then I installed the two resistors in parallel and got 8.4v = + ignition coil KOEO

Then things got weird. I removed one resistor from the parallel and got 6.6v @ coil + KOEO. Completely confused.

But numbers looked good, cranked the motor and she started.

Then tested the coil and was still getting 12v @ + KOER (key on engine running). Then the mechanic recommended I put the resistors where the resistor wire is called for on the I4 wiring schematic. So I did that got 6.6v @ coil + KOEO then I went to crank, heard a "click" then nothing.

Blew a fuse somewhere, time ran out and I had to leave.

I found another wiring diagram in my manual specifically for the I6 i am going to look over it tonight, and try to make some clarity between all these diagrams.

** never in any of these diagrams have I seen the resistor wire running to the starter.

 

[jdarg]

The mechanic putting the resistance wire on the I terminal of the start relay is incorrect.

That wire is typically straight 12v from the I terminal to the coil primary. The "Run" b+ to the coil primary would have that resistor/resistance wire in it.

Frankly I would find another shop if this is as described. The duraspark system isn't exactly some unknown black magic but this guy sounds like he is over his head.

 

[ridegnu]

She lives!

So I had it towed into a shop. Here is what they discovered;
-The wiring diagram I was referring to from my manual was for a I4 motor
-This resulted in the 1.35 ohm resistor wire to be in the wrong place
-A nutter bypass was required (the vacume hoses I am uncertain about)

At which point the mechanic had it running, he then proceeded to set the timing quickly when the resistor wire started melting fast. I asked if it grounded out, he said “no”. I asked how else it would melt, he said too much amperage. The old resistor wire was doing it’s job fine for years although it was rigid, burnt, and cracked, I don’t know how it would fail suddenly.

I replaced it was a ceramic resistor which brought my voltage back down to 6.5v at the + terminal of the ignition coil KEOF. But I noticed once the engine is running and the key is in the run position (ERKO), the voltage at the coil is 12v, even when I remove the bypass wire for the resistor. So does this mean 12v are feeding backwards into the coil somehow?

Next the starter failed, mechanic said he hooked the ammeter up to the starter positive and was getting a reading of 300A going to the started while cranking, he said it was too high. Next the starter solenoid failed he said it was also due to the excessive amperage. I replaced both of those and it fired and I drove it home.

I opened up all the wiring, cleaned, checked over everything, isolated and the loose wires, taped back up with new loom. This is when I noticed that the vacuum hose coming from the distributor was still running to the weber carb. I reviewed a few procedures for the nutter bypass but they are all done with the original carb. Does anyone know how the vacuum hoses should be run on a weber carb after a nutter bypass?

Either way I wanted to set my timing but realized I didn’t have a tach. I hooked up my oscilloscope and set it to “RPM” function. I had some confusion when it came to setting the scope. I needed to know the number of spark signal pulses to one spark plug per 720 two full rotations of the CRANK shaft. From some quick research I came to understand that the crankshaft to camshaft ratio was 2:1, so two rotation of crank shaft meant one rotation of the camshaft, one full cycle of cylinder head and one spark pulse signal. This is how I set the scope but I’m not sure if that’s correct. The signal was erratic jumping between 800 and 13,000 rpm when the motor help steady the entire time.

Then I took the scope and set is to graphing volt meter and hooked up between the connection in the red wires under the dash used for stock tachometer I got a voltage sin wave which was slightly less erratic then the rpm but I think that is simply because it wasn’t amplified yet?

I ditched the oscilloscope and did my best to set the idle and timing by ear, seems to be within reason.


I am going to go out and buy a tachometer tomorrow an try to figure out now how to wire it up aftermarket to an old wiring harness.

 

[gert]

Keith460 did one of the nicest restos I have ever seen on a CJ and he happens to run a weber as well, he has a build thread on one of the websites More questions about weber carb problems... runs rich all the time - JeepForum.com

I have no idea how to use the oscilloscope I use a good old fashion timing light to set my motors. you are right that the cam spins once per cylinder firing and the crank spins twice per firing. I hate it for you sounds like you are having a ruff go at this, something to try that would end your ignition problem would be to ditch the Motor craft and swap to an HEI and be done with the resistance wire. It has been a long time since I messed with the motor craft ignition I also had problems with it and the resistance wire

 

[ridegnu]

OK so this morning I had the the oscilloscope hooked up to the most isolated (from other electrical interference) spark plug lead wire, and I got a much more steady rpm, altough is was still bouncing between 800-1000. When I went and re-checked every plug wire i noticed a much more erratic signal closer to the ignition coil but not on all spark plug wires.

I got an old automotive analyzer produced in the 80's from sears, I hooked it up and got a analog reading the was similar to the best digital signal I got from the most isolated park plug.

Now this is concerning, after warming up the motor, idle or driving. When I shut it off I was noticing a pining noise. Repetitive coming from what sounded like the number 6 cylinder, the pinging would slowly decrease in sound and and tempo as the engine cooled off.

After playing with the distributor last night and driving the jeep around today I noticed two pinging noises, different tempos and volumes coming from two ?cylinders?.