76 J20 electrical probs

[jode]

Hey all - I am trying to get a 76 J20 that is new to me (I have never seen it run before) going and I ahve run into some difficulty.

Symptoms - no spark (verified by an inline spark tester light and by hooking an inductive timing light to the main coil wire (going to the distributor cap) and checking to see if it lights up)

Things that (seem to) check out:
ICM – I swapped the ICM to a new one – it didn’t work, so I pulled the new one out and hooked it into my 76 Wag – it worked – so I put it back in the 76 J20 – still no spark

Coil – I used a light bulb on an alligator clip to check the coil – it checked out the same as my 76 wag. When the ignition is on, the light lights up on either side (+) or (-) of the coil (with the other end of the alligator clip on the (-) battery terminal). However, when I performed this test on the wag, the (-) side of the coil made the light shine very dimly. On the J20, the light seemed equally bright on both the (+) and (-) terminals of the coil (with the other end of the alligator hooked to the (-) battery post.

I am not worried about fuel or vacuum yet, as it seems there is no spark, and I can see fuel being delivered through the see-through filter. I just had a fresh charge put on the battery at Schucks, and it tested out fine.

It is very possible that the wiring is somehow messed up, but I can’t see why this thing will not at least get a spark since the ICM and the coil seem to be in order. Any ideas? :confused:

[illegalFSJ]

Sorry I don't have any help for you, but ya know you're working with the infamous BID ignition system. I had alot of trouble with this on my '77, and ended up repairing or replacing every single part of the ignition system at least once, more often twice. Finally got a points-and-condender distributor out of an old parts wagoneer, installed it, and have been running great with it ever since.
Good luck!

[jode]

Thanks for the encouragement...anyone have any ideas?

[jode]

Where did I go wrong in my analysis?

[jc turtle]

HI JODE, If there is a plug 6" from the dist, cut it out and solder the wires together. this was a fix back in the day for this dist. good luck, John

[jode]

jc - there is!

I had never heard of this...Great to have a place to start looking...I was kinda starting to wonder what could be left to fix...if maybe I had misdiagnosed something.

I'll check tonight and report the results!
Thanks!

[Jlamb]

Is the rotor turning in the dist cap?

[jode]

Yes - I checked that too....

[Joe Guilbeau]

You need to start at the Negative side of the coil and use a voltmeter to measure the Negative side to ground as the engine is being bumped over.

The readings should be a full 12Vdc and then drop to close to ground potential and then alternate back and forth as the distributor tells the ignition to ground and open the negative side of the coil in order to fire.

[jode]

WaaaaaHooooo! She’s alive! I am so stoked! That was some awesome advice from jcturtle…I cut out that factory joint, soldered the wires and vroom! She fired right up! Awesome! Who knew? What is crazy though is that I turned it off soon after I had started it (she is super low on coolant and I wanted to go check everything out) but when I went back up to restart her, same thing – no spark…turns out I blew the ignition module I guess, cuz as soon as I plugged in another module, she fired right up again. She runs great – looks like a nice high oil pressure and a good steady idle - though she does stumble if I gas her hard (and that is with the vac lines all routed wrong and half of them unplugged!) Tomorrow’s job will be getting the vac lines all routed right, and maybe installing a carb gasket – it looks like it was leaking a bit of gas out around the base of the carb. Tonight I dropped her into gear, and everything felt about right (even though the fluid is super low)
She still hasn’t moved of her own accord yet, but I can feel it coming…by this weekend, I ought to be ready for a test drive around the block!
Unfortunately, it looks like my wiring woes are not over yet though…In park, a turn signal indicator comes on – when I hit the brakes, all four turn signals come on – when I drop it into drive, the dash lights come on…yikes…this thing has some SERIOUS wiring issues…whoever owned this before me must really been into screwing up wiring circuits :rolleyes:

[PhilSine]

Cool. Been following the post but had nothing to offer that others didn't beat ne to saying and now I've learned a bit about the plug on the dist.

As far as vacuum here goes.

I don't know what you know so please don't get offended if I overstate something.

The following items are the minimal vacuum items.

1) Vacuum advance on the distributor
2) BIG Vacuum line to brake booster
3) Line from PCV valve to input on carb

That's it. The whole list. Everything else is an option to some degree. The EGR may need a line but I am not sure so don't ask. IMHO if your state doesn't check I say get rid of the thing.

Hook up the vacuum advance from the base of the carb to the distributor and plug the hook-ups on the back of the manifold so that you can test drive the vehicle. Everything else is not absolutely necessary to test drive the vehicle. The outputs on the back run the e-drive, heater controls, and cruise control and nothing else that I can think of.

But, for reference....

from the back you will need the following lines for the following items

1) Mediem sized line going to cruise control. this never leaves the engine bay. If no cruise then no worry.

2) Medium line to the heater controls through forewall above large electrical plug. From the heater controller there are 2 more medium lines, One for the defroster and the other for the heater. I forget which goes where so you get to play with your handy-vac figuring them out.

3) 1 small line going through the firewall near the back of the engine to the e-drive switch. The in goes to the middle position on the switch and the outs to the t-case are the top and bottom ports. The 2 lines going to the t-case go back throughthe firewall using the same hole as the input line and then attach to 2 steel lines to the t-case. At the t-case the steel tube ends and 2 short rubber lines complete the connections. The input is on to of the t-case near the tranny on the passenger side. Feel around, you'll find it. If you get teh placement wrong the first time swap them at the switch, its easier than swapping them at the t-case.

That's it. There are no other vac-lines that I can think of. Small, medium, and BIG are relative terms with respect to the 3 size lines used on your rig.

Now, before you get too involved with re-routing all the vac lines do yourself one big favor. Cut a sample of the medium and small line, take it to the nearest place that does HVAC, and get them to sell you brass fittings (T's and splices). I want to brass and I now never have to worry about the plastic breaking again. Buy an abundance of T's and splices. Buy more than you think you will need because you never know when you might want to add an option like a Vacuum gauge which, by the way, I feel is a must for any FSJ to have in the cab where it can be seen at all times.

Good Luck.

[ February 19, 2004, 11:51 PM: Message edited by: PhilSine ]

[Bronco]

Nice work dude!!! I cant wait to hear how it offroads? You guna let the wife drive it? You need a dog to ride on the back.

[jode]

Holy cow Philsine...you wrote a book!

All good info though...can't wait to get this thing on the ol road :D

[jode]

:rolleyes: Well - I aint outta the woodds yet. The other night, she would start up and run fine...today, no spark again redface.gif

I can't really figure this out...I thought that I had blown the ignition module before, but I tested the one I thought I had blown in my wag and it almost seems to work better then my old one...so that wasn't the problenm before...here's a breakdown of what has happened:

1 Bought truck with jacked up wiring - not running
2 fixed wiring - no spark - not running
3 Got tip in this thread to cut out a factory wiring connector near the distributor - did it - IT WORKED
4 Shut it off
5 Tried to start it again - no spark
6 Jacked around with the wiring a bit and eventually switched ignition modules
7 IT worked - fired right up and ran like a champ
8 turned it on and off several times and decided that the ICM must have been bad or something - thought I had it fixed
9 today - went out to start it - NO SPARK AGAIN
10 verified that the ICM is not fried - verified current in the coil - proceeded to pull my hair out redface.gif

So what is going on? The only thing I can figure is that there is a poor connection somewhere that I keep bumping that makes it work or not work. Any body have any other ideas?

[carrotman]

Jode, on my 76 the Prestolite ignition always gave me fits until I replaced it with the Davis HEI. Part of the replacement was a heavy gauge wire from the ignition switch to the new HEI. The old wire may have been corroded, cause I also replaced the ECU with no spark. Try wiggling the large main wiring harness where it comes into the engine compartment from the firewall. If it sparks, replace the red wire/tracer going to the coil.

[jode]

carrotman - good advice, but judging by the fact that there is power at the coil (and the red/tracer wire), I am assuming that the power from the ignition switch is not the problem - is that a good assumption?

[Fornesto]

Do you have power everywhere else, radio, lights, etc.?

[jode]

No radio, but yeah, all the lights are working (in a seriously jacked up manner...brake pedal activates all the turn signals :rolleyes:

[Joe Guilbeau]

Systematic approach to troubleshooting might help

[jode]

Thanks Joe. Just for all those who don't know what that means (me)...what are you trying to say?
THX

[tgreese]

Joe means you should start at one end and follow the systems through, stepwise, to the end. To do this, you need to look at the wiring diagram and understand what all the voltages and signals need to be at the various points in the electrical path.

I'm working from memory, so somebody please correct me if I make a mistake ... I believe you only have three electrical parts in the system that you can't inspect visually. If you have voltage from the switch to the ECM when the switch is on, then you need a working ECM, reluctor, and ignition coil. The reluctor is a sense coil that is connected to the ECM by that plug you cut out. It is just a little coil that senses the reluctor wheel in the distributor. The reluctor wheel "spokes" moving in and out of the tiny field created by the reluctor coil makes a signal that the ECM senses. The ECM then opens and closes the field wire of the ignition coil to create a spark. Everything else (distributiion of spark, ignition switch, etc.) works pretty much like on a breaker-points ignition system.

You know that the ECM is getting juice. So, like Joe said, you can measure whether the ignition coil is getting an on-off signal from the ECM. If not, then either the reluctor or the ECM is bad. The only test I know of for the reluctor is continuity. I think there's a resistance spec too - if it exists, it would be in the TSM. There is a spec for how close the reluctor should be to the reluctor wheel.

Since you cut out the reluctor plug, I'd first suspect the reluctor is flaky. You need to be systematic though... A to B to C etc.

hth Tim

[jode]

Hmm… I thought I was being systematic…I know the ICM is working (verified several times by plugging it into my running wag), I know the coil has power, I know that the yellow wire that goes from the ICM to the dist. is getting power, so it sounds like I am getting an intermittent short somewhere in between the distributor and the ICM. I thought it was all pretty methodical, and I can't see the sense in going any further upstream (like to the ignition switch) when I have verified all the above to be working downstream. I guess the next question is, if there is something going on in the distributor/reluctor, how would I find out what/where it is?

[ February 23, 2004, 10:51 AM: Message edited by: jode ]

[tgreese]

Hey, not judging your sytematic-ness, but that's what I believe Joe meant.

The reluctor is just a fine piece of wire cast into plastic AFAIK, so the only easy check is continuity, and maybe resistance. You could check L and C too if you have an RLC meter, but without a spec to compare too, it'd be pointless. The reluctor should be available through Wells or Standard at a parts store if you want to just change it. Is there another plug between the reluctor and the ICM? The signal to the reluctor is small, so any little bit corrosion would upset it (thus the plug removal and soldering). I believe there was a Jeep service bulletin that said to clean the plug and coat it with silicon grease to prevent corrosion. The soldering method may have come later. In any case, you need a clean, low-resistance path between the reluctor and the ECM.

You're sure the ECM is good and the ignition coil is good? Don't know if you can see it turning on and off without a scope, but look at the on-off signal to the coil from the ECM (ICM?). You may be able to see it with a light bulb on a couple of clips.

[tgreese]

BTW how good are your solder joints? In radio, cold joints are a prime source of trouble.

[jode]

Originally posted by tgreese:
Hey, not judging your sytematic-ness, but that's what I believe Joe meant. Sorry - didn't mean to be rude...I really appreciate your (and everyone's) help.

solder - I used a cheapo soldering iron, but held the iron under the twisted wires, and held the solder on top of the wires until the solder melted into the wires...the soldering iron never touched the solder...that's the best I know how to do it...any tips?

The plug I cut out (to the best of my knowledge) is just a factory connector...so the dizzy can easily be removed or installed. I didn't think there was anything in it.

Originally posted by tgreese:
You're sure the ECM is good and the ignition coil is good? Coil is brand new and as mentioned above, the truck ran perfectly on it several times, so unless a coil can work great one moment, and then not at all the next, the coil doesn't seem to be the problem.

If by "ECM" you mean the ignition control module, then yes, I am sure it is working. I plugged it into my running 76 wag and it almost seems to work better than the one that i have in the wag!

Originally posted by tgreese:
The signal to the reluctor is small, so any little bit corrosion would upset it (thus the plug removal and soldering). I believe there was a Jeep service bulletin that said to clean the plug and coat it with silicon grease to prevent corrosion. I'm curious about this...where is the reluctor located? Inside the dizzy? where should I clean the plug and coat it? Where the wires enter the dizzy?

[tgreese]

Re solder, as long as you made a good mechanical connection, used the work (not the iron) to melt the solder, had good flow of the solder into the joint, didn't move the joint until it hardened, and ended up with a bright, shiny joint it should be fine.

The reluctor is in the distributor. The wire you spliced goes into the side of the ditributor through a rubber plug. As I recall (cut me some slack here, it's been a while) there's a plastic piece that has a screw through it to hold the little coil inside the distributor. This plastic piece connect to two small insulated wires that go to a rubber plug that seals the hole in the side of the distributor that the wires pass through. Outside the distributor, it becomes the molded wire with the plug on the end that you cut to make your solder joint.

I believe the reluctor assy is all one molded piece from the plug to the pickup coil in the distributor (the actual "reluctor").

No, you're right, there's nothing in the plug except the connection. My question was whether that wire goes through another plug/connector before it reached the (ignition/electronic) control module.

hth Tim

[Joe Guilbeau]

Originally posted by jode:
Thanks Joe. Just for all those who don't know what that means (me)...what are you trying to say?
THXQuestion...What creates the spark?

Answer...Spark is created when a voltage is present (12Vdc) at the positive terminal of the Ignition Coil. When the Negative side of the coil is open the coil charges the secondary windings. Now, when the negative side of the coil is brought to a ground potential current flows in the primary side of the windings.

This interaction creates an expanding and collasping magnetic field, which is induced into the secondary winding of the ignition coil (the Spark Plug wire that goes to the center of the distributor).

So, the distributor sends a signal out to the ignition module that instructs a transistor to open or close, which controls the Negative side of the coil either opening up, or going to ground.

How to test? Place a voltmeter from the Negative side of the coil to ground potential (frame or negative side of battery) and as the engine is bumped over slowly (don't crank) you should see the Negative side of the coil go Hi and Lo (about +12Vdc and then back to either ground potential for just a few volts).

If this happens AND there is still no spark, look to the coild being bad or the spark plug wire from the coil to the distributor or the distributor itself.

[jode]

OK - great advice from all...I found the reluctor (napa PN ECH TW101) should I end up needing a new one.

The signal to the reluctor is small, so any little bit corrosion would upset it (thus the plug removal and soldering). I believe there was a Jeep service bulletin that said to clean the plug and coat it with silicon grease to prevent corrosion.
So if I understand this correctly, the reluctor is the entire plug from where I cut and spliced it all the way through the wall of the distributor to a little coil in there? Does that sound about right? Maybe if I jimmy with that a bit, I can get her running.

Currently I am without a voltmeter (I have two, but both are cheapos and have blown fuses...the fuses are tiny little .75A fuses that I can't seem to find replacements for.) Hate to buy a whole nother one when I already have 2, so I am using the alligator clip and lightbulk trick.

[Joe Guilbeau]

http://209.238.200.129/gw/elec/76/76_FSJ_harnessA.gif

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http://209.238.200.129/gw/elec/76/76_FSJ_harnessB.gif

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http://209.238.200.129/gw/elec/76/76_FSJ_wirelegend3.gif

http://209.238.200.129/gw/elec/76/76_FSJ_locator.gif

[Matt in AZ]

I had a similar, intermittent, problem with my 1976 Chero. It turned out to be the distributor's internal pickup coil, which is known as a "sensor" in the Jeep TSM. Thhe sensor consists of a sort of an oddly "C" shaped plastic thingy that snaps into the distributor, and is (I think) held in with a screw. It has a twin pigtail wire, terminating in a plug that goes to tthe ignition system. The "C" shaped part has the outer edge of the trigger wheel turning inside of it. Alignment is important, but a sensor in good condition will align correctly.

The sensor is susceptible to damage from vibration, being bumped, temperature variations, of just age and bad attitude. The plug connector can also be a problem.

Do you have a copy of the 1976 TSM? It has a very good wiring diagram, which greatly facilitates trouble shooting. (On editing, I see the JPGs above.)

[ February 23, 2004, 07:44 PM: Message edited by: Matt in AZ ]

[jode]

Thanks all - good advice - I haven't had time to do it tonight...but will get to it soon...

[Rande]

Check the starter relay. When you start the truck, 12 volts is fed from the relay to the coil. Then when the engine starts and you release the key, the relay switches the power to the resister wire to feed the coil with 9 volts.

Just went through this with my friend's '83 J20 (my old truck). His relay was intermittantly grounding the power from the resister wire. It would start but as soon as he released the key, the truck would die. I know that is not your exact symptom, it may still be a bad relay.

Seems you have checked everything else.

[ February 24, 2004, 07:55 AM: Message edited by: Rande ]