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Spankrjs' 1984 Long Term Project

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
BW mentioned above what most say to do. Run a relay from the battery for the ignition power to remove any power loss/noise through the stock ignition wiring.

Bill USN-1 on binderplanet has tons of information on TBI setups if you havent seen that yet. They have troubleshooting tips and power checks.

I have a factory harness with my TBI. It has 2 power leads to the fuse panel from the alternator (always hot). I then have the purple start signal wire that goes to the starter/solenoid. There is a second small purple start signal wire that goes to the computer to tell it you are trying to start. The ignition switch that the coil and such are powered on are hot in start/run - pink power wires.

Have you checked that little spark control module that normally bolts to the firewall?
I am pretty sure my power to the distributor is good to go. Even wiggling wires/connectors while hot I have steady power.

My TBI harness is aftermarket, but it is identical to a stock GM TBI harness. Your wire colors sound the same as mine.


I changed the HEI module, since I had a new spare one. Still no start.

I also checked the resistance on the pick up coil, it was at 886, so between the recommended 500-1500 range. The pick up coil wires/connector are good, no change in resistance while moving them. No corrosion inside distributor, still looks new, only 6 months old.

I am a bit foggy, but IIRC, and I could be wrong, the ESCM (Electronic Spark Control Module) is only active while Starting the engine (under 400 RPM). Once the engine Starts, the PCM controls the spark timing. So, if it was bad, maybe it wouldn't Start, but that probably wouldn't explain while it dies while running, unless it is sending some corrupt signal to the ECM????????? I might pick up another ESCM and swap it on, wouldn't hurt to have a spare anyway. I couldn't find anything in the FSM on how to test it, might have to look some more? Could be the ECM went bad, too :shrug:
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
I bought a "spark tester" yesterday to test the spark output, got tired of shocking myself.

At the coil, while cranking, it will initially have a very weak spark, then nothing. According to the spark tester instructions, the HEI should jump to the 30 mark. That gap is too wide for my current weak spark, it will only jump to 20.

I tried three other coils, known to work properly, still the same weak initial spark, then nothing.

I am "thinking" that even though the pick up coil tested alright, it is not working properly, so the HEI is not getting the signal that the engine is spinning over and to let the coil spark:shrug:

I hate to guess and throw parts at something, but besides the computer, not sure what else it can be?
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
I changed the pick up coil, got it to start and run for 5 minutes, then it died again, no spark/start :(

Checked the HEI module, tested as bad. Changed HEI module, it runs again :)

Who knows :shrug:
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
Doesn't that just drive you crazy. You never know when the part goes belly up.
Yep :crazy:

I had lost voltage at the coil and module during all my testing, probably from my jumper wire I made that ran from the + coil to the battery grounding out, which blew the ignition fuse., which I didn't notice at first. So, I pulled all the wire loom off the under hood harness looking for a problem :crazy: I did figure out all the ignition wiring, I think:

Pink wire from second fused spot at under hood terminal (terminal where I had the "Hot fuse" at the battery feed spot) is the pink wire that feeds the + coil. At the + coil, a smaller pink wire feeds power to the + HEI module two prong connector. So, 12 volt goes to coil, then module. This pink wire also goes back to computer and ESCM, IIRC. One thing that was strange, with blown ignition fuse, coil would not have no power, BUT the HEI module would:crazy:

I did not find any damaged wires in the harness, I did find a bunch of Michigan sand :crazy:
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
I drove this one to work this afternoon, and of course it dies in the middle of the street down town.

Popped the hood, found my "redneck" wire coming from the +coil side, wrapped the other end around the +battery terminal, fired right back up.

So, I am randomly losing voltage to the coil/distributor. The jumper wire fixes this. All the wires/connectors under the hood are fine, ignition switch fine. All other systems work fine, just lose power to the coil and distributor.

I guess I need to look and see, but I am pretty sure voltage runs from the mini fuse block, to the computer, then out to the coil/distributor. So, could the computer be bad :shrug:

More wire chasing......................................
 

bigwalton

Picture cravin' AK Postal nut
Staff member
SOA Member
I drove this one to work this afternoon, and of course it dies in the middle of the street down town.

Popped the hood, found my "redneck" wire coming from the +coil side, wrapped the other end around the +battery terminal, fired right back up.

So, I am randomly losing voltage to the coil/distributor. The jumper wire fixes this. All the wires/connectors under the hood are fine, ignition switch fine. All other systems work fine, just lose power to the coil and distributor.

I guess I need to look and see, but I am pretty sure voltage runs from the mini fuse block, to the computer, then out to the coil/distributor. So, could the computer be bad :shrug:

More wire chasing......................................
Hate to think it may be the computer. Seen bad wire inside the insulation in the middle of a perfectly good looking wire. Maybe try bypassing each wire individually?

I thought you’d tried swapping computers?
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
Hate to think it may be the computer. Seen bad wire inside the insulation in the middle of a perfectly good looking wire. Maybe try bypassing each wire individually?

I thought you’d tried swapping computers?
I do have another computer I can plug in. The Scrambler came with two of them, condition unknown on both, I just initially picked one of them and it ran fine, so I figured :woohoo:

I need to look at the other one, maybe it was missing the PROM, can't remember. Good news, a "new/rebuilt" one from NAPA is only like $100, but I don't want to just throw money at it, I already just did with the HEI module/pick up coil, etc :eek:
 

sdsupilot

CJ-8 Member
CJ-8.com Member
Its been a bit, but on my factory harness i wired the computer and coil receive ignition power together. Does that fuse block have a relay for the ignition? I think the simplest test (or possible solution) would be to run a wire from the Jeeps original ignition power to a relay then to the coil. That should rule out fuse block/computer issues if it keeps running.
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
Its been a bit, but on my factory harness i wired the computer and coil receive ignition power together. Does that fuse block have a relay for the ignition? I think the simplest test (or possible solution) would be to run a wire from the Jeeps original ignition power to a relay then to the coil. That should rule out fuse block/computer issues if it keeps running.
I went back and found the Turbo City install instructions in my garage. There ws one wire out of the Turbo City harness that connected to the Jeep harness for power on Start and Run. IIRC, I used the power feed for the Carter Carb computer for this power source because it was 12 volt Start/Run. This one wire then feeds the Turbo City Fuse block, and the fuse block then feeds various circuits, including the coil/distributor. I will have to look and see, but IIRC the Turbo City harness does have an ignition relay. I need to do some more checking:

1) Inconsistent 12 volt supply on Start/Run off the Jeep harness
2) Possibly an intermitent fault at the ignition relay (if it exists, think it does)
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
It's no longer intermittent, its dead for good now :woohoo:

I went to start it the other day, would not start. Hooked back up my "+ Battery to +Coil" jumper wire, fires right up. It will no longer run/start without the jumper wire.

One strange thing: Even with the jumper wire hooked up, it will turn off with the key. I kind of thought it would not shutdown with the jumper wire, but it does.

All other parts of the harness, i.e. fuel pump circuit, work normal without the jumper wire. Also, no relay on the ignition side of the TBI harness. On the Jeep harness/side, everything works normal. Pretty sure it is NOT the "hot on run/start" wire/connection from the Jeep, since fuel pump works.

More wiring/electrical fun :crazy::eek:
 
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