When they say -, that means it applies ground. You have 12v measured. So there is 12v on the line always with no where to go, except when the white wire becomes ground, a pulsating ground to fire the coil.

 

Thanks. So what about the other coil wire?

 

Maybe I'm not understanding but...
According to the diagram you posted, the coil primary wires get connected to the box with correct polarity. The white - wire from the PCM is used by the box to fire the ignition.

Ok, now I see what you are asking, yes the other coil wire would hang. It's 12v through relays and whatever else and not needed any more. If you cut that wire right now, you wouldn't measure 12v at the coil any longer.

 

I measure 12V on the light colored coil wire. 200mV on the dark colored wire.
The snap connector that goes into the bottom of the coil is *disconnected* when I measure it. So I am taking the volt-meter probes and sticking into the disconnected two-pin snap connector. 11.8 Volts across.

This light colored wire is directly connected to pin 19 of the PCM according to the wiring diagrams.

The light colored wire is *supposed* to connect to the white msd wire.

The dark colored is common with the injectors.

So what to connect where?? :-(

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I'm going off a second gen FSM, but your 93 sounds like it's the same.

If you look at the wiring diagram for the coil in 8W-30-11 you see that the dark wire feeds the coil and injectors directly from the ASD relay, I'm assuming that your jeep was off when you did your tests so 200mv sounds right for leaking through a relay. The white goes to the PCM. In most electronic designs if you have a pin that triggers by sinking current that pin will read high when not triggered. You wouldn't be able to get any current out of it though.

The dark wire can safely be ignored. I'd imagine that your MSD box is applying 12V to the white wire to sense the trigger, so the PCM is seeing exactly what it sees with a real coil

 

Interesting....

From https://www.boschsparkplugs.net/learning-center/article/225/heat-range-conversion-chart

I'm going for Champion Racing C57YC with heat range "57" for $40 for a set. Anything cooler and the price sky-rockets.

 

This guy tried the MSD 6A-2 and fried it and got stuck on the side of the road. See post #11.

http://www.jeepforum.com/forum/f13/msd-6a-2-installation-1134378/

Seems he was using too small a gap: #15

Sorry to say, but if you are going to put in a monster spark, you have to do your wires and plugs too. That much should be obvious.

(Although, that said, it wasn't obvious to yours truly that quench, stroke, and higher compression might require a beefier spark. :laugh: )

 

I would put a screw-on cap on the unused wire. Don't know of any isolators. You would the specs of both devices to come up with something. One thing, I would do the splices with connectors so if the MSD fails, you can plug and play back to stock.

 

Yeah, I already bought nice Chrysler-style snap sockets to connect everything together.

No, it's not much reversable :-( Different wires + racing plugs. Stock coil is probably not gonna like it. Already burned two stock coils due to wrong plugs. Though I'll try it in any case.

I'm gonna look into an optical or inductive isolator.

Probably I can use an inductive isolator to drive the magnetic pickup. Just need to get the turn ratio right.

Will be phoning MSD. Will post what they say.

 

You're really overthinking things. Don't cut your factory wires just use the coil adapter MSD made for putting their boxes in Chrysler products with the two round pin coil. This one: http://www.amazon.com/MSD-8889-Wire-Harness/dp/B001PRQE7K/ref=sr_1_1?ie=UTF8&qid=1456674071&sr=8-1&keywords=msd+8889

You just plug one end into your harness and one end into the coil. The MSD box wires match the adapter so you just plug them in add power and ground and it goes. That's what I did about this time last year when I put the Streetfire box in my 93. See here: http://www.jeepforum.com/forum/f13/msd-install-option-3013809/

Seems Coralman was right though about water getting in; I was driving in the rain and it started to sputter then died. Nice thing about the MSD adapter cable is I just unplugged the two plugs and plugged my factory coil back in and was on my way in 2 minutes. Sent the box in to MSD and they repaired it under warranty but said the problem was water getting in fried a transistor. It seemed to add a couple HP down low but not enough for me to put it back in. I'll probably just eBay my repaired box.

You don't *need* to upgrade your wires or plugs for an MSD on our ZJs. Some older cars with tiny wires and old oil-filled coils had issues but our stuff will handle it just fine. Better wires wouldn't hurt anything though. Whether or not such a thing as a better spark plug exists is a whole other discussion.

 

You're really overthinking things.

Yes. I thought as much.

Didn't find your thread on search -- I think I was searching on msd model number.

For my own closure --- does the MSD harness leave the dark wire hanging?

 

Nope, the harness uses the factory +12v wire as the switched power wire to the box and the trigger wire to trigger the MSD. All the factory wires are used. It's very neat and tidy when done.

 

Yes except that other wire is not the trigger. It's the common wire to all injectors and some other stuff. I've measured it and confirmed it on the wiring diagram.

The 12V is the trigger.

 

The common wire should be 12v power. The ECM grounds the other wire to complete the circuit and fire the coil or injector or whatever. At least that's how it worked on mine.

Check out the wiring diagram for the adapter here: http://www.jegs.com/InstallationInstructions/100/121/121-8889.pdf

 

Here's a wiring diagram for the 95 4.0 I stole from this thread: http://www.jeepforum.com/forum/f13/crank-position-sensor-question-2786330/

The coil power comes from the ASD relay so it must be constant 12v. The other wire goes directly to the ECM. Maybe your coil has a replacement pigtail with alternate wire colors? On mine it matched the above diagram 12v on black and nothing on green. FWIW mine came with the alternate blade style coil and I swapped the connector so I could use the more common round pin coil.

Edit: Just went and checked my 93 and got 12v on the black and 0.032 volts on the green which is practically nothing. Just touching the positive lead with my finger reads about the same.

 

edit: Just went and checked my 93 and got 12v on the black and 0.032 volts on the green which is practically nothing. Just touching the positive lead with my finger reads about the same.

Your "12v on the black" is connected to Pin 19. I'll bet you $10.

Here ===>

 

The trigger wire goes to ground to trigger.

The output of the ASD relay is 12V+, it's much easier to trigger by sinking current than it is to deliver high current. And that kind of circuit will be very close to the positive rail when off.

If you made the measurement when the jeep was off then the ASD relay wasn't on. Look at the diagram referenced in that drawing, 8W-30-8, it will show you the ASD relay is connected directly to the positive terminal of the battery.

That black wire is 12V+ when the ASD relay is closed.

 

...

you are not understanding the question

 

Ok, I must have missed it, can you rephrase the question?

 

look at the picture i posted

all the red and green was drawn in by me

is there anything wrong on this picture?

 

Yes, in the green text you have it reversed. The output of the ASD relay (BK Jeep wire, where you have "reroute to trigger") is your 12V+.

The wire going to the PCM is the trigger, which will become ground when it wants the coil to fire.

 

So why is A61 reading +200mV?

The ignition is On when I take these readings.

 

Because you were looking at it with the jeep off. I just checked. The grey with white stripe pin has continuity to the ECM pin 19. That's the trigger wire. The ECM grounds that wire to trigger the coil. The pink or orange wire is the 12v power supply to the coil but it comes from the ASD and the ASD is only closed when the engine is cranking or running. I verified that during cranking the pink/orange wire has 12v.

Edit: to be clear, the ASD is closed when cranking and after the engine starts, not whenever you have the key on.

Edit 2: since my plug was replaced I stripped the loom back to see the OEM wire colors.

 

Because you were looking at it with the jeep off. I just checked. The black pin has continuity to the ECM pin 19. That's the trigger wire. The ECM grounds that wire to trigger the coil. The green wire is the 12v power supply to the coil but it comes from the ASD and the ASD is only closed when the engine is cranking or running. I verified that during cranking the green wire has 12v.

thanks josh

i now understand my myriad conceptual errors --

1. even though Pin 19 is labeled "( - )" it is actually +12V
2. even though the common wire A61 reads 200mV it is actually +12V (ASD only switches on when cranking)
3. even though it is a "common wire" it is not a "Ground" wire.

Ok, so now it is clear how to connect all this :highfive:

Mind you, it was all dead simple to begin with :shhh:

I'm cancelling my order for MSD 8889 because I have much nicer connectors. Search ebay for "Weatherproof Automotive Connector Pair 2-pin" then see seller "steve48348" many connectors.

Updated diagram ===>

 

You either have slight leakage current through the relay or a cheap multimeter.

I just went down to the jeep for a test. The ignition on is not the same as the engine running, I connected the negative lead of my meter to the battery ground, started the engine, and then pulled the connector for one of the injectors. Since as you've stated, the coil wire from the ASD relay is shared with the injectors they should be electrically equivalent, correct?

And with the engine running (poorly minus one injector) you get 13.8V on the ASD relay wire.

 

I have a replacement coil plug so I went back and pulled the loom back to the OEM wire colors. Sorry to confuse.

I edited my post but to be clear:
The dark green/black wire (on mine it's pink because I had the old blade style coil I think) goes to the ASD and gets 12v when cranking and running. This is the coil power supply.
The grey with white stripe wire (also black?) goes to pin 19 on the ECM and is the trigger/signal wire.

At the end of the day if you use the MSD harness it just works.

 

Yup, thats the stuff.

This is one of those "don't overthink it" things. And trust the FSM.

 

Parts list --

1. MSD Street Fire CDI 5520
2. MSD 8203 Blaster 2 Coil
3. MSD 8889 Wire Harness
4. MSD 8213 Chrome Universal Coil Bracket (did not use this)
5. Champion Racing Spark Plugs 82216 (low temp plugs -- then I'll try the mopar performance PCM again and see if it the ping is gone.)
6. Davis Unified Ignition LiveWires C9100YL (got these because I want the yellow to match the engine color. They are the only yellow plug wires I could find.) (they roled a special #3 of 4" longer)
7. Weatherproof plugs from ebay.

To come.....

Custom mounting bracket for MSD box and coil.

 

Should do nicely, can't wait to see it.

 

Champion RC12LC4 (right) vs Champion Racing C57YC cool plugs (left). '93-'96 Jeep FSM says RC12YC which I think is slightly shorter than RC12LC4 (5.2 '97/'98).

Out of the box the C57YC gap is 0.025". FSM says 0.035" or 0.040" depending on the year. I'm going for 0.050" considering this info:

The main determining factor for gapping a spark plug is the compression ratio of the motor. Once you have determined this then you can properly gap your plugs. This chart is a good starting point:
COMPRESSION.......PLUG GAP
Up to 10:5:1.........0.040"-0.060"
10.5:1 - 13.0:1.....0.032"-0.040"
Above 13.0:1........0.025"-0.032"

We recommend using a standard copper plug, 1-2 heat ranges cooler than stock OE; we really have no preference for brands. Although we do suggest staying away from any "HYPE", platinum, or iridium type plugs. When you combine them with a CD type ignition, they can cause pre-ignition problems.
__________________
MSD Tech Support
915-855-7123

Since the Mopar Performance ECU is out, might as well replace the caps. Also re-flowed the solder on the pinouts -- idle seems to change when you jiggle the connector and the stock ECU does none of this. Perhaps there is a bad solder joint.

 

IIRC the L in the part number indicates that it's a long plug.

Edit: Yes.

 

This is revolting --- no wonder they don't sell it anymore

http://www.summitracing.com/parts/msd-asy10124/overview/

although i don't want the non-stock type plugs in case I have to switch something.

so made this MSDBlaster-to-stock converter from the piece of stamped copper they give you with the blaster, and what I turned down from an old bolt on my lathe. These three snap together really solidly.

I think I got the head angles just right -- you can't tell its home-made :banana:

 

That's why I stuck with the MSD factory replacement coil on my ZJ.
MSD Dodge coil PN8228 - 40,000 V
MSD Blaster 2 PN8202 - 45,000 V

That extra 5,000 V really only matters at the ragged edge and the ability to use the stock mount and wires is worth it in my book.

I like your adapter; it really doesn't look homemade. When you tried the MSD tower did you tighten the post to lock it in? I haven't seen one in person but MSD usually makes good stuff.

 

Did not bother buying tower after reading crappy reviews

Bigness of the blaster coil -- got to be better! Ha ha




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surprising there is no nice bracket available to mount the blaster coil in the stock location

seems quite easy to make

it will fit too

i have a simple design in mind