MSD Atomic EFI: Tuning Tuning Tuning

[babywag]

But then wont the coil constantly get 12v? I thought it was all set up to only give the coil 7v when running

That's why I said to use the DS crank/run wire, it's before the resistance wire (or should be). Or tap into the wire before the resistance wire.

The DS run wire is only 7v when running.

The 2 wire DS plug...has 2 wires, red and white. One of those wires "should" be hot in BOTH crank and run.
@ this plug the voltage is BEFORE the resistance wire in the harness, or should be.
Now being how your truck is converted to DS, yours may be different, but that is how it is on regular DS vehicles.

The solenoid is AFTER the resistance wire, between the DS box.

Bust out a test light or a DVM and check those 2 wires @ the DS plug.

[Flip]

Another question that may help me, where the hell IS the resistance wire? Under the hood somewhere in the harness or under the dash?

According to the schematic I'm looking at it comes right out of the bulkhead connector on the engine side of the firewall. That's pretty standard fare, so I'd believe it to be correct.

Another reason to tap off right at the ignition switch.
I've got to run some errands, if you don't still have my number, just email me. That will come to my phone, and I'll call you.
I'll take the schematics with me, so I can at least sound somewhat intelligent...

[Dr. Marneaus]

That's why I said to use the DS crank/run wire, it's before the resistance wire (or should be). Or tap into the wire before the resistance wire.

The DS run wire is only 7v when running.

The 2 wire DS plug...has 2 wires, red and white. One of those wires "should" be hot in BOTH crank and run.
@ this plug the voltage is BEFORE the resistance wire in the harness, or should be.
Now being how your truck is converted to DS, yours may be different, but that is how it is on regular DS vehicles.

The solenoid is AFTER the resistance wire, between the DS box.

It is wired up in accordance with this diagram, which shows taking the switched power source from AFTER the resistance wire

Bust out a test light or a DVM and check those 2 wires @ the DS plug.

My DS box may be wired in weirdly because in general I have no idea what I'm doing and probably had even less idea back then. Both connections on it are at the solenoid, which is after the resistance wire.

image.jpg

[babywag]

Ah, well then you'll need to tap in before the resistance wire...oljeep.com has wiring diagrams.

Should be red w/ tracer...
http://oljeep.com/gw/elec/73/73_FSJ_Wir ... mPage2.jpg

[Dr. Marneaus]

Ah, well then you'll need to tap in before the resistance wire...oljeep.com has wiring diagrams.

Should be red w/ tracer...
http://oljeep.com/gw/elec/73/73_FSJ_Wir ... mPage2.jpg

So, as babywag just mentioned....(was typing this response as he responded apparently) other option is finding the pre-resistance ignition wire. if im not mistaken the wire that feeds the solenoid and coil, coming from the junction on the firewall is the red/green wire, circuit 14.

I checked at the junction in the fire wall and this red/green wire, number 14 has 12+ volts in run, which means its BEFORE the resistance.....but drops to 0 when I turn key to start.

I then checked the blue wire, circuit 13, S terminal, at the firewall, and this is the opposite, as expected, it is 0 in run, 12v in start.

I figured since we have power at the I terminal of the solenoid in both start (12v) and run (7v) , that the red/green wire running to it should have voltage ( 12v from before the resistor, 7v after) all the time in Start or run....but thats not the case. How is that possible?

I was looking into this to avoid having to do the super minor work for the diode scott explained to me, as an alternative, but it seems really weird that the red/green circuit 14 wire drops power at the firewall connection when turned to start.

Is it because im checking AFTER the NSS?

[Flip]

It's because the Start circuit, and the Run circuit are completely separate at the ignition switch. The ignition switch is not built to have power to both run and start at the same time.

Easiest way I can see to make your subharness :

One arm of "Y" to anode of diode.
Cathode of diode (silver end) to the same terminal as the Light blue wire on the Starter solenoid. This provides battery voltage during engine Start mode.

Second arm of "Y" to the Red wire at the Vacuum switch on intake manifold. This wire is Siamesed to the resistor wire at the same terminal of the bulkhead connector. This provides full battery voltage during Run mode.

Leg of solenoid to the small red wire on the MSD box.

Add a second leg if you plan to install the MSD 6A (it will connect to the red wire of the 6A box). You can use a female spade or bullet connector, and just pack it with dielectric grease for now, to keep it clean. Then a bit of tape to keep it from touching anything.

[Dr. Marneaus]

It's because the Start circuit, and the Run circuit are completely separate at the ignition switch. The ignition switch is not built to have power to both run and start at the same time.

Easiest way I can see to make your subharness :

One arm of "Y" to anode of diode.
Cathode of diode (silver end) to the same terminal as the Light blue wire on the Starter solenoid. This provides battery voltage during engine Start mode.

Second arm of "Y" to the Red wire at the Vacuum switch on intake manifold. This wire is Siamesed to the resistor wire at the same terminal of the bulkhead connector. This provides full battery voltage during Run mode.

Leg of solenoid to the small red wire on the MSD box.

Add a second leg if you plan to install the MSD 6A (it will connect to the red wire of the 6A box). You can use a female spade or bullet connector, and just pack it with dielectric grease for now, to keep it clean. Then a bit of tape to keep it from touching anything.

Thanks for chatting with me about all of this yesterday, was definitely helpful.

I dont have that vacuum switch or anything like that. I'll just find another "run" source of power, no issue there.

Only real concern is that when cranking even at the blue solenoid terminal I'm only showing 10.35v when cranking with the starter attached. It shows 12.5v when turned to start with the starter disconnected. Hopefully that 10.35 will be sufficient. It worries me a little thinking about if i'm out on a trip camping and the power has dipped because I used my inverter or power plug or something.

Perhaps I will replace starter and battery cables and terminals. They are kinda scummy looking, not visibly corroded, just crasy and gross... but god knows how old everything is.

[Dr. Marneaus]

I know it doesn't look like much but its getting there. 4 or so hours of work with me and Nightglide rolling around under and next to the jeep. All wires are run now, dropped and removed old tank and fuel pump, removed the lines I need to use again, I removed even MORE superfluous wiring for accessories, made all the leads for the power and ground, made all the fuel lines, mounted new tank, mocked everything up for measurements and cuts, dropped it back out, added a union so I can drop the tank without pulling the under hood lines, added the fuel filter, mounted the lines to the side of the tank, I can now permanently install the new tank.



Several items left however. Need to measure the under hood lines, cut and mount. need to mount regulator. Then, everything will be plumbed. Need to tidy up the wiring by replacing the split loom i removed when deleting a bunch of crap, then build the little diode Y and connect the last 2 wires. Next comes the O2 sensor bung getting welded in, then finally I just need to replace my filler neck with the dual tube version that goes with my tank and connect it with hoses. I THINK thats all.

A few nights working after I get home for a couple hours ought to get it done. I'm hopeful that I'll be able to fire it up before or during this coming weekend.

[REDONE]

Yeah! Gettin' it done!

For Father's Day I want to hear my Jeep run again too.

[Flip]

Looking good!
Was fun talking/texting yesterday. Glad it helped!

The closer you get to the key switch with your connections, the less voltage drop you'll have to deal with.
Stay away from wire tap connectors like Scotch Locks. Wire terminal ends or solder on clean tinned wires will give you much better results.

[babywag]

Progress is always good, your efforts will be rewarded, and you'll wonder why you didn't go to FI a looooong time ago.

I also remembered that I swapped to a full '79 wiring harness on my '73 (duh...), and that would explain why yours doesn't have a single hot run/crank wire like I was thinking it should.
My bad...

Keep @ it, and you'll be a happy camper when it's finished.

[Dr. Marneaus]

Looking good!
Was fun talking/texting yesterday. Glad it helped!

The closer you get to the key switch with your connections, the less voltage drop you'll have to deal with.
Stay away from wire tap connectors like Scotch Locks. Wire terminal ends or solder on clean tinned wires will give you much better results.

I suppose I can check voltage at the big terminal on the blue wire to see if it's any better there or I could even locate said wire even closer to the switch on the inside of the firewall, which is where I intendef to pick up switched 12v anyway.

[Flip]

I suppose I can check voltage at the big terminal on the blue wire to see if it's any better there or I could even locate said wire even closer to the switch on the inside of the firewall, which is where I intendef to pick up switched 12v anyway.

That would be awesome if you can come right off the ignition switch. How's your soldering skills, & gear?
The female tabs can be removed from the connector with pin tools, and you could solder directly to the stem, where the wires are crimped.
just takes a big iron/gun for quick heat. Otherwise the female tabs will start to lose tension.

[Dr. Marneaus]

I've got a big gun but my skills aren't super great

[Dr. Marneaus]

When working on fuel lines....wondering what all is considered a heat source.

Due to the length of the lines and trying to keep things as clean as possible im thinking I'll run the supply and return lines more towards the tranny hump from the linkage forward. My previous line went up the far far driver side, to the outside of the trans shift linkage and crossed over on the firewall. This time im thinking I'll stay to the inside of the linkage, follow the hump up, then cross over below the charcoal canister.

This will put the lines within a few inches of the transmission housing, with the return line potentially touching the transmission housing, though I will try to avoid that. Is this a major concern? Generally I would only really consider the muffler, pipes, and manifolds to be serious heat sources.

[Flip]

Not a major concern since you have a "return system", but generally the cooler the gasoline, the better the burn.
Summit Racing has DEI sleeves that work awesome. I've used this in supercharged applications, where the fuel lines passed near the header tubes. Very impressive stuff.
https://www.summitracing.com/search?Sor ... I%20sleeve

[Dr. Marneaus]

Tank is in. Fuel lines from union/filter to TBI are mocked up and measured for cut. regulator mounted. Got tired and went in for dinner before making those cuts. Will do it today. Hope to have everything 100% plumbed by the end of the night, and hope to drill o2 sensor hole.



(yes, that all clears the linkage without any contact)


Also....I'm having the damnedest time finding suitable fuel filler hose for a tank/filler neck from a 78 wag/chero. I need to go from the filler neck to the tank. Thats about 4.5' of 5/8" and 7/8" hose for the fill and the breather. Anybody have any suggestions where to look?

I can get some -10AN and -16AN braided line but that'll be about $95 for 6' of each. I called a local hose place and they quoted me about $104 for 5' of each. What gives?

the -10 and -16 AN seem to be the best option, but i'm a little worried about whether they will stretch at all to fit over the tank and neck nipples. Also, there seem to be various ID sizes listed for the AN hose on summits site. I guess I'll have to check it. I have the filler neck with me. since its just basically zero pressure line I cant imagine i need anything fancy but even the cheap stuff isnt cheap!

[babywag]

I had a very hard time as well.
NOBODY stocked it, and was hard to find store that was willing to sell it by foot vs. making me buy a whole flippin' box.
All I can suggest is call around, or look for a place that does hydraulic hoses or a marine outfit. They @ least knew what I was talking about.
IIRC my dad tracked some down @ Carquest and shipped it to me.
It was for his truck, so he didn't mind.

[Dr. Marneaus]

one local hose place didnt have 7/8ths hose, only 1", which SHOULD work, but still...not what my current left over old hose bits measure. They had the 5/8ths though. Total for 5' of each was 105 before tax.

the other local place didnt have 1" or 7/8" so screw them.

so far summit is looking the cheapest for me to get -16 AN and -10 AN nylon braided. retarded.

I have $131 worth of hoses and battery/starter cable sitting in my cart on summit's website.

[AwesomeJ10]

FYI on all of my TBI/Vortec installs, I've simply ran 3/8" rubber hose and normal hose clamps. Junkyard TBI setups get the 'cheap' stuff that literally says 'not for fuel injection' (because junkyard TBI is only 10-15psi anyway). Vortec gets the higher end rubber hose made for higher pressures.