lean burn

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dan brooks

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Hello everyone,
fortrucksonly sent me over with my question. I have a 1981 stepside with a slant six. I want to remove all the lean burn wiring and there telling me i have to change the distributer, what all is involved with this swap and is there anything that might be a problem? I feel confident I can do this as I've worked on mopes my whole life. I know there's still active wiring going to the air cleaner as i unhooked it and truck wouldn't start.
Thanks for everything!!!
 
you will need a distributor, ecu, ballast resistor and wiring harness...basically a complete electronic ignition conversion kit...
 
yup, my 85 with a slant 6, had 2 pickups in the distributor. but I also had an 81 W150 years ago with a 318, factory 4 bbl, and plain 4 pin electronic ignition. That truck also had 2 pickups in distributor with vacuum advance, which your slant will not have, because those functions have been moved to the brain box. My 81 had a relay somewhere among the wiring harness to differentiate the start/run functions of each pickup.NO lean Burn on that truck.

You don't have to pull all of the unnneeded wires to the Lean Burn out of the wiring harness, but you can. It would make for a cleaner job. I'd untape it and have a wiring diagram right next to me and go at it. There is a splice (I think blue wire) with 3-4 wires (all same color, it's around the area of the back of the brake booster in harness) going every which way, that comes off the "hot with ignition in run" position. goes to ignition box (or lean burn), choke, and anything needing "hot with key". I think you can trim a couple of those away. There is also a connector many call a "duck foot" with 1 "hot" from the battery splitting 4 ways, along teh driver fenderwell between the battery and hood hinge that needs a close look at. Most of the fusible links join within that black rubber connector. this connector is not able to be pulled apart, unless it is either shorted and burnt or cut apart. if it is OK, you do not have to mess with any of those wires in doing your conversion/// but it is a known trouble spot in these wiring harness, that needs inspection.
the factory service manual shows wiring for both options. (ECU and Lean Burn) I wound up getting my factory service manual from Ebay.

I think 99% of 81+ slant powered trucks in US, had Lean burn from the factory, the 318s (besides California) still had 4 pin ECU til 86, when they went to Lean Burn. 360s all the way til 88 could have come from the factory with 4 pin ECU (and no Lean Burn). Canadian trucks and Mexican trucks a lot more "lenient" with emission BS. which is why service manual shows wiring possibly going "either way" in any given year. some years Lean Burn was on air cleaner, other years it was behind battery within fender.
In my case, my wiring was hopelessly butchered by the past owner. It was a mess. (and that is putting it lightly) I won't get into detail here in this post. I found an 84, 360 1-ton truck (least emissions with heavier GVW truck) in the junkyard with a wiring harness in much better shape (though not perfect) as compared to my original harness. not neccessarily looking for that combo, but "I got what was there for the taking".
It already had ballast resistor and 4 pin ECU wiring, not Lean Burn. Plug and play. I just had to extend a couple of wiring pigtails, mainly the ones going to the coil the distributor and the oil pressure sending unit, but not by alot, taking a V8 harness and making it work on a slant 6. like 4 wires that needed lengthened. Ballast resistor, ignition ECU box, voltage regulator, etc mount in same location on firewall, regardless of engine. Alternator wire length worked out fine with V8 harness on my slant 6.
I did still untape that junkyard harness and check the wiring for damage within (brittle insulation just from age) and retaped it.
I modified my wiring from stock, I did away with all the fusible links and added an underhood fuse box from a newer truck (wasn't from a Dodge product, but wiring is wiring) and ran everything that used to be run thru a fusible link now goes thru a large blade style fuse ("Maxi fuse") included in said fuse box. I have other threads spread among the forums, that I could possibly link (if I can figure out how) that details what I did, and I have a hand drawn diagram detailing which F.L. went thru which fuse holder.... I need to scan to the computer, so I can post it or PM it to interested people....
There is another option, many switch to a GM HEI system on these trucks to get around Lean Burn.... no harder than going to factory Mopar system and you dont have to worry about wiring in ballast resisitor...... go look on slant 6.org.... lots of talk on teh subject there, probably some mention of that option here too, with a search.
Lastly, some of this goes way beyond what you will have to do just to convert your ignition... but still needs to be considered. Wiring is one place that is too important to hodge podge or butcher..... I sure dont want my truck to short out and burn to the ground so I don't do shortcuts in that department. The PO of my truck sure did though.... I had alot of "undoing" to do.

BTW, this is the guy that you met in the campground, and got your gas tank from.......
 
If you have that factory wiring diagram, you can tell which wires go from the plug that went to the plug that plugs into the Lean Burn, pick out the wires from that plug (or those 2 plugs, if yours has 2 plugs) that come from battery hot w/ key, go to the 2 wires that go to the "RUN" pickup in your current distributor, and (I think) one side of coil (one from the "RUN" pickup goes from distributor to other side of coil) and leave the rest of wires in the plug(s) to the Lean burn lie, or pull those out of harness. Your choice. Take those 4 wires, cut from the plug(s) going to Lean Burn computer, and splice the respective wires from that plug to the 4 wires in the pigtail that you get, that plugs into 4 pin ECU. There are multiple line drawings available via Google search that detail the wiring "to" the 4 pin ECU. all of those are in the harness already. if in good shape you can just use what is there. the wiring to the dist and the coil. you dont have to run redundant wiring but you can.
There is wiring to lights, wiring to sensors, wiring to alternator in the harness that you will still need, as they are.
get yourself an electronic ignition distributor from a 1973-1980 slant 6 with electronic ignition, (it will have the vacuum and centrifugal advance that you will need)
talk to member Halifaxhops he has many rebuilt distributors for Mopars available, he's popular here. He's always in classifieds both here and that truck forum, hawking his goodies. That and a carb from same era that has teh nipple for ported vaccuum to run vac advance and you are set. Not difficult, just takes a bit of time.
As an aside, IF you can find a super 6 setup (2 barrel carb and intake) that would be perfect time to upgrade/ IF you want to. Just a suggestion, not mandatory.
 
volaredon said:
If you have that factory wiring diagram, you can tell which wires go from the plug that went to the plug that plugs into the Lean Burn, pick out the wires from that plug (or those 2 plugs, if yours has 2 plugs) that come from battery hot w/ key, go to the 2 wires that go to the "RUN" pickup in your current distributor, and (I think) one side of coil (one from the "RUN" pickup goes from distributor to other side of coil) and leave the rest of wires in the plug(s) to the Lean burn lie, or pull those out of harness. Your choice. Take those 4 wires, cut from the plug(s) going to Lean Burn computer, and splice the respective wires from that plug to the 4 wires in the pigtail that you get, that plugs into 4 pin ECU. There are multiple line drawings available via Google search that detail the wiring "to" the 4 pin ECU. all of those are in the harness already. if in good shape you can just use what is there. the wiring to the dist and the coil. you dont have to run redundant wiring but you can.
There is wiring to lights, wiring to sensors, wiring to alternator in the harness that you will still need, as they are.
get yourself an electronic ignition distributor from a 1973-1980 slant 6 with electronic ignition, (it will have the vacuum and centrifugal advance that you will need)
talk to member Halifaxhops he has many rebuilt distributors for Mopars available, he's popular here. He's always in classifieds both here and that truck forum, hawking his goodies. That and a carb from same era that has teh nipple for ported vaccuum to run vac advance and you are set. Not difficult, just takes a bit of time.
As an aside, IF you can find a super 6 setup (2 barrel carb and intake) that would be perfect time to upgrade/ IF you want to. Just a suggestion, not mandatory.
Click to expand...

Thanks Volaredon, appreciate all the info.
I never fully got that tank in the truck going, something else is going on, I think the gauge cluster is bad as well. Let me ask you this while I got you, I have another dodge truck and I bought it without drivetrain. It was a 6/four speed, I'd like to drop this clean 360/automatic I have into it. Is there a certain motor mount I need for the changeover? I'm assuming the trans mount would be the same. Thanks.
 
I'd run the HEI conversion myself. Don't have to get all crazy with it. I just used a stock slant electronic distributor with an MSD Blaster 2 coil, a Napa HEI module and no ballast resistor. I've blown one HEI module in 13 years (always keep a spare in the trunk) but everything else has worked flawlessly. Try to get original parts if possible and not Chinese or "remanufactured" which have a high failure rate.
 
Yeah that's one possibility, I've thought about trying an hei setup myself. I have already swapped the wiring on my slant 6 truck to factory mopar 4 pin ECU. I have a 78 fury 2 door hard top with a 318 to convert come spring when I get it home from my mom's garage where I store it for the winter.

On the 360 motor mounts the mounts themselves should be the same as the slant 6 ones. The brackets that bolt to the engine and then bolt to the frame by the mounts, are what's different. As I remember the 4 speed takes a different mount than the automatic but same crossmember. The mounts for the automatic is cheap and easy to get.
 
The 360 mount looks like a big U but the corners of the U are square not rounded if that makes sense.
Did you get any of the power train? I have been thinking about switching my truck to a 4 speed with OD, if I do anything besides leave the 727 alone. I was surprised to see a 727 behind the slant in a 1/2 ton, would have expected a 904.
 
volaredon said:
.. That truck also had 2 pickups in distributor with vacuum advance, .... My 81 had a relay somewhere among the wiring harness to differentiate the start/run functions of each pickup.
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That's a bad *** boost retard method! find the one that is retarded 5 degrees and wire it up to a pressure swich so under 6psi boost it retards.
 
pishta said:
That's a bad *** boost retard method! find the one that is retarded 5 degrees and wire it up to a pressure swich so under 6psi boost it retards.
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That's what I'm doing for my nitrous system. But I'm using the dual pickup "lean burn" dist. No advance in the distributor.
 
Charrlie_S said:
That's what I'm doing for my nitrous system. But I'm using the dual pickup "lean burn" dist. No advance in the distributor.
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You can take that shaft out and put one in with the regular advance system if needed. I have done a few for people.
 
halifaxhops said:
You can take that shaft out and put one in with the regular advance system if needed. I have done a few for people.
Click to expand...
I wanted this dist. I was running a single pickup LB, set at 15*. With this dist I can run 20* that retards to 15* when on N2O. This is a race car only, no street driving. Someday, I might do something more sophisticated, but my wife says I'm cheap. I say I'm frugal. I have less then $3,000 in my whole 66 Valiant.
 
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That was $3,000 not $300. But it has run 12.40's with the 225 engine and 12.80's with a 170 in the 1/4. Best of 7.79 in the 1/8 with the 225. Both engines are stock short blocks.
Back to the original thread, sorry for the high jack
 
So then there are 5 degrees between the positions of the start and run pickups? I never knew what the spread was.
 
Chrysler-Lean-Burn-Distributor-2.jpg

GM did the same thing with a 2nd gen HEI module where a grounded pin (pulled low) would retard the spark 5 degrees for starting...another boost retard candidate. Or run that mode and have a 5 advance on demand with the pin pulled high (open)
 
Any system with a ballast resistor is older tech and not as good a spark or reliability. I put an 8-pin HEI module in my 1964 Slant 225, with a later e-distributor. Many posts. From a salvage yard GM 1985-95 V-8 pickup, take the module, coil, and Weatherpack cable which connects the two. The module is inside the distributor cap, and also snip the wires at the pickup to get that connector. I would also grab the 5-pin control cable in case you later get an engine controller which can command spark advance with it (ex. Holley Commander 950). I also grabbed the knock sensor (in water jacket drain) and knock module (on intake manifold), with 1 wire between them. I put the sensor in the slant's drain hole (w/ bushing), but haven't used it yet.
 
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