So, I bought an 86 D100 short bed with, of course, a slant 6 and an automatic a few days ago. It is a bone stock truck with what looks like the factory exhaust still in place. It still has both converters on it, factory air cleaner, a Holley 1945 without any electronics other than the idle solenoid on it, the factory dual pickup distributor,

It's a fairly good truck body wise but has been neglected mechanically. It had a leaky carb that someone had "fixed" with silicone, oil leaks all over the engine, no brake fluid (and no signs of a leak anywhere), a couple small vacuum leaks, a rotted out muffler, squeaks and rattles all over the truck, etc etc.

The engine was missing very badly when I bought it, I had to "two pedal" it to keep it running at stop signs and getting to 50-55 was a long slow struggle. I rebuilt the carb, cleaning all of the silicone and crud out of it, and fixing the gas leaks. I replaced the rubber fuel line, fuel filter, vacuum lines, checked the timing (it's set to 16* which is what the hood sticker calls for), set the air gap on the reluctor/pick up (.006 on the start and .012 on the run), checked the plugs and wires, cleaned the oil film off the coil and distributor cap, and it now runs 100% better than before but it's still not right. It starts easy, idles a little rough in park and shakes the whole truck when its in gear at a stop, seems to miss or "chug" along when you're accelerating from a stop, and seems to run decent once you're up to speed at 50-60. The plugs aren't worn at all, the wires are good, the cap and rotor don't show any arcing or pitting at all. All 6 plugs look the same as far as color and condition.

The plugs are bright white, it looks like you just took them out of the box, even after I've driven it 75 miles or so since the fixes I mentioned before and about 100 miles before the repairs. There is a lot of heat coming off the engine after a drive, more than your average "warmed up engine" would be. I assume a lot of this heat is coming from the exhaust from running so lean. I know they were setup from the factory to run lean for MPG and emissions purposes, but this is extremely lean in my opinion.


So, with those things in mind, I have a few questions for those of you more experienced than I.

1) Would the converters being old or possibly partially plugged cause a very lean condition?

2) Am I missing an adjustment or something common that I haven't mentioned checking already?

3) I've thought of putting a larger jet in the carb, but wanted to make sure I wasn't missing something else before I tore back into the carb again. I didn't really pay attention to what size jet it already has in it while I was doing the rebuild.


Thanks in advance!

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1970 D100 "Dude"
SL6 / 3 speed manual

30 year old convertors are probably clogged and restricting flow for sure. If it has the Lean burn still in tack then it should be swapped for a HEI set up as soon as you can. You will be amazed how much that will improve the running, idle...etc. Plus you can adjust the timing to get better power and economy.

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I've been doing some more research and reading about the lean burn system. From what I am gathering.... a lean burn system could have had 1) a special distributor/spark control system and a regular old carb OR 2) the special distributor/spark control system along with an electronic controlled feedback carb. Is that right?

It looks like I have the lean burn distributor, no vacuum or mechanical advance, two pick ups, etc. But I don't have a feedback carb, its a normal old Holley 1945.

So I understand the distributor swap that you talked about in your reply, but that doesn't affect fuel ratio or the lean condition. Are you saying that the lean burn distributor alone can cause my problems or just saying that it's not an ideal setup and it's best to upgrade when you can?

I am not trying to be argumentative lol, just making sure I am understanding your advice


I've been contemplating taking a drive without the converters to see how much of a difference there is in how it runs. Externally they look fine, uniform color, not rusted out, no noticeable rattles from them, etc. I know that doesn't say a lot about what they look like internally. I will probably take at least the front one off tonight and see how it runs after that.

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1970 D100 "Dude"
SL6 / 3 speed manual

The lean burn spark control system can make your motor run extremely poorly.

However, the spark control system is not beyond the capability of a home mechanic to troublshoot and maintain. The biggest problem with the lean burn distributor system is that most often teither the vacuum transducer on the computer has failed or the computer is not getting a correct vacuum signal to regulate the spark. The hose that goes to the nipple on the computer must see fullmanifold vacuum, no ported vacuum. If the computer is geting the correct vacuum signal and if the transducer is still functioning, then the rest of the system is regular old sensors and grounds and wiring.

I strongly recommend you get a factory service manual for you vehicle sincle it will have instructions on how to diagnose and repair the lean burn system.

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Casually looking for a Clifford hyperpak intake for cheap.

Here is how I did the HEI conversion on my 86, mine was single pickup distributor.

I wanted to mount this in the original location of the Lean Burn computer. The engineers designed the computer housing to hook into the air intake for the engine to help with keeping the computer cool,
so I thought it would a good place to help keep the module cool.
Well I disassemble the computer and found that after pulling the electronics out of the housing I was left with an 8 3/4 inch X 4 inch area for a heat sink. So I picked up a piece of 1/4 in aluminum plate to fit in the housing, shouldn't have any heat sink issues. Some would say that I went thru allot of trouble to mount this module. But the housing is designed with 2 openings one where air is drawn in by the other opening that is connected by a hose to the breather intake hose, there by drawing cooler air across the entire inside of the housing. I have been driving it like this since 2007 and have not had any issues.

Here is a picture of the rewired module and ready to reassemble.
https://skydrive.live.com/redir.aspx?ci ... 6xyhouBGNQ

I kept the vacuum advance pod in there just to plug that hole. Make note of how the pod is orientated when you pull the 2 halves of the housing apart, or it will not go back together easily.
https://skydrive.live.com/redir.aspx?ci ... 8yvF3fYYso

all the wires I used when I did the conversion were all there plugged into the computer. There were 2 wires going to the coil, 2 to the distributor and 1 ground wire.
Here is a link to a PDF of the wire diagram from the factory service manual and wires highlighted that I used.
https://skydrive.live.com/redir.aspx?ci ... s12eOvYLZI
doing this mod I was able to eliminate 15 wires from my wire harness.
I used a 6 pin GM weatherpack that I got from junk yard for $2 to make all the connections. Weatherpack is so that it will disconnect from main harness for removal if any repairs are necessary. Do not attempt to buy this weatherpack new from NAPA just the blank housings are $15 apiece!!!! By the time the guy had figured all the pins and seal I would have had $45 in just one six pin connector. I found mine on a K5 blazer for $2. I was able to reuse most of the seals and bought new pins as needed. I think I ended up with $10 or less invested in the connector.
Originally when doing the conversion I had tried using a dizzy out of 73 dodge truck. It had to much mechanical advance, 30 degrees total if I remember correctly. Grab one from a 78 Volare with Super Six setup and it made huge difference. I also used the Blaster 2 coil as in the article. There was no ballast resistor either.
Hope this will help.
I have been running this setup since 2007, same module.

Dave

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86 Miser 170,000+
2 1/4" exhaust
Holley 1920 #55
HEI MSD BLaster 2
17.8 mpg

I am no expert on anything electrical, but I do know that 95% of all the lean burn systems have been thrown in the trash. Of the remaining 5 % only a small fraction are probably running decent at all. You may be smart enough to be able to make it work better but the system may crap out without warning and then you will be setting along the road wondering why I didn't install that great, simple & cheap HEI upgrade. Ask me how I know this!

I have this "new" 86 truck with only 34,000 miles on it, and the very first thing that will be going is the lean burn system. It is just too easy and affordable not to do. At least for me.

Good luck,

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Rick is right. In the long run you will save yourself aggravation and money by jumping straight to the HEI swap. However, if you are so inclined, it is possible to troubleshoot and repair the lean burn system. It usually just isn't worth it.

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Casually looking for a Clifford hyperpak intake for cheap.

All good advice guys. Don't get me wrong, I am not opposed to doing the HEI swap at all, I'm just trying to get it running decent enough to daily drive it until I get the parts together for the swap.

Tonight I checked the vacuum to the computer, there wasn't any. I fixed that problem as well as losing the front cat. It still has the rear cat, I figured if one was partially plugged, it would more likely be the front cat since it gets the most heat and exhaust first. I didn't test drive it with an open manifold, to eliminate the rear cat and muffler from the equation. It does run noticeably better now, but it's still not 100% right either. It still shakes/misses on acceleration from a stop, but not as bad as before, and it does get up and go a lot better and seems smoother during cruising too.

More to come in the next few days.

Thanks again for all the replies!

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1970 D100 "Dude"
SL6 / 3 speed manual

Yay, progress! I would thoroughly check the engine over for any exhaust leaks and/or disconected wires. Make sure all the connections and grounds are good. Check the temp sensor- after the vacuum transducer it is the most important sensor in the lean burn system.

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Casually looking for a Clifford hyperpak intake for cheap.

Well good news and bad news.....

Good news is that I have found out why it's running rough and seemed like it was missing.

Bad news is that its not a quick and simple fix, it's something to do with the exhaust valve on #6.


I did a compression check tonight after work.... #1 135 #2 130 #3 145 #4 145 #5 140 #6 35 ....nope not a typo.. 35.

I rolled #6 up to TDC of the compression stroke and hooked my air hose up to it and heard a nice steady roar of air through the exhaust. I double checked to make sure it was on the compression stroke, it was, the rotor was pointing at the #6 tower on the cap. No air coming from the carb or crankcase, just the exhaust pipe.

I pulled the valve cover and everything looks fine in the valvetrain. I had the wife turn it over while I watched and all the rockers moved normally. The push rods on #6 look fine and aren't bent or anything. I guess it's a burnt valve from what I am seeing right now.

I haven't went any farther than that as of yet. I guess the next step is to pull the head and see what has happened.

More to follow.

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1970 D100 "Dude"
SL6 / 3 speed manual

Sounds like a burnt #6 exhaust valve...
Let us know what you find once you pull the head.
DD

Tip: For a "quick-fix" I leave the manifolds bolted to the head and lift the entire head / manifold "mass" off the engine, with my cherry-picker".

Tip #2: Even Valve Stem Heights are important on Hydraulic Lifter SL6 engines so be sure to check that. (non-adjustable rocker arms)

Good tips.... I've already unbolted the manifold from the head, but I will probably reinstall in on the head while it's off the engine and then put it back on as one big assembly. It sure would be easier that way.

I will be pulling the head tonight. I got most of it apart last night, all that is left is the rocker shaft and head bolts.

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1970 D100 "Dude"
SL6 / 3 speed manual

I think the lean burn system lead to valve failure, especially exhaust valve faile, due to overly lean conditions. I currently have a 83 hydraulic slant head in my garage that has a severaly failed exhaust valkve, I have talked to several other hydraulic slant owners who have also experienced failed exhaust valves, and now you have a failed exhaust valve. Either Chrysler went to poor quality valves in the 80s or the lean burn system ran the mixtures too lean or the timing in such a way as to lead to excessive cylinder temps.

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Casually looking for a Clifford hyperpak intake for cheap.

I would agree that it's most likely a mix of lower quality valves, too lean of a fuel mix, and timing.

Hopefully it's just a matter of a valve job and not a trashed valve/seat. I would guess that it's not torn up too bad if it still can muster 30 psi of compression.

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1970 D100 "Dude"
SL6 / 3 speed manual

Here are some shots of the failed valve and seat in my head:



This one is interesting because you can clearly see the air injection port above the exhaust valve:

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Casually looking for a Clifford hyperpak intake for cheap.