Hello! I have an 86 D100 with the 225 slant six and a Holley 1945 carb. Last year I developed an issue where the truck would stumble and fall on its face at random times, didnt matter if it was warm or cold and it would happen at random. The problem progressed into happening every single time I tried to drive. To attempt to fix this I rebuilt the carb completely (Looked a little dirty, nothing too bad though). The rebuild did not fix the problem. Some more details about the issue: At idle the truck sounds like what I can only describe as popcorn in the microwave (Sorta a puffing kinda noise) and whenever I try to accelerate under any load at all it starts to stumble and will eventually die out unless I feather the throttle slightly.

Some things to note:
* Carb has been completely rebuilt (including Acceleration pump)
* I can rev the truck all day long with no problems, its only when I put some sort of load on the engine.
* some of the vacuum lines are slightly dry rotted.
* Replaced distributor (No vacuum advance, no points, entirely electronic) (entire thing)
* Replaced ignition coil
* Replaced fuel pump
* New fuel filter
* Has all 6 new Champion plugs
* Good spark and compression on every cylinder
* Previous owner pulled the smog pump and everything California emissions related
* There is a quarter sized hole in the tubing that went to the smog pump from the head.
* Fresh tank of gas
* When the truck dies out/sputters there is a VERY strong rich smell.

My Thoughts (Potential?)
* Have not tested vacuum yet, does not seem different than what it was like before. maybe vacuum leak somewhere?
* Vacuum amplifier possibly bad, maybe not IDK.
*** Sticking EGR Valve - My most recent thought
* Lean burn computer is screwy
* Maybe something related with the smog pump tubing

I hope you guys can help me out as this truck has been sitting for awhile and both my father and I have been scratching our heads wondering what's going on.

Thanks!

The Lean Burn computer, if you can call it that controls ignition timing, and to some extent
the timing chain also does.

Connect a timing light to #1 cylinder and see if the timing stays consistent. If the lean burn system
is operating properly, the timing should increase with RPM’s.
If you see the timing mark on the index on the front cover show late timing, or erratic timing, then I would guess that the lean burn computer or vacuum hoses are faulty. Although another possibility is that the timing chain has stretched and jumped a tooth.

I understand that you will not do this test with the vehicle under load, but the lean burn will still be
operating the same way with the vehicle stationary. You may not feel the symptom with the vehicle
not loaded.

The engine vacuum signal is a major input to the lean burn computer.
With cracked vacuum hoses the signal will not be right.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

92.6% chance that the Lean burn is not working correctly. I would upgrade to HEI if at all possible.
Then get vacuum advance hooked up to the new distributor. That will do nothing but make it run better and get better gas mileage.

_________________
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'm gonna check the hoses tonight to the best of my ability. From what I can tell, there was no difference in engine RPMs or how it runs when I pulled the vacuum lines from the vapor canister. Same thing with the EGR valve too. No difference whatsoever which leads me to believe there's a major leak somewhere. I'll keep you posted as to what I find!

Like Rick said,,,
Save time and effort and swap to an HEI ignition.
Lean Burn systems are known to be not reliable.
There are many posts here at .org that address HEI ignition
or ask a question.
And if you do have a vacuum leak, that also must be addressed.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

After replaceing two lean burn computers, and needing a third, on my 88 Diplomat 318, I converted to HEI.
Used a NOS electronic dist with vacumm and centrifical advance, and a NOS carb off e-bay for a earlier application.
Been on there for a couple of years now, with no issues. JUst returned from a approx 2,000 trip (slant six banquet), and averaged 24.2 mpg. In local mixed driving, I get about 18-20 mpg.
My lean burns never quit working, the timing system would not work correctly, and fuel mileage would go down the tubes.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 225 nitrous
64 Valiant Signet
64 Valiant 4dr 170

Just as an update, I pulled all the vacuum lines yesterday and rerouted them (some were hooked up incorrectly) and the truck actually ran pretty well at least for a little bit. I drove it around for 15 mins or so, but all of a sudden the truck just randomly died out, again no power. The rich smell came back and I had to bump start it every 10 feet or so to nurse it back home (It would not start with the starter motor). It's strange... If I let it sit for like 20 minutes it's good to go for another 1-2 miles. As for the HEI conversion, I just can't find the time recently to take on a big task like this, plus I just don't see converting to HEI if I don't know if the lean burn computer is actually junk or not.

If you are dead set on living with a lean burn equipped vehicle, the following will be invaluable to you:



Converting a lean burn equipped vehicle to HEI is extremely easy. You need all the parts described in the HEI conversion thread, but the installation on a learn burn vehicle is much simpler. You don't need to worry about a ballast esistor. The lean burn doesn't use one and neither does the HEI. All you have to do it install the distributor, with the distributor pickup to the terminals on the HEI module, and then hook the + and - feed from the HEI module to the + and - feeds on the coil. Mount the HEI module and ground it well and you are done. Alternatively, use the + fed for the coil to power a relay that provides full battery voltage to the HEI module. Thats it. TIme your motor and you are good to go.

My advice is to do the HEI swap. But if you don't wat to do that, then you need to follow the above factory service manual troubleshooting and maintenance procedures exactly and make absolutely sure that all vacuum hoses and electrical components are hooked up correctly and functioning. Even then the computer just might not work.

Good luck.

The symptoms you describe can surely be the lean burn. There is no upside to keeping the lean burn at all. Certainly not cost, because just as soon as you break down along the road and have to have it towed, there is the cost of a HEI conversion. It really is easy and if you want it even easier and simpler, just forget the relay. I know some people think you need them, and more power to them. But I have done 4 or 5 installs and none have a relay and I have had zero problems. Checking my voltage at the HEI module, which I always have over by the distributor, has always shown my voltage to be withing .1 to .2V of battery voltage when running. That is perfectly fine. I have no desire to enter one more failure point into my electrical system unless is truly needed. I even ran the lean burn carb on one of mine for a while.

PS. By the time you read all of Reed's great info you could have had the HEI installed!

Good luck to you!

_________________
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

Good advice here.



This is also true.

Reed, you just made my day..... Thank you SO much for that info. While I was reading the HEI Conversion article on here, I was reading what I though said I'd need to swap out the carburetor with a non-electrically controlled one. A BIG expense that I would not do. As for the distributor, I know I can get one but I don't know here to start, what vehicle to look for or what part number to look for. Other than that, how long do you think the conversion would take? I'm all down for doing the conversion but working 9-6:45 Monday through Friday. One last question.... Does the new distributor need a vacuum advance on it and would I need to get a new carburetor (I dont feel like buying a brand new carb for 150+ dollars after gutting and rebuilding the one I have.) Again, Reed: Thank you a ton!!!!!!!!

Reed, you just made my day..... Thank you SO much for that info. While I was reading the HEI Conversion article on here, I was reading what I though said I'd need to swap out the carburetor with a different one. A BIG expense that I would not do. As for the distributor, I know I can get one but I don't know here to start, what vehicle to look for or what part number to look for. Other than that, how long do you think the conversion would take? I'm all down for doing the conversion but working 9-6:45 Monday through Friday makes things difficult. One last question.... Does the new distributor need a vacuum advance on it and would I need to get a new carburetor (I dont feel like buying a brand new carb for 150+ dollars after gutting and rebuilding the one I have.) Again, Reed: Thank you a ton!!!!!!!!

You will need a non-lean-burn carburetor and a distributor with vacuum advance. On lean burn equipped vehicles, even if the carburetor was not controlled by the computer, it does not have a correct vacuum signal for a distributor vacuum advance system.

I would try and get a carb and distributor for a late 70s Dodge truck or van equipped with a slant six. Try a 1978 D150 with a 225 and a single barrel carb if you need a specific application.

I could probably get this swap done in about 20 minutes. But i have been farting around with slant sixes for about 25 years now, and I was the first person to try the HEI ignition swap on a slant six vehicle way back in the early 2000s using a home brew wiring harness. I have converted five or six slants to HEI ignition, both lean burn and non. My advice is build your wiring harness and mount the HEI module before you do anything else. Then all you need to do is swap the distributor and hook up the ignition wiring harness. And swap the carb and run a vacuum hose for the vacuum advance. Easy peasy. Time the engine and you are done.

Okay, so here's my next question.... Is there any way to use the stock 1945 that's on the truck? I read on another post that the port going to the SCC is the same that would go to the vacuum advance on a distributor. If this is the case, why can't I just use the same carburetor vs shelling out $200.00+ for a new carb? I'm getting all caught up in how much this is gonna cost and if it's even worth it. Like I said, I don't wanna shell out the money for a brand new carb when I just rebuilt the one I have. Is there any sort of way I can make do with what I have? Thanks!