I have a 1985 D-100 and have noticed the timing changes. When I got the truck everything under the hood was a mess. Motor didn't smoke, but had cracked exhaust manifold. Replaced carb, distributor, cap, wires, rotor, plugs and manifold. Not able to set timing at listed setting. Pings under a load. Can set it at 10 degrees with very little pinging. The motor runs fine on the hwy. There is no vaccum line going to the module that is on the fender. Where does the line need to run from to the module?

If I understand right, sounds like you have the SCC ignition (spark control computer, behind battery up under driver front fender) The vacuum pod on the SCC should have a vacuum line from the carb's ported vacuum (vacuum advance port) Instead of running a line to a vac advance dist, the computer advances/retards the timing based on signal from the ported vacuum. Missing this vacuum line is likely the source of your predetonation.

Personally, I would ditch the factory ignition. I spent 3 years attempting to get mine to work correctly, and it never was 'quite right' (Also had wandering timing issues). If you do not have to worry about emissions, converting to a 70's style electronic ignition is simple, cheap, and reliable--and your slant will run better. If you have to deal with emissions, you can still swap to an electronic ignition, but you need to use a C.A.R.B. approved ignition like MSD. (MSD is the route I went, and I have never been happier)

-S/6

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The "Silver Bullet"
87 Ram D150

Ran a vaccum line to module and set timing to factory specs. It seems to run a little better, but still getting a little ping. I think I will try a better grade of gas next fill-up. What's involved in changing out to a 70's style ignition system?

Check the rest of the engine for vacuum leaks...there are a lot of vacuum lines with this ignition (I still remember the nightmare that used to be under my hood) and this ignition does all sorts of 'crazy' things when there is a vacuum leak.

Has this engine been rebuilt? Possibly milled for higher-than-stock compression?

Converting to a late 70's style electronic ignition requires several parts: A single pickup vacuum advance distributor (your current dist should have two pickups and will not work correctly with a standard elec ignition), ignition module and a ballast resistor, possibly a new coil. Another option instead of an MP ignition module and ballast resistor is a GM HEI conversion. Do a search on 'electronic ignition conversion' and you will find a wealth of info on both of these conversions.

I do not know about the standard conversion's compatibility with the SCC, as the computer controls torque converter lock-up (if you have an auto tranny) I do know that with my MSD ignition the computer still locked the TC up (similar conversion, but more expensive and a hotter ignition)

-S/6

On my 83 the vacuum line from the ESC module goes to a T-fitting inline with the choke pulloff. This is MANIFOLD vacuum. Don't connect it to ported vacuum, the computer won't know what to do. The vacuum pod on the computer is a tranducer. It uses manifold vacuum to sense engine load, kind of like an early MAP sensor. Vacuum is translated into a resistance value so the computer knows how much timing to advance, or retard. If it is hooked up to ported vacuum, the resistance value will be wrong for a given engine load, causing surging, pinging, and just plain running like crap. Also, check the ground connection for the ESC harness. There should be a ground wire from the harness going to a large bolt on the cylinder head, either under the electric choke timer, or the EGR vacuum amplifier bracket. Make sure it has a good connection, as this can cause similar strange problems.

The ESC system on the trucks with the slant 6 are very basic, only controls the ignition timing and the spark, not the carb. Mine has been working for 20 years on its original computer, so it can't be all that bad....
Those that don't undertand how the system works are usually the first to condemn it by saying don't waste your time just replace it with the older ECU type system. The ESC system actually has a more agressive timing curve than the old ECU style system....and when operating corectly perform just as well.

One more thing on the subject of wandering timing. It might not even be the ignition system. How many miles are on the engine? A worn timing chain with lots of slack in it will show as wandering timing on the timing marks when checking with a timing light....just something else to think about before condemning the ESC system.

Also all those vacuum hoses under the hood only will have an effect on the mixture causing a lean condition which may cause pinging, not the operation of the computer itself, with the exception of the one line to the computer itself. Check for vacuum leaks in the lines and at the carb base gasket. This may cause surging and pinging due to a lean mixture. Again, nothing to do with the computer and how it works.

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"That thing gotta HEMI in it??"

Interesting, my computer did control an electronic feedback carb with an electric idle control solnoid, and the vacuum hose from the carb's ported vacuum was hooked to the SCC vacuum pod. I will have to check tonight to see when the ignition system changed. I thought it was '85, it may be '86.

-S/6

My distributor has a vaccum advance module on it. Do I need a vaccum line going to it or is it the wrong distributor. It is a dual pick-up. The guy I bought this truck from was no genius about motors. Said he had been buying parts from a junkyard. Do not know correct mileage on vehicle and truck is automatic.

If that is the correct dist for your truck '83dude is probably right. Mine had dual pickups in the dist but no advance pod...so it looks like I had the wrong ignition system in mind. My apologies

-S/6

Some carbs did have the Idle solenoid controlled by the computer, not sure on the feedback part though, might be the case if it was late 85 and later. To be sure on the vacuum routing I would confirm it with the Truck's vacuum label under the hood.

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"That thing gotta HEMI in it??"

What you have there is a dual pickup ECU type distributor. If you are running that with the ESC computer then there is WAAAYYY too much advance going on. That distributor has mechanical and vacuum advance trying to do its job while the computer tries to advance it further. The ESC distributor is a dual pickup design, but has no advance mechanism in it whatsoever, with no vacuum advance either. Its a solid 1 piece shaft. This would be why you are getting excessive pinging. Either replace it with the right distributor or go the rest of the way of converting it to ECU style ignition. Obviously the previous owner didn't have a clue as to what was the right distributor or to what he was doing.

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"That thing gotta HEMI in it??"