My '81 with a 351w is starting to run rough and I suspected it was ignition related. The plugs/cap/rotor/wires are fairly new, but no wire looms to keep the wires apart. So I separated all the wires with wire looms, hoping for some improvement. Well that didn't make any improvement, in fact it seemed to run a lot worse since I last drove it.

The Duraspark module had been replaced earlier, but I kept the old module. Just to see what would happen, I replaced the aftermarket module with the original after wiping off all the white grease and cleaning the connections with contact cleaner.

Well, it ran so much better with the original module! Just to see if it was poor connections or modules, I switched back to the aftermarket module. It was better, but still not quite as good as the original.

The big problem was probably poor connection, but it still runs with a slight miss.

So which direction should I pursue? I don't want to get tunnel vision on the Duraspark if it's working as it should now and something else is causing the miss.

Here's what I'm thinking of doing, starting with the easiest/least expensive:

1 Replace cap/rotor/wires with Motorcraft parts
2 Replace Duraspark module with new Motorcraft
3 Install MSD ignition and coil in tandem with Duraspark

BTW: It's a fresh long block but it's using the original distrubutor.

Any advice here would be greatly appreciated.

Scott

 

Since you're using your original distributor, assuming it's a duraspark II, check/ replace your inductive pickup in the distributor, as this tells the module when to fire the coil. Was a problem in the past on my truck and drove me nuts!....Good luck

 

Vince, thank you for the good lead. I wouldn't have thought of that. I didn't consider any electronic parts in the distributor that would break or stop working correctly.

I think that's the first thing to replace, since it's probably still the original part.

Do I need to use dielectric grease on all the connections?

Scott

 

I would

 

If its got a Vacumn advance on it. I would replace the "breaker" plate when you pull the pick up coil.

Gasman
Do you have Gas?
Propane Execeptional Energy

 

No vacuum advance diaphram. So I don't know how it advances, if at all. What's puzzling is that it has the firing order 15426378 like a 302, when it should have firing order 13726548. Also the Duraspark module only has seven wires instead of eight that most wiring diagrams show. There is no purple wire. The moldblock on the module is brown instead of blue.

Thanks for all the help so far. I won't get a chance to replace the pickup until next week. I'll post back with the results.

Here's what the module looks like. Also, I didn't mention it's a California emissions truck.

Scott

https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=9839&.jpg

 

I don't know how your advance works but it has to have some method of advance. I would use an MSD on it's own. You will never have to worry about gromet colors again. You can test the pickup with a voltmeter to see if it is putting out pulses.

 

Thanks Mike. I was thinking the same thing. I was wondering if there is an electronic advance. Either that, or I am just too blind! The problem is intermitent, so the pickup must be working most of the time. I'll consider the MSD when it comes down to making a decision to buy a new module. Then I'll probably kick myself for not doing that sooner!

Scott

 

Well using the original ignition module really didn't to anything. It still runs like a dog.

[font color=blue]Update:[/font color] Stopped at NAPA on the way home and bought a pickup for the distributor for $24. Ford wanted $178 for the same part!!!

However, neither one would do me any good. It seems my distributor doesn't have any pickup or armature. The only part inside the distributor is the rotor. There is no advance mechanism, either vacuum or mechanical! The only wires for the distributor are the coil wire and the individual plug wires.

There is a magnetic pickup on the harmonic balancer. A new one was installed with the long block. So that must tell the distributor when to fire, but I still don't know how it advances the spark.

The brass contacts on the rotor were pretty fried though. Seems when the shop installed my long block, they must have tossed my good cap/rotor/wires in a pile and picked out different ones for reassembly. I know because my parts were aftermarket and whats on it now is Motorcraft.

So tomorrow back to NAPA to exchange the pickup and armature for new cap/rotor/wires. Whether that fixes it or not, I should have at least eliminated that and the distributor as the source of the problem. I'll post back after I replace those parts.

Here's a photo of the distributor after I removed the cap, rotor and adaptor.

https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=10000&.jpg

Scott

 

I didn't know they used DS3's on an 81 model truck...I have developed a hatered for these particular setups.

 

Dennis, thanks for the link. Lots of good info, but unfortunatly nothing applicable to my situation.

electricmaniac2, I've done some research and come up with more information on it. As you say, the module is a Dura Spark III. It's operation is controlled by an EEC III, a computer module. EEC II first came out on California trucks in 1980 and evolved to EEC III for California trucks in 1981. 49 state trucks didn't see it until several years later. Basicly, it adjusts the spark advance and carburated mixture to control tailpipe emissions.

The inputs to EEC II and EEC III are:
- engine coolant temp
- throttle position
- crankshaft position
- exhaust gas oxygen
- barometric and Manifold Absolute Pressure, (MAP)
- EGR valve position

I also found the procedure for aligning the distributor, since the advance is done electronicaly. I'll post back once I've done that and explain the procedure just in case anyone else wants to know.

Now if it will just stop raining so I can get out and work on it!

Scott

 

You don't have that godawful Variable Venturi garbageuretor (carb.) do you?

 

> You don't have that godawful Variable Venturi garbageuretor
>(carb.) do you?

I'm not sure yet. The specs for EEC III call for the Motorcraft VV carb. But the carb on it is a Holley 2 bbl. So I will need to determine if the Holley is a direct replacement for the VV carb and as such, is controlled by EEC, or if it's a fixed venturi. The Holley is a replacement carb installed by the PO.

It may very well be an EEC carb because it is electronicly controlled. The choke has an oil temp sensor which tells it when to kick off.

 

Okay, it seems to be running fine now without missfiring.

Here's what I did:

Aligned the distributor rotor. Timing and all spark advance is controlled by the EEC module but it has to be aligned correctly to begin with.

With the rotor removed, align the smaller notch in the dist. shaft with the notch in the adaptor. With cyl #1 on compression stroke, the timing mark on the vibration damper should be plus or minus 4 degrees of TDC when the two notches are aligned.

I was off by 10 degrees. The procedure then is to turn the engine so the timing mark is at TDC and then loosen the two bolts holding the sleeve assembly on the distributor shaft. Then you can put a screwdriver in the notch in the shaft and turn it so the smaller notch in the shaft aligns with the notch in the adapter. Once aligned, tighten down the two small bolts on the sleeve assembly. You are supposed to use a special alignment tool that fits in both notches and holds them true. Eyeballing it works just fine as long as you don't disturb the alignment while tightening the two sleeve bolts.

Here you can see the two notches in alignment:

https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=10181&.jpg

The other thing I did was coat the electrode blades on the distributor rotor with silicone grease. You do not grease the two high voltage pickups that stand up vertically. I also greased the electrodes in the cap shown at the locations I've circled.

https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=10182&.jpg

I also learned that it does have the normal 351 firing order: 1-3-7-2-6-5-4-8. What's diffent is the order of the plug wires on the distributor cap. Going in the same counter clockwise direction the wires are: 1-5-7-8-6-3-4-2. The way the EEC distributor works is by firing alternatly 180 deg from both sides of the rotor. So #1 fires, turn one the the left and 180 deg and #3 fires on the other side of the cap. Turn one to the left and 180 deg and #7 fires and so on.

Scott