I've searched the forum and can't find anything so here goes...

This is going to be a long post, I apologize in advance.

My 84 with 302/2bbl has been running like junk - idles rough, runs rich, very poor power and terrible fuel economy. I've done all I can with adjusting the timing and carburetor, full tune-up, all to no avail. I'm at my wit's end.

I'm now thinking it has to be something electronic. From what I can tell, it's the Duraspark II system so I performed all 17 tests from the shop manual. One result struck me as odd:

Test 8 which is Ig. Mod. to Dist. Stator Assbly Wiring Harness. I guess greater than 70,000 ohms is good. I receive NO reading. I measured this at the connector which plugs into the module. Now I also unplugged the dist. connector and measured for resistance right off the dist. harness and also received nothing.

Correct me if I'm wrong but wouldn't the engine not even run under these conditions?

All other tests checked out except these 4:

Test 4 for Ballast Resistor - I got a reading of 7.2 ohms across the coil terminal BATT and Ignition Module RED where 0.8-1.6 is acceptable BUT, when key in RUN, coil voltage is between 6 & 7 so maybe a bad wire in the harness? I would still like to test coil voltage with the engine running.

Test 10 for Module to Coil Wire resistance - 33,000 ohms (can this be right? it was 33.2 on the 200K scale). Anything greater than 1 ohm says Module should be replaced

Test 14 for Primary Circuit Continuity rendered a reading of 1.1 volts from green wire of module to dist. ground where 1.5 volts or less says replace module. When I disconnect 4 wire connector at module and measure voltage of green wire coming from tach, I get full battery voltage.

Test 15 for Ground Circuit Continuity rendered a reading of 0.1V where 0.5 volts or less says replace module

So I hate throwing parts at things and hope it fixes the problem. All roads point to the ignition module but my question is: CAN THE ENGINE STILL RUN WITH A BAD MODULE?


Also, my coil primary resistance is 1.6 ohms which is right at the max so I don't know if I should just replace that too?

 

A coil with shorted turns in the secondary can be hard to spot, it will run but the spark will be attenuated.

There can be "bad" parts that will run, but go intermittent when hot, etc.

Is there a fat blue spark at the plugs, that snaps in the air? Orange is no good. That's what matters.

 

I agree with Tedster, it depends on the failure mode so check for a healthy spark at the plugs. "Bad" is not a yes or no, 0 or 1, on or off descriptor.

NumberDummy has often described the classic symptoms of a failing ignition module here:

- Engine dies, can be restarted almost immediately.

- Engine dies, can be restarted in a few hours.

- Engine dies, will not restart.

Is a failing module "bad" or not?

 

In a way I hate the factory manual's test procedures. Before I do the test I always like to read through it and then take a few minutes to figure what they are really trying to achieve and test.

For example your first question; What are they testing? Shorts to ground? If so, then a infinity or "no reading" would be excellent.

 

Seems like you've been throwing parts at it???
If the tests say the module is marginal replace it and do the tests again.

Wonky readings could be a loose lead in your meter, or maybe it just needs fresh batteries?
Really high or infinite readings on harness sections would have me cleaning connections.

What reading do you get for the distributor pickup? (across the orange and purple wires at the distributor connector)
What reading do you get for the coil secondary winding?

 

Actually only parts so far was tune-up and it needed it bad- ran much worse before. Lately it's just been trying to tune by adjusting timing and carb.


If I measure resistance across orange and purple wire, I get 707 ohms.


As for the coil, it checks out - Primary resistance 1.6 ohms, secondary is 9,880 ohms

 

In Test 8, they are looking for an ohms reading between distributor ground and orange wire/purple wire alternately. I don't really know what they're trying to achieve here but according to the required results, they're saying to inspect the wiring harness between module and distributor.

 

So, all that seems good.

A lot of people on the forum say "only Motorcraft" but I use an Echlin TP40 module.

 

Am I removing the plug, keeping it attached to the wire and turning the engine over or using a spark tester?

 

If the secondary side were shorted the ohms reading would be much too low.
Sometimes the reading is okay with the coil cold and it fails when hot.

if you have a spare sparkplug make sure it is gapped close to .044" and use the #2 plug wire so you can easily see it while jumping the starter.

 

Ok, I will try this and see what I come up with. I am buying a module today (BWD), NAPA had nothing in stock until Tuesday and I'm going to get an Accel coil just in case. I'm also going to clean up as many of the connections as possible. Some seem a little corroded, especially the coil terminals which gave me an off-the-charts reading when connected to the coil but when I tested the coil by itself, it was fine.

 

So I started the truck and let it warm up, then measured the supply voltage at the coil BATT terminal, engine running. Came up with 10.6 volts. This can't be right... Should be somewhere around 6-7 I imagine, no?

I think I'm looking at a failed ballast resistor... I have the new ignition module but I don't want to install it for fear of the higher voltages frying the thing.


Thoughts?

 

Ballast resistors are so simple as to be almost failsafe. It's a coil of wire. If it fails, it will likely just read open. There's really no in between on large wirewounds afaik. It has to be tested under load to make sense of the voltages as you are doing, but sounds like it's OK? Ultimately their purpose is mostly to reduce the current.

 

I don't like "hot rod" hot coils on the original ignition system/module. You don't get something for nothing, hotter spark means more current flowing through the module, which can lead to a shorter life from heat.

 

What voltage should I expect to see at the coil BATT terminal with the engine running, assuming all systems are working properly.

Upon further testing, I may be looking at a faulty stator assembly. I get the correct resistance across the orange & purple wires but I am also getting some resistance between the black lead and engine ground, which according to two sources should be no resistance. Also according to two sources, there should be resistance between orange and ground and purple and ground and I get nothing. This, based on the test procedure, would say the pickup assembly is bad. But again I'm dumbfounded - could a pickup test bad but still allow the engine to run, albeit poorly?

I'm seriously just tempted to get a points distributor and throw it in and call it a day. I don't have much patience for this "computer-controlled" stuff.