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Old 05-06-2008, 10:45 AM
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318 "Lean Burn" questions

I've got a friend with a 77 Diplomat, with a 318 that has a 'lean burn' control system. Apparently, at some time in the past, someone 'bypassed' the system. I don't know exactly what they did, it appears that they just disconnected some wires connected to the lean burn computer and must have done something with wires to the ignition coil...

The car did run after all this was done, but now it isn't running. He's replaced the cap, rotor, and coil. He noticed that when he cranks the motor over, he doesn't get a consistent spark, as in it will usually spark once right after he starts cranking the engine, but then may not spark for several revolutions (as in definitely more than 2 rotations) and then may spark 2 for 2 consecutive cycles, and not spark for a while, spark a couple times... etc. I noticed when I helped him with it the other day (before he put on the new cap and rotor) that the intensity of the spark wasn't steady, like the first spark when he started cranking would be nice and bright, then weak, then strong again.

I am wondering, first of all, what I'm going to find when I take the cap and rotor off to look in the distributor. Is this an HEI type system with a pick-up coil and magnet ring, or would this still be a points-type? (I haven't seen the distributor with the cap off yet, I might go take a look tonight, but I'd like to be prepared). I was having some trouble understanding the wiring running to the ignition coil, as it connected to a block that is apparently a ballast resistor up on the firewall, and then there was what looked to me like a small pickup coil (it was a round cylinder with a single wire) that was clamped to a bracket on the manifold, and the wire was connected to the coil...

Any help on this one? I'm more familiar with GM HEI ignition systems, although I do have some familiarity with points from working on older motorcycles, so if someone can explain to me the differences here and how these bits may correspond to those I'm familiar with...

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Old 05-06-2008, 11:35 AM
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lean burn bye bye

The lean burn system never worked very well and standard practice was to replace the distributor with a standard mopar electronic unit and wire in a standard mopar ecu. This sounds like a bad ecu (the control box with 4 or 5 wires feeding into it) or a bad pick up or reluctor in the distributor. Since it was retrofitted to the standard ecu, I would trace all the wires and check the connections as well (some people are happy to just twist the wires together and tape it up.

There is also a ballast resistor in the equation here (or should be) but the symptom of that going is the engine dying when you release the key on startup.

Good luck, take it a step at a time and change one thing at a time and you will find it.
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Old 05-06-2008, 11:37 AM
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wiring diagrams

here is a link to the wiring diagrams for chrysler electronic boxes

http://www.bigblockdart.com/techpages/ignition.shtml
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Old 05-06-2008, 11:45 AM
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Another helpful article

http://www.slantsix.org/articles/lea...rn-article.htm
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Old 05-06-2008, 11:51 AM
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Well, I think I must be looking at the 5 pin setup you linked too...

Now, if the ECU has burned out, how expensive of a piece is that? Is there an easy way we can test the pickup and/or reluctor?

Chris
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Old 05-06-2008, 11:59 AM
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testing

if the pickup is gone, you generally won't get ANY spark (just like an HEI) reluctors will sometimes work intermittently, but my money is on the control module, a bad ground or crappy wiring.

That being said, ignition coils can cause results like this too.

I don't think the control module is very expensive, and I would replace the coil as well.
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Old 05-06-2008, 02:21 PM
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We already got a brand new coil since the car died, so your theory of dead ECM, bad ground, or a wire that came undone all seem reasonable to me. I'll have to check out the price of the ECM, but I'm hoping for a disconnected wire or the like...
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Old 05-06-2008, 06:31 PM
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Ok, we definately have the 5 pin setup here. I found the wire that runs along the left side of the picture you linked to, up to the ballast resistor, wasn't connected.

I connected it, but still no start! ***?

I've also noticed the motor turns over fairly slowly, so we're going to double check the wires to the starter and all (the battery is putting out over 12 volts, and we've tried another battery and jumpstarting...) but I honestly don't know how fast it should crank over, and it IS cranking and IS sparking...
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Old 05-06-2008, 07:54 PM
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You say it is cranking and it is sparking? Do you have fuel?
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Old 05-06-2008, 08:47 PM
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there's definitely fuel getting to the carb, we tried spraying some carb cleaner in there, and during the day we could see fuel coming out of the jets...
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Old 05-06-2008, 08:55 PM
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Does it even try to start with the carb spray?
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Old 05-06-2008, 08:57 PM
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nope, the most we have ever gotten, with carb spray, was the tiniest sputter in the world, never what sounded like more than 1 fire.
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Old 05-06-2008, 09:04 PM
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Check the power going into the ballast resistor and out of it with the key on. Also check the positive side of the coil for voltage while cranking.
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Old 05-06-2008, 09:07 PM
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we checked the voltage at the coil and ballast resistor, it wasn't 12, I think it was something like 6 volts (with the key on, not cranking) and as I said, if we pop out a plug and crank it, we do get a spark...
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Old 05-06-2008, 09:10 PM
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You should have battery voltage going into the ballast and 8-9 volts coming out of it. If not it is bad.
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