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Interesting Ignition Discovery

Old 01-12-2019, 11:16 PM
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Default Interesting Ignition Discovery

A few months ago I picked up a 1988 Oldsmobile Delta 88 with the 3800 LN3 Motor. The car had the famous Magnavox ignition system which was leaking a green goop out the bottom of the ignition module plug. I decided to replace the Magnavox system with the new and improved Delco design. I purchased a brand new D1977A Ignition Module, and three new D555 Coils. After doing the conversion I tested the car out and it ran great at first. After driving on back roads I decided to hit the highway. Getting on the on ramp I put the pedal to the floor and upon shifting gears the car stumbled with a loud backfire out the exhaust. I tried this again without putting the gas to the floor and the car shifted just fine. The car would only backfire if it was floored from a stop or a low speed. The spark plugs and wires were new, I tested the primary and secondary sides of the ignition coils and they tested good. It turns out that the brand new AC Delco ignition module was causing the backfire/stumble at full throttle. I returned the ignition module and purchased an AC Delco D1946A ignition module and that solved all driveability problems, the car now shifts perfect under load at any speed. I guess the moral of the story is a new part inst always a good part.

What is the difference between the AC Delco D1977A and the older D1946A module that I am currently running?

Would love to hear peoples thoughts on this, maybe my findings will help others out there!

Matt
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Old 01-12-2019, 11:35 PM
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My rule of thumb for belts, pads, shoes, tires, exhaust system, etc., it'* ok to go aftermarket....

But when it comes to electronics/electrical, ALWAYS go OEM.
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Old 01-12-2019, 11:39 PM
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The strange thing is the D1977A and the D1946A module were both made by AC Delco. I just cant figure out the difference between the two.
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Old 01-13-2019, 07:51 AM
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The fact that they have two different numbers may mean each is engine specific......
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Old 01-13-2019, 01:22 PM
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I had similar issues when I did the update to my '90 Oldsmobile 88. Upon further review, it turns out I had two plug wires swapped around. After fixing that, I never had any troubles related to it.

The argument for the swap is that the Magnavox system is a bit more prone to issues, and that it requires replacement of the whole assembly when they do come around. Also the Delco setup tends to produce a bit stronger of a spark.

The only feedback I have really heard is that it may not idle as perfectly smooth as it could on the old system. I have never heard of anything like what you are describing, and causes me to suspect there may have been an issue with something.
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