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

My rule of thumb for belts, pads, shoes, tires, exhaust system, etc., it's ok to go aftermarket....

But when it comes to electronics/electrical, ALWAYS go OEM.

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.

The fact that they have two different numbers may mean each is engine specific......

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.