Stepping Back into the Future - - - A brief look at the changes in computer systems from the early days to now

Stepping Back into the Future

I had a 1984 Buick come into the shop that wouldn't start. I haven't seen one of these in years. It was a clean old car; not even a dent in it. The owner had a repair manual he purchased at a parts store, and being the kind of guy who was careful to do the correct thing to his vehicle he conveniently left it on the front seat for me to find.

I turned the key to start, and let things happen as they may. The car would purr like a kitten for about a second or so, and then two very distinctive flames would shoot out of the throttle body. After the flames came flying out the engine would cough, spit, backfire, and for the most part never sound like that purring kitten that it did when it first turned the key. It did this without fail almost every time I tried to start it.

Needless to say, understanding the fundamentals would have to come into play on this one. Why this engine was barking out a flame higher than the hood was an interesting problem and probably a problem I'll never see again. Being involved with the auto repair business for several decades I've seen a lot of the evolutions of the electronic brain boxes on cars. Repairing a misfire is one of those diagnostic challenges that has developed an entirely different approach than in years past. Prior to the advent of the computer a misfire could be easily identified by means of understanding the valve train or the spark control systems.

Codes were no help at all, and quite frankly I wasn't expecting a whole lot of help out of service codes on that old of a car. Service codes of that era were limited and didn't cover the variety of problems associated with the emission output. The customer informed me that he had changed a lot of the basic parts: ignition module, cap, rotor, wires, plugs, coolant sensor, throttle position sensor, and the computer.

Wait-wait… "You changed the computer?" I asked.

"The guy at the salvage yard promised me it was a good one," the owner told me.

"Let me check something, and I'll call you back," I told him.

I nearly forgot to hang up the phone as I rushed out to the shop and dived into the car. There were no marks from a socket or wrench on the two bolts that hold the little cover onto the computer where the prom (EPROM) was located. Now the real question was… is this the correct one for this car? This was going to take a call to the dealer parts department and hope they still had a cross reference on the prom numbers.

Marty answered the phone. I was super grateful I got Marty; he's been in the parts business as long as I've been in the business. I was sure he would remember these old proms. I gave him the numbers and waited for his response. I could hear the keyboard clicking away as he processed the information. Every time I thought he was close to answer he would say, "No, wait a second… it changed again… hang on… OK, here it is… hold on… another change." This went on for quite some time but eventually he came back with an answer.

"That prom fits a 1984 Buick with a V6 engine," Marty proudly told me.

"That should explain the two huge backfires… I've got a 4 cylinder engine in this car. OK, now we better check and see if the ECM is correct."

"It is, as a matter of fact the ECM was the same for both engines back then," Marty exclaims.

"I'll bet you don't have the prom anymore do you," I asked.

"Nope…. Discontinued."

After hanging up the phone I called the customer. He didn't throw out the old computer and it was in the trunk. (Lucky). After pulling the old prom out of the original computer, and installing it in the computer from the salvage yard the car started up and purred like a new again. Pretty weird diagnostics, but pretty cool at the same time. Obviously, the first four cylinders fired in a somewhat correct arrangement but the fifth and sixth cylinder wasn't and that's what caused the blazing fire to shoot out of the throttle body.

I would have to say these types of problems are for the history books these days. Be it a short era in the history of automotive repair based on how long things like the distributor were used in a car. It reminds me of growing up in the 60's and 70's. Working on cars was a weekend past time for guys and gals. Tweaking an engine to get some more horsepower out of it was a great "Do-it-Yourself" or a dad and son event in almost every driveway. Those weekends under the hood were the start of my long career in the auto business, but these days there's not a lot a weekend mechanic can do under the hood, and going to the salvage yard to pick up a computer for the car is just not possible for most makes and models.

It's amazing to me how the systems have changed so drastically in such a short amount of time. Having this 25+ year old car in the shop made me realize how much they have actually changed. But there are still some people who think you can still go to the salvage yard and pick up an electronic component for today's cars. That isn't so for most makes and models anymore. Most components are programmed for one car and one car only and without certain types of scanning equipment you can't use them ever again… and some components are not reprogrammable at all.

After all these years of automotive repair to be able to experience the methods of the old computer based electronic ignition systems after working on today's vehicles made me realize how far we have come in such a short span of time. Ok, I've had my fun, I've got more work to do… time to step back to the future.

As always, I love to hear your comments and suggestions. I'm open to anything. I'll keep writing you keep reading... thanx