Perfecting your GM OBD System

Like so many people I have a GM Crate Motor with their MEFI fuel injection and on-board computer. Like many, I wanted to see how to improve the mileage and performance of this package. 

I had been in contact with Bob Radke for several months. He and his partner Ken Seibert, have a business in Redondo Beach, California, called OBD Diagnostics Inc. They have perfected a computer program that allows them, (or you) to get inside the GM MEFI (1-2-3-4) ECU. Now you can change any, and all settings that GM’s “one size fits all” ECU that you and I would have to live with. Until now. GM’s concern and help is about the same as the guy in charge of your hanging if you lived in the wild, wild west back in the 1800s.

So— a little history on me, and my application, and my vehicle. I have driven a 1950 Ford Panel Truck since I bought it in 1960. I originally ran a flat head six motor (2), and switched to a flathead V-8 (2 motors). In the mid 60s I switched to small block Chevys. I ran a series of ten used motors into the ground, over the following 40 years of continued use totaling, just over 1 million miles. 

As I got older the “fun” of changing motors every four or so years had kind of worn off. So I had a guy build me a 400 small block Chevy. The motor ran fine but used a quart of oil every 400 miles. He wasn’t what he represented himself to be. He ended up buying that one back.

So I decided to buy a New Crate Motor. I chose the (early) 350 horse, fuel injected Ram Jet motor from the GMHP catalog. This motor was just over $5 grand but well worth it. Of course I bought mine (with the MEFI-3) just before they came out with the new and improved MEFI-4. GM had an upgrade kit that had the new MEFI-4 ECU, harness, air intake sensor, and the exhaust sensor, etc. The kit was $800.00 at that time.

The upgrade kit gave me a lot better in-town, back country, and freeway (trip) gas mileage. See references on into this article on the different applications. However in my heart, I knew my motor should do better. And thanks to Bob—it is now doing just that. 

The readout from my OBD system. 

The readout from my OBD system. 

Empty, my truck weighs over 4000 pounds. On my regular trips to Bellingham Washington I am at 5100 pounds. My truck also has the aerodynamics of an old wooden phone booth. So for what it is, and what I have it do—it does really great.

I am running a Ford 9” rear end (3:00 ratio). A ‘64 Chevy truck 4 speed tranny. (granny gear 1st) with an Advanced Adaptors 2-speed tranny in front of the 4-speed box that is “direct and overdrive (27%). This gives me eight forward speeds and two reverse. Or any combination I choose to use. Towing trailers, I run the motor up to 2500 rpm, drops to 2000 rpm between shifts, and usually run at 2000 rpm at cruse. A long hill would be 2500 rpm in 3rd “over” and I would be at 55mph. No pain, no strain! And of course I have the AC on too. Gotta be comfy!!

OK—back to June 27th, I’m in Redondo Beach Ca., just after 8am and have just met Bob. We go over the panel truck, and Bob hooks up his notebook computer, and gear to my 12v power plugs. We put a wide band exhaust sensor into the exhaust system, and we are ready to test and tune. Bob “breaks” into the computer with a special password, and all of my past indiscretions come to life on Bob’s screen. WOW!!!

Henry Duvall with the stories that he shares

Henry Duvall with the stories that he shares

“You have some miles on this motor, don’t you, (just over 60,000 miles on this motor)” Bob proclaims. “I see you rev it up too—don’t you? Lets see, hmmmm,1-2-3-4-5…”

“OK, OK,” I say, “…so I have to spank some of those new cars and trucks on occasion.” I’m just glad this isn’t myDad looking at this, otherwise I would probably get spanked and sent to my room!!

We fire up the truck, and start on “in town” readings. The first thing we learn is it is running quite “fat” and that it is dumping fuel into the motor on “decell” . That’s foot off the gas. We also go out to the freeway for some 65 to 70mph readings. This included some Nail It, and pass runs.

Then it was back to some empty back streets so we could see how it did on pedal to the metal runs. Bob got my truck to launch harder and quicker than it ever had since I had installed it—-And on Regular 87 octane!!

You need to know that neither Bob, or you, with their software, are going to be able to do a “test and tune” on every individual application in twenty minutes. 

This is a half day or so project, with stopping, making adjustments, saving previous runs, comparing, etc. Because Bob loves what he does, and is as meticulous as a brain surgeon, you want to let him work his magic, and he will get your vehicle to run as it never has before. He can do everything short of tightening your lug nuts if you will just let him do his thing!!

Hi Denny,

The main changes made were:Spark retarded 1 to about 1.5 degrees under heavy load for the regular gas, 28.5 degrees total advance under full load.

Fuel leaned down about 10% under idle and light cruise, about 20% under deceleration, and about 10% under heavy acceleration, e.g. 10ms injector pulse width knocked down to 9ms at full load.

Closed loop operation changed to open loop, stock narrow band O2 sensor no longer used.


Below is a copy of my Son’s (Ben) email to me as to how all the above has worked out in “real life”.

Tune up improvement…some math

Pennies per mile comparison (at $4.50 regular and $4.80 premium)

PRE TUNE=12 mpg city, 15 mpg combination town and highway (premium fuel)

POST TUNE=14 city and 18 combo. (regular fuel)


Pennies/mile (before) =480/12 and 15=40 and 32 pennies per mile Pennies/mile (after) =450/14 and 18=32.1 and 25 pennies per mile (a savings of almost 8 cents per mile in town and 7 cents per mile combo driving OR a 24.6% in town and 28% combination driving).

Not bad (Hey—-I agree with him too!!)

I will be making a trip in September from Poway Ca. to Bellingham Wa. I will be towing a 1935 Ford 4 door sedan on a two axel car trailer. My Grandson is going to use this car to restore the ’35 my Mom and Dad bought in 1936. It will take both cars to make one good one. I will document that trip as well, and publish the findings at a later date.

If you have a 350 Ram Jet or a 502 Ram Jet you want to be sure and contact my friends at OBD Diagnostics, Inc. If you have them tune your application, or you buy their software, You will be very pleased, with the out come.

It’s very refreshing to deal with people who love what they do, and do what they love. There is no smoke and mirrors, fantasy claims, BS, false promises, or any of the other things so many other companies do to get your business. If you just want better performance,better gas mileage, better ¼ mile times, or what ever your application is—OBD Diagnostics is the way to go!!!
— Bob's E-Mail

Denny DuVall

I spent the 1st 33 years of life in Borego Valley. The rest in and around San Diego County. I compose music and play piano, write stories and articles. Check it out! I've put off becoming an adult for 69 years, think I'll just play it out 'till the end. Love, Life, and Laughter is my goal and my quest.