Back when everything was mechanical, some fellows were insisting that one highly reputed heavy truck repair shop had on staff a blind mechanic. His specialty had been Cummins heavy diesel engines. He had been twisting wrenches for some 30 years when he lost his vision.
The claim was that this fellow could listen to and put his hand on a running engine and accurately diagnose the problem by the sound and vibrations. I never met the man, so the story told is all I know about him.
I did, however, call a mechanic friend and describe a new noise on my truck, and from that, Bill McCreary made the correct diagnosis. I was calling from the payphone in Mountain City, Nevada, where I was over 150 miles from home. The noise was a whirring sound on deceleration, and it was getting worse.
Bill said it sounded like the pinion nut of the lower gearset on the front driving axle had loosened and was allowing the pinion, which meshed with the ring gear on the differential, to move forward under deceleration, pushing the end of the pinion and the loose nut against the case of the gearbox. He said that under power the pinion gear would be pulled back into place against the ring gear.
He also said that it wouldn’t be a good idea to try to drive it home that way because I would probably rupture the case trying.
I backed the truck and trailer off the roadway to one of the few flat spots against the snowbank and crawled into the sleeper until daylight. It was just as Bill had diagnosed over the phone. About noon, we had drained and disassembled the beast, got the errant nut back in place and torqued to spec via a 4-pound sledge and a big cold chisel. Using the same chisel, I added a fail-safe. I goobered the threads on the pinion shaft using the same hammer and chisel. It never moved out of place in the two or three years it took for something else to cause the drop-in assembly to be replaced with a rebuilt unit.
In 1996, all passenger vehicles and light trucks in the U.S. were required to come from the factory with a standardized diagnostic port. Generic code readers were able to retrieve codes that pointed mechanics to potential trouble areas.
The archaic (by today’s standards) computers were helping to operate and adjust a myriad of adjustments to make or keep an engine running better. To do this, the vehicle had to feed data to the engine control module (ECM), and from that data, adjustments were made on the fly as needed.
The easiest example to illustrate this is the elimination of the manual and the automatic choke as a starting aid for a cold gasoline engine. The choke restricts the air entering the engine, so as air gets in, it sucks more gasoline in, making a richer mixture that’s easier to ignite inside the cylinders. How many times the throttle needed to be pumped and how far out the choke needed to be pulled depended on the vehicle and the ambient temperature plus the engine temperature.
A vehicle that had been sitting for days in 15ºF temperatures took different manipulations than a vehicle in the same 15ºF temperature that stopped by for breakfast half an hour ago. Automatic chokes also varied from rig to rig. A regular question was, “What’s the combination to start that buggy without flooding it?”
Now, the ECM makes all those adjustments, and most current fuel-injected rigs reliably start in the coldest of weather if there’s enough battery to turn the engine over about three times.
It’s still interesting to send a person who has never been around an older vehicle to start something that has a manual, or even an automatic, choke.
As technology evolves, the ECM needs more and more data to function properly. In addition to metering the correct amount of fuel, the ECM also changes the ignition timing for easy starting and for optimum performance driving. Newer rigs have ECM-controlled variable valve timing, and an engine without a camshaft is in the works. A piezo unit will open and close each valve as needed, similar to the piezo units that operate fuel injectors. Even my semi-antique 2006 diesel pickup has piezo units that manage three different fueling events on each power stroke of the engine.
For the ECM to do its job, the inputs from sensors must be there and be accurate. Some sensors must work, or the engine won’t run at all. My 2002 Dodge Durango stopped running intermittently and then finally quit. It was the camshaft position sensor. It had happened enough on that model that the dealer said it was most likely the cam position sensor. The new part was about $49, and it’s never even sputtered since.
The ECM will adjust the fuel rate, the ignition timing and, on some, the valve timing based on the data it receives. If an engine that calls for 91-octane gasoline is run with 87-octane fuel, the ECM will adjust the fuel amount and timing so that the engine won’t detonate (ping or knock) by firing from compression ignition prematurely (before the spark plug fires). A rig made to use 91-octane fuel won’t develop the same power burning 87- or 89-octane since the higher compression ratio needs the higher-octane fuel.
A correct diagnosis requires an understanding of how fuel, air and ignition play together and how a faulty sensor can cause the ECM to be incorrect in tying these three requirements together for an engine to run properly. For example, oxygen sensors tell the ECM if the fuel mix is correct. If the oxygen sensor is defective, the ECM can make the engine run too rich or too lean, neither being a good idea.
Also, consider how archaic the ECM is on what you’re working on, as in, what is the ECM not monitoring and therefore thinking is all okay? To be effective, a person needs to understand how the ECM and other computers on the rig think so it doesn’t outsmart you.
