Are you superstitious? I must admit that I am, just a little bit. What harm does it do to toss a pinch of salt over your shoulder after you knock the salt shaker over on the table? However, if you “knock on wood” to ward off evil spirits and something never happens, does superstition have anything to do with it? Some folks call that good luck and therefore, it has nothing to do with superstition.
The days of the Chevy Vega
When I was very young and impetuous, I successfully drove across the country. Some of you may have also done so when you were 21 as well, and most of you will think, so what? Well, I did it in a 1972 Chevy Vega. Do any of you older folks now affirm that it was indeed, quite a feat? Those younger might not know how problem-prone those cars were, but I can assure you they most certainly were.
It was on the second day of our trip when the car started to surge at a steady throttle. Having not even made it halfway across country (West Texas, to be precise) before trouble occurred, was not a good sign of how the rest of the trip might end up! The surge went away if I accelerated or decelerated. As it got later into the day, the surge continued to get worse. My wife and I were getting worried, so I pulled off to the side of the road to see if I could determine what was causing the problem.
A visual inspection revealed nothing was obviously wrong. The surge was dramatic at idle, causing the RPMs to raise and lower but not rhythmically and the engine was running very rough.
Tired, hot and exasperated, this inexperienced mechanic leaned against the air filter housing — and to my surprise the engine smoothed out. Completely surprised by what had happened, I lifted my hand off of the air filter and the engine started stumbling again! I repeated my actions several times to make sure it was not just coincidental.
I shut off the engine and took the air cleaner assembly off of the carburetor. I noticed the top two-thirds of the carburetor was loose because screws that passed through the throttle body into the underside of the carburetor bowl had vibrated loose and backed out. Air was bypassing the carburetor’s venturi between the two loose parts causing the engine to surge. On acceleration, the carburetor was enriching the mixture enough to prevent a surge. On deceleration, a high-intake vacuum pulled the loose parts together. While cruising, there was too much air entering the intake for the amount of fuel delivered. After performing an emergency repair, I felt fortunate and continued on my way.
Found by accident?
Have you ever accidentally found the solution to a diagnostic problem? Have you ever gotten that lucky? I think all of us experience that every now and then. As a matter of fact, very recently it happened to me again. In my defense, I tried to fix this 2011 Chevrolet Malibu LT with a 2.4L, DOHC, 16v engine and 4-speed automatic transmission the right way, based on the information the vehicle provided, but that information led me nowhere near what was causing the problem.
The customer complaint was “check engine light on” without experiencing any problems driving it. The vehicle arrived in the shop with five ECM codes, three in the Power Steering Control Module, one in the Vehicle Theft Deterrent Module and two in the Generic OBDII side. It was quite obvious that some electrical faults were present recently. The technician cleared all codes out of all modules and found the ECM would immediately set two diagnostic trouble codes (DTCs) as soon as it was started.
Naturally, the shop eliminated all of the basic causes for so many problems such as a bad battery or faulty alternator before calling me. I did some research for them and found a technical service bulletin TSB referencing chafed wires underneath the rear seat, which may cause multiple faults, DTCs and/or customer complaints. The shop technician checked the harness in question and found absolutely nothing wrong with it.
The two Engine Control Module (ECM) DTCs, P0615 Starter Relay Control Circuit and a P0230 Fuel Pump Relay Control Circuit, were shown on the scanner as stored in history and are current codes. After the technician spent several hours attempting to find a cause for the two codes (that would not clear), he then requested a time for me to visit so that I could program a replacement ECM.
There were several attempts I made and each time I was shown a different error message while attempting to program that module. I reinstalled the original ECM but experienced several more errors while attempting to program it. It was time for me to perform some diagnostics.
Getting a hand on the problem
It seemed very odd to me that the car cranked and started up as if there were no problems, yet we had hard codes for the starter circuit and fuel pump circuit. I began with a visual inspection. I noticed some of the relays with their writing in the opposite direction of all others. That immediately raised a suspicion that somebody else had been here before me. I looked at the service information wiring diagram — and the diagram printed on the relay — and determined both relays were installed incorrectly. I thought to myself how lucky is that! I cleared codes with a smile from ear to ear.
My elation quickly changed when I still had the same codes setting again after I started the car. The shop owner asked if I had any luck. I answered, “Yes, all bad.” After all, being unlucky is one form of luck isn't it?
As a side note, those relays made no difference in the way the car started and ran. Don't ask me why reversing the direction of the relay makes no difference.
I began following the troubleshooting charts for both DTCs, which led to "Replace and program ECM," the same as the shop's technician determined. I didn’t believe that conclusion after what I’d tested already. The technician and I spent a few moments going over each of the steps that we both had performed and having obtained the same results, we were perplexed.
Tired, hot and exasperated (and like before, with no direction to go) I leaned on the core support — and immediately pulled my hand back off. It was hot enough to burn my thumb, which was unusual, because the engine had not been run for several hours. I was doing testing with the key on, engine off!
Although when I initially saw it, I paid very little attention to the fact that the negative battery cable had been replaced. It was obvious because of the aftermarket battery terminal connection. Now, however, I focused on that previous repair! A closer inspection of the ground terminal on the radiator core support revealed it had suffered heat damage from a loose installation. No further testing needed to be done. I replaced the wire terminal and relocated it to the stud next to it. I then cleared codes and started the engine. Rechecking for any DTCs proved none were present.
The clues I had earlier — the DTCs the shop recorded when the car arrived (then cleared) — could have led me to this sooner if I would have prioritized one of them (a P0315 “Crankshaft Position (CKP) System Variation Not Learned”). It has been my experience that when a computer claims that crankshaft variation has not been learned that there has been a cause for its amnesia. It was this problem that I could have attempted to address first. However, history codes are just that. They occurred sometime in the past; nobody knows when. I could have also wasted a lot of time with that testing, too.
Once I repaired the radiator core support ground, I performed several different tests on the ECM power supplies battery, the ignition feeds and all of its grounds — which all passed. I called this job done!
Whether it’s called diagnostics or it is called sheer luck matters NOT when the ultimate result is - the car’s repaired. There was absolutely no mention of it in the diagnostics — for either recurring DTC — instructing the technician to check the battery grounds. My finding a poor connection that once repaired solved the problem, was purely good luck. I’ll take luck over a non-billable diagnostic session any time! Oh, and my thumb healed quickly.
By the way, it was that trip I took in my younger years from California to Florida that got me my first mechanic job. The shop owner said if I knew enough to make a '72 Chevy Vega go across country in just five days that I "must know something"! He hired me on the spot!
