from Goss’ Garage by Pat Goss

I’ve been working on, and teaching people how to work on cars for over thirty years yet I still make stupid, time-wasting mistakes. It happens every time I break one the golden rules of diagnostics. Like when I omitted a couple of basic steps in a test sequence because I ‘assumed’ some new parts were good parts. Rules of absolute certainty: new doesn’t guarantee good and omit even one step of a test procedure and every result thereafter is invalid.

In this example a dealer brought me a car with a performance problem but only after his top tech had done everything imaginable to sort it out. I felt trapped because the tech who had been diagnosing the car was very good. The problem had been ongoing and he had spent a lot of time with it so if he couldn’t find the problem how could I?

Unfortunately, I screwed up right from the very beginning; I skipped some basics on the assumption the first tech had already done them. I began with diagnostic equipment and proceeded to test every performance related part on the car but nothing stood out or actually failed. Being stubborn about solving problems I ran a full compliment of specialized pinpoint tests and you guessed it, everything passed.

Okay, six hours wasted, time to review my procedures and results. So I went back over each step and everything was by the book except I had begun at the third step of the required procedure. Step three based on the assumption other tech had done all the basics. Yep, I didn’t follow the rules, a dumb mistake that wasted over six hours of my time.

I hadn’t done a visual check or verified the functionality of the new parts so I went back to step one and started over. The visual test was fine, the battery, alternator and wiggle tests passed with flying colors. Same with the coils, PCV valve, air filter, coolant temperature sensor, mass air flow sensor, throttle body, etc. Everything looked fine but something obviously wasn’t fine because the engine ran horribly.

I was getting frustrated but admittedly I had been avoiding the spark plugs! I had deluded myself into assuming they were okay because they were less than 100 miles old. That self-serving assumption came easily because the plugs on this car were a nightmare to remove. Although there were some minor indications of plug problems on the diagnostic machine I refused to accept that something so minor could cause the car’s relatively severe problems.

But proper procedure is proper procedure so I reluctantly set about removing those miserable plugs. Contorted, cut and bleeding I finally had the plugs in hand and wouldn’t you know it, they looked perfect, so perfect I almost made a truly bone-headed mistake, omitting another step; assume nothing, check everything. So I checked the spark plug gap. Well I’ll be, even great techs make stupid mistakes, the plug gap was wrong. I re-gapped and reinstalled the plugs but I wasn’t 100% convinced this would be the cure.

I turned the key, the engine fired and to my amazement the problem was gone, completely gone. I had fixed the problem car from hell by simply re-gapping its spark plugs. Note to myself, always start with step one or live to regret it.

The lessons: Don’t assume major symptoms are caused by major failures. The answers to seemingly complex problems often reside in the basics. Always start with step one. Never omit a step because every step thereafter could be invalid. Continue through each step, in sequence, until the problem is isolated. Never assume. New doesn’t guarantee a part is good. Test equipment requires human skills, input and interpretation.

Published in by CARCHEX on November 13, 2014