Myth - Test the "Basics" First
Okay - did I get your attention with the title? Or even make you angry? If so, it worked :-) If you are angry, please read on. I am not challenging testing the basics today, I want to challenge what the basics are.
I taught a class for the Indiana EPA over the summer. After the class my friends and I had some great discussion about jobs we misdiagnosed or screwed up on. Someone in the group made a comment that really resonated with me. A mobile tech or the lead diag tech in a shop can really miss the basics. He made an excellent point as to why - you are missing someone to bounce ideas off of. That way when you find yourself attempting to scope the CAN bus on a no communication job someone reminds you to check the cigarette lighter fuse that powers pin 16... Not the best example if you use the AES BoB, but you get the idea.
Back to the myth - check the basics! A car comes into the shop as a crank no start - where do you go? There is no right answer, some could be debated as less accurate or efficient, but we all have our path. From what I have seen many techs that are not up on training resort back to some of the basics they always knew. The car comes in as a crank no start and they are checking spark, noid light to check injector pulse, fuel pressure gauge, and compression test.
In reality a lot has changed in the last 20-30 years on cars, but all of these tests still have some level of validity (still a 4-stroke engine after all). In fact, I will be the first person to tell you I have learned a lot from techs that are more "old school" in approach. How many times have we seen a bad battery cause super weird issues? I have run around in circles chasing issues when the more experienced tech in the shop comes up to me - "hey, did you check the battery connection/condition". Me - "Oh, crap! Can you cancel that (insert expensive part) that I just ordered".
My point here - we need to always keep the basics in our head diagnosing cars, but how and when we test them has changed. When a car comes in misfiring I do not plan to test spark, injector pulse, and compression. Especially when it is a 3 valve Ford, 2 hours later I can have all that stuff done after extracting a spark plug. Oh - and then it was a lean misfire the whole time caused by a bad intake gasket.
I think most of what we do daily can be divided into two test categories: system level testing and component level testing. I see system level testing as checking codes, looking at fuel trims, maybe even scoping at a fuse. To me component level testing is more intrusive, this is anything that involves sockets and back probe pins. I am from Chicago, we use a lot of salt here. I avoid component level testing at all costs, you get good at drilling out snapped bolts around here... not looking for more practice. Breaking stuff aside, component level testing is time consuming. So no, it does not make sense to check the "basics" like we were traditionally taught, that is way too much component level testing. I also believe that some of the component level testing can use improving, the case study below illustrates this.
I was busy finishing up a high-pressure fuel pump in a 6.4 Powerstroke (cab on, ugh) when I noticed the tech in the bay next to me removing all 8 injectors on an Express bus. Looking for a break from scraping all the skin off my forearms I went over and asked what he was up to. He said that there was an entire bank of injectors coding and the van had severe intermittent driveability issues. He had checked injector pulse with a noid light at the injectors. He was in the process of swapping the injectors bank-to-bank. After all of that it had the same codes and he concluded that the PCM driver for that bank was most likely bad (not sure why). A new PCM was programmed in by a friend of mine, he reminded the tech that it would be a good idea to make sure one of the injectors was not shorted taking out the driver. The van ran fine for a little while, but after some extended test driving it acted up the same way again with the same codes.
I was asked to scope current at the injectors, assuming that one could be shorted. Everything looked fine when the van ran okay, but when it acted up the current dropped down. I did not think there was necessarily a driver issue, because there was some current, something was being switched. I decided to also scope the voltage feed (red is inj voltage, blue is current) to one of the injectors. As you can see, the voltage would drop to 4 volts when the injector was firing. It would get even worse as the vehicle warmed up more.
This is a super basic issue - we have an injector that needs two things... power and ground. One of them is not performing properly. So yes, we do need to think about the basics, but test them differently. 4 volts and a good ground was enough to pulse the noid light, not enough properly fire an injector though. I pulled a wiring diagram to start chasing down what I thought would be a broken wire from the fuse box. Bonus, no testing needed! Going back to my basic electricity training it was obvious what was wrong by looking at the diagram. There were two power feed wires per injector bank, I was losing the whole bank of injectors and coils. The splice is internal to the fuse box. A fuse box fixed this van. So yes - we need to test the basics, but how we test them should be re-evaluated regularly.
And that,,,,,,,,,,,,,,, is a pretty,,,,,,,,,,,,,,,,,,,, basic post :) Very good thoughts. !!
Awesome Job and Great points Matthew Shanahan.
Very great post, exaclty. Check the basics but with a path, wouldn’t want to disturb a a issue and make it a intermittent issue as well. Like also what happens a lot, to me. Maybe even a couple of us. We forget about the connector, pin tension, pins not shorting together in the connector, and we chase our tails.
Thank you for sharing! Great write up! W/an added case study example!
Hi Matt, Nice write up! The only thing I would add is ....Use the notes feature so the others know where and what your channels are. And for God's sake man use a sync!! ;-) You have 4 channels for a reason. Great to see you in Chicago. Best to Kat.
Normally I do lol This one was a little sloppy, it was the end of a long, hot day... also we were driving this thing around with the dog house off. My brain wasn't working so well.
Hey Matt!!! Now here is the question of all questions: Did the tech assist you with the diagnosis? Did he learn anything? I've been in your position far too many times; having to step in after the tech got in a little too deep and missed something, or went the wrong way. How do you deal with situations like that? I try to use them as learning experiences, show the tech a technique, maybe take a
Knowing Matt, if this technician didn't learn from this, it's not from Matt's unwillingness to teach him. Very good point though Chris. I think that trying to teach working technicians in the field can be frustrating when they don't have the desire to learn. I would encourage everyone in this position to try not letting this discourage you. Don't give up but don't get discouraged. Some will have
Another tech in the shop helped me, he had some great ideas and input. He has really become proficient with a DSO over the last year and feels comfortable diving in. I always try to turn everything into a learning experience, and anyone is invited along the way. One frustration I have with the industry is how narrow sighted we can be about billing out hours. A lot of the management training
You are so right! It is hard to get another tech to hang with you during a diagnosis because management always wants them working on something else instead. Brings up again about taking training, no matter the source, into the ROI/Labor rate calculation. It's a shame to have to pull a tech off a job and give it to someone else. It destroys confidence and the desire to learn if you feel the shop
GREAT POST, Matt You brought up very good points. One is make sure that you have covered the basics, Have a REPEATABLE diagnostic procedure and DON'T SKIP. I always start with a GOOD Dynamic Battery test (see attached waveform). The second point you brought up was something that happened to me personally. As you know, Matt, I first had a Diagnostics only repair shop, it was 3 GREAT Diagnostic