Service bay war stories are great when new hands are holding the guns.
One of the most beneficial things about fixing real cars in an automotive program like mine is that hands-on repair jobs really shorten the learning curve, and that's what teaching automotive is all about. Live work jobs give automotive students in training a sense of purpose and direction, and the pace of the repairs we do in my program is structured to match the pace of similar work in a busy shop. One of my goals is to keep the students busy, engaged and working smart. Watching the rotors and drums spin on their lathes is silly when you can be installing the new brake shoes.
When one of my people is working on a car of his or her own, there is an added impetus, and it's great fun to watch the light bulbs come on as they punch their way through a big job. Eric acquired a 1994 Dodge Stealth for $500, which had, for some reason, been partially disassembled. The previous owner had planned on removing the heads, but didn't get past the upper intake before he decided to sell the car.In one of our service bays, Eric reassembled the engine and attempted to start it, noticing in the process that the timing belt was brand new. That was clue No. 1. It wouldn't start, and it was evident from the audible sound of uneven compression that something had gone wrong with the air pumping ability of at least one cylinder.
But there was another problem – it had no spark. I showed Eric that if the coils have power, but there is no pulse present at the primary trigger, then the crank sensor needs to be checked. So, we did that. Measuring the crank sensor signal at its connector, we found power and ground at the connector, but no signal was being produced with the engine spinning. The odd thing was, the next morning when he resumed his work on the car, he began fiddling with the coils again. I had to again explain why the coils weren't the problem.To physically inspect the crank sensor the tire needed to be removed. But the odd rim on the Stealth had an irritating theft-resistant lug nut in the deep lug holes. So he turned the wheel to the left, worked the serpentine belt and balancer off from there and found the crank sensor shattered into three pieces.
The original scenario played out like this: The engine had jumped time, and the owner had replaced the timing belt (obviously failing to notice that the crank sensor was destroyed). When the engine wouldn't start, he assumed it had bent all the valves, and he began the process of removing the heads, but stopped right after he got the manifold off and sold the car.With a $110 crank sensor in place and the timing marks fastidiously checked, the engine started, but ran badly. It had, indeed, bent the valves on the No. 3 cylinder (center front). Eric removed the heads, replaced the valves that were bent and reassembled everything. The car ran like a sewing machine.
We had to exercise some real problem-solving skills to get those silly locking lugs out of those deep holes. That car was a learning experience for Eric that I never could have provided with trainer vehicles!
It was a hotbed of problem solving, troubleshooting, failure forensics and in-depth repair, and I love those experiences. The experience Eric gained from removing and reinstalling the cylinder heads, replacing the valves and putting that nasty DOHC V6 back in time were invaluable.
If all that engine work wasn't enough, the clutch had worn to the point that it had no free play and was actually slipping when we test drove the car. A dash to the shop manual and quick adjustment at the pedal clevis took care of that problem. The point is that, what Eric learned on this Stealth he bought would fill a thick chapter in an automotive textbook, and he's light-years ahead of where he would have been if he hadn't bought the stone-dead Stealth.
The 2003 TrailBlazer
For our next curve-shortening job, one of my fellow college instructors brought her brother's TrailBlazer in for service because it was killing the battery. Further, the aftermarket DVD player didn't work and the speedometer supposedly was dead. Her brother had purchased the vehicle used with all these problems. In addition to the electrical concerns, it sounded like the engine was running too fast after a cold start.
I tossed the parasitic drain problem to one of the high school students I teach first thing in the morning. This young fellow is only 17, but he is a virtual prodigy when it comes to electrical problems. One of the first things he did after isolating the parasitic drain with an ammeter was to drop the knee bolster to reveal about 20 pounds of superfluous wiring and electronic gadgetry that had been added by some aftermarket shop under the pretense of installing theft protection. I called my colleague and she gave us permission to remove all those non-essential parts and return the vehicle wiring to its original configuration.When the job was done and the original wires were soldered, heat shrank, bundled, and taped, the parasitic drain was gone, and the speedometer worked. But the tachometer was dead. It made me wonder if I had received flawed third-party information. The student also rewired the DVD player using an otherwise unused circuit in the fuse box under the back seat, an arrangement that worked well.
We attacked the tachometer problem with the scan tool. The instrument cluster computer was reporting a tachometer signal to the scan tool, but the needle wasn't responding. I thought that if a re-flash at the dealership didn't fix this issue, the cluster would need replacing.
We also received a DTC P0495 code related to the fan, and we attempted to operate the fan via scan tool output commands. We could increase the speed of the fan, but it wouldn't decrease (it takes as long as three minutes for the fan to slow down after such a command is received). I found a bulletin (GM No. 06-06-02-003) that said the fan tended to make more noise on the TrailBlazer than the fans on most other vehicles, and not to replace the $400 fan clutch offhandedly for noise concerns.
However, we had a fan-related code, and the fan wouldn't respond to our commands in the allotted time frame. The customer was confused by all of this (the code was gone, but the fan didn't sound very different after we replaced it) and remained somewhat dissatisfied. On the other hand, the code was gone and the fan did what we told it to. One way or another, the wiring repairs we did would have been fairly expensive at a regular shop.
Another TrailBlazer, almost exactly like this one, came in with the driver door module making funky clicking noises and windows that wouldn't work. The module wouldn't talk, so we replaced it. The clicking was gone, but the windows still wouldn't work. The students thought we had misdiagnosed the problem until I showed them in the shop manual that the dealer had to sync the module to the vehicle. Everybody involved with these two jobs learned things they might otherwise have missed if they had simply been reading a textbook or doing exercises.
The 1999 Ford Ranger
This one came in on the hook from a good ways out. It belonged to a student from another department and his concern was electrical. He was driving up the interstate when the headlights grew dim, the gauges quit working and the truck died. He fiddled half-heartedly with the battery terminals for a bit before calling a wrecker and paying a $200 tow bill. One of the battery terminals had been totally compromised, so we replaced it with a solder-on brass terminal and cleaned the other one for good measure.
Some folks might disagree with that extremely simple fix, but for 30 years I've seen dirty battery terminals cause vehicles to stop running while people were driving. Yet, some technicians believe it can't happen.
To digress a bit, there are also some people who have told me through the years that if you remove the cooling system thermostat, the vehicle will always overheat. But as seasoned technicians, we all know most cars (the giant majority) will run downright cold with the thermostat removed. The tenacity of the few who believe the overheating thermostat principle defies comprehension.
For another minor digression, I once had an oddly misguided instructor at a Chrysler training center who tried to convince 12 seasoned technicians (myself among them) that resistance in an electrical circuit never produces heat. We were all rolling our eyes at that one!
The 2000 Silverado
This one was fun — the heater wouldn't blow warm air. Thinking of the thermostat, I asked about the engine temperature, but the owner said the gauge was displaying around 200 degrees like it always had. It was as he said, and a brief study of the schematic showed the familiar five-wire temperature door actuators.Pins 5 and 7 are power and ground, pin 10 is the 5V feed and pin 9 is feedback from the door position pot. Pin 6 provides control to the logic circuit that drives the door. If that dark blue wire is shorted to ground, the door swings one way and if it receives 5V, the door swings the other way with the pot voltage ranging from just above 4V (hot) to about 1.5V (cold).
We measured 12V on pins 5 and 7, along with a nice healthy 5V on pin 10, all with the actuator unplugged. With the actuator plugged in, we measured 1.53V on pin 9. When we turned the temperature control knob on the head, voltage only rose to about 1.6V. As we backprobed that little connector with our meter, the actuator started working right, making its full swing. A new actuator typically is in the center, and the control head swings it both ways to find the stops.
We had either disturbed the board connections and woken up the actuator or triggered the head to find its stops when we disconnected the component. Pin fit didn't seem plausible during our inspection, but it might have been an issue. The life of GM connector terminals (according to a GM instructor) is from four to seven disconnects.
Conclusions
Exercises and planted bugs, while necessary, are not the best way to learn. War stories are good in the classroom, but if a burgeoning technician is to gain real skill from automotive work, he or she has to get out of basic training, pick up the wrenches, meters and scan tools, and gain experience on the battlefield. In my program, that's what we do.
Richard McCuistian is an ASE-certified Master Auto Technician and was a professional mechanic for more than 25 years. Richard is now an auto mechanics instructor at LBW Community College/MacArthur Campus in Opp, Ala. E-mail Richard at [email protected].
