Behind the Door at The DERP -- The Extended Extra Session

Yet another session of perhaps several. A CM Playlet from OPH.

(An earlier session was published previously here.)

[The door opens. Prof. Panquehue enters and joins Profs. Bryndza and Stilton, who are already seated.]

Panquehue: Did I miss anything important?

Bryndza: Of course not. All life was suspended, awaiting your blessed return.

Stilton: Sorry. We can’t just rerun the whole class for you. See if a classmate will share his or her notes.

Panquehue: I saw Jack in the hallway. He said he’d be right in after he took a pit stop.

Stilton: Pit stop? Luxury!

Bryndza: It occurs to me that I worked straight through lunch, and I haven’t been in a restroom since shortly after arriving on campus at eight.

Stilton: Teacher’s bladder. Also quite useful on long trips.

Bryndza: Limits exposure to lavatories in airplanes and skeevy highway rest stops, too.

Panquehue: Potty break notwithstanding, Jack’s several minutes late, isn’t he?

Bryndza: That clock isn’t running; it just happens to be close to the current time. Maybe that will come in handy sometime.

Panquehue: Ah. Chekhov’s gun.

Stilton: Clever device. Interesting I hadn’t noticed it there earlier today.

Panquehue: Interesting but not surprising. So much doesn’t function around here, we just stop noticing. We’re habituated.

Stilton: Hmm. I haven’t seen Wensleydale lately. Has he announced his retirement?

Panquehue: He has, for certain values of the word ‘announce’. But I haven’t heard a specific date.

[A knock is heard.]

Bryndza: Come in. It’s unlocked.

Jack: I’m sorry if I kept you waiting. I brought some bottled waters if anybody’s thirsty.

Bryndza: That’s very kind of you. I’ll take one. Thank you, Jack.

Stilton: Thanks, I’m good. Maybe in a few minutes.

Panquehue: Me too, thanks. Let’s get right to your test. Case one. Please read it.

Jack: “A client presents with a stock 1995 Bodze Exploit, five-speed manual transmission CV4 model, with ninety-eight thousand miles on the odometer. Complaint is an intermittent hard stumble during moderate acceleration. Client states that when it happens, it’s almost always when the accelerator is about one-third to the floor in first through third gears, and it’s one to five pronounced jolts till he reacts and changes the accelerator position. Car runs fine otherwise. Client confesses he ‘knows enough about engines to be dangerous’ and that he’s already done some work on it. Question 1. Of the following procedures, which is the most reasonable to have tried first?”

Panquehue: And you answered B, which is ‘remap the air-fuel curve in the ECU,’ for the reason that it has the words ‘air’ and ‘fuel’ in it, but you really wanted to answer ‘re-jet the carb,’ yes?

Jack: Yeah, that’s right.

Bryndza: Where did you get the idea that the problem was in the carb?

Jack: I learned a lot from my grandpa. He had a motorcycle shop where he was kind of a legend. I worked there weekends and summers as soon as I got old enough.

Bryndza: You must have enjoyed your time there to be pursuing a related field.

Jack: I thought I’d take it over one day, but Gramps passed while I was a senior, and my mom and dad didn't think I was ready for it and they don’t know much about bikes, so they sold it to the other guy who worked there. But he made some bad deals and ended up bankrupting it in only a few months.

Bryndza: I’m very sorry to hear that. Both about your grandpa and the shop.

Jack: It’s a pizza place now. I went there a few times, but it’s just weird to see it that way. I swear I could still smell the oil and the exhaust . . . it’s still in the wood . . .

[Bryndza subtly shifts a stack of books on the table to reveal a box of tissues.]

Panquehue: So, then, your grandpa taught you about carbs?

Jack: Yeah. The number one cause of stumbling during acceleration we saw in the shop was that the bike was tuned for the mountains up-state and needed re-jetted for sea level here.

Stilton: Then let’s add your idea as one of the answer choices . . .

Panquehue: Answer F, ‘carb needs re-jetted’, as it is said.

Stilton: Right. Now we’re going to go through the thought process that should help weight the answers against each other. So let me first ask, what kind of carb on this CV4?

Jack: A lot of bikes are sidedraft, but cars are mostly downdraft, so I’ll say downdraft.

Stilton: OK, let’s file that for later. Answer B mentions an ECU. What’s that?

Jack: Engine control unit. That’s a computer which uses the readings from the sensors to determine how much fuel to inject, when to fire the spark plugs, stuff like that.

Stilton: Are you seeing a problem yet?

Jack: No, I’m not sure what you’re getting at.

Panquehue: You said ‘inject.’ Passenger cars in the U.S. are all fuel-injected since the 1991 model year. We’re talking about a 1995 model.

Jack: Doh! No carb. Dumb! But what about remapping the fuel curve? That can still be right, right?

Stilton: Well, maybe in the sense that you can swat a fly with a sledgehammer. But the ECU would be programmed from day one for all conditions to be encountered over the life of the car, assuming everything else is within service limits. So, really, remapping shouldn’t be needed.

Bryndza: How about we go back to answer A, ‘replace the TPS.’ What’s a TPS?

Jack: Throttle position sensor. That tells the ECU how far open the throttle is and how much air is going into the engine along with the MAF, the mass airflow sensor itself.

Bryndza: But they never go bad, so we can just skip that one.

Jack: But as we learned in lecture, when they get old, some TPS designs . . .

Bryndza: Lecture? That’s just book facts. What’s that got to do with any of this?

Jack: Huh? You're torquing me, right? You lectured that when an old TPS gets a dead spot, and the throttle lands on it, the ECU thinks it’s somewhere else, and the mixture goes off.

Bryndza: Ah, you came to class that day. Excellent. So this dead spot could be, perhaps, where the accelerator is one-third to the floor?

Jack: Well, typically not that high, but not out of the question, whereas . . . oh! The stumble!

Stilton: You’re starting to like answer A now, aren’t you?

Jack: Yeah, but let’s go through the others anyway and see if one of them is better!

Panquehue: That would be great, but you’ll be doing that when you rewrite your exam. We should move on to another question to get more exposure to the process while all of us are here.

Stilton: Before we do, let me ask. Your grandpa, did he teach himself how to work on bikes?

Jack: I don’t really know, but our customers said Gramps was like a concert pianist who didn’t need to read music. He just knew how every part fit together and he tuned by ear and feel. I never saw him work through things like we’re doing here. He went on instinct.

Panquehue: Thank you for sharing that. I would have loved to have met him. But isn’t it probable that he was so practiced at working through things that it just looked instinctual? That’s how the legend will live on within you, Jack. You will practice. So, question two, now, please.

Jack: “The client did the procedure selected in the previous question, with no discernable improvement. Supposing the O2 sensor was intermittent, he ran the car with it disconnected for several miles, with a marked decline in the stumble. But when he installed a new sensor and connected it properly, the problem returned as before.“

Bryndza: Most vexing, this!

Jack: “Of the following conditions, which is the most consistent with all symptoms described thus far?” So, I had narrowed it down to A, ‘stuck idle air control valve,’ and D, ‘lump of carbon fused to spark plug ground electrode,’ but I couldn’t decide so I put A.

Panquehue: What was your justification for A in your essay?

Jack: I was still going with the air and fuel theme. I said maybe it would be like a vacuum leak.

Panquehue: I can see where you were going, but no. You shot from the hip. It was open book, and you could have looked it up and seen for yourself that the air through the IACV still has to pass the MAF, so the ECU could still likely keep the mix near stoichiometric. And idle RPM would have been too low or too high, which wasn’t noted in the case. So why did you initially like the spark plug answer?

Jack: I was thinking it was like oil fouling that can lead to rough running.

Stilton: You probably saw that on two-stroke bikes, but how about four-strokes?

Jack: I guess not. And if this car was burning oil, it would have been noted in the case write-up.

Stilton: Well, sometimes details get overlooked, but on average, I’d agree on that point. So what’s up with the O2 sensor here?

Jack: The client must have replaced a bad part with another bad one, otherwise the new part should have fixed it.

Stilton: Or, perhaps more likely, the old TPS and O2 sensors were still working fine, and the cause is elsewhere. What would disconnecting a working O2 sensor do?

Jack: It means the ECU can’t read the oxygen level in the exhaust, so it runs open loop using its best guess as to fuel delivery based off of only MAF and TPS readings.

Panquehue: And because fuel economy is paramount, open loop running is pegged slightly lean, yes?

Jack: Actually, no. Lean running can lead to detonation and/or pre-ignition, which can melt a piston, so open loop defaults to rich to leave a safety margin at the expense of some fuel economy and CO output.

Bryndza: Tell us more about causes of detonation and/or pre-ignition.

Jack: Well, timing too advanced, gas too low in octane, coolant temp too high, carbon deposits on the valves or . . . spark plug! It all fits! Disconnecting the O2 sensor made it run rich and masked the pre-ignition caused by the carbon on the plug! I knew I should have gone with answer D!

Bryndza: No, you shouldn’t have. That might have gotten you a point on the test, but you thought it was oil fouling and you were wrong. See that clock? It’s not even running, but several minutes ago it showed the right time. It hasn’t been right since, and it will be wrong for almost twelve more hours till it is only briefly right again. How is getting a right answer for the wrong reason any better than that stopped clock?

Jack: I guess it isn’t.

Bryndza: But on the subject of time, we should stop here and let you get to your other studies.

Panquehue: Let me say, Jack, that I have a new appreciation of your actual knowledge, which it now seems can be directed towards real analysis and perhaps identifying solutions.

Stilton: I concur. As we said last session, it’s not a simple matter of shortcutting to the answer that looks closest to what you think is right. You could consider each answer choice an hypothesis, which, if true, has predictive power regarding consequences. If those consequent things don’t hold true, then you’ve likely refuted the hypothesis, hence that answer.

Panquehue: So, after Jack rewrites his exam again, I think we need another session.

Bryndza: Not all three of us. I can proctor the rewrite and give him our standard litany of effective use of the question banks, active learning, et cetera. So, Jack, you’ll email me to schedule that ASAP?

Jack: Yeah, soon as I get home. [Getting up] Thanks for your time, professors. Have a good evening. [Exits amid ad-libbed waves and good-byes from the others.]

Stilton: [to the door] I actually think that did go well.

Bryndza: [to Panquehue] You had a CV4, didn’t you?

Panquehue: Yes, that was my case, but there was no client, only me. I also didn’t swap out the old O2 sensor; it tested good, so I re-installed it. I did swap in a new TPS, but that’s just as quick as testing the old one, and a ten-dollar part near end-of-life, why faff with it, right? When I recognized the open-loop enrichment thing, I knew I should read the plugs. [Stilton arises.] First plug I pulled, I found the carbon lump, but happily no metal deposits to suggest piston melting. The other plugs were unremarkable . . .

Bryndza: Stilton! What are you doing?

Stilton: [lifting the clock off its wall hook] I’m taking this damn thing home. It’s either a dead battery and I’ll bring it back working, or it’s trash that should have been dealt with accordingly long ago. I weary of these incremental institutional indignities. Whether 'tis nobler to suffer the slings and arrows . . .

Bryndza: Taking up arms against the sea? Or you could put in a work order like normal people.

Stilton: Plant operations and IT wipe their asses with the work orders I put in.

Bryndza: Then raise a righteous stink at the next faculty governance meeting.

Panquehue: O Bryndza. It’s such a wonderful idea and I want to agree with you, but I’ve been here just enough longer than you to know what will come of it, which is to say, precisely nothing.

Stilton: Worse! They’ll create a whole new admin position, ‘Chief Officer Of Timepieces’ or some bafflegab, and we’ll have regular surveys about ‘are all your hourglass needs being met?’ and workshops on ‘spring forward without letting those with different scheduling styles fall back’ and three layers of forms and approvals just to get a damn clock or its battery fixed or replaced. Nope! This comes home with me. I hope it IS broken, because then at least I can autopsy it.

Bryndza: This isn’t about the clock.

Stilton: This is . . . you are my allies. We do good work. I’m still learning how to let that be enough.

Panquehue: But this is nowhere near all there is! There is, for example, beer.

Stilton: Indeed, that there is! Join me for one at Murph’s, you both? Anyone? My treat?

Bryndza: School night.

Panquehue: Sorry. Bryndza alludes succinctly and ominously to our long day tomorrow.

Stilton: Well, in the face of such airtight logic, I shall repair to my domicile forthwith and toast us with a medicinal single malt ere I commence my evening ablutions. I’ll have a working clock tomorrow. Maybe I’ll patch in a wireless remote cut-off.

Bryndza: Have at it, but don’t lose sleep to the project. We’ll do drinks some night soon.

Stilton: I’ll hold you to that, and my earlier offer stands. A good eventide to you both.

[Amid ad-libbed good-byes, Stilton exits, followed by the other two, who shut the door behind them. Fade.]