Captain Obvious

That's one of my favorite Far Side cartoons ever. I've even heard that "My brain is full" phrase uttered in technical project meetings. Maybe even by me...

You do know that the signal coming from those VR pickups is polarity dependent, right? Even though it's an A/C signal, the phasing is important. So my guess, based on what I'm reading. is that you had it hooked up backwards earlier on, but with all the alligator clipping and such, you "accidently" swapped the polarity and got it connected properly. And FYI... That's the reason they used two different sized lugs. That forces you to get the polarity correct when you make the connections to the terminal block. The posts in the terminal block are sized such that you can't connect it wrong. Poka-Yoke.

Sorry to hear that. Since you came to us two days before it was due, you were clearly desperate. (As evidenced by the fact that you came to us! ) Well it at least sounds like the grades going into that project were good enough such that even a poor grade on that one, there was enough cushion to maintain a passing grade for the semester. Hopefully that's the case. The wording of the assignment made it sound like it was a group project... Was there input from other team members? Or despite the description, was it an independent effort?

So how did this turn out? Or don't you want to talk about it?

Remember that engines don't want to run slow and they hate running at idle. They also hate running cold. So it wouldn't be unusual for it to run poorly until it warms up. But once it warms up, it should be much more robust. And once the engine warms up the WTS should be about 250 Ohms. So if it runs better at 2.5K even after warm-up, then there's something going on. If it wants a higher resistance on the WTS, then it sounds like you're running lean. But for confirmation, you should be able to do some quick and dirty tests to see if it's rich or lean. I know you already know this stuff, but just in case: I assume you've got some of the vacuum connections on the intake manifold blocked off with rubber caps? Like the brake booster connection? You can pull the cap off a tiny bit to manually modulate some additional air into the intake manifold and see how the engine reacts. If the speed goes up and it steadies out, then you're probably running rich. If it get's worse and starts to misfire, you're already lean and making it worse by letting extra unmetered air in. Move slowly though... A little bit of air here can make a big difference. You can also adjust the mixture by moving the AFM position around, but same thing... A little motion there can make a big difference. It's squirrely. Have you ever taken a measurement on the ATS? It should be reading about 2K Ohms at your ambient this time of year.

@Av8ferg, Where did you get the O-ring and lock ring for the fuel sender? I'd like to pull mine out and figure out why it's not accurate, but I would like have an O-ring and lock ring on hand before I take it apart. I'm assuming if I have new ones here, I'll be able to re-use the old ones.

Haha!!! Thanks for the coverage!!

I'm not a timing expert, but I wonder if you would even see much of an impact at no load condition even if the advance mechanisms (centrifugal and vacuum) were working at all. I mean, on the road under load, you'd be losing lots of power and would certainly notice it. But under no load conditions, I'm not sure you'd see much impact. I can't easily disable my mechanical advance, but maybe I'll try disconnecting my vacuum advance and seeing what happens. As for the distributor signal to the ignition module... The VR is just a changing magnetic field cutting through a coil. The faster it changes, the higher the induced current and the higher the voltage that could be generated in an attempt to push it. So yes... The output voltage is proportional to the rotation speed. That said, however, it has to work well enough at starter cranking RPM or the engine would never even start. And I'm assuming your starter spins a lot slower than even a low idle speed.

IIRC, there are no ground connections to the EFI harness other than the large wire that leads directly over to the battery. All the other connections (other than the thermotime) are derived inside the harness from that one single ground. I don't think the distributor pickup is supposed to be grounded in any way. In fact, in an effort to prevent noise pickup from any other sources in the car, it's twisted pair to reduce antenna loop area. I haven't looked at in depth though. On my 77, that terminal block does not connect either side to ground. Don't know for sure about 75. I also believe the electronics portion of the AFM is floating and not grounded inside the case. So if they ground the AFM case, it's most likely another interference prevention technique. Faraday cage. Grounding the ECU case as well would do the same thing. All the electronics inside are floating with respect to the metal shell, but it can help to reduce outside interference from things like the ignition flyback. In the end though... I doubt any of that is the root cause of the problems you're having. Sounds like it's getting better though!!! Step by step!

Can't touch this.

And for today's amusement, the part of Captain Obvious will be played by siteunseen.

Oh yeah. Got it. Duh.

What do you mean by that? Do you mean the same amount of fuel spritzing from each injector? If so, that's the way it's supposed to be. Why would that bug you?

I wanted the above to stand alone, but as to your other questions about the switch... You can get the key-in switch out of the rest of the assy without dismounting everything. The only tricky part is prying off the indicator ring that shows the key positions (LOCK - OFF - ACC, etc). If you can pry that off, you can pull the switch out and replace it without having to dig any deeper. Personally though, I'd just bite the bullet and pull the whole thing off the column and do it on the bench. It might be just as easy in the end.

You don't "need" the shear bolts. They are a theft resistant device intended to make it difficult to disable the steering lock by taking the whole lock assy off the steering column. But honestly, I don't think any thief is going to mess around with it at all. One or two well placed hammer whacks on the top of the assy would probably crack the lock assy right off the column regardless of what screws were used to hold it on. Even if all the screws were traditional "normal" hardware, I don't think a thief in a hurry is going to take the time to remove them. Just crack the whole thing right off the column. Whack. Done. Unless there's some non-stock additional theft resistance stuff installed, I bet I could steal most Z cars "gone in 60 seconds". I've not tested the theory, but I'm confident. it would cost me a window (if the doors were locked), a steering column clamshell, and an ignition switch assy. With nothing more than a hammer. Less than 60 seconds. Gone. Let everyone think about that and take the necessary precautions.

If I was desperate, I believe my conscience would allow me to re-use the outboard bearing even after pressing the stub back of once it had been installed. The outboard bore is sized such that it's a press fit, but not a uber tight one. That's why the slide hammer works. If it were a real tight press fit, you'd need hydraulics to take it apart because a slide hammer wouldn't cut it. However, I'm not sure I'd do that if they'd been assembled and disassembled ten times. In any event, it's academic since new ones are on order. I also really really doubt it's a bearing issue. Even without seeing the parts, I'm at 90% sure the issue is the stub axle and not the bearing. Just for the sake of the investigation, I hope you can eventually conclusively determine exactly what was going on. I like the forensic stuff!

Yeah, I definitely think there's something else going on. There's absolutely no reason you should need to disconnect the WTS to improve anything. Disconnecting that should do nothing but produce billowing clouds of eye burning rich fumes. Have you checked the timing with a timing light? Should be able to get a quick and dirty measurement if you can keep it running long enough. Are you sure you have the thermotime and WTS connectors in the correct positions (sorry, but have to ask). If you think you're looking for an intake leak, you could smoke the system. The injectors are powered through the dropping resistors as shown. Bank of four and back of two. On the low side, they are grounded in groups of three. (1, 2, 3) and (4, 5, 6) through the two output power transistors. Wish I was closer to give you a hand.

I like the line down the middle of the garage. Your side. My side. Your side! My side! Stark would be happy.

I think the best way to look for runout would be to put the whole thing together as intended and then indicate (mag mount on the strut tube or something) off the hub. Maybe check both along the drum mounting surface for runout in the longitudinal direction, and also along the four rounded sections of the outer perimeter of the squared off hub for runout in the axial direction. Of course, this is all assuming the old rusted hubs are clean enough to even get reliable measurements. Did you make double dog sure that the distance pieces were square ended? Some of the distance pieces that have crossed my bench had been modified by previous handlers and were ground on one or more of the ends chasing a problem. Not only were they too short, but they weren't square on the ends anymore.

Jason, Oh! Sorry! I must have gotten my wires crossed... I thought you were on the road already. It's easy for me to rule stuff out from the comfort of my chair, but I really doubt that it's an issue with the new bearings. So I think that if you're still chasing this issue, you really need to figure out a way to stick something down inside the hub and take a direct measurement on the distance between the two bearing mounting surfaces and see if that number lines up with the length of the distance pieces. Sacrifice a pair of cheap calipers like I did or something.

I considered something like the lathe, but the problem is that even though you can chuck something up and adjust it to be perfectly centered (within the limits of your measuring equipment), that centering is still only at one point along it's length. The jaws are never good enough that you can assume the shaft sticking out of the chuck is perfectly normal to the chuck jaws. The optical method you described crossed my mind as well, but I don't know if the gap would be large enough to see. I've got a granite block designed for such things, but don't know if I would be able to see a quarter thousandth gap even with a strong light. And a quarter thousandth off from center at the journal could translate to more than that at the edge of the outer bearing race. Back when they made the stub shaft, they turned it "between centers" (That's the two little holes in the ends.) To produce the shaft, they mounted the raw stock between two points that were located in those holes. But the problem now is that those holes are all rusty and worn and I doubt you can trust the accuracy anymore to the level required to check the journals for runout. But if you could, that's probably the right way to do it. Fixture the whole thing up on the granite block... Mount the stub between centers and indicate each journal. I'm not a machinist and I'm sure someone working in a metrology lab would be able to do this in a snap.

Woof. I feel for ya. Do the math. Get the grades. Collect the paycheck. In theory, it'll be worth it in the end.

If the control loop is working properly, then theta should be very small. Problem is to make the control loop work properly. Actually for the second section, if you are allowed to use the feedback pot on the pendulum shaft, "theta" becomes a "concept". You just need volts: "The pendulum angle is measured with a single-turn potentiometer, with ±10V output corresponding to ±160˚ of rotation" That means you've got +10 V when the pendulum is almost horizontal in one direction and -10V when it's almost horizontal in the other. You've got +/-16 degrees per volt or (the inverse of that) 125 mV per degree around vertical. You're striving to keep the pendulum pot output at 0.00000 volts. And every 125 millivolts you are away from that is one degree off vertical and the sign of the voltage will tell you which way you are off.

Cool. It's money, but those bearings aren't the kind of thing you want to do any more times than necessary. Glad to help and good luck with the rest of it. Keep us posted as to how it all turns out. I'm having a hard time picturing a good way to measure things to look for problems (like a bend) with a stub axle. You need good reference points and I'm not sure what you would use and how you would fixture it. The only precision surfaces on the axle are the bearing journals, but how would you detect a minute bend in the shaft between the two? What you're really looking for is that the two bearing journal circles are not on the same axis center anymore. How would you fixture to detect that?

Wow... That's no fun. At all. Due in two days, huh? I'm assuming this is a final project for a control theory class? I can't give you any hard answers, but might be able to help a little bit in some areas. First thing to do would be to define the project... It appears to me that there are two major approaches that should be applied to solve the problem: a) First approach (the "classical control method") in which the single output of the system should be the cart position (NOT the pendulum angular position). So the only thing you have is the force required to move the cart. If the pendulum is not vertical, the force required to move the cart in the direction of the (off center) pendulum will be greater than if the pendulum were perfectly vertical (in equilibrium). And the force required to move the cart AWAY from the (off center) pendulum will be LESS than equilibrium. So it sounds to me that the "classical control method" would be to rock the position of the cart back and forth (sinusoidal) and measure the force required to move it. That force should be able to be derived by the current necessary to rotate the motor. That's where the PD lead-compensator stuff comes in... You should be able to keep the sine wave constant and as small as possible. And there is some doubt about the success of this approach as laid out in the original problem. You are supposed to program it all up this way and see if you can make it work. And if not, explain why not. For example, the control loop may not be stable and you may find that the sine wave required is increasing in amplitude until you run out of track length. I suspect this approach is not very robust and resistant to outside applied interference (the bump nudge described in the problem). b) The second approach allows the student to utilize the position feedback on the pendulum and it becomes a more direct control loop. Move the cart in the direction the feedback pot tells you to and strive to keep the output of the feedback pot at 0V. That should be much faster and more accurate feedback than using the cart force and should be able to do a much better job of compensating for externally applied interference. (Proof is left to the student.) If I understood the project correctly, then I would break it down into pieces: Write some equations for the force required to move the cart independent of the pendulum. Write some equations for the force on the cart due to the position of the pendulum (this is the part that Blue started working on above). Then combine the two. Write some equations for the relationship between the rotation of the shaft and the linear position on the cart. Write some equations for the electrical energy required to rotate the shaft. Etc... I'm so glad I graduated!!