Captain Obvious

LOL. "We gotsta know." Thanks Dave. So we have a confirmation that the documentation for the 75 seems to be accurate. The 76 is still the odd-man out with the conflicting documentation, but 75 looks good. And by the way... I believe the fuse for your hazards is two down from your turn signals. Labeled "Dome Light". I believe that one runs the 4-ways too.

Yes, it's possible. And that is what I would recommend to the OP if he's really wondering what the numbers really are.

Thanks Dave. Just to confirm. You're saying that on your 75... When you pulled the forth fuse up from the bottom (which is also the forth down from the top) that your turn signals stopped working?

@MikeThat's good to hear. I'm guessing that the number of covid cases in WA has dropped off significantly and that has driven the relaxation of the restrictions?

Haha! Hopefully someone else will chime in!

At this point, I'm not confident until or unless someone pulls some fuses on 75's and 76's and notes what goes dark. I had said earlier that everything from 74 to the end used #3 left as the turn signals, but looking at the diagrams again, it appears the both 75 and 76 used #4. But at least for 75, the picture of the fuse box cover agrees with the details elsewhere in the FSM for that year.

I have both hard copy of a 77 manual and an electronic version and I think they match. 77 works out fine for me, but 76 does not. So I'm not sure which way 76 goes... I agree that the fuse block cover is tangible evidence held in my hand and I would be inclined to just go with that, but the issue shows up on the whole-car wiring diagram, not just that detail on page BE-12. I couldn't screen shot the wiring diagram to highlight the issue because it's too big and would be unreadable anyway. But on that wiring diagram, it shows the forth fuse down powering the turn signals. So I guess the idea of expanding my master fuse diagram to earlier years is dead in the water until someone with a 76 can answer that question.

The problem I'm having is in the documentation from the 76 FSM. Kinda goes like this: Here's a snippet from the 76 FSM showing the fuse block layout. Note that it shows the turn signals (FLASHER) coming from the third fuse down. This makes great sense to me since every other year from 74 through 78 uses the third fuse down on the left column to power the turn signals: And here's a 76 cover I have here that confirms the accuracy of the pic in the manual: But then here's another snipped from the same FSM that details the turn signal circuit, and it uses a different fuse. According to this detail, the turn signals come from the FOURTH fuse down: And important to note that the wiring diagram agrees... According to the wiring diagram from the same FSM, the turn signals come from the FOURTH fuse down. So which is correct..... The parts of the manual that say third fuse, or the parts of the manual that say fourth fuse?

I took a couple minutes and looked at the 76 wiring diagram. The fuse list I posted above will not work easily for 76. They really screwed with some things in 76. Enough that it makes me wonder if it's a documentation issue, or if the 76 car really matches the FSM. Anyone with a 76 want to do some poking around to help the cause?

If the signal from the distributor pickup (the red and green wires) gets interrupted, the engine will shut off. No question. So "plausible"? Absolutely. However, if the insulation on the wires inside that outer protective jacket is still intact, then I might question the probability. But certainly plausible. I'm trying to come up with something that may be likely to "act up" when sitting still at a traffic light with the engine at idle. I'm not sure an interruption in that signal would be any more or less likely to occur under those conditions.

My most recent interaction with Riley was this past April, so it was only three months or so. At that time, everything seemed fine. I hope he's OK...

Thanks for the vote of confidence, but I'm not an A/C guy. I don't even know enough to be dangerous.

Oh, then forget about what I said about coming down off load to idle. That's not it. You had mentioned earlier that you thought it would be ignition related since it didn't stumble before it shut off. In my experience, there isn't any significant stumbling when the fuel pump shuts off. It just dies. So how about this (since you have a 78)... Your oil pressure drooped enough in your hot idling engine and opened up the fuel pump switch and shut off the fuel pump? Or the "L" terminal on your alternator is acting up at low RPM's. That could also shut off the fuel pump.

Bummer. Was hoping it was just an instrumentation issue. We're back to where we were before. Keep us posted!

I would start by watching for the situation to occur again and try to get a feel for what's going on. I think all this poking around with the ECU as a culprit is premature. My car would sometimes shut off when I pulled up to a stop. Engines don't like a rapid drop from load to idle. It's just unstable. Modern engines running a fast control loop use technology and speed of response to take care of it, but back in the old days, it was never uncommon to pull up to a stop sign and sometimes have your car stall. If your car was tuned properly and running good, it was "rare", but it did happen. I think mine was caused by a rich fuel mixture, a BCDD that was disabled, and an idle that was set a few RPM lower than spec.

OK, so that's an original 78 ECU and there's no software in it. In other words... I don't think there's anything inside that can that would cause a lean-boot that would last the length of the drive and then be reset by a reboot. Still sounds like a software issue to me. And with that in mind... Something we haven't discussed in depth... Jonbill had asked earlier "when it is in this "lean" state, does it feel normal to drive, or hesitant?" Your A/F meter is the only entity attached to the car that has any software in it. Let's consider the prospect that it's a measurement phenomenon and not "really" occurring? So can you tell from driving the care while it's in the lean-boot state... Does it feel lean, or does it feel the same as when it's not measuring lean?

Forgot to ask. There are some things on that diagram that might not really make sense to some people... Do you know what means when there is a fuse for "defogger switch" and a completely separate different fuse for "defogger relay"? Does that make sense? (Just in case it didn't make sense) The "defogger switch" is the low current side. It energizes a relay (the "defogger relay"). The current going through that fuse does actually ever get to the defogger itself. The fuse feeding the defogger relay is the high current side and provides the current that actually flows through the defogger. But the tricky part is... If EITHER of those fuses is burned out, the defogger won't work. Does any of that make sense at all? LOL. I also don't like "steering lock switch", but that came right from the documentation. That is the "will activate the beeper if the key is in the slot while the driver's door is open". But I ran out of room. Haha!

Not pretty, but I'm hoping it's accurate. I'll give it some time to cure and then I might spend a little time making it look prettier. And if I get a chance, maybe I'll look at some 76 or earlier. I don't know much about the 240's, but I believe everything 260 and 280 had both lighter and glove box lamps. Maybe your bulbs are just burned out?

I traced a couple more fuses. Note that this has not been checked by anyone else, but here's the latest. Also note this is for 77 and 78. I haven't looked into any years earlier than that:

That connection to the 77 voltage regulator is the "IG" terminal and I don't remember the details of that what that connection does. I converted my 77 over to the 78 style internally regulated system a couple years ago, and as part of that conversion, I purged my brain of the finer details of exactly how the external voltage regulator works. I used to know, but now that I don't need to know anymore... Most of it left. So, having a 78, you don't really need to know either.

I traced a couple more fuses. It's not pretty, but this is just what I have so far. I'm not going to bother making it pretty until it's been checked by other people. This is for 77 and 78 (with differences between the years noted if there are any): Hopefully someone who is bored will check my work?

Ever notice those weird holes at the bottom of the fuse box? : I think there might be an obscure mention of it in one of the FSMs. That said... If you know you're blowing fuses, you might want to carry more than just three spares.

Well let's hope tit was an infant failure on one of the 2017 fuses and not a real issue. You'll find out at the most inopportune time. Do you have the spare fuse holders populated in your fuse box?

Yeah, it's always unnerving when a fuse blows. You put a new one in there and wonder how long it's going to be before it happens again. So was the fuse that blew a new one? Or do you think it was from 78? The reason I ask is that if it was an old one from 78, I wouldn't' worry too much about it. In fact, I would replace all the fuses with new ones. Time probably hasn't been kind to them.

I took a look at the 78 wiring diagram, and the fuse that powers the voltmeter powers the following: Hazard flasher Steering lock switch (which then feeds the left hand door switch, which then feeds the door open warning chime) Voltmeter needle For 78, that's it. Just those three things. So since I know that the top two fuses in the left hand column are for right hand and left hand headlights respectively, we have three of the fuses sussed out (for 77 and 78 at least) Someone else can take a couple fuses, and pretty soon, we'll have them all done!