Captain Obvious

It really is the current that matters, but to make things easier to think about (and apply in use) they spec it by voltage instead. The relay coil has resistance. You apply a voltage to that resistance, and current flows. The higher the voltage, the more current will flow. Apply a high enough voltage, then enough current will flow to create a strong enough magnetic field to pull the relay in. But for most applications, you don't want "a relay that pulls in at 160 mA". You want "a relay that works on 12 Volts".

I'm not sure I would call it "lame" but some of the aftermarket sprockets have the timing marks on the back and some don't even some of the good name brands don't have the marks on the back we went through a bunch of them recently here on the forum search around on the site for more info and as for the "brass" link it doesn't line up with the dimple every rotation it only lines up every now and then we talked about that recently as well and I believe it lines up every eleven cam rotations but you should search around for that too just to confirm for sure.

Thirded. (or fourthded?) On the low end of the spec range. What number was it your machinist recommended? I know you told me, but I don't remember what he said. Glad the indicator survived the trip. Always a little apprehensive shipping measuring equipment. And don't forget that you'll likely have to grind the ring gaps. Make sure you're ready for that!

LOL. Of course they are! What's next in line?

Haha!! I'm not quite to that level. How about a fanny pack with a handful of Canadian Tire gift cards and some ibuprofen topping out at 88 km/h?

Excellent! Glad you got that one issue knocked off the list. Now on to the next one!

Yes, there's actually two of them. one in front of the plate and one behind. But I believe those two small holes will be blocked off by the simple plate. It's the big ones that need additional work other than just a flat plate.

Here's a pic of what you'll be looking at. The large hole no the left of the pic leads to the front side of the throttle butterfly plate and the hole right in the middle leads to the back side (intake manifold side) of the plate. The BCDD plunger is a valve that regulates the air passing between those two holes. Problem is you completely remove the plunger so those two holes are wide open to eachother. Figure out a way to plug at least one of those holes and then put a sealing plate on. RTV gooped into the holes should work, Just don't start the engine until it cures so you don't suck still soft RTV into the intake manifold. Whipped up a quick sketch to show what's going on. Fill the yellow cavity with RTV maybe? :

Yeah, with the throttle body upside down and the plate removed, you should see the holes. I've never made a block off device for the BCDD and the only easy suggestion I have is to fill the whole lower cavity with RTV to seal the hole and then put the plate on. Really rough way to do it, but certainly simple. Just make sure you don't squeeze RTV up into the throttle body where it matters. I've heard of people taking the throttle body off and welding the hole(s) shut.

Agreed. I'm assuming that when everything was brand spanking new, tight fitting hoses and gaskets, little blow-by, and all that... Maybe it made enough of a difference that they felt they needed to disable it at idle (and WOT), but these days on worn engines with probable small leaks elsewhere, it's just a tiny unaccounted for offset that doesn't make much difference.

Quick empirical test... I pinched off my purge line on both a first started cold engine, and a fully warmed up engine and I had no discernible change in my idle quality or speed. Doesn't mean much, but I got that. Could mean my valve is closed. Could mean my valve is hanging open, but doesn't make much of a difference either way. Could mean my pinch off was not a complete seal. If I get energetic, I'll pull the control line and apply mouth vacuum to it at idle (to force the valve open) and see if I get any discernible change. But I'm running out of Z days now before the weather turns and they salt the roads!

About the smoke test... Since the BCDD is simply a bypass around the throttle plate, if that's where your problem is, it won't show up on a smoke test. Both sides of the throttle plate are in the same "closed system". Does that make sense? And, I can tell you with 100% certainty that if you just slapped a flat plate on there where the BCDD used to be, you've got a problem. You don't need a smoke test for that.

Here's a couple threads that might add some additional explanation: https://www.classiczcars.com/forums/topic/58760-1977-280z-with-81-83-engine-persistent-2000-2500rpm-high-idle/ https://www.classiczcars.com/forums/topic/56940-79-280zx-fast-idle-2200-rpm/

Yeah, you can't just plate off the BCDD like that. Creates a big leak around the throttle plate and your idle will be sky high. There are a couple other threads where people had that problem and installed some workarounds. I'll take a quick look and see if I can find something.

How did you block off the BCDD? You can't just pull it off and slap a flat plate in it's place. That won't work:

Agreed. The orifice in the neck of the carbon can is pretty small. Even if my valve never closes, it's not like it creates a big vacuum leak. I bet that over half the 280's out there have other accidental vacuum leaks bigger than that one, Haha! So even if mine is open, I probably just tuned it out like an offset. But my idle is lower than yours. I'm running 600-700. Maybe I could hear a difference if I pinched off the purge line.

Thanks again Dave. I think I'm going to look at those Pathfinder CARB cans next time I'm at the junkyard. My car runs fine, even at cold idle, but if I'm pulling air through that can at idle when I'm not supposed to, I could fix that. One thing I've clearly noticed in colder PA is that the mixture is definitely richer as ambient drops. I think they ran the gain on the air temp sensor a little too high. No way I'm going that deep into the ECU to change it, but I think that's the case. I was running a little lean in the summer, but as the temps have dropped, I can smell that I'm richer now. Especially when cold.

Thanks Dave. Good timing... I was in here at the same time you were. My read on the spring is the same as yours. Under some circumstances, the vacuum could be the same on both sides of the diaphragm, so in order to get it to open, they need to bias it to the "open" side. And I agree that it would be interesting to see how one of the original carbon cans behaved with a new diaphragm. So about your most recent tests... Makes perfect sense that you would run rough (on a hot engine) with a completely disconnected and hanging open purge line. Big vacuum leak. Also agree 100% that the fact that it actually LIKES the additional air on a cold engine is because it's running richer when cold. It's supposed to be richer when cold, but I think they may have gone a little far with that. And there's also a "after start" enrichment that boosts the mixture a little bit more right after you let go of the key. I've measured it and it tapers off over about thirty seconds. So if you had just started the engine, it's even a little richer. So on the most recent test above, on the old can, you don't know if the valve was open or not, right? Maybe you could apply your "push down on the cap" test. If it's really that borderline, then the additional thumb pressure might snap it closed? I'm thinking that forty years of that spring pushing up against the cap may have bowed the cap up a couple thousandths?

Dave, A while ago I was messing with my carbon canister and noticed the exact same operation you described... Able to pull air through the purge line (using lung vacuum) with no vacuum on the control line. My assumption (just like you) was that when there was more vacuum on the purge line (with the engine running), the diaphragm would be pulled down and seal off the purge hole. You're saying that's not normal? You're saying it SHOULD seal with no vacuum on anything? How can that be with the spring in there pushing the diaphragm away from the sealing seat?

Actually for ten miles, those plugs look good to me. Maybe a tiny bit rich, but not bad. Remember this isn't a closed loop engine burning all nice and clean and stuff. You do need to make sure the engine is getting up to temp though. Figure out if you have an instrumentation issue, or are you really running that cold?

Anyone have a confident source for the details about these two cam grinds? Anybody>

I've got a hardcopy of the 83 manual and .pdf of the EM sections of 81 and 82.They don't do any differentiation between turbo and non-turbo. The 83 manual seems to cover both turbo and non-turbo, but on xenon there's also a "turbo" version for 81, but the EM section is incomplete.

I've not seen one for the 260. What tool would you be using to create the diagram? There's a great one for the 77 done in AutoCAD. Would it save you work to start from that and modify it for the 260, or would it be just as easy to start from scratch?

Glad to hear your making progress. LOL. Don't get busted.