'75 280z #6 cylinder acting weird

[Roblaw]

OK. Got some more time under the hood. When I suck real hard on the vacuum advance hose, I can hear the arm actuate in the dizzy and my tongue will be sucked in the hose and stay there until I pull it off. Seems good. With the light hooked up, revving the engine, timing advances from 8 degrees at idle to off the timing scale. Seems good. So, I advance the timing. It maxes out at 15 degrees at idle with dizzy turned to the stops.

Took it on a run with this timing and no appreciable difference in power. Idle was a little higher but no seat of the pants pull/torque. Revs past 5K without issue but slow getting there. Feels like it's missing cylinder or multi cylinder inputs. 

Engine wants to stall when oil cap is removed.

Does any of this spark anyone's brain synapses?

[Roblaw]

I must have heard myself talking when I said "feels like it's missing a cylinder". I pulled plug wires one by one and engine stumbled on #4 cylinder. The wires were all shocking me too, even with rubber gloves on, super fun. So, pulled the plug, burned it with a torch (old dirtbike fouled plug trick) cleaned it up in the plug cleaner, regapped it, shot it with contact cleaner and blew it off. Drum roll please........... the car finally ran like I remember a Z running ?. So, I cleaned all the other plugs the same way just for good measure. Also going to get new wires, don't really expect that will make it run any better but at least I won't get shocked anymore. 

Now, on to the next problem. The car idles real high when pulling up to a stop. If I pull the pedal up with my foot, it'll calm down. Doesn't stick like this revving in the driveway.

Seems like I read some threads that address this problem..

The 15 degrees max advance at idle still has me puzzled but at least it runs good now.

[Roblaw]

My mistake. When I pulled the plug wires, all cylinders stumbled the engine except #4 cylinder.

[Zed Head]

That would be about a 17% power loss.

The 15 degree limit, or less, is a fairly common problem.  Somebody in the past probably installed your oil pump incorrectly.  Or you have the wrong base on your distributor.  You don't need more than 15% initial.  You can wait on fixing it.

Getting these things tuned up right is a long slow process for most, after they've sat.

[Dave WM]

10 hours ago, Roblaw said:

I must have heard myself talking when I said "feels like it's missing a cylinder". I pulled plug wires one by one and engine stumbled on #4 cylinder. The wires were all shocking me too, even with rubber gloves on, super fun. So, pulled the plug, burned it with a torch (old dirtbike fouled plug trick) cleaned it up in the plug cleaner, regapped it, shot it with contact cleaner and blew it off. Drum roll please........... the car finally ran like I remember a Z running ?. So, I cleaned all the other plugs the same way just for good measure. Also going to get new wires, don't really expect that will make it run any better but at least I won't get shocked anymore. 

Now, on to the next problem. The car idles real high when pulling up to a stop. If I pull the pedal up with my foot, it'll calm down. Doesn't stick like this revving in the driveway.

Seems like I read some threads that address this problem..

The 15 degrees max advance at idle still has me puzzled but at least it runs good now.

The idle problem is the BCDD, I think its supposed to act that way. below 10mph it disables (idle drops). Mine does the same, not a big deal.

the design is trying to avoid high vacuum, lean run, high temp exhaust smog stuff. with out a computer and bunches of sensors it just does some crude things by todays standards to keep that from happing. At least that is my take on it from reading the FSM emission controls section.

Edited February 23, 2020 by Dave WM

[siteunseen]

My BCDD had a high idle when I first got the car running decent.  I was able to adjust it now it's fine.  If yours drops when you pull the pedal up that has me thinking your throttle blade is gummed up and sticking.  If it stays high without fooling with the pedal I'd clean the throttle body but if it drops down after a few seconds you need to try and adjust the BCDD.  It's very easy to do just by driving around your neighborhood and turning the nut on bottom.  It'll get better one way and worse the other way.

[Zed Head]

14 hours ago, Roblaw said:

The car idles real high when pulling up to a stop. If I pull the pedal up with my foot, it'll calm down. Doesn't stick like this revving in the driveway.

Might be a dirty throttle body and blade.  Nissan changed the PCV system in 77 because the PCV gases were gumming up the throttle.  The fact that you can stop it by moving the throttle back with your foot is a sign.  Mine only did it when the engine got good and warm.

[siteunseen]

If you decide to clean the throttle body take your time with that accordion boot from the AFM to the throttle body.  It'll split if you look at wrong.  I wouldn't even try to get it off without first unsecuring the afm from its base.

Once you have access to the opening an old toothbrush or 2 and some lacquer thinner will clean it up like new.

[Roblaw]

Thanks to both of you. I'll be cleaning TB in the next couple of days. Zed, funny you mentioned the PCV routing change. When I was putting the engine bits back together, I looked at pictures of 280z engine bays and noticed the PCV arrangement was different then mine.

So much to learn. At least my other car obsession (Ford Maverick Grabber) is a simple beast.  

[siteunseen]

I rerouted my early '77 to the better pcv route.  Here's the thread. Thanks again Captain.

 

[Captain Obvious]

 

[Roblaw]

Finally reinstalled the exhaust heat shields last night after clutch install. Then I started fiddling with the BCDD and found the bolt on the bottom hanging down moves in and out freely about a 1/2 inch, kind of floppy. When pushing in, there is what could be described as soft resistance. However, the bolt can not be twisted with just my grasping fingers. Is this normal or has the bolt been completely backed out which I believe would render BCDD inop?

When I get more time, i'm going to pull the TB and clean it up.