New owner of '77 280z from Upstate SC

[the_tool_man]

34 minutes ago, Zed Head said:

If the wire in the AFM vane causes the pump to run then it seems like the fuel pump power circuit is in good shape. 

My thoughts, exactly.  Don't forget, we got the engine to run by mechanically forcing the AFM vane open.

[dtshaw66]

Wonderful 280 and a great find! Welcome to the club.

[rossiz]

the pcv hose runs from the block under the distributor, above the exhaust manifold to the underside center of the intake manifold. it gets hot and rots out on the bottom, often causing a huge vacuum leak. the next spot would be accordion boot that connects the afm to the throttle body - cracks in the valleys of the accordion are hard to see and leak a lot. bad grounds/plug connections and vacuum leaks are where your problem most likely resides - i'd be surprised if the afm is the culprit due to being out of calibration. lots of folks go there too soon and fiddle with it (me included) when the issue was a combination of many small problems adding up. siteunseen is right about the gunk that can build up from the pcv connection - this could cause a mechanical issue in the afm vane or throttle body, but again i'd adjust the afm spring tension last in the series of tests. if you do decide to fiddle with the afm clock spring, be sure to use a sharpie to mark the starting point (mark a gear tooth and the housing) so you can get back to zero should things go awry...

the injector connectors have a little spring clip that must be pressed in order to pull them off the injector - start with the one that is easiest to access/see and figure out how it works, then pull them all one-by-one and use a dental pick/deoxit/400 grit paper/whatever to clean connections. be careful w/the plugs - they get brittle w/age & heat and want to disintegrate. 

oh, (and sorry if i've missed this or you've already done it) check your fuel pump relay is working properly - it should send power to the pump at key position "start" and then at "on". you may need to pull the starter solenoid wire (simple, no tools) put a test light at the contacts (i'd go right to the pump behind the passenger side rear wheel) and have someone turn the key to both positions to ensure you've got power. 

[siteunseen]

If you'll pop the cover off the afm and "finger" the weighted sweeper contact to make sure it moves nice and smoothe, those can get stuck after sitting for a long time.  I bought one back in the late '80s for next to nothing because all it would do was idle.  Trailered back to my Dad's and started fiddling with different things and found that the sweeper was stuck.  Pushed it loose and sprayed some electrical cleaner on the contact path and it ran like a champ.  Also in '78 they rerouted the PCV hoses to get the one from the valve cover away from the front of the throttle body.  Google images of '78 280 PCV hoses and you'll see what I'm talking about. FWIW

And I think most of us secure that black cover back on with zip-ties. 

 

[the_tool_man]

Progress. It runs!

Sort of.

I removed the AFM, and after opening it, realized it had been messed with.  The glue blob on the locking screw was broken.  And it looks like the black gear has been adjusted 6 teeth clockwise from where it should be.  At least that's what the white marks on the body of the AFM and the black gear seem to indicate (see photo).  I went through the electrical tests, and found that the fuel pump cutoff circuit was intermittently open.  A quick pass over the contacts with some emery paper and alcohol fixed that.  Everything else on the AFM checked out fine.  The air passage was dirty.  So I cleaned it.  I decided not to attempt any adjustment of the black gear yet.

Anxious to see if that fixed it, I reinstalled the AFM and started the car.  As long as I gave it enough throttle to maintain 2000rpm or more, it ran.  But it sputtered and smelled sooty like it was running rich.  I tried the "fingering" test with the AFM to see if I could effect the mixture.  But it didn't seem to make any difference.  I ran it for about 15 minutes, letting it warm up.  I'm not sure why I did that, other than in the hopes that running that Star Tron through the injectors might clear things up.  It didn't.

Still, now that I can get it to run, I've eliminated fuel pump and ignition as the source of the issue.  Now I can go through the troubleshooting process to get it tuned.

Tomorrow, I pull the wheels and get them re-shod.

EDIT: I just noticed the last several posts with good ideas for easy stuff to check.  I'll test for vacuum leaks and bad connections tomorrow.  I'll also look at the plugs and see what that tells me.  Be patient with me.  I've not spent much time tuning pre-OBD cars.

Stay "tuned", lol.

Edited February 13, 2016 by the_tool_man

[Zed Head]

Don't know for sure if your 6 teeth is adjusted to the lean side or not.  I think that it makes it lean, tightening the spring.  Could be that somebody was trying to fix the rich condition by leaning out the AFM.  Pushing the vane in adds fuel, so all you were doing was making it even richer.

The first impactful thing you'll want to do is to measure the resistance of the coolant temperature sensor circuit, at the ECU connector in the cabin (Pin 14 to ground?).  Compare the resistance you get to the temp. v. ohms chart in the EFI Guide or the Engine Fuel chapter.  If it's too high, or even open, the ECU will add a bunch of fuel, because high resistance means cold.  If that number is in range, check fuel pressure (check it anyway), and check the color of your injectors.  Sometimes people think that installing turbo injectors will add turbo power.  They should be light green or tan, not purplish-brown.

Found it - 

[EuroDat]

Unfortunatly its very common to find the afm has been messed with. I have three spares and the one in the car the same. All but one had the lids glued in place and looked like they were untouched.

They probably adjusted your afm to lean out the rich running problem. Its more than likely why they parked it.

It could be a number of things causing rich running. The temp sensor is a good place the start. Leaking injectors or a csv (cold start valve) stuck open or leaking badly. A fuel gauge will tell you a lot about the fuel system. Its also handy to have enough fuel line so you can strap the gauge the a windscreen wiper to check it while driving.

[siteunseen]

The Throttle Position Switch could be stuck or sticking also.  It should go off idle contact around 1500 rpms then hits the wide open contact at around 3500 rpm if i'm not mistaken.  Pop the cover off and make sure.  You can do it alone, twisting the throttle rod while eyeballing the vane.

http://atlanticz.ca/zclub/techtips/tps/index.html 

[rossiz]

zed and euro are on it - people tend to jump to the most complex part (the afm) to try and fix what is often the cumulative effect of several much simpler issues. problem is, you will never get it running right unless ALL the little things are correct. your first priority, before buying any parts would be to undo all the fiddling of PO mechanics and get the system working as designed - this means:

1. sensors must be working right - if the numbers you get from zed's test chart are off, start at the sensor location (front/bottom of your thermostat housing) and clean/check then there's a set of bullet connectors about midway up the manifold to clean/check then you can check the sensors themselves if you are still getting bad numbers at the ecu.
2. you can disable the csv (cold start valve) which is just a 7th injector over by the throttle body - it fires up when the engine is cold adding extra fuel and they have been known to leak or get stuck, i think because it is located in an area that gets exposed to the pcv crud. you can disconnect the fuel line from the csv to isolate that potential problem and it should run just fine after a little warm up - the csv should only stay on for starting, not much more.
3. all your grounds & connections - this may seem silly, but there's a huge effect on the system if there are poor grounds or corroded connections, as the ecu reads resistance from the sensors and this resistance is amplified greatly from corrosion.
4. vacuum leaks - check every single hose, especially the pcv. you will probably wind up replacing all of it since it's cheap and easy so i'd do it once and be done. be aware that there are different size hoses, so you may want to cut small pieces out of each one and bring them to the parts store to ensure you get the right ones. then be sure to replace hoses one at a time so you get them all connected correctly - look for a diagram so you correct any mistakes a PO may have made in this dept.
5. beware of dry, brittle fuel lines - as you're fiddling in the manifold and wiggling things the high pressure lines can develop hairline cracks leaking tiny streams of fuel onto the exhaust manifold. a bad thing. i've replaced them on my z and on another forum member's for this very reason - keep a watchful eye.

[the_tool_man]

First, I visually inspected all of the vacuum hoses.  I couldn't find anything wrong with any of them.  I even removed the large hose from the valve cover and intake coupling behind the AFM, just to make sure (losing part of the wire hose clamp in the process, grrrr).  All looked good.

Second, I performed the "yogurt cup test".  I'm not sure that really does anything.  After using a yogurt cup, of all things, to block the intake, and taping over the T fitting on the vacuum hose to the valve cover, I disconnected the brake booster vacuum line at the firewall connector, and used some clear vinyl tubing to pressurize the intake.  I found that it built pressure immediately, until I felt something give way, and then had a constant leak accompanied by a trumpet sound.  When I sucked on it, it would pull vacuum immediately and hold it.  I'd let the end of the tubing suck against my lip for a few seconds, just to make sure.  The weird thing is, I could remove the oil filler cap or the plug in the end of the hose to the valve cover, and it made no difference.  So I don't know any more than I did.

Next I pulled the ECU connector and measured the resistance of the coolant temperature sensor circuit (pin 13 to ground).  It measured 13MOhms, essentially open circuit.  That's not right!  Tomorrow, wife permitting (it is Valentine's day after all), I'll check that circuit as suggested.

[siteunseen]

It seems like I've read a bunch of times that bad ground connections cause them to run rich? Vacuum leaks cause lean running. If I remember right, I've read so much on these cars.

[Zed Head]

5 minutes ago, the_tool_man said:

Next I pulled the ECU connector and measured the resistance of the coolant temperature sensor circuit (pin 13 to ground).  It measured 13MOhms, essentially open circuit.  That's not right!  Tomorrow, wife permitting (it is Valentine's day after all), I'll check that circuit as suggested.

13 Mohms is Arctic.  That's going to add extra fuel for a cold engine.  50 F should be about 4 kohms.  Read rossiz's post about the path to and from the ECU to the coolant temperature sensor.  There are several spots it could open or be misconnected.

Doesn't sound like you have any vacuum leaks.  The PCV valve under the intake manifold is spring-loaded one way and gravity the other.  So it might take a bit of vacuum to pull it open.  It's easy to remove and you can't really hurt it.  It might be gummed up.  Worth unscrewing and taking a look.  Careful with the hose.