78' 280Z stumbles under throttle application

[Virto]

It'll have to wait until tomorrow, at best - midnight is not my favored time for running out to the garage to do some wrenching.

I'll pull them again and report back when I get the chance. Weather is supposed to be iffy so I'll see what it's like after work tomorrow.

[Virto]

No chance to pull them tonight - some pretty heavy storms came through and took out a few trees. If I'm lucky, I'll get to them tomorrow.

Thanks for the patience!

[FastWoman]

No problem! We'll be here!

[Virto]

Here are the plugs, ordered 6 - 1 left to right.

I've had to move the car a few times and I haven't encountered the stumble again, yet.

Oh, and I'm pretty sure these are BPR5ES-11, so they're hotter than the 6'es. I intended to pick up 6'es but didn't notice my error until I got home. I'll end up replacing them eventually, but they shouldn't hinder my attempts to solve other issues.

Edited June 25, 2013 by Virto

[FastWoman]

Well, the good news (to me) is that your plugs are fairly consistent from 1 to 6 -- no wild outliers. That suggests to me that your injectors are probably not clogged. (If they were, it would be to different degrees with each one.)

Aside from the hot ground strap, I'd say your plugs look a lot like mine did when I was running rather lean -- lots of carbon, at least for plugs that haven't been run very long. I realize carbon fouling is a classic indication of a rich mixture, but in my experience if the mixture is lean enough to cause partial misfiring (whereby a slow, incomplete combustion results in backfire through the intake), then it can also cause carbon fouling.

One great way to determine whether your mix is out of whack (and in what direction) is to remove the plastic cover from the side of the AFM and to finger the counterweight to see how it impacts the idle. If fingering it slightly CCW causes the engine speed to pick up a lot, that would suggest your engine is running lean. If fingering it slightly CW improves idle, you've got a rich mixture. Ideally, fingering it in either direction will result in a slight drop in engine speed. Of course this is at idle, and what matters most is off idle. But still I found that the proper mix at idle gave me the best mix on the road.

There's an idle mixture screw on the bottom, outlet side of the AFM, but I've not found it to do much of anything. I have mine set 5 turns open.

[FastWoman]

Oh, and FAIW, 1978 seems to be the year of the "lean drift." There's something about the '78 ECU!

[Virto]

That little box is the TVS, correct?

I remember reading that lean can cause carbon buildup, and I'm sure it was in one of your threads. I also know I've read about the ECU before, but I'll have to go back and search to try to refresh things in my mind.

I'll have some assistance this weekend, so I'm likely to swap the fuel pump and install an in-line filter. I'll also pull that under-hood fuel filter bracket and work some magic on it, one way or another.

[FastWoman]

TVS = Throttle Valve Sensor? (a.k.a. TPS -- Throttle Position Sensor?)

No, I'm talking about the airflow meter, which is the device between the air cleaner and the throttle assembly. It has a vane inside that meters the airflow. The ECU (Engine Control Unit, a.k.a. "computer") delivers fuel according to the amount of air metered. If you move the vane by hand, you can change how much fuel is delivered.

I'm probably the one who indicated an extreme lean condition can result in misfiring, resulting in carbon buildup. Perhaps this only happens with a marginal ignition (which mine was at that time). There's very little information beyond the dogma that a (somewhat) lean condition results in white, chalky plugs. However, I know for a fact (because it happened to me) that an extreme lean condition (that results in intake backfires) can result in carbon fouling. The reason for the backfire, BTW, is that the mixture is so lean that it burns neither well nor quickly. It's because it burns so slowly that a combustion cycle can persist into the following intake stroke, creating the backfire (or so it was explained to me).

[Virto]

You're right - I was looking up info on the TVS when I made this post and that image kind of stuck in my mind, but that's not located down by the AFM.

Do I have to remove the air temp sensor to get at the clockspring inside the AFM?

Yes, I'm positive it was one of your threads where I read about the carbon issue, and I've been through the threads regarding adding a resistor or potentiometer into the (air?) temp circuit.

With the fuel pump audibly struggling, it's still suspect, so it'll get the swap treatment. I may try messing with the AFM before I put the car's butt up in the air, though.

[siteunseen]

You just have to pop the black cover off to get to the spring. Here's something to look at

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

Go down half the page and you'll see FINGERING written to the far left and a picture of a left thumb moving the counter weight. LESS FUEL to the left, MORE FUEL to the right.

Edited June 27, 2013 by siteunseen

[Virto]

Awesome link, hadn't see that article before. I'll be keeping a reference copy.

[Virto]

Ran out in the rain for a little birthday shopping.

Picked up all new clamps that are solid instead of the stupid slotted hose-killers. Grabbed some new 3/8" fuel hose and a 3/8" in-line fuel filter to put between the tank and the pump. The parts store didn't have 5/16" line in bulk rated for EFI - they had some 2-foot pre-pack sections for TEN BUCKS that I passed on. I'll have to grab some later on.

New bottle of brake fluid too...depending on how things go I might try to bleed out the brakes this weekend as well.