78' 280Z stumbles under throttle application

[siteunseen]

I use the brake booster hose bung, it's bigger and easy to get to.

[Zed Head]

I use the tiny little port that supplies the AC reservoir (the white bottle on the passenger side). Removing the FPR hose will change your fuel pressure and your air/fuel mixture, changing the way the engine runs (richer). I wouldn't use that one.

[Virto]

I don't have the vacuum reservoir - the factory AC was removed before I bought the car.

I've used the brake booster hose to seafoam the truck, so that should be fine for a vac test. Good call on the FPR, would cloud the results.

[Virto]

New plug wires are on and boy, they sure are pretty. It wasn't until I was halfway done pulling off the old cables and then laying them out with the new ones to check length that I noticed the NGK boots had a little sticker on them to indicate which plug they were for. >.>

I can't get my fat hand down past the washer bottle to pull the vac line off the brake booster, so I pulled it apart at the T connection. Then I realized my vac gauge didn't come with an adapter large enough for those big fat lines, so I'll have to make a trip to the hardware store at some point. I did notice a hard metal line that runs down next to the exhaust that comes from the intake manifold. I have a feeling that this is the vacuum line that connects to the modulator on the side of the transmission. The vac lines on the top of the manifold are nasty, cracking and gummy feeling.

Which changing the coil wire, I noticed what appears to be some vac line that runs under the AFM - connected to nothing. I didn't trace it back to see what it's connected to, but the vac line was just hanging down in the engine bay.

[Wade Nelson]

Sounds to me like you found the cause of your lean stumble - find where it's supposed to connect, reconnect it, and see if stumble goes away.

[Virto]

The stumble went away once the fuel pump was changed - the old pump was almost entirely plugged with sediment and rust.

I'm going to take a look at the FSM later on today and see what I can find. Is the distributor vacuum advanced? It's located right in that same area. I didn't have my little light with me, so it was hard to follow to a source.

[FastWoman]

There's a vac line that should connect to your distributor advance, and then there's another that runs around the front of the engine and across to the carbon canister cap. Then there's a return hose (fatter) that goes from the cap to the intake. Any open vacuum line is going to cause your engine to run lean. You should go through the entire vacuum system and replace all the hoses, whether they appear to need it or not. Sometimes a line will look perfectly good but will have a crack in it.

[Virto]

After seeing the condition of some of the lines, especially on top of the intake, I'm inclined to agree - it should all be replaced.

Now the issue becomes determining what sizes of line I need to essentially re-work the entire system. It doesn't look like there's a full vacuum diagram in the FSM - something I admit I liked having in the Chilton's manuals for my old F-series trucks.

In any case, it might have to wait a while before I can do the work, since I'm pretty tapped out for the month. Was hoping to get it back on the road this summer, but we'll get there little by little.

EDIT: I found the tubing routing diagram under engine tune-up in the FSM. Really hard to make out everything on the page, but sure beats nothing.

Re-edit: What the hell is the "3-way connector" vacuum hose? I noticed that my carbon canister doesn't have anything connected to the little raised cap portion on the top. The diagram says it leads to the "3-way connector" but it's really hard to trace on the picture.

When I moved the canister to replace the water pump, I noticed it had a large-diameter hose hanging down from it connected to nothing. I left it as it was - does the vent line just hang down?

Edited July 22, 2013 by Virto

[Virto]

Found a much better copy of the vacuum diagram via google images. Still clear as mud, but at least I can read this one.

[Zed Head]

The three-way connector is just a typical Tee fitting. One line connected to the throttle body (ported vacuum, only active when the throttle is off-idle), the other line ran to your vacuum advance canister on the distributor and the last one ran to one of the nipples on the cap on the carbon canister. The one to the carbon canister was used to open the main vacuum line to the manifold that would clear the canister of adsorbed gasoline vapors on the carbon.

The last line on the canister cap was connected the vapor tank (reservoir tank in the FSM) back above the gas tank. If it's not connected to the canister it might be hanging around spewing the occasional gas fume in to the engine bay.

[Virto]

I assume there's a metal hard line that runs back from the engine bay to the vapor tank in the rear. I'll have to see if I can find anything that's just sitting open and re-connect it. It could explain some of the gassy smell the car has always had. The car ran immeasurably better once the fuel pump was changed - if the vac advance and other lines are just hanging open, I wonder what it could really feel like to get on the gas.

Fuel pressure tester arrived today. Always fun to get a box in the mail, like a mini-christmas.

[Virto]

Picked up some new vac lines and set to work this morning. It's amazing just how well the car ran with so many hoses dry rotted or split. I found 3 that were falling apart - and that's just in one area.

The three-way connector (or t fitting, if you're normal, ) up front was connected to the vac advance and the throttle body, but left open on the 3rd side, so I ran a new hose and reconnected it to the carbon canister. Reinstalled the battery hold down after I saw it hanging on the wall - apparently I'm stupid and overlook things often. Started her up and took her out for a shakedown.

When the transmission shifted into second, it was so smooth that I didn't even notice. The car is rusty, dented, filthy inside and out - but the smile on my face while poking it around town makes up for all of it.

Had her out for about half an hour in stop and go stuff. Good idle, no hesitation, oil pressure good, temp good - mood: better than good.

I'm sure I'm not done running into problems, but thanks to all of you, I've gotten through some and if it comes to it, I'm sure I can get through more. Thank you all, so, so much.