280Z Difficulty starting

[Zed Head]

So, as far as I can recall I don't believe the ONLY think I did under the hood before the starting issue showed up was fuel filter replacement.

There's a fairly large vacuum hose directly from the intake manifold plenum to the cap of the emission's carbon canister, in the vicinity of the fuel filter.  You might check that.

 

I've used the carb cleaner trick.  Since it's only a squirt, if there was a spark you'd just get a flash.  But you do need to be careful.  The other thing about it though is that it will dissolve some paints, and the glue on tapes.  It's potent stuff.  I wouldn't use it on a good-looking engine.  Stater fluid is a potent solvent also but more flashy/vaporous.  If you decide to try one, experiment on a known (self-created) leak to see how little it takes so you don't dissolve things by accident.  The tiny vacuum bottle hose on the top of the plenum is a good practice spot.

[siteunseen]

 I don't have a vacuum gauge.

Parts stores loan those out if you need one.  There's a lot of diagnostic testing you can do with one.  http://www.atlanticz.ca/zclub/techtips/vacuum/

Edited August 12, 2015 by siteunseen

[Marios280Z]

Parts stores loan those out if you need one.  There's a lot of diagnostic testing you can do with one.  http://www.atlanticz.ca/zclub/techtips/vacuum/

Thanks, this article is pretty good. I did not read it very carefully, but it didn't look like he mentioned what the symptoms would be with a vacuum leak? I'm guessing that the idle vacuum reading would lower by couple of inches?      

[Marios280Z]

There's a fairly large vacuum hose directly from the intake manifold plenum to the cap of the emission's carbon canister, in the vicinity of the fuel filter.  You might check that.

 

I've used the carb cleaner trick.  Since it's only a squirt, if there was a spark you'd just get a flash.  But you do need to be careful.  The other thing about it though is that it will dissolve some paints, and the glue on tapes.  It's potent stuff.  I wouldn't use it on a good-looking engine.  Stater fluid is a potent solvent also but more flashy/vaporous.  If you decide to try one, experiment on a known (self-created) leak to see how little it takes so you don't dissolve things by accident.  The tiny vacuum bottle hose on the top of the plenum is a good practice spot.

Will do. I know which hoses you are talking about.

[Marios280Z]

Last night I had few minutes so I opened up the TPS cover to look at the connections. They did look OK, but since  I was there I cleaned it up gently with a small file, sand paper and followed with electrical connector spray cleaner. Crossed my fingers and went to bed. This morning, still with my finger crossed, I primed the fuel pressure and attempted starting...Unfortunately it gave me some trouble with a typical symptoms. Another item checked off, more to come. 

 

I also quickly looked a the the large vac hose that runs between intake manifold and the carbon canister, as mentioned by Zed Head, and it looked OK. I will try to get a  replacement this weekend just to be safe.I also tested starting fluid with the vac hose going form the manifold to the FPR. Small spray of it mad her rev up like an 18 year old girl. I did not have time to do vacuum leak test last night, plus the engine was too warm for my comfort to start spraying starter fluid.

[Captain Obvious]

Well unless I'm misinterpreting your spray test results above, it sounds like you've found at least one vacuum leak so far. Good.

 

Remember that, in general, vacuum leaks have more impact when at idle then when at full throttle. And running lean has more impact when the engine is cold than when it's hot. Hopefully your start stumble issue turns out to be a couple vacuum leaks.

 

Don't forget to check the PCV tube under the intake manifold. It's a typical leak location and since it's underneath and not as easy to see, it can be missed.

[Marios280Z]

Well unless I'm misinterpreting your spray test results above, it sounds like you've found at least one vacuum leak so far. Good.

 

Remember that, in general, vacuum leaks have more impact when at idle then when at full throttle. And running lean has more impact when the engine is cold than when it's hot. Hopefully your start stumble issue turns out to be a couple vacuum leaks.

 

Don't forget to check the PCV tube under the intake manifold. It's a typical leak location and since it's underneath and not as easy to see, it can be missed.

Actually, yes you misinterpreted y spray test  . I unplugged the vac hose to FPR to get a bench mark and to see how the engine would react when introducing started fluid into the vac line (simulating vac leak). That's all. I did not actually perform the vac leak test yet.

 

I forgot to mention but the other day I replaced the PCV valve since I purchased it some time ago (they were inexpensive and I've header that they can get clogged and stuck). The hose at the PCV end looked OK, but I have not investigated it on the other end. It's kind of hidden back there behind the throttle body and it looks like it actually expands in size as it connects to...something...

Edited August 17, 2015 by Marios280Z

[siteunseen]

The end that connects to the valve is smaller than the other end that connects to the tube coming out of the block.

 

Here's a picture showing where it goes, the red line, and the block tube is covered with blue painters tape.

 

 

here's another block picture with the tube sticking out,

 

 

 

 

 

 

[Marios280Z]

Thanks siteunseen. If that's your engine, I'm jealous...Very clean, no more hose and wire nest and much simpler fuel rail.

[Captain Obvious]

Oh. In that case... Nevermind. Hoping you DO find something.

 

Other typical area of concern is the boot after the AFM. If that one leaks, you'll run lean. Often cracks down in the valleys of the corrugations.

[Gary L]

I have not tried this, so I'm not suggesting its safer or will work, but I've heard a less messy way to check for vacuum leaks is use a small propane torch with the gas on very low next to where you suspect the leak is (un-lite of course) and if gas is sucked in a leak it'll also increase the RPMs. Again, I haven't tried this, but may be others on the forum have.  It would be quick, easy, and less messy.

 

Gary

[Captain Obvious]

I've heard of the propane method as well. I tried it once on my motorcycle and didn't get any effect, but that was because I didn't have any leaks.

 

So I can attest to the popularity, but haven't experienced the results personally.