Weird Fuel Leak... Somewhere...

[FastWoman]

Hi all,

 

I was driving home in my '78 280, and I smelled the strong scent of raw gas at a light.  I drove a few blocks home and parked the car, and I sniffed the hood vents -- raw gas.  I popped the hood and looked around.  I could find no leaks anywhere, visually.  However, I could smell raw gas fumes in the column of hot air rising up around the front of the engine.  The strongest smell was just next to the oil filler cap over the #1 injector (forward extend of the intake manifold, just above the forward tip of the heat shield between intake and exhaust. 

 

Some of the intake manifold webbing looked slightly "wet," but it appeared to be oil seepage from the valve cover (and did not smell like gasoline).  However, there is a drain hole at the center of the webbing, between 3 and 4, where raw fuel could potentially drain onto the heat shield, such that fumes could waft up between the shield and the intake, just where I was smelling them.  This is all in theory, as I couldn't identify any leak.

 

I have a priming switch on my pump, so I was able to pump the system up to a full 36 psig, the highest pressure the system ever sees.  The pressure gauge holds steady at 36, so nothing appears to be leaking NOW.

 

The engine is bone stock.  The intake and EFI have been recently overhauled (a few years ago).  Replacement injectors are Standard FJ3.  All hoses are new and have Comp Cam clamps.

 

Any ideas as to likely sources of this leak?  Should I tighten all of my clamps a fraction of a turn, or is that courting trouble?

 

Thanks!

 

Baffled in Virginia,

Sarah

 

[Zed Head]

Sometimes I use a dry shop towel, the blue ones, to find small leaks.  The light blue turns dark when it gets wet.  Just touch it to all of the interfaces and see what turns color.

 

Also wouldn't hurt to put a screwdriver to the clamps.  I've found that the Gates brand EFI hose, although of apparently high quality, tends to creep over many heat cycles.  I've read that today's clamps are all spring tension clamps, designed to keep constant tension on the hose.  The hose is probably designed for the newer systems.  The screw types are constant diameter and the hose can creep and loosen up.  My Gates hose took several tightenings until things stopped moving.  I'll bet your hose creeped and all of your clamps are looser than when you installed them.

[Captain Obvious]

I can probably explain why you didn't see gas when the engine was hot. The engine was so much higher than the boiling point of the gasoline that it vaporized almost instantly and didn't form a puddle. I would surmise that's why the smell was so strong, but there was no liquid present.

 

As for why it didn't leak once you got it back to the stable and pressurized the system, that's puzzling.

 

I've wrapped injectors, fittings, etc with a paper towel and use masking tape to hold the towel wrap in place. If there's a fuel leak, it'll stain the towel and show up even once dry. Keep it on for a couple days and then unwrap and look for a stain to see if that's where the leak is coming from while hot.

 

And I agree with the thoughts that there's nothing wrong with giving the clamps a snug-up. As long as your hoses have been replaced sometime in the not too distant past and are not all hard and brittle, give 'em a little tightening.

[FastWoman]

Thanks, guys!  I'll go ahead and snug the clamps up and see if I get any more fumes.  If I do, then I'll start exploring with paper towels and such.  As I've never re-snugged the clamps, I suppose they might be loose.

 

On a side note, I'm very gun-shy about this matter.  I had a fancy (but poorly machined) stained aluminum billet fuel filter leak and then pop open atop the engine in my '66 Mustang.  I had been smelling raw gas for days but couldn't locate it.  I attributed it to carburetor weirdness.  However, when it popped open, it dribbled fuel all over the engine, which dribbled on the headers, and then the engine caught fire!  (Fortunately there wasn't too much damage.)  Of course I also hear tales of V12 Jags catching fire.

 

I guess I'd better carry a fire extinguisher for a while!

[Captain Obvious]

I guess I'd better carry a fire extinguisher for a while!

 

Yes you had better.

 

Hope you get to the bottom of it soon. Fuel leaks like that are a pain in the butt. I did a little digging into devices to help find a leak and research indicated two things: 1) The typical human nose is one of the very best detectors to find gasoline leaks. It is extremely sensitive to even small amounts, and 2) The human nose unfortunately gets "saturated" very quickly meaning that you very quickly lose the ability to detect the scent.

 

In other words, it works great, but for a very short amount of time. 

[rossiz]

could also be part of the re-circulation system - the gas going back to the tank and/or vapor collection which would only "leak" (liquid or vapor) when the car was running...

[FastWoman]

I was thinking that too, rossiz, but I couldn't find anything wet there either.  For the smell to be where it was, it would have to be a leak at/around the FPR or a crack in the hard return line. 

 

What I've done so far is to let the gas fumes dry up, so my nose can again help me locate the problem.  I topped off the pressure in the fuel rail last night after the engine cooled, and this morning it is only a few psi lower (which could be the really cold temperature).  There's no scent of raw gas.  So I guess I'll fire up the engine after I locate a fire extinguisher.  Maybe I'll see something dripping or spraying.

 

I really wish I could trade out this problem for an intermittent electrical one!  I wonder whether there a gremlin fairy somewhere who can grant my wish?  (Stray gasoline scares me.)

[Chickenman]

Have you snugged the Fuel line clamps yet? Better to do it sooner than later.

 

There are a lot of fuel and emission hoses in the engine compartment that can leak. Check the hose clamps on them all. Fuel injectors, FPR,  Fuel filter.. check all of them. Inspect the hoses carefully for any signs of rotting or cracks. If suspect replace all of the relevant hoses. Make sure that you get good quality FUEL INJECTION rated hose ( it should be re-enforced and clearly marked as a high pressure Fuel hose. Be sure to use new Fuel Injection clamps.

 

While you're at it, put the car up on a hoist and check around the rear fuel pump and fuel tank with the engine running. I've seen leaks from FI pumps at both the O-Ring and also the electrical contacts. I you see any weeping at these points, replace the pump. Check the sending unit as well. These can leak from either a old O-ring under the retaining ring and also from the Electrical contacts. The electrical contacts have a small o-ring underneath to seal them, and this dries out with age.

 

As new sending units for the early 280z's are next to impossible to find, you can repair the electrical contact leak. Remove the sending unit. ( Drain the gas tank and observe all safety advisory's ) .Clean the areas around the electrical contacts with a SS or Brass wire rotary brush ( Dremel or similar ). Then apply JB Water Weld  around the connections. This product is magic and seals water, petrol, diesel, hydraulic fliuds and most chemicals. It will even cure underwater. Ordinary JB Weld will eventually be dissolved by Gasoline, but JB Water Weld will not. It's product description specifically mentions it's use for repairs of Fuel Tanks and Oil Pans.

 

I used it to repair the weeping electrical connections on the Fuel Sending unit of my 1976 280Z when I could note source a new one or a good used one. That was 6 months ago and so far I have not seen a single drop of fuel from the Fuel Sending unit. Of course I installed a new retaining ring and O-ring.  BTW, Nissan still carries those parts t and they are cheaper than MSA or any other supplier.

Edited November 21, 2014 by Chickenman

[Chickenman]

Regarding Fuel tank. While the car is up on a hoist and you've drained the fuel tank, it would be a good idea to check and/or replace the main hose to the fuel pump and all other vent hoses. The main hose to the fuel pump is quite large. 13mm or 1/2" as I recall.  Add a METAL inline fuel filter between the fuel tank and the fuel pump. A Fram Gxxx ( I'll find the correct number later ) works well as a Fuel Pump pre-filter. I do not like using a plastic fuel filter in this area. A rock can fly up off the road and shatter a plastic fuel filter

[FastWoman]

Thanks, chickenman!  However, I already did all of that stuff 3 years ago.  All of my rubber is new'ish.  Tank is clean.  Pump is new'ish (old one failed).  Injectors are new'ish.  I do need to replace my prefilter, but it's not leaking or anything.

 

I just let the car sit for a while until I got to it today.  The pressure was still holding rock solid at 30 psig, same as it was the night I put it to bed.  I opened the garage door, put the transmission in neutral, released the emergency brake, started the engine, and watched... and waited... and watched more... and sniffed... and waited.... and adjusted the fuel/air ratio (CTS mod)... and waited... and NUTHIN'.  I think my conclusion is that I don't have a cracked/broken part and that it must be a loose hose connnection.  I'll tighten the connections up tomorrow.  (I won't be driving until then.)

 

I found a little extinguisher that's the right size for the car and will be carrying that for a while (probably permanently, even to put out someone else's fire -- a good thing to have).

[Captain Obvious]

Bummer... The intermittency just makes me nervous. You know the problem didn't magically go away by itself forever, right?. A smoking gun (not to be confused with a smoking car) would really be nice on stuff like this.

 

I had a (non-Nissan application) leaky injector that leaked slowly out through one of the seams in the injector body. But it wasn't intermittent, just slow.

 

Good luck with the hunt. Maybe you vurped a little into your carbon can? Shouldn't happen, but just tossing ideas.

[rossiz]

yeah, sux when a problem like that just sorta goes away... 

 

with the engine running (to keep the system pressurized and circulating) did you try wiggling/moving hoses around? could be vibration related to the car while driving - grasping at straws, but trying to replicate it.

 

or maybe the porsche in front of you was pissing gas and it got sucked into your fan and sprayed through the engine bay...