Rubber elbow. Fuel or vacuum?

[Scholz]

Hello friends, in the process of changing all the hoses in my 98 S70t5 and I've got an elbow jutting out of my manifold to a hardline. that is just absolutely decrepit. I plan on replacing it. My only concern is its fuel, rather than vacuum and I don't want to be without the part if it disintegrates upon removal.

So, pic is attached, on hand I have plenty of 5mm silicone tubing from other vacuum lines I've replaced. Will they work in my application? Thanks in advance.

[misha]

I'm pretty sure that silicone hoses works well as a fuel hose replacement.In other words....for every application.

[FLXC90]

If you are referring to the line from the vacuum tree( thing with line and two capped ports), then plastic, then to the vacuum check valve(black/white disk), yes it is a vacuum line

If, on the other hand, you mean the larger plastic tube, that is emissions tubing, so yes, silicone can be used there also.-edit, d'oh thanks Erik

[Scholz]

The elbow in question connects to the black hardline that is crossing above the manifold in my picture. Probably on its way to my fuel pressure regulator near the passenger wheel well.

I've never used silicone hose as a fuel hose if it turned out to be one. so that's where my trepidation occurred. If it is no issue, I will replace with confidence.

[erikv11]

It is indeed a vacuum line, and runs vacuum (to the FPR), not fuel. You are good to go with silicone.

[jreed]

+1 on erikv11's comment. I've had a short piece of blue silicone tubing in that location for the past four or five years, ever since my original one developed cracks and crumbled. I used the thick wall tubing because it resists kinking a little better than the regular thin wall tubing. The angle from the intake manifold nipple to the black metal line is pretty sharp and occurs over a short distance.

[combatkarl]

I didn't have any silicone hose available. I found a quick fix to replace the hose from the intake manifold to the "fuel rail" tube -highlighted in yellow. At the auto parts store, I found Item # 47092 Vacuum Elbow 1/4" from Dorman Help! products. Any O'Reilly or Advance Auto should have it. I tried a straight piece of vacuum hose, but was not happy with the results or kink in the hose.

[Scholz]

When I replaced this elbow, I got a sniff of fuel vapor. Indicative of a problem with the fpr or injectors? Car runs amazing with stable boost development up to around 10 psi. But maybe once every five minutes or so I get a subtle miss, or hesitation. I'm essentially at stage zero now with vacuum lines, ignition, oxygen sensors, with good compression values, so it's been hard to diagnose.

[erikv11]

Just a whiff of vapor is normal and OK. Strong fuel smell would indicate a ruptured diaphragm on the FPR. Injectors don't come into play here as far as the fuel smell goes..

A bad FPR would be a more general problem, not every five minutes. That's a tough one to diagnose though. Other fuel supply possibilities could include clogged injector, or fuel relay issues. On the air side, a quirky throttle position sensor or MAF can do that but I wouldn't just throw parts at either of those unless you have a known good one to troubleshoot with (swap it in).

[Scholz]

I appreciate the response. In my head, I had ruled out clogged injectors because my fuel trim adaptives are great. Long term stays +/- 2% and short term never really looks absurd. Fuel pump and relay are brand new blue box with less than 3k miles on them.

I had suspected a faulty coil, but have the mpg I should along with power.

I looked at the idle air valve as a cause as its far more pronounced at idle. (It may not even happen under load, hard to tell.) As a matter of factly, it just happened to me in park with the a/c on along with an rpm drop. At any rate I cleaned the iacv and throttle body and installed a new gasket on the throttle. No dice.

The TPS is an interesting idea. My torque app has it fluctuating slowly around 11% at idle. I hadn't thought of it as an issue until now. And the MAF is a brand new bosch unit.