Fuel in my intake plenum

Imcoz · Imcoz's Garage

Car was loading up and blowing very rich exhaust. Opened the lid and noticed fuel dripping from the bottom of the upper portion of the intake plenum. (beneath where the Idle Control Valve Muffler is located). Will be removing the air-box, and mass air sensor to get a better look.
- any one familiar w this symptom?
- could it be a bad cold start injector (not even sure there is one)?
- anyone experience a cracked plenum on a 3.6?
- the intake popped much like older 911's do which typically is remedied by those familiar aftermarket pop-off valves.

Any insight appreciated.

Imcoz · Imcoz's Garage

It's looking like it's a torn diaphragm inside the fuel pressure regulator. Fuel passes on one side of the diaphragm in side the component. On the other side of the FPR there's a vacuum line attached which goes to the upper portion of the intake plenum. The pressure in the fuel lines looks like it was pushing fuel past the torn diaphragm and up the vacuum line in to the plenum at a relatively high rate. There seems to be no other way fuel could get in to the intake this way.

If anyone has thoughts on this, please comment, otherwise I hope my post helps others.

bazar01 · bazar01's Garage

Yep, that's the only way excess fuel can get sucked into the intake, through a torn FPR diaphragm. $166.75 from Pelican.
How many miles on the car? I have 120k and still enjoying it. Do I need to plan on a replacement to avoid getting stranded?

Imcoz · Imcoz's Garage

Quote:

Originally Posted by bazar01

Yep, that's the only way excess fuel can get sucked into the intake, through a torn FPR diaphragm. $166.75 from Pelican.
How many miles on the car? I have 120k and still enjoying it. Do I need to plan on a replacement to avoid getting stranded?

Very low miles, but almost all track miles, probably just abused. Not sure why it would have failed, but it definitely failed the bench vacuum test. As far as keeping a spare around, you can get these things, plenty of 'em around. Pelican has 'em

In my experience its good to have an extra DME and a fuel pump around for an older car.

H20 LOL · 10-28-2012, 06:53 PM

Happened to me too. It was the WUR.

rbogh901 · 10-31-2012, 11:44 AM

I have heard of this but have not seen it. Do you have a photo of where you are seeing the leak?

Imcoz · Imcoz's Garage

Quote:

Originally Posted by rbogh901

I have heard of this but have not seen it. Do you have a photo of where you are seeing the leak?

This is an illustration of the fuel pressure regulator. The fuel travels from the flow side (5) of the component through a rupture on to the vacuum line (1) up in to the intake plenum.

The fuel itself was leaking from the bottom of the upper portion of the plenum.

cjoenck · 11-05-2012, 10:32 AM

You sure you are looking at fuel and not oil? I would think that fuel would immediately evaporate on a warm engine. Oil on the other hand is more likely.

Imcoz · Imcoz's Garage

Quote:

Originally Posted by cjoenck

You sure you are looking at fuel and not oil? I would think that fuel would immediately evaporate on a warm engine. Oil on the other hand is more likely.

It was fuel for sure. The fuel pressure regulator was bad and let it in through the vacuum line. I replaced it and cleaned the remaining components well. Was lucky enough to get it up to Lime Rock the day after and it ran flawlessly. In fact I believe there may have been a very small fuel leak at the regulator which caused the engine to run and idle somewhat poorly before the regulator completely failed.