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Old 06-28-2013, 10:23 AM   #1
Type2
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Default Fuel smell under positive boost, load and 50psi+ fuel pressure

Starting a new thread to get fresh feedback instead of burying it 10 pages back in my build thread. I have a gas smell on the highway as soon as my fuel PSI hits about 50, I am under load, and my boost gauge reads anything greater than 0. Smell comes rushing in through the vents. Sometimes it's not too bad, other times it's noxious. As soon as the boost gauge reading drops back down under 0 and I am no longer under load, the smell goes away.

A perfect example of this is when I have cruise control on and I am on an incline - once my boost gauge goes from negative to 0+ the fuel psi goes up and I smell gas. If I goose it while passing someone - same thing. As long as no boost or no load, no gas smell.

I have examined the gas lines and no leaks. The smell began immediately after I replaced my old fuel pump with a Walbro 255 and I was actually seeing decent fuel pressure. I have a fuelab fpr and I don't see any leaks at idle. I do have two small segments of fuel line I could replace - about 12" total. All other fuel line is brand new.

This morning I thought I would be sneaky and connected the green test connectors to put it into test mode - this runs the fuel pump and brings the fuel pressure up to 50 psi. I checked the fuel lines, fpr, injectors, all ruel rail components expecting to see fuel squirting from somewhere... Nothing. No fuel smell anywhere. Sticking my nose deep in the engine bay and following the fuel lines - just normal engine smell.

This seems to indicate the smell only comes on during positive pressure, and therefore fuel pressure is not the sole culprit.

Any ideas?

Only other thing I can think of, and not sure if it is related or not, is that sometimes if I am on the highway - for instance, today - I was cruising about 75 and went to pass a semi - I put the gas pedal down about 10% - we're talking barely partial throttle - and it got all herky jerky on me. A more technical explanation is that the boost gauge went from 0 to 5 psi, then bounced up and down until I completely let off the gas. I did it again with more conviction (more throttle) and it passed the semi no problem.

Relevant Mods:

Engine & Power:
0. Borg Warner / AGP S200sx_RS_56 Turbocharger .63, A/R (55lbs/min)
1. Ported & gasket matched intake manifold
2. Grimmspeed 8mm phenolic spacers
3. TGV Deletes
4. Custom 3" CAI - deleted MAF
5. Crawford AOS v2 universal
6. Relocated IAT sensor to intake manifold
7. STi TMIC

Fuel:
1. Walbro 255
2. DW 850cc side feed injectors
3. Perrin side feed fuel rail kit

Tuning / Boost Control:
1. Open source speed density
2. Hallman Pro RX MBC
3. TiAL MV-R 44mm wastegate (set to 1.0 bar)
4. Omni Power 4 Bar Map Sensor
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Old 06-28-2013, 10:38 AM   #2
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Did you smoke test your manifold for a leak between the tgv/heads?
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Old 06-28-2013, 10:55 AM   #3
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Quote:
Originally Posted by dstroy View Post
Did you smoke test your manifold for a leak between the tgv/heads?
I've heard of a smoke test, but not sure what it is or how to perform one. I'll do some digging.
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Old 06-28-2013, 11:10 AM   #4
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sounds like it coud be an fpr issue, possibly torn diaphragm.

when your manifold crosses the 0psig mark, the fuel is no longer pulled through the reference line and into the manifold to be combusted.

do your green connector test with the reference line unplugged. it should remain bone dry. if not, there's your culprit.
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Old 06-28-2013, 11:54 AM   #5
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If you just replaced your fuel pump, Id suggest checking the oval gasket between the fuel pump housing and the top of the tank to make sure it wasnt torn or warped. That would cause a fuel smell inside of the cabin.

Is the smell like straight raw fuel?
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Old 06-28-2013, 12:10 PM   #6
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Quote:
Originally Posted by ride5000 View Post
sounds like it coud be an fpr issue, possibly torn diaphragm.

when your manifold crosses the 0psig mark, the fuel is no longer pulled through the reference line and into the manifold to be combusted.

do your green connector test with the reference line unplugged. it should remain bone dry. if not, there's your culprit.
EXCELLENT! That will be super easy to diagnose. I'll check it out as soon as I get a chance.

Quote:
Originally Posted by fr0st_wrx View Post
If you just replaced your fuel pump, Id suggest checking the oval gasket between the fuel pump housing and the top of the tank to make sure it wasnt torn or warped. That would cause a fuel smell inside of the cabin.

Is the smell like straight raw fuel?
The smell is coming straight from the vents. Not filling up from the back. And it dissipates quickly. No smell in the back of the cabin. I thought about the oval gasket, but I was super careful when I replaced it, and it was in great shape.

It does smell like straight raw fuel. Almost like someone is misting fuel inside my a/c vent for a couple seconds under boost and load.

That said, it's probably not bad to double check anyway, just to be sure. Thanks for your input!
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Old 06-28-2013, 12:13 PM   #7
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I took a video this morning b/c the FPR was making a hissing noise like water flowing through a garden hose. Remember the green test connector is plugged in, so it is cycling the fuel pump.

Pay close attention around the 9 second mark! Let me know what you think. Is it supposed to sound like this?

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Old 06-28-2013, 01:57 PM   #8
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I'd check around for a leak....mine sounded similar when I had a leak off my aps fuel rail.
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Old 06-29-2013, 03:40 PM   #9
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Quote:
Originally Posted by ride5000 View Post
sounds like it coud be an fpr issue, possibly torn diaphragm.

when your manifold crosses the 0psig mark, the fuel is no longer pulled through the reference line and into the manifold to be combusted.

do your green connector test with the reference line unplugged. it should remain bone dry. if not, there's your culprit.
I tested this this morning and no leaks. So it must be something else. Thanks for the suggestion, however.
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Old 06-29-2013, 04:24 PM   #10
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Quote:
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I tested this this morning and no leaks. So it must be something else. Thanks for the suggestion, however.
the next thing I would do is pressure test the intake tract. Could be an injector leaking on its seat.
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Old 06-29-2013, 04:31 PM   #11
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Quote:
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the next thing I would do is pressure test the intake tract. Could be an injector leaking on its seat.
You mean a standard boost leak test? I'll have to pull one of my subscribed threads and see how to make a tester.

I've thought about the injector leaking too. Figures, just after I sold a set of 4 recently tested and cleaned injectors.
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Old 06-29-2013, 09:25 PM   #12
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Try letting it idle and apply a small amount of pressure to the plug of the injector and see if fuel sprays everywhere or out of the fuel rail. May not be clipped in all the way or may have a partially torn o ring.

Its not the gasket on the fuel tank as I suggested if its a raw smell from my suggestion a few posts up then, that smell is more like vapor or fume of gas smell.


You could try upping the FPR to the pressure it would be at where you start smelling the leak, IE if its at light boost while driving, unplug the vac reference line and up it to around 50psi and see if it starts to smell at the higher pressure and it may help you locate where the leak is if its in a specific spot in the engine bay, either by hearing it or sniffing it out.
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Old 06-30-2013, 09:14 AM   #13
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i don't think it's a fuel leak directly, as it occurs at too coincidental a pressure: right where manifold pressure goes from vac to boost.
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Old 06-30-2013, 05:29 PM   #14
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I don't know where else the smell would be coming from other than the holes in the firewall for vac lines etc.. That's my guess is that as air comes across the motor from the hood scoop/front of the vehicle, its going in through those access points and giving the raw fuel smell and its only happening when the fuel pressure goes up from reaching that positive boost point..

Its not really a coincidence that once fuel pressure goes up it starts to leak.. thats when the leak seems to be happening..
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Old 06-30-2013, 07:02 PM   #15
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Quote:
Originally Posted by fr0st_wrx View Post
I don't know where else the smell would be coming from other than the holes in the firewall for vac lines etc.. That's my guess is that as air comes across the motor from the hood scoop/front of the vehicle, its going in through those access points and giving the raw fuel smell and its only happening when the fuel pressure goes up from reaching that positive boost point..

Its not really a coincidence that once fuel pressure goes up it starts to leak.. thats when the leak seems to be happening..
Around the 19 second period on the video you can see I have a small amount of fuel line I have not yet replaced. There is a small solenoid or transducer looking thing I'm not sure if I need or not.
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Old 06-30-2013, 07:12 PM   #16
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You need to replace that with the proper type of line as it could be leaking towards the firewall, and the dampeners arent necessary if you have them built into your FPR. I know the aeromotives have them built in. Looking at how its frayed towards the end of the hose and probably not able to clamp down all the way cuz those clamps are meant for fuel hose, not braided line is probably the culprit.

It may not leak around idle fuel pressure (35psi~) but it is probably leaking at around 50psi~, thats why I said try upping it at idle.
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Old 06-30-2013, 11:39 PM   #17
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Originally Posted by fr0st_wrx View Post
You need to replace that with the proper type of line as it could be leaking towards the firewall, and the dampeners arent necessary if you have them built into your FPR. I know the aeromotives have them built in. Looking at how its frayed towards the end of the hose and probably not able to clamp down all the way cuz those clamps are meant for fuel hose, not braided line is probably the culprit.

It may not leak around idle fuel pressure (35psi~) but it is probably leaking at around 50psi~, thats why I said try upping it at idle.
Good call. I'll replace it and remove the dampener. Less points to leak.
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Old 07-01-2013, 07:20 AM   #18
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Quote:
Originally Posted by fr0st_wrx View Post

Its not really a coincidence that once fuel pressure goes up it starts to leak.. thats when the leak seems to be happening..
leaks don't suddenly happen at X psi. the fact that he doesn't smell fuel at all while in engine vacuum is a critical clue to the issue.

question for OP: when you removed the fuel pressure regulator manifold reference line while the car was running to check for a torn diaphragm, did you see a leak suddenly start from some other point?

if not, then the "fuel pressure causing leak" theory is disproven, as the rail would be at the exact same pressure as it would be at 0 psig MRP.
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Old 07-01-2013, 09:23 AM   #19
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friend of mine had this same issue (only smell fuel during boost) it ended up being an injector o ring, he had recently removed and installed them(injectors)- so it made sense. Looking under the hood for leaks at the injectors never was enough though.

just thought I'd share.
edit: this was on an 05 legacy GT, also side feed :P
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Old 07-01-2013, 10:07 AM   #20
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Quote:
Originally Posted by ride5000 View Post
leaks don't suddenly happen at X psi. the fact that he doesn't smell fuel at all while in engine vacuum is a critical clue to the issue.

question for OP: when you removed the fuel pressure regulator manifold reference line while the car was running to check for a torn diaphragm, did you see a leak suddenly start from some other point?

if not, then the "fuel pressure causing leak" theory is disproven, as the rail would be at the exact same pressure as it would be at 0 psig MRP.
No, I sure didn't. It was bone dry. HOWEVER, the Fuelab FPR had a greasy film right where the AN fitting is for the fuel return line (the bottom AN fitting on the Fuelab - see pic below). I am not sure if the hose is/was leaking or if the AN fitting o-ring didn't seal. I tightened the t-bolt clamp on the return hose this morning as well as removed the old fuel line with the bumper.

I had difficulty detecting fuel smell this morning until the tail end of my commute, and I'm not sure if it's in my head or what. Either way, the smell is significantly reduced. I'll have to let it go a few days to make sure.



Quote:
Originally Posted by SenorDucK View Post
friend of mine had this same issue (only smell fuel during boost) it ended up being an injector o ring, he had recently removed and installed them(injectors)- so it made sense. Looking under the hood for leaks at the injectors never was enough though.

just thought I'd share.
edit: this was on an 05 legacy GT, also side feed :P
I really should have put new o-rings on my injectors when I finished my engine build, but they only had about 1000 miles on them and looked perfect. If the FPR and fuel line doesn't solve my issue, I'll go that direction next. Thanks for the input.

And agreed - every time I look under my hood it's bone dry! Really frustrating!
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Old 07-01-2013, 09:15 PM   #21
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Fuel smell is definitely not gone. Injectors or manifold perhaps. I am using Grimmspeed 8mm phenolic spacers. Perhaps I am leaking around them. Maybe I should have used sealant. I bought them used and they had sealant residue on them. I lightly sanded them, perhaps I didn't plane it completely flat?
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Old 07-02-2013, 12:15 AM   #22
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it still wouldnt cause a raw fuel smell that potent. Give the injector o rings a check..
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Old 07-02-2013, 08:15 AM   #23
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Quote:
Originally Posted by fr0st_wrx View Post
it still wouldnt cause a raw fuel smell that potent. Give the injector o rings a check..
I'll pull the injectors and replace the orings for good measure . Have to wait until Thursday or Friday unfortunately. I'll update afterwards.
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Old 07-05-2013, 08:18 PM   #24
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I pulled the driver side injectors yesterday and examined the o-rings. They looked fine, but I replaced them to be sure. I also replaced the final 12" segment of old cloth braided fuel line. It appeared to be in need of replacement. No fuel smell yet, but I have yet to take it out on the highway which is where it really stinks.
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Old 07-06-2013, 12:14 AM   #25
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hope it goes well
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