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Fuel leakage

  #1  
Old 03-29-2011, 10:51 AM
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Default Fuel leakage

blazer 1990, 5.7L with TBI injection.
about a month ago i rebuilt my TBI system, i bought a complete set of seals, a membrane and etc. everything went great, the engine runs beautifully.
a few days ago i picked up a smell of gasoline in the passenger compartment, i looked under the hood and i saw the entire surrounding of the seal
that sits on top of the block and under the TBI body, and the area around the top of the block, soaked with gasoline, and little puddles, yes! puddles of gasoline on the top of the block.
i dried the area, and gave the bolts, holding the TBI, a touch, also gave a touch to the fuel lines nipples, started the engine and waited for something to happen..
the seal, and it's surrounding stayed dry, the block is dry and everything looks good, except i can still smell gasoline when i drive..
i sneaked a peek under the hood today after a 5km drive and everything is still dry - so there's two things i can't explain:
- how the top of the block and the TBI area got so soaked?
- how come the leak haven't returned and i still smell gasoline?
plus i really don't think that nudge i gave to the bolts miraculously fixed the leak..
 
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Old 03-29-2011, 12:24 PM
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Stupid (just checking), but did you replace the o-rings where the lines connect to tbi?

My first guess would be you have a leak by the fuel pressure regulator. Happened to me when I rebuilt mine, the brass bell housing was warped from a PO over-torquing the torx screws, and when I put it back together it didn't seal quite right. Or maybe you didn't torque them enough (you NEED to use a in-lb torque wrench to tighten all of the TBI torx screws)

I fixed my problem by cutting my own gasket from NAPA's felpro rubber-fiber gasket paper (FUEL-RATED, it's grey and comes in a small roll). The teflon of the fuel pressure regulator diaphragm just isn't thick enough to seal if the bell housing isn't perfectly flat.
 
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Old 03-29-2011, 01:47 PM
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i gotta be honest... and stupid but i didn't replaced the o-rings, i oughta do it. but i did checked those lines and I'm 99% sure they are perfectly dry.
i've cleaned the entire tbi components on my kitchen table - i took my time and rubbed the hell off of each part, they were smooth as a baby's behind when i finished with them.
so i believe all the parts got a good seal.
if by diaphragm you mean that orange membrane, then i believe it got a good seal. (if not how can i be sure that the fuel pressure regulator isn't leaking?)
by the way all of this still isn't explaining why the block was drenched with gasoline the other night and today it was completely dry..?
 
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Old 04-01-2011, 03:52 AM
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i got a clearer view today after rebuilding the entire thing.
the red circle points out the body seal - which is soaked with gasoline.
and the yellow circle points out the diaphragm and the little window which i can see the bell's spring through. i can see fuel on the spring but i'm quite sure that the diaphragm is dry on the out side, i can't really point out the source of the leak..
the truck is currently out, because the everything gets soaked with fuel so I'm not sure it's safe to drive it.
any help guys?
 
Attached Thumbnails Fuel leakage-dsc00117.jpg  
  #5  
Old 04-01-2011, 04:54 AM
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Some things doesn't look right with that diaphragm seal. The fuel looks to be coming from there and soaking the lower surfaces. If your seal on the intake hat is doing its job, you really wouldn't notice too much of that getting out on top of the engine. Eventually it would just get sucked into the throttle body, but if the seal wasn't sealing up properly, it could allow it out intermittently.
 
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Old 04-01-2011, 06:25 AM
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it's a bit misleading - the diaphragm's surrounding Teflon is actually two layers. when i closed the bell housing it looks like they've separated, but i'm 99% sure that the surface of the diaphragm inside is whole.
as for the lower seal, it seems like an internal bleeding. i can't really see the source of the leak, all i can see is that it gets soaked when the engine's running.
i can't imagine a reason why it won't do it's job. the surface is clean, the seal is brand new, and the torx screws is tight properly around it.
i really don't know how to find this leak..
 
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Old 04-01-2011, 06:51 AM
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There are only a few places that fuel could leak out. That lower seal is just an air seal and doesn't actually seal against fuel leaks. There are o-rings around each of the injectors that seal fuel pressure. Then there are the threads in the bottom of the pod that the fuel line connectors thread into (the bosses where the connectors go into like to crack), and there is the gasket surface for the fuel pressure regulator.

You should see some of the Teflon diaphragm, but with as tattered as that edge looks, I just wonder what it looks like further in.
 
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Old 04-01-2011, 07:33 AM
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the o rings around the injectors sits nice and tightly.
the threads that the fuel lines connects to were my usual suspect, but the transparent o ring that sits there is new and the threads is firmly tighten.
i got a little dentist mirror, i looked there while the engine was running and it looks dry.
you mentioned the gasket surface for the fuel pressure regulator - which one is it?
about the diaphragm - can i make my own gasket to insure that it will seal properly or maybe apply some silicon - or i should just leave it the way it was intent to?
 
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Old 04-01-2011, 07:43 AM
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of course the diaphragm is new as well, if i haven't mentioned it before..
 
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Old 04-01-2011, 08:27 AM
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Application of silicone around the FPR diaphragm is not advised. You could hinder the operation of the FPR.
 

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