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#1 |
![]() Join Date: Apr 2004
Location: ATL. GA.
Posts: 2,170
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Just a quick ? On removal of the fuel cap on the 93 I get a lot of pressure release. Normal? I ask as I get very little on the 91. Do I have an issue with the evap system? Would to much pressure cause a rich idle?
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Steve 1990 Steel Blue/Black #2355 1990 Red/Red #1473 1991 Quasar /Black #118 Sold 1991 Turquoise/Black #766 Parted Out 1993 Yellow/White #179 Sold 1990 Black/Gray #1361 Headers/4:10s Sold |
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#2 |
![]() Join Date: Feb 2011
Location: San Marcos CA
Posts: 1,802
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It only takes about 3-4 seconds to vent the fuel tank pressure through the purge solenoid so it won't enrichen the idle for all practical purposes. If you still have a stock exhaust, you can sometimes hear the hiss if things are just right.
I would have to review info in the FSM, but I don't think the purge lasts very long, just during the engine start-up to suck the vapors out of the charcoal canister and the top of the tank. I think it may turn on during lean cruise- or maybe a small duty cycle on/off as a controlled vacuum leak, but I can't say for sure on the obd1 GM cars, but some of the emissions stuff is pretty interesting. |
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#3 |
![]() Join Date: Apr 2004
Location: ATL. GA.
Posts: 2,170
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When I remove to fuel cap regardless of fuel level after a drive I get a noticeable whoosh of air. Just want to be sure the system is working properly.
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Steve 1990 Steel Blue/Black #2355 1990 Red/Red #1473 1991 Quasar /Black #118 Sold 1991 Turquoise/Black #766 Parted Out 1993 Yellow/White #179 Sold 1990 Black/Gray #1361 Headers/4:10s Sold |
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#4 |
![]() Join Date: Nov 2013
Location: Jacksonville, NC
Posts: 48
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My 95 has a lot of pressure as well when I remove the fuel cap, interested to see if this means anything?
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#5 |
![]() Join Date: Jan 2009
Location: Portland Oregon metro area (Washington side)
Posts: 3,207
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only thing I could find on gas cap pressure testing wast this from the EPA. It seems to allow for a certain amount of leakage.
Are people seeing a true pressure build up OR a vacuum build up? Gas Cap Test (1) Cap Installation. The fuel cap, or caps, shall be removed from the fuel inlet(s) and installed on a portable or bench test rig using the adapter appropriate for the gas cap as specified in §85.2227(d)(1)(ii). (2) Leak Measurement. The gas cap leak rate shall be measured and compared against a 60 cc/min at 30 in. WC flow standard. Pressure decay measurement using instruments with a 1 liter head space shall be made from an initial pressure of 28 in. WC and be compared against a loss of 6 in. WC in 10 seconds. (3) Cap Replacement. The fuel cap(s) shall be replaced on the fuel inlet and tightened appropriately.
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Scott ![]() Vett owner since 1979._It's about the car and the people |
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#6 | |
![]() Join Date: Apr 2004
Location: ATL. GA.
Posts: 2,170
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![]() Quote:
Found the same info. There are a few posts over on the other site but no definitive answer.
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Steve 1990 Steel Blue/Black #2355 1990 Red/Red #1473 1991 Quasar /Black #118 Sold 1991 Turquoise/Black #766 Parted Out 1993 Yellow/White #179 Sold 1990 Black/Gray #1361 Headers/4:10s Sold |
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#7 | |
Join Date: Dec 2012
Location: NC
Posts: 1,786
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Makes me think that tank angle, and gaseous pressure increase, forces fuel through the EVAP line, instead of just vapors... (I keep the tank full too). On LT1 top end rebuild, I was greeted on second day by steady drip of fuel from disconnected lines, whereas it was NOT dripping shortly after dis-connecting the first day.
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I'm getting my snappics / threads removed blindly as fast as I can, to get in compliance with copyright / license TOS on the boards here (lots of FSM pages and other copyright / license violations on my part; sorry guys). And thanks to all the guys who didn't whine when I posted those FSM copyrighted / licensed stuff in my threads... ( :thumbsup: [b]and to think I complied with a mod's request to delete a pic of him in a Challenge Car in NCM Museum, so he wouldn't get in hot water)[/b] Thanks to several guys here for sending parts FREE; BearlyFlying, WeGone, Geezer, GoldCylon, and more there, TonyD, mike100, fletchusmc... 1990 #2794; 4L60e Stage V by RPM Transmission, TCI Dedicated TCM, OBX Stainless, Power Effects 3" [IMG]https://lh5.googleusercontent.com/-GHpfzty7DVU/UQn-0Ru2xAI/AAAAAAAAA14/08mz1p4QLD4/s445/Screenshot-5.png[/IMG] Last edited by Schrade; 04-17-2014 at 02:23 PM. |
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#8 |
![]() Join Date: Apr 2007
Location: Lake Bluff, IL
Posts: 2,067
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Mine too. Seems like pressure, not vac. --Bob
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2016 Long Beach Red Z06 #10281 "POPS Z" 1995 Polo Green #409 "WARP TEN"--Haibeck 350/510 package, 4.10s, Hurst, Stock Exhaust with QTP Cutouts --Sold but still running strong 1993 Quasar Blue #161 "HIL KING" --Sold but still running strong, now with more than 120,000 miles 1967 Marlboro Maroon/Saddle Corvette Coupe 300 hp/4-spd --Sold a long time ago ZR-1 Net Registry Founding Member #95 NCM Lifetime Member Favorite Quote--Attributed to Mickey Thompson: "Too Much Horsepower is Almost Enough" |
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#9 |
![]() Join Date: Jan 2009
Location: Portland Oregon metro area (Washington side)
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Well, I don't get a pressure build up on mine. Maybe it's time to visit the FSM at page 6E3-C3-2.
At the bottom it speaks to "FUEL TANK PRESSURE CONTROL VALVE" and on subsequent pages shows that valve, operation theory and the Evaporative Emissions Control System Schematic. Maybe the fuel tank vapor pressure is not getting relieved?
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Scott ![]() Vett owner since 1979._It's about the car and the people |
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#10 | |
Join Date: Dec 2012
Location: NC
Posts: 1,786
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What if the purge of vapors was CONTINOUS? That's something I always thought on, when I spent $300.00+ / day, keeping a small delivery fleet rolling (@ $1.79 / gal). One night, I was talking about that with the Ops Manager, when the line hauler was late. He told a story about a friend who devised something like that with a carb'ed car late '70's, who then submitted it to one of the big 3. He said shortly afterward, his friend disappeared. He said he got a letter from his friend several years later, from Canada, who was doing 'very well', after signing something, and then getting a big check... Only some safety mechanism is necessary, to prevent a mis-fire from lighting up the tank...
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I'm getting my snappics / threads removed blindly as fast as I can, to get in compliance with copyright / license TOS on the boards here (lots of FSM pages and other copyright / license violations on my part; sorry guys). And thanks to all the guys who didn't whine when I posted those FSM copyrighted / licensed stuff in my threads... ( :thumbsup: [b]and to think I complied with a mod's request to delete a pic of him in a Challenge Car in NCM Museum, so he wouldn't get in hot water)[/b] Thanks to several guys here for sending parts FREE; BearlyFlying, WeGone, Geezer, GoldCylon, and more there, TonyD, mike100, fletchusmc... 1990 #2794; 4L60e Stage V by RPM Transmission, TCI Dedicated TCM, OBX Stainless, Power Effects 3" [IMG]https://lh5.googleusercontent.com/-GHpfzty7DVU/UQn-0Ru2xAI/AAAAAAAAA14/08mz1p4QLD4/s445/Screenshot-5.png[/IMG] |
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