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Old 08-21-2014, 07:35 PM   #1 (permalink)
ericgarvin
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Fuel cap

After replacing with a new diesel cap I am still getting a noticeable whoosh when I open the fuel cap. Is there a modification to the cap itself to fix this issue. Or is there something wrong with the venting system?


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Old 08-21-2014, 07:45 PM   #2 (permalink)
Glagulator
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The cap is the venting system. I drill a tiny hole in the cap to bypass the valve and never worry about it again. Hole is on the inside and does not exit the exterior part.
I had a stuck cap collapse the fuel tank, on vacation of course.

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95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine & main harness, converted to OBD2, PMD to bumper...
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Old 08-22-2014, 12:25 AM   #3 (permalink)
Bison
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There is a small rubber valve on the underside in the cap, just remove it.
I did that on all my trucks.
The black top of the cap snaps over the white insert and can be separated by prying the tabs in the cap away to the outside one at the time and lifting up on the insert.
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98 GMC 2500 hd sle 6.5td ext cab l box 4x4 auto 4.10 difs 268000 km. HOME REBUILD ENGINE at 268.000 km,currently 307.000
Removed CDR an installed PROVENT CRANK CASE OIL SEPERATOR/VENTILATION VALVE,3 1/2" straight pipe.
PMD heatsink relocated to inside air stream in pass fender between batt and air filter.PMD is easely accessable.
Other mods, to nummerous to mention.
95 GMC SL 2500 6.5td ext cab sh box auto, 409.000 km,CDR vented to atmosfeer at 307 k, remote pmd, extra glow bypass/LP test switch, relocated OPS ,in cab fuel gauge .High idle switch,new paint.Foot dimmer swich for simultaniously high/low beam. The Wife's pride and joy.
89 GMC 2500 sle 4x4 ext cab 6.2 na stock 740000+ km, engine rebuilt at 660000 km, rusting out now, but runs like new.
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Old 08-22-2014, 11:08 AM   #4 (permalink)
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Quote:
Originally Posted by Glagulator View Post
The cap is the venting system. I drill a tiny hole in the cap to bypass the valve and never worry about it again. Hole is on the inside and does not exit the exterior part.
I had a stuck cap collapse the fuel tank, on vacation of course.
That is what I did too. No more worries.
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Old 08-22-2014, 12:58 PM   #5 (permalink)
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Does it matter exactly where to drill hole or anywhere on the inside part?
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Old 08-22-2014, 01:14 PM   #6 (permalink)
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This works. Hole could be smaller, that bit was already in the drill.

FuelCapMod.jpg
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99 CREW LONG SRW C3500 work truck 199k+ mi. orig. motor & trans 4.10, modded engine harness, new oil cooler & lines, all new front end parts and poly bushings, trans poly mount, all new brakes.
96 SUBURBAN K2500 wife's truck 210k+ mi. orig. motor & trans, 3.73...
95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine & main harness, converted to OBD2, PMD to bumper...
95 C1500 Suburban 6.5td rebuild tranny, convert to DB2, replacing as many parts as I can.
96 C2500 Suburban 7.4L converting to 6.5td w/ DB2, 4L80, 3.73
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Old 08-22-2014, 03:22 PM   #7 (permalink)
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Thanks exactly what I wanted!
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94 C2500 Suburban, vin F, 06' 10.5 AAM axle swap w/4.10's & disc brakes, PMD in bumper, Batt Ter mod SS, K47/snorkel delete, HX40/ATA CAC , 2.5" x-over, 4" Diamond Eye, AC delco OPS & OPS mod, FTB (drilled out IP fitting), FRC10 w/dual filters, tank sock delete, LS oil cooler lines, FD and pulley 11/14, 2k year waterpump, 2k fan, modded Hayden fan clutch, Teds injectors, Bosch GP,GS Trans/EGT/Boost gauges, TCC lock mod, aux trans cooler, Buddy's 6 gun tune, 2" lift w/285/75/16 on stock dmax wheels, 240k and counting. GONE BUT DEARLY MISSED!
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Old 08-23-2014, 02:44 PM   #8 (permalink)
Steve83
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Why does everyone care about a little noise enough to risk fuel contamination??? It's not like the fuel is so full when you take the cap off that it could spray out - the tank is nearly empty, and it vents while you're unscrewing the cap.
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Old 08-23-2014, 02:54 PM   #9 (permalink)
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Quote:
Originally Posted by Steve83 View Post
Why does everyone care about a little noise enough to risk fuel contamination??? It's not like the fuel is so full when you take the cap off that it could spray out - the tank is nearly empty, and it vents while you're unscrewing the cap.
See glagulators post #2. It also allows the fuel pumps to function more efficiently.
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94 Suburban 2500 4x4 F vin 149k and ticking
Claymore grille ornament
Fan clutch mod to fix overheating problem
OPS mod
Straight factory piped weed burner
Snorkel lobotomy
Walbro frc10 and pre-LP filter(bypassed for now)
Upper intake web removed
Dorman lifetime PMD w/#9 resistor relocated behind the front license plate
Battery terminal mod
50+ cetane diesel from Southern States
Fuel filter/manager raised 8"
Boost gauge
otherwise pretty much stock
2015 F250 crew cab long bed 6.7 powerstroke
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Old 08-23-2014, 03:00 PM   #10 (permalink)
Bison
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Quote:
Originally Posted by Steve83 View Post
Why does everyone care about a little noise enough to risk fuel contamination??? It's not like the fuel is so full when you take the cap off that it could spray out - the tank is nearly empty, and it vents while you're unscrewing the cap.
It's not the fuel contamination, it is excess vacuum you have to worry about.
Excess tank vacuum is hard on the IP and the LP and can cause a tank to collapse.

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98 GMC 2500 hd sle 6.5td ext cab l box 4x4 auto 4.10 difs 268000 km. HOME REBUILD ENGINE at 268.000 km,currently 307.000
Removed CDR an installed PROVENT CRANK CASE OIL SEPERATOR/VENTILATION VALVE,3 1/2" straight pipe.
PMD heatsink relocated to inside air stream in pass fender between batt and air filter.PMD is easely accessable.
Other mods, to nummerous to mention.
95 GMC SL 2500 6.5td ext cab sh box auto, 409.000 km,CDR vented to atmosfeer at 307 k, remote pmd, extra glow bypass/LP test switch, relocated OPS ,in cab fuel gauge .High idle switch,new paint.Foot dimmer swich for simultaniously high/low beam. The Wife's pride and joy.
89 GMC 2500 sle 4x4 ext cab 6.2 na stock 740000+ km, engine rebuilt at 660000 km, rusting out now, but runs like new.
Waldon Wheelloader repowered with 6.2 na.
3 tractors dsl ,72 AC 940 whj loader,ASV 4810 Positrack skidsteer
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