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Author
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Topic: fuel pressure dropping off.
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Duncan Motors
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Member # 7045
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customers car from another guys driveway build that i seem to be having to go over. trying to do a fuel pressure test at just turning the key to prime the gauge and it fall off immediately after hitting peak. two cylinders where fuel washed bad which started the engine rebuild and the vast amount of other things im having to go over,if im correct feul presure should hold for how long before falling off? wondering if i should pull plugs and see how many cylinders are yet with out cranking the motor except to just open the vavles.
Posts: 6310 | From: Vallejo | Registered: Sep 2006
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dean-93
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Member # 9401
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the intank rubber line from the pump to the fuel hat was cracked on a buddys car and it would only pull 20 psi and drop of immediately
Posts: 1175 | From: novato and fairfeild | Registered: Aug 2009
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Tom Renzo
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Member # 13165
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posted
Fuel pressure should hold for a couple of minutes. Could be a cracked in-tank line as posted above. Or the check valve in the pump. Pressure regulator diaphragm ar leaky injectors that you indicated flooded the cylinders. Hope this helps. Good luck sir
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I spend money i don't have. Building cars i don't need. To impress people i don't know.
Posts: 557 | From: CT | Registered: Sep 2013
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Duncan Motors
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Member # 7045
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there is a check vavle in the pump?
Posts: 6310 | From: Vallejo | Registered: Sep 2006
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Tom Renzo
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Member # 13165
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Bilt in to the pump.
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I spend money i don't have. Building cars i don't need. To impress people i don't know.
Posts: 557 | From: CT | Registered: Sep 2013
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JohnB
Tech Moderator
Member # 969
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posted
Bad fuel pump. The check valve is internal to the pump and maintains line pressure while cranking.
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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NK2186
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Member # 12319
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posted
the pump only kicks on for a moment when you turn the key to on. The pump is on full time when you crank the engine.
hotwire the pump i think you can do it from the self test diagnostic connector under the hood and then test for fuel pressure.
also check the two injectors for the cylinders that were fuel washed make sure the tips are good
[ 2014-05-11, 03:38 PM: Message edited by: NK2186 ]
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90 LX 5.0 - Stolen/stripped
89 LX 5.0 - Stolen and missing as of 7-24-13. LIC# 4HIP151 :(
99 Cobra
00 Exploder
Posts: 400 | From: Haystack | Registered: Aug 2012
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SacStangDriver
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Member # 8304
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does car not start immediately? if so if you hold pedal to floor(clear flood mode) does it start instantly? year make model?
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Need sidework done at great prices? I work on all makes and models from engine work to gears. Check engine light problems too. 916 912 3493
Posts: 1217 | From: sacramento | Registered: Mar 2008
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Duncan Motors
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Member # 7045
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posted
haven't got that far was just getting everything ready, fuel pressure, smoke test, rad pressure test, etc. i just realized fuel would drop almost drop immediately, its a brand new bbk 255 fuel pump, somebody told me they don't have the check valve in them anymore, any truth to this?
Posts: 6310 | From: Vallejo | Registered: Sep 2006
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Tom Renzo
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Member # 13165
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Never used a BBK but logic would tell me residual pressure would be a must for fast starts and to keep the fuel lines purged of air.Normally check valves are on all the electric pumps to accomplish this. Makes no sense for a pump not to have a check valve but as i said i never have used a BBK. I would be shocked if the pump did not have the valve.
Key pump run is also used to build pressure before a start. Normally it is programmed for a few seconds if engine is not started and pressure comes up fast.
[ 2014-05-15, 02:35 AM: Message edited by: Tom Renzo ]
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I spend money i don't have. Building cars i don't need. To impress people i don't know.
Posts: 557 | From: CT | Registered: Sep 2013
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Beastly GT500 TVS
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Member # 9723
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posted
What about the regulator
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91/E85 tune by SHAUN AT AED
700HP/700TQ ON E85
10.78@129MPH 1.644 60FT
WWW.AEDHP.COM
Posts: 893 | From: 707 | Registered: Jan 2010
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Secnd2nun64
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Member # 1431
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Cycle the fuel pump without cranking and then pull the spark plugs out of the cylinders that were washed down with fuel. You might have a couple injectors stuck open/ need replacing.
Posts: 1460 | From: CA | Registered: Jun 2002
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Duncan Motors
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Member # 7045
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posted
NEW REGULATOR, BBK USES A WALBRO PUMP, SO I DOUGHt THERES ANYTHING SPECIAL <sorry about the caps lock>in a bbk compared to others, i swapped all the injectors, 2 brand new sets, first set was by somebody else driveway skills, this last set is by trick flow right out the box, aeromotive regulator also right out the box, replacing the old aeormotive one lol. not sure what else besides the pump. u have to prime this thing 4 or 5 times to reach 40 psi. driveway certified guy changed in tank pump as well. thats where ill go now thanks for all the input tp everybody, i am over my head in garbage ive been straitening out on this car and just getting hot around the collar, again thanks for all teh input fellas, i very much apperciate it.
Posts: 6310 | From: Vallejo | Registered: Sep 2006
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Tom Renzo
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Member # 13165
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posted
Also try disconnecting the injectors. The ECM might be holding the injectors open.
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I spend money i don't have. Building cars i don't need. To impress people i don't know.
Posts: 557 | From: CT | Registered: Sep 2013
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NK2186
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Member # 12319
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It is possible the check valve is bad in the pump however I did not find much info regarding it having one or not.
What condition is the filter? A clogged filter can cause a lot of problems if it is really old. If it hasn't been replaced tell your customer it should be done (especially with new fuel system components)
Check the picture below and try testing the pumps fuel pressure with the fuel pump jumper in place as per the diagram. If pressure doesn't drop off pull the plugs on those cylinders that are getting fuel washed and see if any fuel comes out while the fuel pump is still on. If fuel comes out then you know where to troubleshoot.
http://forums.stangnet.com/attachment.php?attachmentid=40907&d=1134531771
Good luck!
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90 LX 5.0 - Stolen/stripped
89 LX 5.0 - Stolen and missing as of 7-24-13. LIC# 4HIP151 :(
99 Cobra
00 Exploder
Posts: 400 | From: Haystack | Registered: Aug 2012
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Tom Renzo
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Member # 13165
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posted
Personally i have never seen a fuel injected car that does not hold shut down residual pressure. You have to section off the system to trouble shoot this one. Injector leak down is a definite possibility. Good luck
[ 2014-05-15, 04:34 PM: Message edited by: Tom Renzo ]
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I spend money i don't have. Building cars i don't need. To impress people i don't know.
Posts: 557 | From: CT | Registered: Sep 2013
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Duncan Motors
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Member # 7045
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some very gd ideas just listed i wouldn't of though of thanks again im on it and will post the results thank u again.
Posts: 6310 | From: Vallejo | Registered: Sep 2006
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Duncan Motors
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Member # 7045
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posted
so checked everything out, it ended up being the areomotive fuel pressure regulator. funny that's two in a rox, under inspection of tearing down teh reg found a machining burr on the seat that the spring loaded ball rest against, so this isn't the only time ive seen one of these reg take a shit, im
over aeromotive now so whos makes makes flawless fuel stuff now? looking for boost reference with a 1 to 1 ratio???
Posts: 6310 | From: Vallejo | Registered: Sep 2006
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Beastly GT500 TVS
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Member # 9723
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posted
quote:
Originally posted by Duncan Motors:
so checked everything out, it ended up being the areomotive fuel pressure regulator. funny that's two in a rox, under inspection of tearing down teh reg found a machining burr on the seat that the spring loaded ball rest against, so this isn't the only time ive seen one of these reg take a shit, im
over aeromotive now so whos makes makes flawless fuel stuff now? looking for boost reference with a 1 to 1 ratio???
makes sense it was the Regulator
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91/E85 tune by SHAUN AT AED
700HP/700TQ ON E85
10.78@129MPH 1.644 60FT
WWW.AEDHP.COM
Posts: 893 | From: 707 | Registered: Jan 2010
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