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No fuel pressure and Dry Primary bowl |
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tmancusi
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Joined: Apr/25/2009 Location: WI Status: Offline Points: 395 |
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Topic: No fuel pressure and Dry Primary bowlPosted: Jun/08/2012 at 8:32pm |
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I'm really confused on this one. I seem to have a fuel problem. The car is a '68 390 AMX with a Big solid cam, torker intake, ProForm 750 Mech Secondary carb, electric fuel pump, fuel regulator, serviceable 8" fuel filter mounted under the trunk, 12 gallon fuel cell. Was running fine 2 weeks ago. Motor has around 100 miles on the rebuild. Then she started running really rough and wouldn't hold an idle. Then it killed on me last week and wouldn't start. Thinking it may be bad gas, I filled up with some racing gas and isopropyl. Seemed to be getting better. I thought the bad gasoline was now working it's way out. Today drove to work and back, won't hold an idle. Have to do the old put it in neutral and keep foot on gas to keep from stalling. For the trip home I adjusted the idle to 1200 rpms, that got me back. Anything lower and it stalls.
Here's where it gets really strange. Fired it up to poke around (at least it starts), cranked the idle back up and my fuel pressure gauge shows Zero pressure. My primary float bowl started out with some gas, but dried up as it ran. Again, as long as the RPM's are above 1200, it keeps running. Not great but doesn't sound horrible either. Has anyone come across a problem like this? Thanks for the help. This is while the car is at 1600 rpms: Here is the primary float bowl empty while running: And the secondary float bowl full: Edited by tmancusi - Jun/08/2012 at 8:35pm |
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'68 AMX 390 4-Speed
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17tamx
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Joined: Dec/23/2008 Location: Peoria, AZ Status: Offline Points: 1122 |
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Posted: Jun/08/2012 at 9:24pm |
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Start at your electric fuel pump and disconnet the out-put line so you can run the fuel into a clean container. This will let you look at flow so you can see if it is a pump problem or a regulator problem. If flow is good see if it is making good deadhead pressure. If no deadhead pressure the check valve in the pump may be stuck open. If the deadhead pressure is good than re-connect and then check your fuel flow after the pressure. This sounds like it is a deadhead problem or a fuel pressure regulator problem to me.
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Kirk P. Fletcher
70 AMX BBG w/Shadow 390 4sp 71 SC360 Wild Plum Ram Air 4sp 67 Rogue Convert 343 4sp 66 Rogue Hardtop 290 Auto 66 440 Convert 232 Auto |
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tmancusi
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Joined: Apr/25/2009 Location: WI Status: Offline Points: 395 |
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Posted: Jun/09/2012 at 4:15pm |
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Thanks for the advice. I'm going to try and get on it tomorrow. Otherwise I'll be in Florida until the 21st so it unfortunately might have to wait 'till then. I'll keep things posted.
Just want to say thanks again for this forum. It's really fantastic having access to the expertise and experience of this great group of guys who care enough about our hobby to help out people they've never even met. Edited by tmancusi - Jun/09/2012 at 4:16pm |
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'68 AMX 390 4-Speed
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FuzzFace2
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Joined: Jul/05/2007 Location: Connecticut Status: Offline Points: 6374 |
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Posted: Jun/10/2012 at 11:54am |
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Now I know why you thought it could be the filter. What Kirk posted is good info.
Good luck
Dave ----
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75 GremlinX v8
76 GremlinX i6 (sons) 70 Javelin SST 390/4sp (360/5sp now) 70 Javelin 1/4 Drag car 360/auto |
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blaine H
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Joined: Feb/24/2012 Location: Bethlehem, Pa Status: Offline Points: 15 |
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Posted: Jun/10/2012 at 7:08pm |
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Check the power valve - may be ruptured or gasket not seated right. Raw gas may be flowing right past it not letting the bowl fill.
blaine
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tmancusi
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Joined: Apr/25/2009 Location: WI Status: Offline Points: 395 |
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Posted: Jun/10/2012 at 10:42pm |
Will do. I wasn't able to get to it today...free time was spent replacing an AC sensor in my 2000 Xterra. At least that seems to be fixed. I did just now take a quick peek. Haven't run the car since Friday and the primary bowls were dry at that time. Tonight, they are half full. Does that mean anything? Thanks. |
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'68 AMX 390 4-Speed
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FuzzFace2
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Posted: Jun/10/2012 at 11:50pm |
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Power valve could be an issue why it does not idle but not why the bowl will not fill. If that was the case you would hydro lock the motor with that amount of fuel going down the intake and not fill the carb.
I would still start at the back and find out why no psi on the gauge. Once that is fixed you can then deal with carb issues.
Dave ----
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75 GremlinX v8
76 GremlinX i6 (sons) 70 Javelin SST 390/4sp (360/5sp now) 70 Javelin 1/4 Drag car 360/auto |
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tmancusi
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Posted: Jun/11/2012 at 9:52pm |
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What is the correct fuel pressure?
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'68 AMX 390 4-Speed
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PHAT69AMX
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Joined: Jul/07/2007 Location: SW Ohio Status: Offline Points: 2810 |
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Posted: Jun/11/2012 at 11:08pm |
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6 psi for a Holley type carburetor is the recommended fuel pressure.
If the primary float is not closing off the needle it will not build any pressure.
Sure sounds like the primary fuel bowl is dumping fuel into the intake
as fast as the gas is coming in through the needle and seat.
Agree a ruptured power valve diaphram as a possible culprit. Edited by PHAT69AMX - Jun/11/2012 at 11:15pm |
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FuzzFace2
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Posted: Jun/11/2012 at 11:25pm |
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Ok at 6psi how much GPH or GPM fuel is that? I still think you would hydro lock the motor if you were to flow that fuel right into the intake.
Have you opened out the secondaries to use up the fuel in that bowl if not it will sit there it the cows come home.
Dave ----
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75 GremlinX v8
76 GremlinX i6 (sons) 70 Javelin SST 390/4sp (360/5sp now) 70 Javelin 1/4 Drag car 360/auto |
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