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Old 05-29-2003, 12:01 PM
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Post Fuel Pressure

I didn`t have much faith left in my fuel pressure gauge, so I ordered a new one, a liquid filled job, I installed it, and set the pressure at the regulator at 4 psi, I set the floats and idle mixture, it ran great, although i didn`t take it down the road, i came in to make some calls, let it cool off, then went outside to check it again, fired it up and let it idle, fuel pressure said 7 psi and it would barely idle, the fuel level in the bowl went to over the top of the glass site, so again, I set the pressure at 4 psi, reset the floats, reset the idle mixture, it ran great again, I took it down the road 2 miles, then came back, it ran fine, got in the driveway and the idle starts to flucuate, up and down, I get out and check the fuel pressure, it was at 2 psi, so again, I set it at 4, reset the floats, and reset the idle, what`s going on with this thing? I can`t get the fuel pressure to stabilize, and it`s causing all this havoc with idle mixture and float levels, it`s been going on a while now, and the new gauge brought to life what the problem was finally, but now I need to figure out how to get past it, I`m running a stock pump with return line, a holley regulator, and a demon carb. if it`s any help I have the carbon canister vapor line left open, should I seal it up so the tank can hold pressure? the gas tank used to always hold pressure, i installed a pump with no return line and the pressure was building up and overcoming the needle after I shut the car off resulting in a major flood. so I installed the pump with return line and left the vapor line open, is this the problem? when the car had the stock engine it always held pressure, do GM cars require this? it`s a 86 cutlass supreme. any help would be appreciated.
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Old 05-29-2003, 12:18 PM
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DV, I'm going to be of no help on this one, but I know what you are going through because the same exact thing was happening with my brother's 350 (also had a deamon on it). I just kept reseting everything everytime the bowls would flood. The weird thing about it is it hasn't happened in about 5 months. Don't know what was causing it or what fixed it. It just doesn't happen any more. Hope you get some help in here...I'd like to know what people have to say.
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Old 05-29-2003, 12:24 PM
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I had the same problem on my car and I had to replace the regulator. I believe the Holley regulators are rebuildable, but I just went ahead and put on a new one.

I have always made sure that my tanks were vented and did not build up any pressure or vacuum.

Dean
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Old 05-29-2003, 12:48 PM
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yeah I forgot to add the regulator I just installed a rebuild kit in about 2 weeks ago, I don`t like Holley products, mostly because there lack of quality control, the first regulator I ordered didn`t work, I sent it back and got another, it didn`t work, this one worked until the seal started leaking, and that`s why I got the rebuild kit. if I remove the regulator, the fuel pressure is 14 psi, I`ve been down this road for a long time, the first SBC I ran in the car had no fuel pressure problems at all, I removed it and installed another 350, that`s when all hell broke loose, the fuel pressure hit the roof and the only difference in this engine from the last was the cam, everything else was the same. I swapped pumps, carbs, fuel pump rods, nothing did any good, last thing I did was install a Crane cam in place of the comp cam and added the new demon, it ran fine with no regulator, and no flooding problems, then about a month ago it wouldn`t hold a idle, then I found out the fuel pressure was going hay wire again, so the regulator went back on, and now this, I`ve never had so many fuel pressure problems in my life. I did install a carter electric pump on it, and ran it with the regulator, but I decided it had to go, the constant hum of the pump running drove me nuts. there seems to be no reason why this happens, 2 of my friends have a cutlass with a SBC, neither have this problem. so I`m at just as much a loss on this one as yall are, and to top it off, i`ve spent hundreds of dollars trying to cure it, and there don`t seem to be one.

[ May 29, 2003: Message edited by: DoubleVision ]</p>
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Old 05-29-2003, 05:45 PM
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Ok update. I ran the car some more, everytime I let it cool, restart and check the fuel pressure, it`s never where I left it, I can set the regulator down to where the gauge says zero and rev the hell out of the car and it`ll refill the bowl right back where it was. I can`t set the primary float level either, if the fuel level is at the bottom of the sight window, I can turn the adjustment not even a quarter turn, the fuel level will go over the sight window, so i took the demon apart, but I didn`t see anything in the bowl or anything wrong with the needle and seat, except I believe most needles have a small piece of rubber on the tip to seal it, this one does not appear to have one, so i`m wondering when I had the excessive fuel pressure problem I likely blew the piece of rubber off like I did countless holley`s and Q-jets. so I guess it`s back to the old drawing board, I wanna just set fire to this thing it`s been so many headaches.
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Old 05-30-2003, 12:16 AM
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Wish I could help on that carb problem, but it's out of my league. I'd have shot it a while back. As far as vapor line is concerned, I've had a cigarette butt in mine since 1972.
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Old 05-30-2003, 05:13 AM
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Usually when I have a problem like this, I like to go back to the orginal setup or a known setup that works. If it were me, I would ditch the canister and the return line. Then get a bone stock fuel pump with no return or canister vapor line. Also get rid of th regulator.

It seems like you may have several problems to me. If you are getting 14 psi, it is not a stock pump obviously, or it is defective. It is possible that the vent is plugged on the pump or regulator causing one of them not to regulate properly. Also, you should not have to reset the floats at all once they are set. I dont understand why you keep resetting them. If there is no fuel after they are set, they are being starved.

Maybe some of this rambling will trigger something to help you figure it out. It is hard to trouble shoot something I cant see or get my hands on, but I am betting it is something small.

Chris
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Old 05-30-2003, 06:21 AM
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There are aftermarket higher pressure needle jets for what you need to control the fuel pressure, plus their made of a different rubber base material.
This place has a great price on rebuild kits that have them.
http://www.cnc-motorsports.com/default.asp

[ May 30, 2003: Message edited by: 1BAD80 ]</p>
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Old 05-30-2003, 06:45 AM
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I would still bet that your problem is with the regulator, or the pump. The regulator is supposed to "regulate" the fuel pressure so that it remains steady at whatever you set it at right? But what gets me is you have had this problem with more than one regulator.

If the pump isn't putting out a consistent pressure itself, then I'm sure the regulator would not be able to maintain a constant pressure. This could be due to a faulty pump, trash/water in the fuel system, or maybe some wierd tank venting problem. I guess you could even have a problem with the pick-up tube in the tank or some of the rubber lines back at the tank.

You may want to try a new set of viton tip needle and seat assemblies too. I have never seen the tips come off a needle, but it's possible. Keep us posted.

Dean
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Old 05-30-2003, 06:55 AM
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Hey DV what pump are you using anyway? You probably mentioned it in an earlier post but could you refresh our memory?
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Old 05-30-2003, 07:06 AM
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I know this is rather elementary, and I'm not sure if I saw it mentioned in your post or not, but have you checked the fuel filter? I would inspect both it and the supply lines for clogs. I guess I'm lucky that the fuel supply on my vette is still a pretty simple process.
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Old 05-30-2003, 10:56 AM
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The pumps I`ve tried are bone stock pumps. They all came from advance auto parts, the first pump fits a 1979 camaro Z28, I used this pump since I installed the first small block years ago, I used it again on the small block that`s in it now, when this problem came about, I got another pump from a friend, it did the same thing, I went and got a new pump with no return lines, for a 75 chevy truck, I tried it, same problem, any mechanical pump I`ve tried be it new or used, they all do the same thing. I`ve blown the rubber tips off many needle and seat assemblies, 2 Q-jet needles and 1 holley. I`ve spoken to many tech lines, carb shops, all to no avail, no one seems to have the answer to this, and there is no reason why it should be doing this, I left everything the same when I did the engine swap, I didn`t modify the fuel system in any way. as for filters, I`m running 2, and there both new, one by the tank, and one off the fuel pump. If I run the pump without a return line, fuel pressure is controlled decently by the regulator, until I shut it off, then it overcomes the needle and seat, I can watch it rise above the sight plug when i shut the car off, and according to all the tech lines I`ve spoke to about this, they all say it`s not suppose to have pressure after it`s shut off. Believe me, I`ve spent countless hours of time trying to figure this one out, and I`ve spent hundreds of dollars, I`m sure over $1000 by now, just trying to solve this problem. the real kicker is, when I first got the new cam and the new carb, It didn`t have this problem, I thought for sure the lobe on the comp cam was bum, being it was the only part I didn`t reuse during the rebuild. I can start the car and watch the fuel inlet line going to the pump, the line moves everytime it pumps, it`s as if it`s being opened way further than a normal one would be. I had a hunch that maybe the cam bearings are bad, and the cam has too much side load causeing the problem, but the bearings are new, and I checked them when I installed the new cam, there was no slop and no visable wear, so I thought maybe one or two of them maybe out of round, I just don`t know, all I know is, I`m sick of this thing acting the way it does for no reason that I`ve found yet.
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Old 05-30-2003, 11:44 AM
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could it be something to do with the venting of the fuel tank cap or the vent lines from the fuel tank itself. Perhaps there's pressure building in the tank that is only being released at the carb end. As a test maybe run it without a gas cap to see where the level goes.
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Old 05-30-2003, 02:50 PM
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[quote]Originally posted by engineczar:
<strong>could it be something to do with the venting of the fuel tank cap or the vent lines from the fuel tank itself. Perhaps there's pressure building in the tank that is only being released at the carb end. As a test maybe run it without a gas cap to see where the level goes.</strong><hr></blockquote>

I had the same thought. Especially since it builds pressure after killing the engine.

Chris
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Old 05-30-2003, 03:17 PM
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I just swapped back over to the non return line fuel pump, set the pressure at 4 1/2 psi, left the return line and vent line open, I also removed the gas cap. I took it down the road, it ran great, was nice and throttle responsive, idles good, I got back here and got out and checked the pressure, it had dropped to 3 1/2 psi, I left it like that, now letting it cool off to see what the pressure will be when I restart, however, I did notice when I shut the car off, the gauge held 3 1/2 pressure, for about 30 seconds, then slowly sank down to zero, I checked the floats to make sure it didn`t flood the carb, neither level rose at the carb, so i "think" it`s fixed, but next I will buy a new gas cap, and see if it helps any, I`m starting to think I got some stopped up lines somewhere, as I tried to blow thru the vapor line and couldn`t, think i`m gonna check back over them real closely again, as last time I blew thru them with air, they were okay, but not this time. thanks guys.
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