Another fuel pressure problem
08-14-2007, 09:05 AM
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Another fuel pressure problem
I have a fluctuating fuel pressure issue after boating for a few days this past week. This is on a 496mag HO with the Whipple supercharger kit. This includes an SX Performance (I think) electric fuel pump and a boost referenced fuel pressure regulator. I have a mechanical gauge plumbed directly to the fuel system. A couple of years ago I had a similar problem. The anti-siphon valve on one tank was allowing air into the line. First day out last week everything was running fine and the fuel pressure was rock steady.
Next day I noticed the fuel pressure had started to fluctuate occasionally. I would be runnning along at a steady 3000 rpm with the fuel pressure steady at 44 psi. Then it would occasionally flutuate between 35 and 44 for about 2 or 3 seconds and then hold steady again. The engine didn't hesitate or stumble. After this I paid closer attention. It would happen on either tank. I tried to push the boat a little to see what would happen. Approaching 4000 rpm or a little higher the pressure would climb to about 45 or 46 psi and then suddenly drop down to 30 and bounce between 45 and 30. I immediatly backed off the throttle. That evening I did a visual check on all the fittings and connection and couldn't see any obivious signs of a loose fitting. The next day was the same except that I noticed that the fuel pressure would fluctuate when coming on plane and then steady again. So I just ran the boat easy and avoided any hard running.
I'm thinking I have air getting into the system. I just wondered if anyone had any other thoughts before I start hanging upside down in the engine compartment for a few hours?
Next day I noticed the fuel pressure had started to fluctuate occasionally. I would be runnning along at a steady 3000 rpm with the fuel pressure steady at 44 psi. Then it would occasionally flutuate between 35 and 44 for about 2 or 3 seconds and then hold steady again. The engine didn't hesitate or stumble. After this I paid closer attention. It would happen on either tank. I tried to push the boat a little to see what would happen. Approaching 4000 rpm or a little higher the pressure would climb to about 45 or 46 psi and then suddenly drop down to 30 and bounce between 45 and 30. I immediatly backed off the throttle. That evening I did a visual check on all the fittings and connection and couldn't see any obivious signs of a loose fitting. The next day was the same except that I noticed that the fuel pressure would fluctuate when coming on plane and then steady again. So I just ran the boat easy and avoided any hard running.
I'm thinking I have air getting into the system. I just wondered if anyone had any other thoughts before I start hanging upside down in the engine compartment for a few hours?
Last edited by ComfortablyNumb; 08-14-2007 at 09:07 AM. Reason: grammar
08-14-2007, 11:27 AM
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You said it fluctuated coming plane that is a moment of heavy load. It could be many things. I think a good start would be the high pressure filter. Then I would check all fuel fittings starting at separator filter. remove inspect and loctite. It is possible to over tighten and crack aluminum pieces check carefully. You said it did it on both tanks so check selector valve. Air leak or obstruction can cause that problem. Check electrical connections on fuel pump.
Good Luck,
Jim
Good Luck,
Jim
08-14-2007, 01:51 PM
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Thank you for your advice Jim. I was able to check the electrical connections one evening and they looked solid. I didn't see any fluctuations in the volt meter when this would happen.
I was going to move along each fitting and filter forward from the tank selector and then bypass the selector for a test run.
I did put some gas in after the first day from my fuel cans. The very next run is when the pressure started fluctuating. I could have had some crap in the can but that seems odd because I always get my gas from the same station. But on a boat, with the pounding that they take, anything can happen.
thanks again
Pat
I was going to move along each fitting and filter forward from the tank selector and then bypass the selector for a test run.
I did put some gas in after the first day from my fuel cans. The very next run is when the pressure started fluctuating. I could have had some crap in the can but that seems odd because I always get my gas from the same station. But on a boat, with the pounding that they take, anything can happen.
thanks again
Pat
08-14-2007, 02:52 PM
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WHERE IS THE FUEL REGULATOR RETURN RUN TO. WE HAVE HAD A FEW RETURNED TO THE FUEL WATER SEPERATOR AND UNDER HIGH LOAD (wot) THE PUMP WILL CAVATE THE FUEL AND THE AIR GOES THRU THE FILTER AGAIN AND THE PRESSURE DROPS.
08-14-2007, 03:28 PM
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Bingo. A good friend installed a whipple onto his 496HO last fall.(a former pro drag racer and engine builder W/ lots of experiance). Ran into the same problem.Could not get it to hold steady. Basically figured out the ruturn line that was being put back into the imco fuel filter/seperator was causing the problem. I have also seen this same problem with fuel injected off road cars as well. After he re-routed the return line to the tank,the fuel pressure was rock steady.
Darrell.
08-14-2007, 03:46 PM
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Jb-fse and DMOORE have a good point. The return to the tank is a better way. It may or may not be your problem. Merc took the simple route so rigging was easy when they decided to use their setup. The race injected motors use hi and low pressure pumps and catch cans in their fuel systems. Whether you return your fuel to the tank or to the separator you should still ensure you don't have any air leaks or obstructions.
They're many answers.
Good luck
Jim
They're many answers.
Good luck
Jim
08-14-2007, 05:05 PM
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I've got to take a look at the setup tonight. I do believe that the return line runs directly to the fuel filter/separater. But I've not had this problem the previous 2 summers. Everything has been steady.
I've also wondered about the fuel vaporizing in the system. In Denver we have ethanol in our gas. My trip was to a lake at 7500 feet in elevation. I know that sometimes our gas has more ethanol in it than allowed. Just a thought that I had. But I'm still going to check out everything.
Thanks for the good advice.
I've also wondered about the fuel vaporizing in the system. In Denver we have ethanol in our gas. My trip was to a lake at 7500 feet in elevation. I know that sometimes our gas has more ethanol in it than allowed. Just a thought that I had. But I'm still going to check out everything.
Thanks for the good advice.
08-14-2007, 06:38 PM
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I'm mistaken, on my setup the return line first runs to the Whipple supplied fuel cooler and then to the factory filter/separater.
Last edited by ComfortablyNumb; 08-14-2007 at 06:38 PM. Reason: spelling worse than usual
08-14-2007, 07:49 PM
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I have the same setup as you and have noticed some fluctuating from time to time. I would like to return the fuel to the tank but am not sure how to do it, there are two tanks.
08-14-2007, 08:29 PM
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If you are going to return to the tanks, it should be to the top of the tank. One way would be to have a fitting made to tap in the fill lines. If you tee the return and balance the length and rise of hose they should feed evenly.
Jim
Jim
