Elroy Jetson Posted February 21, 2007 Share Posted February 21, 2007 Is the fuel pump on the GL10 supposed to vary pressure with engine RPM? I always thought that the fuel pump was just an on/off deal. Mine puts out about 30 psi at idle and climbs steadily to about 50psi at 5k revs. That is with the reading before the pressure regulator, of course. Wayne Link to comment Share on other sites More sharing options...
Cougar Posted February 21, 2007 Share Posted February 21, 2007 I believe the pump pressure should normally be around 50 psi, with fuel injection anyways. I think the lower pressure you seeing may be due to low voltage at the pump when the engine is idling. I would check the voltage at the battery and the alternator to see if there is a difference between the two readings. The alternator may have a output problem or the belt is slipping so you can check that also. Link to comment Share on other sites More sharing options...
Roger87ea82t Posted February 21, 2007 Share Posted February 21, 2007 Is the fuel pump on the GL10 supposed to vary pressure with engine RPM? I always thought that the fuel pump was just an on/off deal. Mine puts out about 30 psi at idle and climbs steadily to about 50psi at 5k revs. That is with the reading before the pressure regulator, of course. Wayne The fuel pressure will vary with engine vaccum. The specifications are 26 -32psi at idle with the vaccum hose attatched to the pressure regulator and 30 -36psi with the vaccum hose disconnected at idle. This is for MPFI systems.......Roger Link to comment Share on other sites More sharing options...
daeron Posted February 22, 2007 Share Posted February 22, 2007 Is the fuel pump on the GL10 supposed to vary pressure with engine RPM? I always thought that the fuel pump was just an on/off deal. Mine puts out about 30 psi at idle and climbs steadily to about 50psi at 5k revs. That is with the reading before the pressure regulator, of course. Wayne The pressure that the fuel pump puts out, is largely irrelevant. it needs to be a specific percentage higher than the car wants.. The pressure regulator uses intake vacuum to ensure a steady pressure of XX PSI in the fuel rail (i dont have a turbo, so listen to Roger unless someone says he is wrong) The pressure regulator then sends back to the tank any excess fuel, in order to maintain that pressure in the fuel rail. As long as your fuel pressure in the rail is staying consistent, you should be OK. This scenario may well be one that might lead to failure of the pressur regulator quicker than ordinary, but I have never heard any info on what people's fuel pressure readings are BEFORE the regulator.. so who knows. As far as I know, it may be perfectly normal for your 50PSI fuel pump to put out pressure varying with voltage/current being received.... Try your pressure gauge on the fuel rail, AFTER the regulator, and see what you get. That number is much more important to the running of the engine. Link to comment Share on other sites More sharing options...
Roger87ea82t Posted February 22, 2007 Share Posted February 22, 2007 On MPFI the fuel pressure is the same from the fuel pump to the injectors. The pressure regulator is like a valve that bleeds off the pressure from the system and returns it to the tank. There are 2 ways to enrichen the fuel mixture on the MPFI. One is have the injector stay open longer, spraying more fuel into the cylinder. That is controlled by the TPS, MAF and the computer. The other way is to increase the fuel pressure so more fuel will pass through the injector for a given time. That is contolled by the pressure regulator which is controlled by engine vaccum. On my turbo wagon the pressure would run from 30 - 45psi depending on how much you are accellerating.........Roger Link to comment Share on other sites More sharing options...
Skip Posted February 22, 2007 Share Posted February 22, 2007 If I may be so bold, I would like to add to Rodger's excellent explaination. " The pressure regulator is like a (relief)valve that bleeds off the pressure from the system and returns it to the tank." This regulator is positioned after the fuel rails thus maintaining the pressure above the injectors. "On my turbo wagon the pressure would run from 30 - 45psi depending on how much you are" boosting, as the fuel rail pressure is a function (or measured from - if you will) the intake manifold pressure (as per the FSM*) As the boost pressure increase so does the fuel pressure above the injectors, thus keeping the mixture "fat" (also known as "rich"). This done in an effort to prevent detonation. During this time the ECU ignors the 02 sensor and relies on the FPR and PWM** of the injectors to keep it fat. An aftermarket RRFPR (Rising Rate Fuel Pressure Regulator differs in so much that the pressure increases at a rate that is higher than the factory increase. This follows what Rodger astutely points out in refernce to increasing the fuel injected from the injectors. Sorry if this make it as clear as chocolate milk. *Factory Service Manual ** Pulse Width Modulation Link to comment Share on other sites More sharing options...
Cougar Posted February 22, 2007 Share Posted February 22, 2007 This is interesting. I didn't realize the regulator was placed after the fuel rails. Thanks for the good info Skip and Roger. Link to comment Share on other sites More sharing options...
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