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Carhelp4u, Pontiac Technician
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Experience:  ASE Certification
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1996 bonneville: 3.8l..installed a fuel pressure gauge..injector rail

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I have a 1996 Bonneville 3.8l engine with a serious fuel problem(I believe). I have installed a fuel pressure gauge in order to try to trouble shoot the events. The engine will start and the fuel pressure on the injector rail. Here is where the problem shows up.I can drive about a mile but not try to accelerate. To ad throttle.the engine begins to surg, holding throttle will cause the engine to stop running. If I let off on the throttle the engine will continue to run at an idle. Checking the fuel rail pressure has dropped to 10-15 psi. The engine will continue to idle but will die if I ad throttle.If I do this I can see the fuel rail pressure drop to 0 psi the engine stops.
Is this a supercharged engine? Have you replaced any items at this point? What is the initial pressure reading of this fuel system upon start up? Are you getting any check engine lights?
Customer: replied 7 years ago.

This is not a supercharged engine have not replaced any items the fuel rail pressure is at48 to 50 psi at the start mode.It will contiue to idle but I notice a slite flikker on the pressure gauge but remains at over 42 psi. A road test will show the engine drops to idle setting. I can get it home on idle but cannot accelerate. Holding throttle pressure will kill the engine and checking fuel rail pressure will be at 10-15psi .The engine will continue to idle at the low fuel rail pressure but I haven't timed for how long.If I kill the engine, leave the ignition switch in the run possition, fuel pressure will not return to the fuel rail, turning the ignition switch off then on the fuel rail does not pressurize. going to crank start the fuel pressure will go to 50 psi. The engine will start and run, however a road test will produce the same results so the problem is still with me. I have checked the fuel filter it's clean. and done a few other tests and in doing road tests I had the same problem but I could get home buy stoping the engine the doing a start I could limp home on a couple of restarts. I have purchased the factory shop service manuals and I have the ability to do a lot of the trouble shooting but do not have the scan tool.I can read the schematics and work with a digital multimeter. I have isolated the fuel pump connector there are 4 wires going to the fuel tank 2 are for the sender, 2 ( a purple and a black) go directly to the fuel pump. applying +12 volts to the purple lead grounding the black wire the pump should run and build pressure on the fuel rail It does not.

I will be trying a couple of other ideas that I have noticed but will wait on a reply from you. by the way, I have not located the fuel pump control module It is not behind the rear seat back or anywhere else in the rear portion of this vehicle as the manual indicates and finding the module would be a great help. Maybe it's under the instrument panel. I have searched there also but didn't see any box that looks like the photo shown in the manual. I need some professional assistance. .

Thanks for that info. My gut instinct is telling me that this is a fuel pump problem. I have seen many electric fuel pumps that after running some time build up heat and begin to drop fuel pressure just as you are having. The pressure reading you are getting upon start up is correct. Some of the testing you are doing is incorrect though. This car does not have a fuel control module as this is only an option for the supercharged engine. The fuel pump connector is also different than what you stated. The supply voltage to the fuel pump is via the gray wire at this connector. So applying 12 volts to this point should make this pump operate. Another test that I feel may be important would be a leak down test. What I would like to see is simply a test where you cycle the key from off to on to get your peak pressure (48-55psi) and then simply turn the key back to off. The pressure should slow drop around 5 psi. If you see the pressure just simply drop 20 psi in just a few seconds then we really need to look at the chance of a faulty fuel pressure regulator, or a leaking injector as the culprit. Let me know od any findings you may have! Good luck!

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