Buick Century Repair Advice
Fixing a Hesitating BMW 528 and a Buick Needing Fuel Pressure Specs
Your auto repair questions answered about a 2001 Buick Century with a fuel pressure problem and a 1988 BMW 528e that hesitates.
This weekly Q&A session answers your questions about cars and trucks. This week explores a BMW 528e with a hesitation and answer a fuel pressure question.
Question:
After my BMW is completely warmed up, it hesitates (loses power) in small bursts - usually after about 20 minutes of driving. These bursts will eventually worsen to the point where the engine will almost feel like it's about to die completely. It literally feels like it's running out of gas.
Feathering the gas pedal will keep usually keep the engine running and often the problem will intermittently go away, but it will not go away completely until the engine has cooled down again. Unfortunately, the cycle repeats itself the next time the car runs. The problem usually starts after slowing down from one constant speed at about 55 to 60 mph and is worst in the 45 to 50 mph range. No "check engine" lights show and the tachometer does not drop off sharply indicating a loss of electrical power. There is a slight increase in water temperature just before and during the periods of power loss.
The fuel pump relay appears good, and the fuel pressure regulator is brand new. Chevron Techron fuel injector cleaner has been run through the system. The air bypass valve has been cleaned (which helped to smooth out the idle). The temperature sensor and temperature switch have been replaced (The thermostat housing has been completely bled). Brand new spark plugs, distributor cap, rotor, wires, and a new fuel filter have been installed. During the engine rebuild (about 1,700 miles ago), the throttle position sensor was adjusted (it was WAY off).
The next troubleshooting project is primarily to check out the two fuel pumps (the Robert Bentley shop manual has a reasonable plan for this) for pressure and current draw and to test the pressure regulator under varying vacuum. Other suggestions? -- like how to check out the DME or how to ensure the fuel lines are connected to the injector rail properly - in and out.
Installing new "Easter Eggs" in the car that don't fix the problem is quite costly. This has never happened during the 1,200 mile break-in period following the engine rebuild. Please help.
- 1988 BMW 528e (10/87 production date)
- 2.7 liter with Bosch Motronic 1.1 electronics
- Automatic transmission: (ZF 4HP22)
- 200,600 (about 1,700 miles on completely rebuilt engine and
- transmission - including cylinder head refurbishment)
- ABS brakes
- P/S, A/C, Cruise control
- Rack and pinion steering
Thanks in advance, Tim
Answer:
The Motronic is a nice system but the only problem with it is you need a scan tool to do any checking on it. Your plan of testing the fuel pumps is the next logical step. If the auxiliary fuel pump is starting to go bad, it will display these same symptoms.
The Bentley book may or may not say differently, but here is the procedure from BMW with the proper readings.
- Connect a suitable pressure gauge inline between the cold start valve and the supply hose or to the main fuel supply hose, ensuring that the gauge is properly installed to prevent fuel leaks. Nominal fuel pressure with engine running should be 2.5 bar (36 psi).
- Disconnect and plug the vacuum hose to the pressure regulator. Start the engine and observe the pressure gauge. Reading with the hose disconnected should be approximately 2.7 bar (38 psi).
- Reconnect the vacuum hose to the regulator and observe the pressure gauge. The reading should drop down to approximately 2.3 bar (33 psi).
- Accelerate the engine several times while observing the gauge. Pressure reading should rise briefly as engine is accelerated.
- If the reading obtained in step 2 is too low, briefly pinch off the return hose from the regulator while observing the gauge.
- If the pressure reading rises with the hose pinched, pump, tank and lines are satisfactory.
- If the pressure readings observed in steps 2 and 3 are not as specified and the pump, tank and lines are satisfactory, or if the regulator fails to alter pressure in response to engine vacuum, the regulator should be replaced.
Keep in mind however, that the car must be displaying the symptoms when you do the tests. Otherwise everything will check out good.
Question:
What should the fuel pump pressure be on a 2001 Buick Century 3.1 liter V-6?
Manley Olson
Answer:
Here you go Manley!
Key On Engine Off: 52-59 psi
That's all for this week. Feel free to browse the archives for past topics and other resources. And, as always, if you are stuck and need an immediate answer you can always call Vince on the phone.
