Fuel pump on/off

[cujogood]

I searched for an hour trying to find a similar problem/fix. Its a 2000 Malibu. Just replaced my fuel pump 2 days ago thinking all problems pointed to fuel pump. Was losing power especially up hill and would turn over and over before starting like it lost its prime or pressure. Yesterday I tried turning it over and the pump wasn't coming on everytime I turned the key to power the pump. I did this more than a dozen times with the Bu starting 50% of the time. When I heard the pump come on it would start first turn. Had fuel pressure checked at rail(43psi) new filter and pump replaced with a used one from an 2001. Where do I go next?

[ctwright]

Sounds to me like your contacts are worn out in the fuel pump relay. Replace your fuel pump relay.

Not sure if everything else that is supposed to cut on with your key in the on position is coming on either though. Usually an intermittent problem like that leads to a switch, anything basically with contacts, so a relay as well. Could also be your ignition switch. Just check first that you are getting power to the coil inside the relay with the key in the on position. You should have four connectors in to your relay. 2 for the control side of the circuit, there is a coil between these to connectors, one of them should have 12 volts to it with the key on. The other two are for your power circuit witch actually sends 12 volts to your fuel pump by closing two contacts. What happens is this.

You already have 12 volts on one side of the power circuit, the wire going to the relay, and there is a open set of contacts b/t that wire and the wire going to your fuel pump.

When you supply 12 volts to your coil side by turning on the ignition, the coil energizes and by magnetism pulls the set of contacts close, completing the power circuit, supplying 12 volts to your fuel pump.

If those contacts are bad, some times they may get a good connection and sometimes they may not, and sometimes they never get a good connection.

Hope that helps.

[Jetex]

I have not got a wiring diagram specific for your model. A typical GM system works like this :-

Turn ignition on. Pump relay gets energized via ECM and contacts on relay feed power to pump. Pump runs approx. 3 seconds, primes fuel rail and relay switches off. Crank engine and engine starts. Engine runs and contacts on oil pressure switch close which now feeds power to pump. This is a safety interlock to prevent the engine running with no oil pressure. In the GM drawing I have, the pump relay can be removed with the engine running and the engine will continue to run. The relay is only used to prime the fuel rail.

Maybe your oil pressure sensor has defective contacts?

[ctwright]

Originally Posted by Jetex

I have not got a wiring diagram specific for your model. A typical GM system works like this :-

Turn ignition on. Pump relay gets energized via ECM and contacts on relay feed power to pump. Pump runs approx. 3 seconds, primes fuel rail and relay switches off. Crank engine and engine starts. Engine runs and contacts on oil pressure switch close which now feeds power to pump. This is a safety interlock to prevent the engine running with no oil pressure. In the GM drawing I have, the pump relay can be removed with the engine running and the the engine will continue to run. The relay is only used to prime the fuel rail.

Maybe your oil pressure sensor has defective contacts?

Thanks for adding the extra help there, my Nissan is like the way I told him. I did look at my haynes manual for my buick and it is exactly like you said with the oil pressure switch. But I'm still going with the fuel pump relay seeing how he said it's when he turns his key on half the time it works and half the time it don't. Either way it should turn on when he cuts the car on. So I'm still thinking something in his ignition switch or his fuel pump relay.

[brcidd]

Originally Posted by Jetex

Turn ignition on. Pump relay gets energized via ECM and contacts on relay feed power to pump. Pump runs approx. 3 seconds, primes fuel rail and relay switches off. Crank engine and engine starts. Engine runs and contacts on oil pressure switch close which now feeds power to pump. This is a safety interlock to prevent the engine running with no oil pressure. In the GM drawing I have, the pump relay can be removed with the engine running and the the engine will continue to run. The relay is only used to prime the fuel rail.

Maybe your oil pressure sensor has defective contacts?

I just looked at your wiring diagram- there is NO oil pressure switch in the fuel pump circuit.... I used to think like Jetex does- and it was true in my 77 Vega- if oil pressure went low, car stalled.. but ever since about 1988 or so here is what happens.

The Oil Pressure Switch in the EFI System

There seems to be some confusion in the auto repair industry today regarding the role of the oil pressure switch in today's fuel injection systems. Many people think that the oil pressure switch turns off the fuel pump in case the engine loses oil pressure. This in turn shuts down the engine to protect it from internal damage. This is not the case in most vehicles.

Many vehicles today have electronic fuel injection and many tie in the oil pressure switch to the fuel pump circuit. However, the switch does not act as a safety at all. Instead, in most cars, it serves to continue operating the fuel pump in case the fuel pump relay fails. This would enable the vehicle to reach it's destination. The symptom of a failed pump relay, in this case, would be hard starting or prolonged cranking. The reason the car would start at all with a failed fuel pump relay is that after cranking for several seconds the oil pressure may be high enough to close the oil pressure switch and connect voltage to the fuel pump. The pressure needed to close the switch contacts is around 4 PSI.

Also, many manufacturers do not use the oil pressure switch at all in conjunction with the fuel pump circuit.

Hope this helps.. a wiring diagram is always the best thing to reference...

[ctwright]

I know I'm getting off the subject now about his question, but this got me looking at both haynes manuals now. It doesn't show anything in the one for the nissan I have for oil pressure switch in the electrical diagrams, or even in the index does it mention the words oil pressure like it does for my buick. Is there a way to add a pressure switch to the engine somehow if it doesn't come with one? Should there already be a plug somewhere that I can take out and add in a pressure switch or would you have to drill through and thread somewhere? It's a 95 sentra.

[brcidd]

I've Tee-ed in an extra switch on a few of mine- they use standard plumbing and pi[e threads- so it is easy to do- just nack out currentsensor- put in a small pipe with a tee- and the use a known oil pressure switch- like off of a GM Safari or Astro van- the contacts close at 4 psi= then wire your fuel pump through that switch.-- I saw 2 Astros burn up their engine due to low oil pressure- 16 years ago- is when I discovered the way the circuit really works= then I wired the circuit "my way" as to turn off engine if no oil pressure-

Seems the car manufacturers don't want you stalled in the middle of the freeway- they want the engine to always run to get you to safety- even if there is no oil pressure....they probably got sued once too many times....

[Jetex]

I have a 2000 Cavalier circuit diagram on hand and the oil pressure switch is used to supply the fuel pump after the fuel relay drops out. So it seems as if GM was using that system at least up to then. The Power Control Module energizes the relay and after 3 seconds drops it out. I strongly suspect my 2004 4cyl. Malibu is using the same system. If I switch on the ignition and don't crank the pump stops running after 3 secs. I don't think they are using fuel rail pressure to switch it off. It's easy enough to check. When I have time I'll start the car and pull the pump relay and see if the engine stops.

Coming back to the suspect pump relay. Swap the relay out with another on the relay panel that has the same part #. Be sure to double check the number. There are normally quite a few relays with the same part #. Just mark your suspect relay with a marker. It's easy to get confused.

[brcidd]

Hate to be a PITA but...There seems to be some confusion here- I have online access to the OEM GM factory service manuals for 1998 to present... I just looked up your 2000 J-car-(both engines are the same) the fuel pump relay drives the injectors and fuel pump- the fuel pump has no connection elsewhere...What reference are you using?? Maybe if you look at your oil pressure sensor we can completely figure it out...

Also I looked up the oil pressure sending unit- it has only one terminal- to run the gauge or switch

Here is how the OEM service manual describes the fuel pump circuit for a 2000Cavalier

An electric fuel pump (2) located in the modular sender assembly is used to provide fuel pressure. To control fuel pump operation a fuel pump relay is used. When the ignition lock cylinder is turned to RUN position, the fuel pump relay activates the electric fuel pump for approximately two seconds to prime the injectors. If the PCM does not receive reference pulses after this time, the PCM opens the fuel pump relay power circuit. The relay will reactivate the fuel pump when the PCM receives reference pulses

Here is the wiring diagram for your 2000 Cavalier fuel pump

[brcidd]

Here is what I have for a 2004 Malibu fuel pump circuit....sorry so big- but it is easier to read that way....



Here is the description for an 2004 Malibu

The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel sender assembly, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.
The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel sender assembly inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter contained in the fuel sender assembly and the fuel feed pipe to the Fuel Injection System. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel sender assembly. The function of the venturi pump is to fill the fuel sender assembly reservoir. The fuel pressure regulator, a part of the fuel sender assembly, maintains the correct fuel pressure to the fuel injection system. The fuel pump and sender assembly contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times

The fuel pump is mounted in the fuel sender assembly reservoir. The fuel pump is an electric high-pressure pump. Fuel is pumped to the fuel injection system at a specified flow and pressure. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The control module controls the electric fuel pump operation through a fuel pump relay. The fuel pump flex pipe acts to dampen the fuel pulses and noise generated by the fuel pump.


Also the engine oil pressure switch is a "one" terminal switch- used only for oil pressure gauge or light...

[Jetex]

Hello brcidd

I've sent an attachment in PDF form in reply to your e-mail notification. It's a scan from my Chiltons manual that covers the 1995 to 2000 Cavalier. I do not have access to factory manuals so must depend on what I can lay my hands on.

As you can see, according to Chiltons, the pump is wired through the oil pressure switch. If I am wrong, then I do apologize. However, I feel this is a worthwhile discussion and opens up more avenues in trying to locate the problem of the original poster.

[cujogood]

Thanks for all your comments. I did switch out the relay but to no avail. I asked a co-worker who claimed he had similar issues with a Dodge and he said he end up changing the ignition assembly. The key was a loose fit causing the said problem of fuel pump working less than 100%.

[rhandwor]

I would make sure you have a good ground connection a loose ground will cause these problems.

[brcidd]

For what its worth- My Mitchell-on-Demand also agrees with the OEM GM Service manuals in both the 2000 Cavalier and the 2004 Malibu wiring diagrams- the oil pressure sending swith is a single terminal in both.

So why don't you just look at your oil pressure switch- and count the wires coming out of it- this will easily prove which wiring schematics are correct. I don't have a J-car handy...or I'd look myself.

[Jetex]

I will be checking the oil pressure switches. I don't want to labor the point but it is still possible that even with a single connection on the oil pressure switch, by using logic circuits, an interlock can still be achieved. The discription of the operation of the circuit you posted says the pump relay drops out after 2 secs. after ignition on. What conditions must be met before the relay is energized again? Altough the oil pressure switch has only 1 contact which is no doubt used to turn off the low oil pressure light, the same contact could also be used as an input to a logic circuit. This might then allow the circuit to energize the pump relay again when the oil pressure is correct.

Note that pin 8 of the PCM is named "fuel pump relay control" and although it depicts a simple switch it might in fact be a rather complicated circuit which depends on its operation for other logic inputs. Modern car electronics tend to integrate as much as possible into low cost components. By using a cheap integrated circuit the manufacturer has saved on a set of contacts and terminals on its oil pressure switch.

Please note that this is only wild speculation on my part and I don't want to be drawn into a lengthy argument about this. If I am talking crap you may beat me to death.