Residual Fuel Pressure

[Johann]

In regard to the fuel pressure check valve the '97 service manual is somewhat vague. In the pump description it says the valve "maintains pump pressure during engine off conditions" and under the regulator description it says the valve "maintains some fuel pressure when the engine is not operating".

On my '97 when the key is turned to run the pressure rises quickly to 55 psi (book spec) but when the pump shuts off after one second the pressure drops in a few seconds to around 4-5 psi and holds there. If the check valve is supposed to hold "pump pressure" of 55 psi I've got a problem but if it only needs to hold "some" pressure I'm OK. Which is it?

 

[Jack B]

I believe the system should hold 50-55 psi indefinitely. If the check valve holds on the supply end and there are no leaks it should not drop. I have never seen mine drop below the 55 psi between starts. I have an in-car gauge and when I turn the key switch on the pressure is indicated. If the pressure drops it probably does not means much except at some point the car will become hard starting.

 

[1TONY1]

Is your car getting hard to crank ? You will need a fuel pump module.
If anybody is interested, I have a NEW 255 liter Walbro pump that is a plug and play replacement. No modification needed.

 

[Bad_Byte]

This is a very timely post. I have a 97 that is hard to start exactly as Jack B said it probably would be.

I have a pressure gage on the manifold and if I repeatedly turn the key on and off to start the fuel pump and cycle it several times I can see the pressure rise. However, as soon as it rises it drops and mine drops all the way back to zero.

Johann mentioned a check valve. Is it integral to the fuel pump or is it in the pressure regulator? Can it be replaced without replacing the fuel pump or is it in the same location as the fuel pump?

Thanks for any assistance.

 

[Jack B]

Tony:
how to you overcome the difference in the height (shorter) of the Walbro versus the oem pump.

Bad Byte:
The regulator is integral to the pump.

 

[1TONY1]

Tony:
how to you overcome the difference in the height (shorter) of the Walbro versus the oem pump.

Bad Byte:
The regulator is integral to the pump.

I'll have to tell you that offline Jack. I destroyed one new Walbro before I got it right and I have many hours in finally making it right.
Also....I'm pretty sure the regulator/check valve is a seperate piece in the top of the pump module. In Dodge trucks you can replace them......I never found another factory "in tank module" regulator that runs as much pressure as a Viper.
Another FYI....the later model pumps are different on the top than the Walbro. The replacement modules now being sent out are like the late model pumps/modules.

 

[Johann]

Mine is hard to start after a long heat soak cycle. I'm wondering if the drop in pressure is the pump check valve or an injector leaking. After several seconds of cranking after a heat soak it acts like it's flooded (doesn't start clean).

If the tank check valve is the problem I'm tempted to install an inline check valve to avoid the hassle and expense of a module change.

 

[Bad_Byte]

If the tank check valve is the problem I'm tempted to install an inline check valve to avoid the hassle and expense of a module change.

Exactly, good point.

I wonder if anyone has thought of this approach and how difficult it would be. I wonder if there would be any issues with where it is installed since the fuel line acts like an accumulator and volume for the first start is supplied from the quantity of fuel under pressure.

Mine simply loses pressure and the pump can't build up the pressure in only one cycle before shutting off. Repeatedly cycling the key on and off allows the pump to build pressure enough start and from then on its fine. I have noticed a rich (read flooded) start if I press the throttle during the start cycle probably a side effect of not starting right away.

 

[J DAWG]

Is your car getting hard to crank ? You will need a fuel pump module.
If anybody is interested, I have a NEW 255 liter Walbro pump that is a plug and play replacement. No modification needed.

Tony


let me know if you still have it. Give me a price that includes labor on my RT .