gauges installed, not good!

[JBevans]

Okay I have a question, this may be a stupid one,but I am going to ask anyway.



The lift pumps on the trucks are electric right??? So they are either running or not. So how is it possible to monitor the fuel pressure using any gauge, if the pump is either on or off????

 

[Archive]

calfroper. . yes the pumps are electric. . the problem with an electric pump vs a mechanical pump is that as the speed of the engine increase and/or the load increase the VP44 (injection pump) needs more fuel. The mechanical pump's speed will increase to help maintian the pressure/flow needed as engine rpms are increased. On an electric pump it runs basically at one speed. (except at start up, and uses a pulse width modulated signal to control the pump speed then. ) As the speed/load is increase the electric pump does not increase. . (like you said, basically on or off. ) but the demand for fuel is greater by the VP44, so the pressure will drop. I hope this doesn't sound too basic. .



The problem with the LPs has been either the built in regulator going out. . losing pressure. . or the bushes going out in the motor on the pump, and the pump slowing down. . equaling in less flow. .



My LP has fair psi at idle and no load. . but goes almost to 0 when under a load. . and the dealer says it OK. . :{ but I know its not. .



I hope this helps a little...

Bryan

 

[jsnyder]

Stock pump still kicking

I just finished my fuel pressure guage install and am getting 12-13 at idle, 9-11 cruising, and 7-8 at WOT.



I'd have the lift pump checked myself.



Jason

 

[Archive]

I'm not sure what I'm going to do... have a trip the next few weeks, with the truck, if it survives the trip... The pump might have an electrical failure. . (of course will fail while it is on the trailer. ) If U know what I mean...

 

[JBevans]

Thanks TractorNut..... don't worry about the basics... I just couldn't figure out why spend the $$$$$ on gauges when it is an electric pump... and when it goes out it goes out, and there would be no way to see it coming or not.

So by what you say... . if you have a gauge... at a constant load the pressure should stay stable... . and if load is added then set constant at the new load, the pressure should decrease and then become stable. If the pump was going out then the pressure would continue to slowly decrease.

????

Thanks

 

[Archive]

True to a point. . yes it will slowly decline in its volume. . Most people report their pumps pressure get really eractic before they die. . others just a slow decline until they are dead. . If the pump is not putting out its full volume, you could have problems.



I'm going to use some hydraulic pump figures, but the same applies. . If the lift pump puts out 6 Gallons per Min. (GPM) and the main pump only needs 3 GPM all is OK. . but now we have a big load and the main pump needs 8GPM. . but the LP is only supplying 6. . We have a problem. . Cavataion. . a miss, stumble. . We are watchin the pressure between the two pumps...



Just hope to catch it before it is completely dead. .

(I'm also 99% sure it was the VP44 pump- that is lubricated and cooled by fuel. . no fuel or cavitating fuel, is hard on a pump like that. (I've to so much on different fuel systems, I cann't keep them a part, but I see no oil lines on the VP44, so that must be it. . )

Bryan

 

[Bpostel]

TractorNut,

The isolator is about 4" around. I mounted it to the lip that runs around the top of the firewall. The lip is covered with rubber moulding. Mine is mounted right beside my cluth reservoir. The fuel line runs from the top of the fuel filter canister to the isolator. Then another line runs from the isolator to the gauge. This line is filled with water and anti-freeze, so there is no fuel running into the cab. As far as installing everything, it's pretty simple. I ran the line down the a-pillar and through the fuse box. There's an opening behind the fuse box, so there's no problem getting to the fuses. I ran the line through the grommet that contains the main wiring harness. I punched a seperate hole through the grommet and ran my hose through it and into the back of the isolator.