Westach fuel pressure problem

[AggieJustin]

Here's the deal...



I installed a Westach fuel pressure gauge setup on a friend's truck, exactly like the one I'm running on my truck. The sender is remotely mounted near the PDC connected to a tapped banjo going into the injector pump. Just ahead of the sender, I've got a T with a schrader valve for attaching my mechanical gauge for troubleshooting.



So I install the setup, fire up the engine and the electric gauge shows 6 psi. I put the mechanical gauge on the schrader and I see 12 psi. Take a test drive down the road, as actual pressure drops the reading on the electric gauge drops proportionally. 10psi is ~5psi on the gauge. I pull out the multimeter and check the resistance readings on the sender. They are out of line with the specs given by Westach, so I get a warranty replacement sender thinking that will solve the problem.



I just put the new sender on Saturday, hopped in and fired it up. The gauge is still reading low. Not half like before, but still lower than the value I see on the mechanical gauge. I pull out the multimeter again to check the resistance of the sender and the readings are right in line with Westach's specs: 250 ohms at 0psi, 34 ohm for 16psi. I was seeing around 46 ohms at 12-13psi. But the gauge still only shows 7 psi and fluctuates as you drive, with the actual pressure.



Any ideas what might be wrong? I double checked all the gauge connections the first day and everything matched the instructions. The gauge wires are 18ga, run through the parking brake cable grommet. There is one other wire run through there, but it is disconnected from it's power source. Anyone have any methods for checking out the gauge?



It seems hard to believe that I'd get a bad sender and bad gauge at the same time, but I guess anything is possible. I'm just out of options without starting over again.



Thanks, JM

 

[RustyJC]

Justin,



If you have Westach's resistance versus PSIG table for the sender, substitute a fixed resistance in place of the sending unit and see what the gauge reads. If it's still low, the problem is in the gauge or wiring. If it's OK, the problem is in the sending unit or its ground wire.



Move the fixed resistance to the output post (the one that goes to the sending unit) of the gauge and ground the other side of the fixed resistance very close to the gauge. If the gauge now reads OK, there's excessive resistance in the wiring between the gauge and sending unit. If it's still low, check the voltage at the B+ (switched power) post of the gauge. If it's significantly lower than battery voltage, the problem is likely in the power supply wiring. If it's OK, the gauge is probably bad.



Before sending it back, however, I'd rig up the gauge and sending unit on the bench and pressure test it with a known accurate mechanical gauge teed in with the sending unit. Use air pressure, water pressure or whatever you have.



Rusty

 

[RJOL]

Justin...



It's been a few years since I installed mine, but I do remember that the directions wanted you to make sure that both the sender and the gauge were grounded to the same point. Also, if your using a extension hose to the sender, you might try to bleed out all the air to the sensor. When I change my fuel filter, I always loosen up the connector at the sensor and bleed the air out of the lines... Good luck...

 

[rweis]

When I ran my gauges I ran a seperate ground wire to the dash pod from the battery. Made it a ground bus. Grounded the gauge and the sender to it (see above comment to ground both to the same point).



Have had zero problems for about a year now.



Bob Weis

 

[AggieJustin]

Thanks for the suggestions guys.



Rusty, I'll try out those ideas this weekend. Is there an easier way to set up the fixed resistance, besides getting a couple of resistors where I know the resistance?



As for the ground, the wire coming from the ground pin on the gauge goes to the sender and then to the ground (the bolt where the sender is mounted to the fender). So the gauge and sender use the same ground. The one thing I just realized that I didn't check was the resistance between my ground and the battery to make sure it is a good ground.



As for bleeding air out of the line, I've found that you really don't even have to bleed these. Once you start running it, the air works it's way out. I depressed the schrader that is just ahead of my sender and there was fuel there when I pulled my mechanical gauge off.



Anyone else, keep the ideas coming. It'll be Saturday before I get my hands back on this project so I'll take all the suggestions I can get.



Thanks,



JM

 

[Huff N Puff]

Reading the pressure going right into the VP44

May cause a pulsating reading,because the positive pulses of the fuel pump may resonate with the negative pulses of the VP44s vane pump causing a really erratic reading, with a mechanical gauge and a inaccurate reading with a electrical guage. If you left it that way you would wear the sending unit or a mechanical guage out. When I had my mechanical guage at the VP44 it would make the guage buzz it was so bad. The fix is to move your test port closer to the lift pump. Merv