Fuel Preasure needle bouncing all over the place....EFI @ the schrader valave

[Last Real Texan]

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After the Supercharger install I wanted to verify the accuracy of my electric gage....Got the right guage to go into the schrader valve and @ first it was pretty steady but I needed to change the pick up to 1/2 inch and install new shut off valve. Well now I fred it iup and the fuel preasure is all over the board looks like the guage is vibrating badly and I can not get an accurate reading to save my life. I am guessing that I have an air leak somewhere in the new pick up or valve connections some where. I am sure it is not in the pick up beacause I ran it with no shutoff valve and the preassure was steady...then installed new valve and now this.

What causes the mechanical guage @ the rail to bounce around wildly say from 20psi to 50 psi when the electric guage on the dash stays stable@ 35psi......Any thoughts?

Mechanical is at the Schrader valve...
electric is at the FMU unit from Procharger...
Help!

Bryan

[BigGrizzly]

I believe your electric gage is dampened by the by the diaphragm in the sender the mech one is a boron tube. is it oil dampened? What is the max pressure of the manual one?

[Last Real Texan]

I believe your electric gage is dampened by the by the diaphragm in the sender the mech one is a boron tube. is it oil dampened? What is the max pressure of the manual one?
Max preasure on the gage is 100 psi.... But the needle is bouncing from 20to 50 so fast it looks like one needle. I was thinking this must be an air issue.....maybe it was I was running the boat on a down hill incline with the fuel pick up in the back of the tank on the high side of the hill....maybe t is sucking air through the pick up....The gauge is an automotive diagnostic kind that has a relief tube on it to bleed the air out just before the gauge, no it is not oil dampened. Like I said it did not do it sunday when I ran it on the hose with Bill before the valve install today. I.E. tank fitting pick up, to -8 hose end, to the fuel sep, to the fuel pump. SO no valve. Now with VAlve it does it.



It is either the valve assembly, or the pick up is at the point it is sucking air with the fuel because of a low fuel situation because of the slight incline forward where the boat is parked when running on the hose.

Will air cause this?

Bryan

[LKSD]

Check for an air or fuel leak. Also make sure you dont have any blockages in the line or pick up.. Did you remove the check ball from the tank fitting when you went to 1/2' ?? Also a remote possibility of a bad or mis adjusted regulator or bad / leaking injector.. Unless you have a bad gauge.. Hard to tell for sure without being there, but start with double checking the simple stuff first.. Also make sure that the mechanical gauge is on properly.. Jamie / Lakeside

[Last Real Texan]

First thing I am going to do is add 25 gallons of good stuff to the tank....will cure the problem if the pick up is sucking a little air due to the incline.

Second thing will be to remove the valve I installed between the tank pick up and the hose to the engine....will cure problem if it is in the valve.


I will then go from there if need.....will get a liquid dampened guage from granger for fuel and replace the existing test guage I have now...will cure problem if it is the guage.

Should not be too big of deal to fix I am thinking.

Bryan

[MOP]

Good idea to keep a check on plug color until you get straigtened out.

Phip

[justleft]

Is preasure reading constant with out the engine running ?

Does the bouncing frequency increase with RPM's ?

Sort of sounds like the injectors are squirting more fuel than can be delivered
to the fuel rail or maybe regulator is sticking open.

b

[mrfixxall]

Did you get a new fuel pressure regulator with the kit? where did you mount it? the viberation from the engine will make the needle bounce around if its mounted any ware solid..if its bolted to the motor try loosing the bracket and leave it hanging free not touching anything...(the viberation rattles the diaphram in the regulator and gives it a erattic reading)

[The Hedgehog]

Did you get a new fuel pressure regulator with the kit? where did you mount it? the viberation from the engine will make the needle bounce around if its mounted any ware solid..if its bolted to the motor try loosing the bracket and leave it hanging free not touching anything...(the viberation rattles the diaphram in the regulator and gives it a erattic reading)

Tex is tied up for a while so I will answer. He did get one of those typical boost reference regulators. Not exactly sure what he mounted it to (maybe the back of the head) but it was at the back of the engine on top. The regulator is where he is mounted the sender for the electrical gauge. It is steady. To verify accuracy, he hooked up a mechanical gauge to the shrader valve on the rail. I believe that it is the mechanical gauge that is going crazy.

[mrfixxall]

Tex is tied up for a while so I will answer. He did get one of those typical boost reference regulators. Not exactly sure what he mounted it to (maybe the back of the head) but it was at the back of the engine on top. The regulator is where he is mounted the sender for the electrical gauge. It is steady. To verify accuracy, he hooked up a mechanical gauge to the shrader valve on the rail. I believe that it is the mechanical gauge that is going crazy.

if he used one of those screw on mechanical guages he may want to try running the boat and bleed the air out whylr its running..sounds like he got a air pocket..

[BigGrizzly]

The logic Tex is using is perfect. Just ONLY do ONE thing at a time , that way you know exactally what cured it.

[Last Real Texan]

Back from the Abyss and getting a broad stroke Sanch .....will post more info in the next couple of days....when I finish testing things I will do to try and fix it.

.


Thanks for the help thus far
Bryan