WS6HUMMER

I just installed a new/rebuilt VP44 from MWFI and a FASS 95GPH lift pump, along with a BD low fuel pressure light. The problem I'm having is as soon as the truck starts making boost the low fuel pressure light starts rapidly blinking but the moment I lift my foot it goes away. I just spent very close to 2 thousand dollars on my truck and I cant drive it because I'm afraid I'll hurt the injection pump. Has anyone ever had this problem?

All the fuel line connections are dry as a bone, not even any diesel residue, I even checked the new fuel line for kinks and its good. I dont have a FP guage, and when I put on the FASS and the BD light it got rid of the only 2 schrader valves/test ports I had to hook up a test guage. I appreciate any and all the help I can get

BTW I cleared all the codes and got a P1693

MSquare

The 1693 is a companion code. You should have had something else. I would step away, take a break and then go over all the connections on the FASS, step by step and make sure your connections are correct. It sounds like something is not hooked up correctly.

And after that, before you do ANYmore power upgrades, get gauges installed. That is the #1 rule for any Bombs.

WS6HUMMER

I work @ a salvage yard and 2 weeks ago one of the salesmen ordered a lady a sending unit for her 12v truck but the plug on top was wrong. So they asked me if I could take her old sending unit and the new one to make one, so I did. When I took her old one apart I discovered her reason for changing the sending unit, the guage worked fine but her reason for changing it was it was running funny. The suction tube about 1/4 the way down spirals like a coil spring and then goes straight down to the bottom, well where it spirals the sending unit bucket had rubbed a hole in the line and air was getting into the fuel system.

I have been over the entire FASS line and everything is good and dry, I plan on dropping the tank this afternoon and hope I find a cracked line or a hole rubbed in it. It really sounds like air is getting into the system.

About the guages, what all do you reccomend? The TST box has a oil temp,boost,&pyro. What brand or type of FP guage is good/dependable. I really wanna play it safe with my new Injector pump. Thanks for your help.

Hummer

crobtex

I now nothing about the fuel pressure lights, but most agree that a gage is better. Any name brand gage will work, just be sure to get one that goes to 30 PSI. Some of the DTR advertisers offer several brands of gages. Also, some folks have plumbed a "T" into the line, post filter, to attach their FP gage.

FWIW, you are on the right track to equip your truck with the necessay system monitors.

MSquare

I have Isspro EV's. They look very much like your stock gauges. I don't like the digital gauges, you have to actually read them, with the analog, you can galnce at them and tell where your at.

Can you hear the FASS pump running? Good ground? All electrical hooked up based on the FASS instructions?

Good luck

WS6HUMMER

It looks like the fuel pressure is only dropping as low as 9 Psi but the low pressure light flickers on and off as soon as the truck makes any boost.

BTW I dropped the tank and everything looked real good, I even pressurised the suction tube and found no holes or cracks.

Diesel-Dan

Can you duplicate the issue by reving the truck in the driveway? If you can, you might try the "5 gallon bucket test" so eliminate the tank. What you need is a 5 gallon bucket (or similar contairer that will hold about a gallon of fuel.) and fill it up about 5-6" worth of fuel. You can use the FASS return line to do this. Place the return line and suction line in the bucket at the same time or you will empty the bucket in about a min or 2. Duplicate your test and see if you can get the pressure to drop.

Check your fitting at the top of the tank.

What pressure you seing at idle?

Indicator lights are good...but i would always run one with a gauge. More or less an attention grabber if you loose fuel pressure.

Where and how are you tapping for pressure?

WS6HUMMER

I have about 18PSI @ idle and 9-10 on wot.
It only does it when it makes boost so I cant duplicate it even by putting it on jack stands (Ive already tried). I also dropped the tank and thougroughly checked out the suction tube and the rest of the sending unit, it all looks good and holds pressure. I'm testing my pressure after the stock filter which is new, I'm using the schrader valve that screws in the banjo in the VP44, I have to temporarily remove the low FP warning switch to do this.

Thanks.

Diesel-Dan

SO you have a HPFP then???

PaulDaisy

I would suspect that the sender for the low pressure light is faulty or calibrated to a higher pressure than usual. Plumb in a tee at the schraeder valve and watch the light and the gauge together. I would bet that with your power upgrades the VP drops the pressure at the intake quite a bit, and this is what is turning on the light. Monitoring the gauge and the light at the same time (while driving) will immediately answer the question.
Of course, you will end up installing a gauge in the cab, but it is something you were planning to do anyway, right?... The light was just a reminder in addition to the gauge.
If the pressure does in fact drop enough, tuning up the FASS may be needed to give enough flow to the VP.
-P

WS6HUMMER

Yes, the one without all the fancy filters, the 95GPH.

WS6HUMMER

Yeah, it was a bad low pressure pressure sensor, I called MWFI and told them what was going on and no questions asked they sent me a replacement.
Must be a common thing for them not to question me too much, got the new one in and the only time it lights up is for half a second on startup. Thanks

Diesel-Dan

Glad to see that fixed your issue. Let me know if you have any other questions!

WS6HUMMER

Thanks Dan, I understand you are the man when it comes to anything technical, I really appreciate your input & time on my issue.