vorra65

Goofy problem's with my 98.5, regarding F/P pressure readings. Usually runs at 13/14 tooling down the road unloaded-least that's what the gauge says. Recently, I've noticed that my pressure will drop to 8 and stay that way till I pull over and shut down and restart. After restarting pressuure goes right back to 13/14. Now during this procedure, when I pull over to restart-I shut it down and when I turn the key back to start there is NO pressure loss. What I mean, is that the L/P doesn't run like when you cold start. So it seems that there is good pressure right off, on the restart. This is the way it happens every time I get the pressure drop. I just pull over, shut er down and restart-viola good pressure.

I have installed-
Vulcan big line, with a relocated L/P back by the tank.
Geno's F/P kit-electrical Westach (spl?) gauge with isolater, column mounted gauge.


I talked to Eric at Vulcan, who was very helpul, and could have sold me parts-but instead offered advice for free-Thanks. He said, more than likely I have an intermittent F/P sender that's giving me the false readings. Recommended a mechanical under the hood-which I am installing today.

Anyone else, experience this with the electrical F/P gauges?

If it were a true pressure drop, or a L/P problem-why after shutting down and restarting does the pressure go back to normal?

Dr. Evil

What does the mechanical guage say?

Id say put the mechanical guage in the cab...having it under the hood is useless because the fuel pressure at idle means virtually nothing. You want to see the fuel pressure at Wide Open Throttle (WOT)...and having the guage under the hood makes it kind of hard to see it.

vorra65

I see the point Dr E, but wouldn't having the gauge under the hood somewhat perform the same function? If I'm cruising along with 13/14 and it drops to 7/8-I pull over and the electrical still reads 9/10 at idle and the under hood reads 13+ at idle would it not indicate that the electrical sender may be the culprit?

What would an electrical spike do to the sender, since it does send the signal via ohm's? If say, the contacts in the sender spiked or the continuity were broken for a split second, would it not then give a false signal? And then upon shutdown/restart it re-set's to the correct voltage?

I'm no electrical whiz by any means, just exploring all possible ideas.

I do like the mechanical in the cab idea, and will eventually upgrade to that. I just went electrical initially, for ease of install and $$.

qwest

Are you switching anything else on or off,

My boost gage was acting weird, had a switch for an add on in the camper.
The noise spike was messing up the gage ( freezing it )
had to put a capacitor accross the switch.
Just a thought...

Dr. Evil

No...because you want the pressure reading at WOT (with your foot all the way on the floor)...how can you see it when the hood is closed? Like I said, pressure at idle doesnt tell you anything...

To properly test your sender you need calibrated pressure test equipment. That is to say, you need to introduce measured pressure from an instrument that is calibrated to a known pressure standard - thats really the only way to tell if your sender is ok...

Unless you have access to this kind of equipment, it is just easier to install a mechanical guage in the cab, at least in my mind it is.

Check your grounds...make sure you have a good grounds on bare metal.