I have an electric fuel pressure gauge in the cab, it worked fine for a while and suddenly started reading staying very high on the gauge, mostly on the high peg. Checked it with a mechanical gauge and it was a rock steady 10 psi at the inlet to the VP... I called Geno's and they said I needed a new sending unit, ch ching!! installed that and now it reads reasonably until it gets to 10 psi then it goes to the high peg, but is apparently semi correct below 10. I see 8-9 psi on the electric and 7ish on a mechanical both sensed at the VP inlet at cruise and 5 on the electric an 2ish? on the mechanical. The electric goes to the high peg on trailing throttle and the mechanical goes to 7-8. Talked to Geno's about the erratic gauge and they said grounds, grounded the heck out of the sending unit to no avail, any ideas before I tear down the interior to get the fn gauge out of the pod and then try to figure out how to better ground the gauge itself?

Thanks

 

I never have trusted or had good luck with electric fuel pressure gauges, only use mechanical.
What good is a gauge that you can't trust?
Almost better to have no gauge at all.

 

I agree and thats why I put a mechanical under the hood, I had HOPED that they would agree more or less so I could have a real time indication in the cab rather than have to stop and pop the hood all the time.

Do you have a mechanical fuel pressure gauge in the cab? no issues with having fuel under pressure in the cab?

Thanks for the input

 

that pressure is to low for the vp44. it needs to be 16 psi. you will never get a ep to last if you do not put a snubber in line and mount the sender on the firewall away from heat and vibration.

 

Would depend on the gauge brand and how it was set up. Electric gauges and their senders are susceptible to damage from the hydrodynamic fluid pulses coming from the VP. Even if you can subdue the pulses through snubbers, the ULSD is harsh and can work its way past sender seals.

 

If you want reliable and accurate go mechanical, liquid filled if its on a p7100.

If your worried about fuel leaking in your cab put a ball valve under the hood.

Electric fuel pressure gauges have never worked on these trucks, He!! the electric fuel gauges don't even work.

The funny thing is most people think the factory oil pressure gauge is somewhat right....most swing at least 65-80 psi when cold

 

I agree. a $15 glycerin filled gauge from ww granger is the only way to go

 

I ran a Dakota Digital electric fuel pressure gauge for many years until the ULSD compromised the sender seals. By that time the company had upgraded their design to combat the issue, but I wasn't willing to spend the money to see how well the new design would hold up. In saying that, I did have the option of simply buying another of the same sender I had since it was still available for much cheaper. But not being sure how long that replacement sender would hold up to the ULSD, I opted to change my entire setup to a mechanical gauge with isolator. As already mentioned, there's no point in having gauges if you cant trust what they're telling you.

 

the isolator is a troublesome piece of junk that when it fails it sends water and antifreeze back toward the injection pump. all of the equipment and trucks for the last 70 years has diesel to the gauge.

 

I cant remember a thread in the past ten years or so where anyone has ever had an isolator fail. And if it would fail, it would push fuel out, not let anything in. Thats not to say that the few CC's of coolant would harm anything either. Also, I have to rebuke about diesel fuel running to the gauge in trucks. Maybe in equipment but to the best of my knowledge, diesel in the cab is illegal for a legal on road vehicle, which is the reason there are zero mechanical fuel pressure gauge kits which dont include an isolator. I could be wrong so if you know anything better.....

 

Thanks guys, the mechanical gauge under the hood is a liquid filled 0-30# from Jegs and has been under the hood for about 2 weeks after the non filled mechanical gauge failed and started pouring fuel out on the ground and everywhere else. The sending unit is mounted to the firewall up near the hood and has the snubber sold for it by Geno's but I hadnt thought about the new fuel mix being incompatible with the sender seals, I'll investigate that some further.

I keep hearing different numbers as being the minimum acceptable to the inlet of the VP, the FSM says you should have 10psi at the inlet of the filter housing and the filter should drop no more than 5 psi, that to me says 5 psi at the inlet to the VP is adequate. But Id obviously like more and I expected more from the FASS. When I first installed the FASS i had what I have now and they sent me a new relief valve spring and tld me to expand the original spring a bit. That upped the pressure quite a bit but when I installed thenew spring it was essentially back to where it is now and was before I expanded the original spring.... to be honest, this whole lift pump/fuel pressure/gauge BS is really causing me to wonder if I shouldnt just cut my losses on the whole cummins experience. I hate heading off wondering if I'll make it home or if it's going to cost me thousands of dollars I dont have

If I use a mechanical gauge in the cab, and I dont want to use an isolator, what do y'all use fo rplumbing and where do you mount the gauge?

Thanks for the input guys, lots more to think on

 

You can take what I say with a grain of salt but the FSM is information put together before a decade of accumulated consumer/owner/aftermarket research and data and experience. And the FSM says no less than 10 psi at the VP, not 5. And the general consensus to date is that 15 psi is the minimum psi for maximum VP lubrication, cooling, and reliability. With your FASS, idle psi should be around 20 psi as normal pressure drop from idle to WOT is around 3-5 psi for those pumps. Just noting that there is NO pressure "too high" for the VP but anything over 20(ish) isn't necessary and only causes over-circulation of the fuel.....unless the added psi is needed in trying to keep the WOT pressures in check. But if you have to have idle psi really high just to offset WOT pressures then there's other issues, or a LOT of fueling going on.

As for your question about how to plumb fuel to a mechanical gauge in the cab..... I think you kinda answered you're own question with that first statement. This is why isolators exists.