SIXSLUG

Heading east yesterday my fp gauge starts jumping around. Steady 1850 rpms around 60 MPH pulling Snoqualmie Pass, gauge falls down to zero then back up to 16 then down around 8-10, then all the way over to hanging straight down. Interestingly, when it dropped and I mashed the pedal it picked back up over 12 psi.

I am running an IISPRO 0-30 off a snubber at the elbow of the big line kit at the vp, and am figuring it is the gauge. I changed out the filter and opened the water in fuel drain and got a good blast of fuel out of it. The FASS is purring as normal and felt smooth.

I am feeling confident my gauge is shot and have already conferred with a guy at ISSPRO and they assured me my set up was good and the gauge is still under warranty.

Am I missing anything?

Thanks, Kurt

KATOOM

SIX are you running a mechanical ISSPRO? If so, are you also running an isolator? I'm following your thoughts on the gauge but I'm just not understanding why or what in a mechanical fuel pressure gauge would allow the needle to drop to 0 and then regain a pressure signal. I would suspect a faulty isolator unless you dont have one.

SIXSLUG

Hi Katoom, thanks for the reply...

I'm running an electric ISSPRO with the sensor at the end of an Autometer snubber right at the elbow at the vp44 inlet, where the banjo would be.....

It settles at 15-17 psi at idle and jumps around, twitches a bit. It will be fine and then at speed it will start to bounce lower and lower to 0, then shoot back up and drop. Sometimes going all the way over past 30 til it is pointing down. The warning light never comes on. Very erratic.

KATOOM

SIX that sounds like to me either the sender or the gauge. ISSPRO is a great company and they usually have troubleshooting procedures for specific gauge setups. If you've already confirmed that with them (per your first post) then sounds like you're taken care of.

Not to throw any more monkeys in your wrench.....but I'd suggest moving that sender away from the VP inlet since the hammering it takes at that direct location is too great. I have my fuel pressure gauge line tapped into the bottom 90* outlet at the fuel filter housing. My prior electrical gauge setup had the fuel running up another 5 - 6 feet of braided SS line to the sender with JIC fittings, but eventually the ULSD worked past the senders seals (it was an older non-solid state design). Now my mechanical gauge setup has the same configuration except the SS line now stops at a tee fitting where I have a test port, and then more braided SS runs the rest of the way up to the gauge.

Greg Reed

That sounds like the sending unit. I had an electric Nordskog gauge and it would do the same thing , fluctuating pressure reading, when the sending unit was going bad. Mine was mounted on top of the filter canister, so VP pulses should not have been an issue. I went through 4 or 5 sending units before going to a mechanical gauge.

SIXSLUG

Thanks for the replies. I reviewed my e-mails to ISSPRO and my intention was to relocate the sender...just haven't had time. I would like it to be post filter canister so I can monitor my filter restriction, however I religously change the fuel filter every other oil change at a 5000 mile interval, so it should be fine...

I can tee off the fuel hose between the canister and vp and place the sender there, about a foot off the vp. Does this sound reasonable?

Merry Christmas, Kurt

KATOOM

Plumbing a tee in-between the filter and the VP is fine but you can also get a tapped 90* which you can place on the outlet of the fuel filter house. Might be easier for you. That way you can keep the readings post filter just in case.
Pushlock 1/2 X 08 FJIC 90 Deg Tapped

But really the added buffering comes from the snubbers and the added line up to the sender. So get another snubber and mount it right before the sender. Two is better than one. But really how the snubbers work is by taking a larger volume pipe diameter and reducing it into a minuscule size orifice which then opens back up to a larger diameter pipe. That change effectively reduces the spikes.

Also, you can keep that elbow on the VP and stick a schrader test port in it so you can have a place to test fuel pressure.

SIXSLUG

That's a plan, then. Thanks for the part number!

I can use the wrench I had to cut down for the filter housing outlet again!!

I have a 600 mile trip west planned on 12/26 so this will lessen the stress knowing what I know now.

SIXSLUG

Unbelievable! I woke up to a leaking lower rad hose yesterday morning and replaced all four with high quality USA made SS ones and my fuel pressure gauge is working again!! I didn't touch anything near the sender or wiring. It's a Christmas miracle!!

Seriously though, I don't know why it started working normally again, as I have acquired the tee and other parts but haven't gotten into it yet....Mike at ISSPRO sug't it was a wire issue since it throws over to the 6 0clock, so I will be checking that after I tee the snubber and sensor over closer to the filter cannister.

Thanks for all the help on this one, Happy New Year y'all!

KATOOM

Hey if its working then awesome..... Probably just a loose wire/connection.

SIXSLUG

I know,right.

So I relocated the sensor and snubber to just outside the filter canister off a push lock tee and replaced the original location off the elbow with a schrader as sug't. I also pulled the gauge and re-snugged the wires into the connector as sug't by Mike at ISSPRO. I may have felt a slight seating....result= steady 18 psi with no ratcheting/twitching. Needle movement is smooth and even.

I'll post some pics to my album later.

Thanks for all the help!

SIXSLUG

Couple updates:

Since teeing the snubber and sender about 10" back the fuel line I have a smoother needle, still a tiny bit of twitching and a reading of about 1 psi higher fuel pressure than when mounted off the vp elbow before. The gauge drops smoothly to around 14-15 psi on hard acceleration then comes back up to about 17-18 psi.

I have the red hot wire for all 3 gauges plugged into the spare location #16 in the fuse panel on the left side of the dash, with an in line fuse. My backlighting shuts off when my grid heaters fire. Is this normal? After warm up they operate normally if my headlights are on....

KATOOM

Sounds like its working for you. Except I'd check into the voltage to the gauge lighting and the grounds because it shouldnt do that. Are you sure your batteries are doing OK? Whats all the other lighting do at that time?

SIXSLUG

It's just the gauge lighting. The voltage gauge drops down and the headlights dim a bit, like usual when the grids fire....

I expected the dimmer feature to be finicky on the gauges since they are LED lights, I just figure the voltage draw of the grids and because of where I hooked in they were dropping out.

Fuse location 16 was empty and called out as 'spare' in the owners manual. It is wired and hot when the ignition is on, however, my gauges only light when the headlight switch is on either on position. I grounded tehm to the frame in the fuse panel area..

KATOOM

Ahhh..... I didnt realize they were LED. I forgot the newer ISSPRO's were LED lighting. That would explain them shutting off when the voltage drops. Although, maybe confirming with ISSPRO would be the best move.