Electric Fuel Pressure Monitoring for pre-555 EFI engines

370Dancer

Well-Known Member
Oct 2, 2006
2,472
Suncoast of Florida
Boat Info
1998 370 Sundancer
Engines
380hp MAG MPI Gen VI with V drives
I was having a hard time accurately measuring fuel pressure with a hard to reach, schrader valves and mechanical gauges. I decided to build my own.
Here's the story in pictures.
Blank gauge: $5
LED voltage readouts: $2
12v 100 PSI senders: $30
Misc fittings and wiring: $10.00
I now have full time fuel pressure monitoring. 1.9-2.0 volts is my nominal "good"
https://www.dropbox.com/sh/ze4b7dgnx5m726r/AADFerDXE4vHnYu9l3uM1d8ua?dl=0
 
I've got that same fuel rail and plenum. I just extended mine with some npt fittings, so my mechanical fuel gauge screws on easily.
 
Correct. .5v to 4.5v = 0 to 100psi
25lbs per volt assuming they are dead on. I was more interested in relative readings between the 2 engines. the Port is still lower than the Starboard by a bit, and during the 3800 RPM run, I could see it fluctuating between 1.6 and 2.0 momentarily. I was orginally going to just extend and leave the schraders on, but I got interested in a full time monitor, so here we are. So, I think the regulator is next, but no rush.
 
I've got that same fuel rail and plenum. I just extended mine with some npt fittings, so my mechanical fuel gauge screws on easily.
I'm still thinking about whether I can come off the back port near the distributor, and put the schrader valve there. Not much room, and it looks like the fuel line from the Cool Fuel 2 to the rail may be too much in the way to mess with it.
right angle in one direction or the other to get to an accessible spot for a mech gauge.
 
I just came off the front with a 1/4" to 1/8" reducer then a 45* elbow, and a 3" nipple an plugged a compatible standard FP fitting to it.
 
Interesting. the port is 1/4" as is the factory schrader fitting. I figured 1/4" fittings all the way. My front port is occupied with the sensors, which do come down to 1/8". I was just going to see if I could make it out the back side without displacing too much factory routing. So far, I don't have much hope, but I've taken a while to get other things done right. This might be one more.
Meanwhile, I'm back to boating at speed when I can afford it and need to, and trawling when I'm going nowhere. I watch go fast PWs go by me all day long. First one direction, then the other, then back again, then back again. I'm a fan of speed for a purpose, not for the hell of it. But not always....... ;-)
BTW thanks for your help and insight, as well as douglee25. I ain't scared, but I do verify before I pull the pin on most things.
 
Correct. .5v to 4.5v = 0 to 100psi
25lbs per volt assuming they are dead on. I was more interested in relative readings between the 2 engines. the Port is still lower than the Starboard by a bit, and during the 3800 RPM run, I could see it fluctuating between 1.6 and 2.0 momentarily. I was orginally going to just extend and leave the schraders on, but I got interested in a full time monitor, so here we are. So, I think the regulator is next, but no rush.
The regulators are here. best price and OEM parts at that, found at boats.net
860349A1 REGULATOR KIT (Mercury Marine) $125.14
I'll also be looking at routing the fuel return to the tank instead of the separator, and possible relocation of the starboard CF2 as discussed in another thread.
Scoflaw, are the fuel lines between the separator and CF2 anything special in your opinion? I know they have SS fittings, so just cutting them off and making new lines becomes problematic. No one wants to try to weld those onto a new hose. By no one, I mean a professional custom shop here.
 
I cut the tubing and fittings off the OEM lines, then put a flare on the tubing. Bought high pressure fuel line and clamps from the auto parts store. Also wrapped the lines with a heat shield sleeve.
 
I cut the tubing and fittings off the OEM lines, then put a flare on the tubing. Bought high pressure fuel line and clamps from the auto parts store. Also wrapped the lines with a heat shield sleeve.
So AN6 or AN8 to accommodate the flare?
Stuff like this?
https://www.amazon.com/gp/product/B07BDFGZQ1/ref=ox_sc_act_title_1?smid=A26XZY1DGLFZZH&psc=1
https://www.amazon.com/gp/product/B07PJJZW6C/ref=ox_sc_act_title_2?smid=A2NMBIZOMZLC5C&psc=1
https://www.amazon.com/gp/product/B07KLJSVKK/ref=ox_sc_act_title_3?smid=A1W30H4E1OR4L&psc=1
 
No not that stuff except the wrap shield. Get 3/8" high pressure fuel hose. No stainless, just black rubber so it clamps better and get the high pressure clamps to go with it. not those wimpy worm clamps like in your pic
 
high pressure hose clamp = T-bolt clamp?
I have some of these in various sizes...
T-bolt.png
 
That would certainly do it, didn't know they made them that small. The return line fitting your looking for, that splices into the fuel fill hose is available at cp performance.
 
Excellent, thanks for sharing. Been wanting to that exact setup for a while now.
 
I cut the tubing and fittings off the OEM lines, then put a flare on the tubing. Bought high pressure fuel line and clamps from the auto parts store. Also wrapped the lines with a heat shield sleeve.
What the H did you flare your cut off fittings with? Harbor Freight crap can't touch it, just pushes it down the "clamp", no matter how much I compress the die.
Guess I have to take them to someone who know what they are doing.....
Going to go with pinch clamps. No T clamps small enough for 5/8 OD.
 
I finally got the harbor Freight thing to grab by putting a folded piece of sandpaper around the tubing, and sticking it in the big vise. Too cool out now to see if I've eliminated the vapor locking. Next summer will tell the story.
 

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