Engine Fuel Pressure, useful, how do I measure it?

[vas]

hello all,

finishing with my black boxes measuring all sorts of things on the boat and engines/generator, will report in detail soonish I hope as the weather is rather cold to do anything useful onboard...
Now, one thing I could measure and I don't is fuel pressure. I mean there's an option to measure it in NMEA2000 sentences, both Garmins and Maretron do support it and I've got spare inputs in my boxes.
on my non electronic engines I now measure and report on the NMEA2000 bus the following:
EngineRPM (*)
TurboBoost (*)
EngineOilPress (*)
EngineOilTemp
EngineCoolantTemp (*)
AltenatorVoltage (*)
EngineCoolantPress but I'm cheating as I use that for the seawater circuit pressure (checking for clogged heat exchangers and failed impellers)
EGT temp
(the * ones are also on analogue VDO gauges on the lower helm, only RPM on the upper helm)

and for the gbox

TransmissionGear
OilPressure
OilTemperature

I do understand and know the expected values and the implications of lower or higher for each one of them and can easily set limits to get warnings on each plotter and display on the NMEA2K bus, that's ok.

I do get from external devices:
FuelRate
EngineHours

but I haven't got any sensor measuring:
EngineFuelPress

I can happily live like that tbh, just wondering if it's something easy I may bother.
I wont if I have to mess about with the fuel pump, or tap in the pipe from the prepump thing to the fuel pump. So first question is WHERE do you tee off/tap/whatever to measure fuel pressure???

Also wonder what's the actual use of it. I can understand higher vacuum on the prefilters implies clogged filters, but what's the warning sign for the fuel pressure? OK, could also be clogged filters, but also a leak in the system or what?
Especially for the generator (that I seem to be having recurring issues with leaking CAV filter like now that the diesel tank level is lowish and seems to be drawing air, needed a bleed if left for a week or two) could I tee off between main filter and pump and monitor that pressure is NOT dropping?

cheers

V.

 

[MapisM]

No idea about where and how the pressure sensor should be connected, but in the commissioning protocol of my boat upon first seatrial, among several other parameters not monitored by the analogue instrumentation, the MAN engineer had also the fuel pressure checked.
So, there must be a way to do that also with fully mechanical engines, as mine and yours are.
Btw, he measured (and flagged as OK) a result of 3.1 bar, constant throughout the whole RPM range.

With the boat instrumentation, I have no way to re-check that, but I don't think it's a relevant parameter to monitor.
A less than normal fuel pressure would be immediately reflected in a lower engine performance, I suppose.
But I can see why you'd like to include it once the displays can handle it, of course.

One parameter I'd be more interested to be able to check is the EGT, instead.
Did you already post anything about how you installed the EGT probes, which I either missed or forgot?

As an aside, it's interesting to see that your original VDO gauges include the boost pressure.
That's now standard with electronic engine displays, among many other parameters, but pretty rare back in the days when the choice of which instruments to install was up to boatbuilders. Well, done, Versilcraft!

 

[vas]

thanks P.,

I'll wait for anyone to chip in, and if not I'll ask my mechanic tomorrow although that 3.1bar throughout the rev range could easily mean measure between the primary and main pump (or there's a blank in the pump body itself as it was in the twindisk box where I fitted my other pressure sensors.

Re boost gauge, I'm afraid it wasn't Versilcraft as the boat was originally featuring DD later replaced with the IVECOs by the PO. Even so, I bought and added the gauges after the issues with the stuck port turbo back on the delivery trip.

EGT, was an easy enough task, removed the exhaust elbow, tapped and welded the fancy nut that came with the EGT probe and that was it. OK, it is after the turbo (approx 200mm) and 150mm before the mixer bit.
checking my logs 800rpm is 180C and ~1200rpm is 260C I guess I should add a hundred + degrees for a proper before turbo placement of the probe. Happy to have a reference and be able to compare.

cheers

V.

 

[5teve]

If you are measuring fuel pressure then it would be worth measuring pressure at the bulk fuel filter to detect any vacuum (ie blocked fuel filters , pick up etc) I think there should be a point on the on engine filter to put a sender too for the lift pump pressure, as otherwise you would need to measure each injector line which would be a bit silly! Lift pump pressure won't be much.. I think sbmar recommend a 20psi gauge on the Cummins..

Steve

 

[MapisM]

that 3.1bar throughout the rev range could easily mean measure between the primary and main pump

Yup, I can't think of any logical alternative.
Upstream of the primary pump only makes sense for measuring vacuum, as you said in your OP and also 5teve in his post.
And downstream of the HP pump, there's nowhere to connect, aside from injectors lines...

 

[vas]

Steve, yes, this makes sense, was having a look at the bosch_pe(S)_inline_fuel_injection_pump_service_manual.pdf I found in a folder and almost fell asleep, not v.exciting read I'm afraid. There was a mention of the medium pressure being around 31psi. Noway you can measure injector lines as these are 3000psi

so, will have to check on the on engine filters for any blanks then and get a couple of 5bar senders on the cheap

V.

 

[5teve]

Haha brave reading that kind of thing... It's worth having a look at some mechanical gauge setups (sorry again look at sbmar for some ideas) then just replicate with sender's... It should be a moment's work compared to what else you have done ?

Steve

 

[vas]

Haha brave reading that kind of thing... It's worth having a look at some mechanical gauge setups (sorry again look at sbmar for some ideas) then just replicate with sender's... It should be a moment's work compared to what else you have done ?

Steve

yep, I have an assortment of WIKA mechanical gauges up to twindisk box oil values 300psi or so, and box full of adaptors to get them to fit in the available holes. Will try that for sure before, what I don't like is that unlike engine/gearbox oil, every tampering means bleeding, although the IVECOs with their bosch pumps are easy to deal with, the generator yanmar is a pain.

cheers

V.

 

[rafiki_]

Vas, are you looking at pressure either side of the low and high pressure pumps? To check just one of these makes little sense imho, so you would be looking at the pressure at 3 points? What are you going to do with the info? I guess the most interesting might be the high pressure to injector? Any drop might indicate a failed pipe? Potential fire hazard?

 

[MapisM]

I guess the most interesting might be the high pressure to injector? Any drop might indicate a failed pipe?

Never heard of anything like that, and I don't think it would even be technically feasible.
Besides, I suspect that the HP pump would immediately be unable to provide adequate pressure also to all other injectors, so the engine involved would die PDQ - probably even before an alarm could go off.

 

[vas]

P.,

no idea really, hence the thread. NMEA2000 PGNs have "space" for just one fuel pressure. No, don't know which one they expect.
Would make sense to have the one just before the main pump, after the liftpump and after the engine diesel filter.
30psi is easy to measure and I guess a drop would denote block filter or some sort of issue on the supply.
Granted, engine power would suffer, so not sure if it would give an early warning on something.

For sure measuring 3000psi on the pipe going to the injector for a few milisecs wouldn't be feasible, further I'd need one for each injector.
I guess things like that could be done easily on the ECU controlled common rail engines?

cheers

V.

 

[MapisM]

I guess things like that could be done easily on the ECU controlled common rail engines?

Not even on those, I think.
In fact, coming to think of it, I've seen several MAN CR powered boats, but I would bet that there's no such thing as CR fuel pressure, among the many parameters available on their displays.
Happy to stand corrected from anyone who has these engines/displays, though.

 

[Assassin]

Very easily with a non electronic engine, what pressure do you want to read?

Fit a flow meter between the fuel line to injector pump and another in the return line back to tank and deduct the return from the inlet and you have accurate readings, some units have combined flow and return in one unit and the return pipe may need lengthening to fit it and this does deduct the return from the flow and gives fuel flow rate ans generally these need a power supply and earth fitting, or you can get the electronic units as seperates or combined units and the modules for your guages is they are a common type, which VDO are.

Fuel pressure can be difficult and this depends on your fuel pump arrangement, if you have an "in tank" or "in line" or lift pump type electric fuel pump to feed your engines fuel pump then between the electric pump and engine fuel pump will give line pressure, if your engine fuel pump lifts directly from your tank then you will only ever measure vacuum as the suction side goes from the tanks to your engines and is under constant vacuum until the pump raises it to injection pressures.
On the high pressure side you can get a module which fits between the injection pump and injector pipe, or injector pipe to injector and you will need your pipe shortening to compensate for the extra length and these can be manual, electric, or electronic.

 

[MapisM]

On the high pressure side you can get a module which fits between the injection pump and injector pipe, or injector pipe to injector and you will need your pipe shortening to compensate for the extra length and these can be manual, electric, or electronic.

Have you ever seen that actually fitted to any marine engine?
Far from pretending to have seen them all, but definitely quite a few, and I never came across anything like that.
Regardless, I'm not sure I would want any kind of sensor in between the HP pump and any (let alone every!) injector.
Reasoning being, only what you don't have never breaks...

 

[5teve]

Fuel pressure can be difficult and this depends on your fuel pump arrangement, if you have an "in tank" or "in line" or lift pump type electric fuel pump to feed your engines fuel pump then between the electric pump and engine fuel pump will give line pressure, if your engine fuel pump lifts directly from your tank then you will only ever measure vacuum as the suction side goes from the tanks to your engines and is under constant vacuum until the pump raises it to injection pressures.

Not strictly true as the lift pump is before the on engine filter generally (I think??) So the lift pump to filter / injector pump is under low pressure from the lift pump and if tank is high, then it will be under head pressure continuously when not pumping.

Between lift and bulk filter (closest to tank) it will be under vacuum when running, which is great to monitor as it indicates filter trouble, as would an increase in pressure on the post lift pump side indicate on engine filter issues

Steve

 

[vas]

thanks guys, to sum it all up:

My IVECOs layout is that I have Separ prefilters/waterseparators -> liftpump -> main engine mounted filters -> highpressure pump -> injectors. FWIW, lift/highpressure pumps are in one Bosch assembly, just a copper pipe leaving going halfway round the block to the two filters and back to the highpressure part.

so my options are:

A. between Separs and liftpump: measure vacuum, checking condition of Separs
B. between liftpump and main engine filters: measure fuel pressure and combined condition of Separs and lift pump
C. between main engine filters and high pressure pump: measure fuel pressure and combined condition of all filters and agility of lift pump
D. highpressure side, is not an option IMO

Seems that IF I decide to go ahead, I should tap somewhere along the C route.
I guess this pressure (say 25psi or there abouts) stays put with the engine off and turning the key to on position even before cranking you have an idea of potential fuel leaks and any need for bleeding the circuit.

cheers

V.

 

[Portofino]

Basically only fit any kind of sensor to a system whereby if the said sensor fails for what ever reason it’s isnt gonna end up mission critical .
I wouldn’t mess .....interfere with the existing fuel lines, chopping and adding bits in ........If it can go wrong it will .

 

[vas]

Basically only fit any kind of sensor to a system whereby if the said sensor fails for what ever reason it’s isnt gonna end up mission critical .
I wouldn’t mess .....interfere with the existing fuel lines, chopping and adding bits in ........If it can go wrong it will .

that's the plan anyway!
and IF I have to cut the fuel line between filter and highpressure (at 25-30psi) I'd fit a tee and a easy way of blocking the sensor if needed (a stopcock quarter turn thing before the sensor most likely)

I wouldn't be surprised if there is a blank in the engine mounted filter housing for such a thing, just that I've not had the time to visit the boat and check. Maybe later today, weather looks good!

V.

 

[5teve]

I'd be looking for a blank on the filter housing measuring before filter... That way a pressure increase will show if filter is blocked or blocking... Post filter won't show much I wouldn't have thought. You only have one channel?

Steve

 

[vas]

I'd be looking for a blank on the filter housing measuring before filter... That way a pressure increase will show if filter is blocked or blocking... Post filter won't show much I wouldn't have thought. You only have one channel?

Steve

doh! you're definitely right Steve, makes more sense that way. It's going to be a faster responding indication of problems in main engine filters as it may still be able to provide the right pressure to the highpressure pump but struggling with it wont be visible in option C.
so option B it is then. Will report on my blank spotting findings later

cheers

V.