Fuel Return Valve Issue?

[dom14]

Hey guys,

I thought the fuel return valve was working fine after doing few tests on it(RB30 carby model), but apparently it isn't.
RB30 fuel return valve is "piggy backed" via engine RPM sensor unit.
Basically, when engine rpm hits around 1500 or more the Fuel Return Valve closes & effectively allow less fuel to return
back to the tank, which in turn increases the fuel pressure when engine's under load or accelerator pedal is pressed, allowing more fuel to the fuel bowl(carby).

My carby's been having issues with rich mixture(carbon soot build up on spark plugs) and hesitation when mixture is leaned to address the excessively rich mixture issue.

I can't say for sure, but it appears blocking the fuel return line and stopping fuel from getting to the fuel return valve appears to have fixed the problem.

Does this mean I've been having a fuel pressure issue, rather than a carby issue(rich mixture)??!!

Blocking fuel return line has improved the carby float level as well. Before it was very low.

Do I have a malfunctioning RPM counter unit(I think it's under the dashboard in driver's side) or a malfunctioning
Fuel Return Valve?! Or do I have a week fuel pump(in tank stock pump was used)
How does that having more fuel pressure improve excessively rich mixture issue?

Doesn't low fue bowl float level mean leaner mixture, rather than richer mixture?

Thanx

[garett]

do these carbys have a gauze before the needle and seat ? if it has a tiny bit of dirt it can give you a low float lvl. incorrect setting of the float arm might also give this low lvl. a fuel pressure gauge would be handy on this one after you check the float lvl setting.

[mudnut]

Have you checked the voltages present at idle and above 1500 rpm? What is the resistance of the coil?. After confirming that there is no voltage at idle, I would remove the solenoid and check to see if it is seating /sealing properly. Does it click in and out when given a 12 volt feed? Follow the procedure in the manual to release the fuel pressure before removing the solenoid.

[dom14]

Another thing I forgot to mention was that without blocking the Fuel Return Line, the float bowl would not get any petrol at all.

It did earlier, but not anymore. Fuel was pumping, it's not getting into the carby float bowl.

I'm guessing the fuel pressure is not high enough and when I block the fuel return line, the fuel pressure goes up a bit and carby float bowl fills up??!!

[dom14]

Have you checked the voltages present at idle and above 1500 rpm? What is the resistance of the coil?. After confirming that there is no voltage at idle, I would remove the solenoid and check to see if it is seating /sealing properly. Does it click in and out when given a 12 volt feed? Follow the procedure in the manual to release the fuel pressure before removing the solenoid.

I didn't check the voltage, but I tested it following the way you outlined in the RB30 thread by checking the fuel flow from the Fuel Return Valve when revving the engine. When I rev the engine, Fuel Return Valve clicks & pretty much blocks the fuel flow on fuel return line. So, I thought it was working the way it suppose to(allowing less fuel to return to the tank).
I'll check the voltage at 1500 rpm and above & resistance & other tests you mentioned above, shortly.

[dom14]

do these carbys have a gauze before the needle and seat ? if it has a tiny bit of dirt it can give you a low float lvl. incorrect setting of the float arm might also give this low lvl. a fuel pressure gauge would be handy on this one after you check the float lvl setting.

Yes, they do. There's a gauze outside the carby(bunjo bolt with a gauze filter in it) at the fuel entry, and then also gauze filter in the accelerator pump plunger/piston, but they are pretty clean, no blockage. Just to be safe, I'll change the fuel filter as well. Float arm is apparently bit low, 'cos fuel level in the float bowl is always bit lower than half, but i though it was ok.

As you advised, I should check the fuel pressure straightaway. I'll do that shortly.

[dom14]

Have you checked the voltages present at idle and above 1500 rpm? What is the resistance of the coil?. After confirming that there is no voltage at idle, I would remove the solenoid and check to see if it is seating /sealing properly. Does it click in and out when given a 12 volt feed? Follow the procedure in the manual to release the fuel pressure before removing the solenoid.

I checked the voltage on the wires.
I got bizarre readings at first. At idling it was showing no voltage then revved it jumped into incrediable 30+ volts.
I thought it must have been a momentary fault with the multimeter.

I stopped the engine for few seconds and restarted and did the test again.
This time it shows 13.6v at idling & jumps to zero when revved to around 1500 rpm or more.

I'm still wondering whether the power to the Fuel Return Valve from the rpm sensor/sender is somewhat faulty, though
above bizarre reading might have been from a multimeter fault, 'cos

There's no way rpm sender/sensor unit can produce such amount of voltage?!!!!
What do you think?!

[mudnut]

Without popping the case for the ERS I couldn't tell you what sort of signal it could produce. It deals with a pulsating voltage so if it has reactive components such as chokes and capacitors, theoretically (if the right fault conditions exist ) it could produce a voltage spike.

Also a faulty solenoid coil can produce a spike as the magnetic field collapses. A lot of solenoid coils can have a zener diode or capacitor to kill the spike.

I would do the test again with another meter and use a knockometer (plastic handle of a screwdriver) to gently tap test the components and wiring harness.

Did the solenoid click in and out with a 12 volt feed?

[dom14]

Without popping the case for the ERS I couldn't tell you what sort of signal it could produce. It deals with a pulsating voltage so if it has reactive components such as chokes and capacitors, theoretically (if the right fault conditions exist ) it could produce a voltage spike.

Also a faulty solenoid coil can produce a spike as the magnetic field collapses. A lot of solenoid coils can have a zener diode or capacitor to kill the spike.

I would do the test again with another meter and use a knockometer (plastic handle of a screwdriver) to gently tap test the components and wiring harness.

Did the solenoid click in and out with a 12 volt feed?

Solenoid definitely clicks, 'cos I can always hear it, even from inside the car when driving.
BTW, resistance between the pins of the fuel return valve solenoid is 24 ohms.

I basically disconnected the wire goes to the Fuel Return Valve solenoid and checked the voltage at idling & revving high.

When you said, "Also a faulty solenoid coil can produce a spike as the magnetic field collapses. A lot of solenoid coils can have a zener diode or capacitor to kill the spike",
Did you mean the RPM sensor/sender unit under the dash that forwards the voltage to the Fuel Return Valve?

I know about that unit from RB30 thread, but I have no idea on how to test it? I'll have to read your posts in RB30 thread again.
It basically picks the signal from the ignition coil and translates that into forward voltage accordingly, doesn't it?

Since it's an electronic unit, it's prone to fail just like any other unit, isn't it?
And that means, if the RPM sender/sensor unit doesn't work properly, then vehicle won't be running properly under load, 'cos it may end up starved of necessary fuel pressure to fill up the float bowl with necessary level of fuel?
That kinda produces symptoms that are consistent with weak fuel pump/pressure or carby float issues, doesn't it???!!

Come to think of it, RB30 carby patrol isn't that simple after all, even though it's apparently less complicated than EFI RB30.
Electronic things can go wrong inside and it can still leave you with plethora of problems.(Like the case in mine with Fuel Pump Control Unit).

[mudnut]

Yep. The return valve coil. And as you have said, if the valve is receiving a feed over 1500 rpm or it is not seating properly, it might cause the problems you have cited. I wonder if you can get hold of another valve and ERS. If there is a break or reduction of signal to the ERS it might let the valve open at the wrong time.

[dom14]

Fuel pressure(just after fuel filter) shows around 1.5psi. And that's not by tapping into it but by plugging the pressure gauge directly into it.(I ran the engine with the petrol left in the carby float bowl). Revving high won't make any difference, but it shouldn't anyway, 'cos the power to the fuel pump is from the battery.

It should show bit more than that I reckon. What do you think?

I'm not sure whether intank pump's weak or whether its' not getting enough voltage.
Tachometric relay's doing the job of FPCU now.
Voltage was ok when I wired it up & tested it.
I'm just going to give direct battery power to the pump and see whether it can produce a better fuel pressure.
That way I can rule out whether the pump's not getting enough power from the tachometric relay.

[mudnut]

Is that pressure with the fuel return blocked?

[dom14]

Yep. The return valve coil. And as you have said, if the valve is receiving a feed over 1500 rpm or it is not seating properly, it might cause the problems you have cited. I wonder if you can get hold of another valve and ERS. If there is a break or reduction of signal to the ERS it might let the valve open at the wrong time.


I'm inclining more and more towards dodgy fuel pump(intank) one from what I've seen so far, rather than dodgy fuel return valve or ERS unit.

I need a good second opinion on 1.5 psi fuel pressure. That doesn't sound right, does it?!!

I also just realized how naive I've been with my auxiliary external fuel pump plumbing.
It's an absolute PITA to connect the auxiliary pump even at the comfort of home garage 'cos the access is harder than I thought.

All the good reasons for me to setup a "shut off cock" with a Y joint, so I can switch from one pump to the other without
having to swear at the sky. :)

[dom14]

Is that pressure with the fuel return blocked?

Yes. It's blocked. That's the only way I can get the carby float bowl filled with petrol.
Classic sign of low fuel pressure than carby float issues, isn't it??!!

When I tested the intank fuel pump before fitting it back in the tank, it came out ok.
It may be an intermittent issue, hence the reason I plumbed and wired up the external pump, yet
I've done a dodgy job with my plumbing in terms of convenience to hook up the external pump plumbing to
the supply line. It's not a switching job in a flash as I previously claimed. :)
Electrically it is. Plumbing wise I stuffed it up it by the sound of it. ;)

[mudnut]

The Haynes manual states 20kpa fuel pressure. Or converted to psi (kpa x .145) =2.9 psi.

As a side issue, has the fuel pump been wired to turn off while you are running LPG?. I think they really aren't designed to continually pump against a blocked line so that's why they install a return valve.

[dom14]

The Haynes manual states 20kpa fuel pressure. Or converted to psi (kpa x .145) =2.9 psi.

As a side issue, has the fuel pump been wired to turn off while you are running LPG?. I think they really aren't designed to continually pump against a blocked line so that's why they install a return valve.

That's the way it was wired previously. The fuel pump was pumping continuously, even though the troll was running on LPG almost all the time. But, it goes back to the tank via fuel return line when idling, but not so when the vehicle is on the road on high rev. Probably that's the reason for the failure of the in tank pump.

I changed that. Now the fuel pump only runs when the fuel selector in on petrol.

When I tested the intank fuel pump on the bench, I kinda noticed it has kinda fail safe mechanism to automatically get rid of excess pressure if the fuel line is blocked(or the fuel return line is blocked). Basically, the pump has a some sort of valve that drips petrol back into the tank. This mechanism may be kinda faulty in my pump now 'cos it's been overused due to dodgy LPG conversion electrical wiring before. I think it was pumping petrol back into the tank all the time. That may be the reason for low fuel pressure from the in tank pump. Either way, it looks like the in tank pump is stuffed and can't be relied on at all(unless fuel return line is blocked, 'cos low 1.5 psi pressure apparently is a good match for the spare carby that's in the engine right now).

Yes, the recommended fuel pressure for RB30 carby Patrol is around 3psi. The external pump is rated between 3-5 psi, which is consistent with my test readings today.

BTW, I've got news for you. PEEL tachometric relay surprised me today by showing that it functions as an "auto primer" for few seconds by running the external pump when I turned on the ignition. (I connected the plumbing to the external pump and it's running on the external fuel pump now.)
Basically there's a bit of capacitance stored inside the PEEL tachometric relay that does the job of auto priming without intention or it's purposely designed with electronics inside that to do that job. I obviously didn't notice that before 'cos the in tank pump noise can't be heard from inside the vehicle.

The external pump produces about 4-5 psi pressure directly(no tapping), which apparently is bit too much for the carby 'cos the float fills up more than half(with fuel return blocked). With fuel return line connected, the pressure apparently is too low, 'cos the float level goes down too much.

I think I need to adjust the carby float level anyway.

Basically, in tank pump's weak pumping is fine if I block the fuel return line.
External pumps stronger pumping is too much with fuel return blocked, & too weak with fuel return connected.
So, it's all confusing & directs me that I need to adjust the carby float accordingly.

Tomorrow I'll start where I left this evening & sort out this problem for good, one way or the other.

[dom14]

After connecting the external pump, today I did the fuel pressure test with Fuel Return Valve(FRV) connected.
The results are confusing.
Fuel pressure is way way too low according to the fuel pressure gauge.
If I block the FRV, then the fuel pressure jumps back to 4psi or so.
I used Y joint to tap into the fuel line for connecting the gauge.
Fuel pressure obviously recover a bit when I disconnect the gauge and put fuel hose back the way it should be,
but float is still too low to be comfortable.
I'll have to adjust the carby float & see how it goes.

See the videos & pictures below.

Fuel Pressure test external fuel pump(RB30 Patrol) e (https://www.youtube.com/watch?v=o8ImtxR8uTg&feature=youtu.be)

Fuel Pressure test external pump - revving & accelerator pumping (https://www.youtube.com/watch?v=JARGj7i1ds4&feature=youtu.be)

Any ideas guys?

I know I need to adjust the carby float leve, which I didn't have enough time today to do.

But, assuming the fuel pressure gauge is accurate(which I believe it is), there has to be a FRV related reason for the low
fuel pressure, has it not?! 'Cos if I block the FRV the fuel pressure comes back to an apparent normal value.

[dom14]

Looks like I'm on my own?! :D

[mudnut]

Try a different FTV and see what happens. Patrolapart or Readies should have one. Maybe someone here has a spare one lying around. I have never had one apart so can't tell you how it can fail. Maybe theres a bit of crud stuck in the valve seat?

[dom14]

Try a different FTV and see what happens. Patrolapart or Readies should have one. Maybe someone here has a spare one lying around. I have never had one apart so can't tell you how it can fail. Maybe theres a bit of crud stuck in the valve seat?

Good tip. I'll pull the fuel return valve out completely and give it a clean and fiddle.

BTW, I've been wondering, is the FRV in RB30 an FRV or a more of Fuel Pressure Regulator in technical terms?
I know you documented it as a fully open valve at idling and sort of fully closed above 1500rpm or so.
The tests I did on it sort of concurs with that. Yet, I can't help speculating whether it's designed as a Fuel Pressure Regulator(incremental trigger sort of)
rather than on/off valve that activates on a fixed rpm.
I've been looking into aftermarket adjustable fuel pressure regulators and ones meant for other vehicles that I can probably modify for the RB30.
I'm sure Nissan has designed an rpm triggered fuel return valve for a reason, but they apparently didn't do a great job with the design of Fuel Pressure Control Valve. I'm thinking about mechanical sort of fuel pressure regulator, but obviously I need to diagnose the fuel return valve properly first.
On to it, now.
Cheers

[mudnut]

In simple terms it is an on off solenoid.

[dom14]

In simple terms it is an on off solenoid.

This is the ebay adjustable fuel pressure regulator I was thinking about.

http://www.ebay.com.au/itm/SPECO-ADJUSTABLE-CHROME-CARBURETOR-FUEL-PRESSURE-REGULATOR-1-6-PSI-512-00-/121407889601?hash=item1c447960c1:g:hecAAOSwbqpT6Nn a

[dom14]

One thing that I've learnt from this saga so far with the two Nikki carbies & fuel return valve is that how sensitive the RB30 Nikki carby to the fuel pressure. If the fuel pressure is 4-5 psi, the float level rises too much. If the fuel pressure is too low(1psi or less) then the float level is way too low as to starve the carby of fuel and cause it to run lean and hesitate on accelerator pumping.

[lsmitti]

Hey Dom14, what ended up being the issue in the end? The Fuel return solenoid or pump?

[mudnut]

Dom has been a bit quiet, lately. I can't remember what his solution to the problem was, either. Try this thread, http://www.nissanpatrol.com.au/forums/showthread.php?28517-RB30-Facts-Figures-and-Helpful-Hints/page3

[lsmitti]

Hi all, ended up being the fuel pump.

For anyone else with a similar problem a simple test is to pull the fuel line off the top of the fuel filter. Attach a pipe to the top of the fuel filter and run it into a container. Turn the key enough to hear the fuel pump start and measure the amount that ends up in the container after 1 minute.

Mine had pumped a mere 200ml at most in 1 minute. From what I can find online it should be closer to 900ml - 1 litre in 60 seconds.

Based on this it seemed the fuel pump was the likely cause since I had replaced the fuel filter and left the fuel tank Cap off when testing to ensure there wasn't an issue with negative pressure etc.

If you get enough volume into the container I would then be looking at the fuel return solinoid, carby inline fuel mesh filter (banjo bolt) or the carby itself as these bits are all after the fuel filter which is where the above test tests up to.as such.