Welcome to the Nissan Patrol forum. To post a question and to see less adds on the forum then you will have to register
first. We are an easy going friendly forum so join in the conversations and feel free to ask any questions.
Become a forum sponsor for only $20 and see no adds with faster page loading times and many extras benefits.
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.
Last edited by dom14; 29th November 2016 at 06:56 PM.
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.
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.
Last edited by dom14; 29th November 2016 at 07:17 PM.
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.
Last edited by mudnut; 29th November 2016 at 07:56 PM.
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.
Last edited by dom14; 29th November 2016 at 11:59 PM.
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.
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.
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?
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
Reply With Quote
Originally Posted by mudnut
