Fuel to Carby Problem in GQ RB30

Wonder if somebody can help me with this. I have a 3.0 liter petrol/gas 1995 RB30. It runs fine on gas, but I have a problem with petrol. To cut short the long story of my various tests, here's what it comes down to.

Between the fuel filter and the carby is a fat "cylinder" that I assume to be a fuel return device. It has one spigot on the carby side, which is the outlet sending fuel into the carby (via the solenoid that shuts off petrol when running on gas). It has two spigots on the fuel filter side - one spigot takes in the fuel line from the filter and the other spigot sends out a narrower fuel line that, I assume, leads back to the petrol tank, though it appears to do so via a wired box (electronic valve of some type?) behind the grill, that accepts this hose from the cylinder and sends out another hose running back along to the tank. You can probably tell from this the cylinder I'm talk about, but in case it isn't clear I'll upload a photo of it (removed).

If I charge the float chamber with fuel, and bypass this cylinder, the motor idles indefinitely (first dropping fuel level in the float chamber window, then coming back up again to half way when the fuel pumps through, and staying stable at this level). But with the cylinder hooked up, the fuel level in the carby just drops until empty and the engine cuts out. If I keep the cylinder connected, but block off the return spigot (say with my thumb), then the fuel gets into the carby fine, and the engine idles indefinitely. I notice that if I blow into the return fuel pipe (while I have this hose disconnected and my thumb over the spigot) then there's no resistance, so the fuel return line seems to be fully open.

I'm guessing that possibly the fuel return is stuck open when it shouldn't be (maybe a problem with that electronic connector this pipe leads into?). Alternatively, maybe the return is meant to be constantly open and my problem is that the fuel pressure is inadequate (I guess with really high pressure, fuel would still flow into the carby even with the return open, given that the return spigot on this cylinder I mention is slightly narrower that the inlet spigot going into it from the fuel filter). A third possibility, I guess, is that this cylinder itself is faulty, but I'm guessing that nothing too smart is meant to go on inside this little tin - it seems like an empty cylinder with 3 spigots (and when I blow into any spigot air shoots out the other two without resistance).

Advice would be hugely appreciated. Does anybody reckon they know what's going on here?

All best,

Colin

That's your charcoal canister ?? Pollution thingy

Is your fuel return solenoid working properly? As far as I can work out, that is the solenoid towards the D/side front, with the blue wire with the yellow stripe and brown wire into the connector. According to the manual, it lets fuel flow back at idle, until the engine speed increases to above 1250 -1400rpm, then the amount should diminish. Maybe it is stuck fully open, or not getting the correct input, so it is taking too much fuel from the carby.

Thanks threedogs and mudnut for these quick replies. I reckon you might be onto the problem mudnut. I checked the cables on this fuel return solenoid and get no voltage reading at idle. Can't tell whether the voltage kicks in at higher revs (I'll need to wait until I can get someone pushing the accelerator). Any idea whether there should be 12 volts going into this at idle?

The thing that puzzles me though is that it sounds as though this solenoid *should* be open at idle, and it *does* seem to be open at idle (as I say, I can blow into the return tube connected to the solenoid, and I get no resistance). But unless I block off the flow into the fuel return, not enough fuel get into the carby to keep me idling. Maybe that points to the fuel pressure being lower that it ought to be.

What do you reckon?

Colin

The manual I have reckons the fuel pressure is supposed to be 20kpa approximately for the Rb30. I would Check all of the connections and the supply voltage to your fuel return solenoid and fuel pump, and the resistance of the solenoid, coil, before going deep. Unfortunately my manual does not list a voltage to the solenoid, sorry. To fit a fuel pressure gauge, you have to release the fuel pressure. To do that, you pull the fuel pump fuse and run the engine until it dies and crank it for a few seconds. To get higher revs, to test the voltage, just use your hand throttle, if you have one fitted. Just pull it out to get the desired revs, and rotate it clockwise to lock it on. I will try and get voltage measurements and solenoid resistance readings off my rb30 tomorrow. Its too late to do it tonight.

Great stuff mudnut. I'll take a look at this tomorrow, starting with the wiring and supply voltage to the fuel return solenoid (while locking the revs up using the hand throttle). If you get a chance to take the readings off your own RB that would be really helpful. If things look okay down there, then I'll be stopping by Repco to get myself a fuel pressure gauge. Thanks again for your help with this.

Okay, Colin, I unclipped the return fuel solenoid and dug out the two rubber grommets which seal the wires in. I then checked the resistance with a couple of multimeters, and it had a resistance of between 20 to 25 ohms. So it would draw just on half an amp, which is okay. I can hear it drop out at 1450 to 1500 rpm. The voltage readings to the solenoid are at idle 12 to 14 volts and zero volts above 1450 rpm, which is what you would expect. I am clutching at straws now, but maybe the seat on the solenoid is worn, which is letting too much fuel through? I have used some silicon to reseal the wires, making sure no silicon is between the wires, so there is no chance of current tracking between the two. The manual states there is a way to check the flow, but we will see how you go with the above info first.

Just a heads up for anyone with an RB30. The Haynes manual I have, lists the electrical system in chapter 12, page 12-15, as : Starting, charging and ignition systems - 1990 and earlier models. In fact, it has most of the correct wiring for my 1994 Rb30.

You're a hero mudnut, to put so much work into helping me along with this. Can't tell you how much I appreciate it. I followed the steps that you took yourself and it's clear I have an electrical connection problem down there at the return solenoid. I'm not getting any voltage reading at idle at all, and I can take it up to way over 2000 revs without any sign of voltage showing up. Guess I must have broken wire somewhere, so I'll now take a crack at tracking that down. You're heads up on the Haynes manual is very helpful too - I have page 12-15 open before me right now, and I'll see if this works for my '95 RB too. Looks like I need to track down the "engine revolution unit" and see if my blue/yellow wire makes its proper connection between this unit and the fuel return solenoid. Better wait until the weekend before I start messing around with this, but I think I'm now on the right track. Thanks so much mate.

No worries, mate, that is what this forum is all about. I was also curious to see what readings an operational solenoid gives. I hope you find it to be an easy fix. When you find the unit, let me know where it is, thanks.

Does anybody know where the engine revolution unit is situated on an rb30, is it in the distributor?

Its not in the dizzy, but is connected to the other side of the resistor - I cannot find engine layout to confirm where it is mounted

Yeah, I've had the same problem trying to locate it, because the manuals I have downloaded are for tb42 and td42, apart from the abridged version.

Bump. Anybody?

Sorry mate, I've no effen idea lol. Have you tried looking on vl forums or would it be different for efi?

Yeah the efi are different. I have been to busy to go tracing the wiring to find it and there is stuff all about the unit, even using the search function.

Okay, folks. I traced the wiring for the resistor and engine revolution unit, which control the fuel return solenoid. The resistor is cable tied on the top radiator hose and on my multimeter it has a resistance of 1800 ohms. (1.8kilo ohms). It looks like a little rectangular brown cap and has a yellow-black wire and a blue wire. There is also a capacitor for a different circuit next to it. The engine revolution unit is located high under the dash, above the fuse panel on the drivers side, mounted on the wall. It is a greyish rectangular plastic box and has blue-yellow, brown, black and yellow-black wires. I am unwilling at this stage to disturb it to check the voltages while it is running as it has other wiring in and around its loom. But if someone has those voltages please share them with us, thank you.

Quote:

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Originally Posted by mudnut

Yeah the efi are different. I have been to busy to go tracing the wiring to find it and there is stuff all about the unit, even using the search function.

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Mudnut, it was one of your contributions that let me know that my sort of diagnosing engineers lived in these electronic woods. :)