HELP - Removal / testing fuel sender unit

[GeekOKent]

hummm a good thought. I can't remember how or why I thought that but some googling seems to confirm my thoughts that the 1 gauge does both tanks. A light is supposed to come on when the sub-tank is being used but again I haven't seen this. I also haven't come across a second gauge.

Yes. 1 gauge. Shows diesel in tank currently 'engaged' . And there is a little 'sub' light that comes on when the sub tank is selected. I can take pictures etc in a few days. If needed. However the actual manual.for the truck says the same thing

 

[StarCruiser]

Nick, you say the gauge has never worked, do you mean that you run from one tank and the gauge reads correctly. You switch to the other (sub?) tank and everything works as it should but the gauge drops to zero? Or does it stay in the same position?

Your switch has a lamp between pins 1 and 2 by the looks of it.

The relay will either have three sets of changeover contacts (11 pins in all) or be split across more than one relay. My guess is that it may be combined into a module or ECU which could be simply a box of relays. Once you find this you should have all the main and sub tank wires to check at that point. It could be the result of corrosion on a plug, as the signal is very low level it can be blocked by corrosion or a slightly poor connection. I would expect the module to be under the dash and clearly labelled but I could be wrong.

 

[nick_the_fish]

Thanks GOK I knew I saw it somewhere. Like you say it is in the owners manual.

@chapel gate thanks for the link. Some useful stuff in there.

@StarCruiser Rich, if I think back it may have worked in the VERY early days but we've had the truck for 10 years no so can't really remember.

do you mean that you run from one tank and the gauge reads correctly. You switch to the other (sub?) tank and everything works as it should but the gauge drops to zero? Or does it stay in the same position?

The needle stays in the same position - but everything else works fine. The engine can run from the sub-tank.

I'm going to have a good dig around today, so i'll let you know. I like the idea of disconnecting the solenoids - i'll give that a go.

 

[StarCruiser]

Ok, here’s a theory for you.
1, the changeover is managed by a ‘module’.
2, the module contains several relays, one of which changes over the gauge.
3, the relay responsible for changing over the gauge has a fault either internally or externally that stops it operating. This could be a ‘dry joint’ where solder has cracked, or a corroded track on a circuit board, or it could be the coil in the relay has broken.

So once you’ve found the module, test each relay coil in turn. This may be tricky to isolate them individually though so first look for breaks or poor soldering. You may need to unsolder the relays from the board to test them in isolation.

From your description of what is happening I suspect your problem lies within the module not within the wiring or the sender.

One caveat, when you switch off, does your gauge go to zero or stay at the last position?

 

[nick_the_fish]

Sounds like a good theory Rich. Yes when I turn off the ignition the needle drops to zero.

Taken the truck apart this morning. I've traced back the wires from the solenoids to the loom that runs along the passenger sill but can't find them where they emerge by the passenger footwell. I've also tried starting at the switch and working backwards but they quickly all become pale blue and disappear off in the directing of the dashboard.

I'm assuming this thing is going to look like a relay, or look like something that houses a few relays, or at the least only have wires going into one side of it?

 

[StarCruiser]

I’ve no idea to be honest, I’m guessing and going by generic troubleshooting. I would expect a box a bit bigger than a fag packet with a connector on one side as you say but it could equally have several connectors. I believe there is a ‘Body Control box’ on 100 series which may well be present on the 105. It may be in that, though as a sub tank is likely to be an option, I doubt it.

I’m running out of suggestions I’m afraid short of locating a FSM and looking for it there.

 

[nick_the_fish]

Thanks Rich, i'll keep looking. Its got to be there somewhere right, and assuming its somewhere semi-accessible there are only so many places it can be. When Amy is back from London at the weekend i'll disconnect the solenoid and listen for the click.

Will keep you updated

 

[Chris]

Nick, I found this item called 'switch - fuel control' It's somewhere in the middle of the dash / console. Any value?

 

[nick_the_fish]

where did you find that @Chris It looks like Toyodiy but I don't get drawings when I look....

I have had the centre console out but i'lll whip it out again and have another look. Certainly sounds like the part. Although that one is on an automatic, but hopefully it'll be the same.

 

[Chris]

It is TOYO Nick. But I get the drawings too. That's why I was a bit bemused yesterday when you said you'd looked and couldn't find anything. Yes I did put in that it was a manual but sometimes the drawings are only relevant for the parts they're showing rather than have two drawings (man + auto) to show exactly the same bits.

I'm guessing you'd like the drawings too, huh?

 

[nick_the_fish]

sure would. What do I gotta do to get those bad boys?

 

[Chris]

I'll be in touch

 

[StarCruiser]

The fact the fuel gauge drops to zero on shut off but doesn’t move or drop to zero when you change tanks just adds weight to my theory. If the fault was (sub tank) sender related, I.e. open circuit, the needle would drop on changing tanks. If the fault was a short to earth the needle would go to the full position. As it doesn’t move, it clearly retains a signal part way which can only come from a correctly connected working sender. As your tanks can be at different levels but still read the same for both, and the main tank gauge works fine, it can only be that a relay isn’t changing over.

 

[Chris]

Nick, I am presuming you have the FSM? You may not as it's a 105 but I have the 80 version and that has a section on the fuel transfer system with diagrams and trouble shooting etc. Looks like this ...

 

[StarCruiser]

It looks like it’s a different setup Chris. There seem to be only 4 terminals on the sub tank switch. Also it seems the gauge changes over with the switch, according to the 105 manual.

Interesting looking at the 80 setup. I’m guessing the solenoids are changeover ones on the fuel side? Simple system.

 

[Chris]

Well as I said - but there may just be a gem in the section. I have this system and there is no gauge changeover on mine. It reads actual content on two different gauges at the same time. I could have grafted the second sender in but it seemed like too much work. I think for Nick it would be easier to fit a second dial!

 

[nick_the_fish]

Nick, I am presuming you have the FSM?

Nope afraid not. I've been trying to get one for ages but haven't found one

The fact the fuel gauge drops to zero on shut off but doesn’t move or drop to zero when you change tanks just adds weight to my theory.

Its reassuring that I don't need to worry about broken cables etc. Just got to find this relay. Now Amy's back from London we can try to listen for clicking, although presumably depending on which part of the relay is broken it might not actually be making clicking noises?

I had a look in the location mentioned in post 28 but could only find this

which I think is a Servo motor(?) and probably not connected to the fuel switchover (A/C maybe?)

Interesting I also noticed this

It doesn't show on the photo but the connector joins to the block that the other cables from the switch join to. Theres loads of un used connectors in my 105 because it is a very basic model, but this one has dirt on and looks like it might have once been used. Its a long shot but i'm wondering if at some point someone has removed something (like a relay module) and forgotten to put it back on (she has after all spent a lot of her life in Africa as a service vehicle for a water company).

I found a part number for the 'switch - fuel control' mentioned in post 28 and they are £35 on Amayama. Unfortunately there isn't a photo but I might pick one up. If it is the part it might at least help me know what i'm looking for.

I did think about putting in a separate fuel gauge, but I like to keep things as close to the base build as possible so that I don't inadvertently make more problems than I solve. I don't mind adding electrical things on the leisure battery side but don't like changing this on the factory install side.

Anyway thanks for all your help on this so far chaps. The search continues...

 

[Chris]

Well it's progress Nick, of sorts

 

[StarCruiser]

I don’t think there would be a relay module missing as such as the solenoids change over but the gauge stays put.

I’ve been giving Chris’s post some thought and if you have a pair of solenoid valves just like the 80 then I expect they will work just the same. Also thinking that the underside of your truck is 80 series to a large degree, it makes sense that they would stick to the same way of doing things. Inspection of the solenoid valves to see if they have one pipe from each fuel tank and one going to the engine bay each plus a shared two pin connector would confirm this.

Thinking on, if that is the case, the Body is a 100 series and the gauge is the bit that’s different, utilising one not two gauges. This could well be switched using only a standard changeover relay not a box of relays as I first thought (sorry for the red herring here it’s not as if you’ve had to take the dash apart or anything ). You may also be correct that you won’t get any clicking if my theory is right.
So, locate your relays. This one will likely be a 5 terminal one. If you remove these in turn and watch for the fuel gauge to drop to zero then you will have found it. Swap it for an identical one temporarily and try your sub tank switch and you should hear it click and see the gauge change. Test across the coil pins if you can work out which they are, and you should see a connection of a number of Ohms if it’s good or no connection if it’s toast!

 

[nick_the_fish]

Yep still trying to figure this out folks!

I managed to get a load of 100 manuals from a really helpful chap on IH8MUD (37 in total) all of which apply, in parts to the HZJ105. There are 1000's pages but among them I found this

which references the fuel tank select relay that we could be looking for. Question is, how would you read the diagram? Behind the tail light (I've looked there and can't find it) or under the car near the fuel solenoids (looked there also).