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Post by daveh on Feb 15, 2016 20:30:16 GMT
i posted here as i guess this is both mechanical and electrical
for some time i have been sorting a few of the problems on my mk1a p5
and during the various jobs i have run the car to check the jobs done are
working as they should the tank got very low on fuel and the dash gauge
was showing empty, so i have topped the tank up with about 5 gall of fuel
but the gauge doesn't show movement, it was working when i got the car.
i have checked the two wires and they are connected and when the ignition
key is turned on the gauge dose flicker to the empty mark but no further, so
i'm thinking the sender unit has given up. does anyone know if the sender can
be removed and refitted with the tank in situ:? and are these sender units still
available? i have not changed the spade connections at the tank sender end just
in-case it's a electrical connection problem. is there a test to check the sender unit
before removal
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Post by Warwick on Feb 16, 2016 1:37:18 GMT
Before you do anything else, try rocking the car vigorously from side to side to get the petrol sloshing around a bit, just in case the float arm is simply stuck.
Another simple cause could be that you haven't put in enough yet to get beyond the reserve level.
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Post by djm16 on Feb 16, 2016 6:05:37 GMT
AS above.
But, if sender or wiring fail, the gauge usually goes high.
[edit]: darn it, have I got that the wrong way round, open circuit low, short circuit high?
Is your temperate gauge reading correctly? it uses the same voltage regulator. If both temp gauge and petrol gauge are reading low, then it is likley the voltage regulator is faulty. But do not just replace it at random, test it!
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Post by johnwp5bcoupe on Feb 16, 2016 8:54:32 GMT
The first basic test is to take the wire off the tank sender and short it to the chassis if the rest of the wiring gauge etc is ok you will have a full tank reading, you wont harm anything then let us know? Once you have done this test and assuming you get a full reading it will be a case of removing the sender/rheostat, the locking ring will be difficult for you to remove with the tank in situ so for ease remove the tank! it will be worth it any way to see what it's like inside? the sender as long as its not corroded through can be cleaned and reused  |
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Post by daveh on Feb 16, 2016 12:29:21 GMT
many thanks for all the help and info. i cant start the checks at the moment
i have to go for a eye test today but as soon as i get back i will get on it.
and hope i don't need to replace the sender.
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Post by djm16 on Feb 17, 2016 2:07:56 GMT
A common fail in those senders with brass floats is for the float to leak. Just give it a gentle shake and you will hear the petrol sloshing around inside the float. Some of the holes are microscopic. The float is essentially non-repairable, so do not waster your time. New floats are available on eBay, but not labelled "ROver", more likely early Ford etc. from USA.
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Post by daveh on Feb 17, 2016 13:21:10 GMT
a update on the sender unit. there are two wires in unit on top of the tank one black and one green. the black wire goes to anouther unit on the tank along with a red wire, the green wire goes in to the harness, if i un plug the green wire the gauge on the dash shows a full tank i tried to earth the black wire but nothing changed the temperature and dynamo gauges are working perfectly it's just the fuel gauge that only moves to empty, as much as i can i have tried to rock the car and i did hear the fuel splashing but a vehicle of this weight is a bit had to make it roll about i dont know if this gives anymore info on what or where the problem is   |
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Post by johnwp5bcoupe on Feb 17, 2016 15:53:43 GMT
I just got the wiring diagram out I see you have a fuel oil switch  I had a MK1a and forgot that well it was a long time ago!!! Any way if you remove the earth and the gauge flips it looks like the tank rheostat is your problem if you remove the black the same thing will happen as the gauge is looking for a path to earth and your black wire connection is stuck at the earth position ie least resistance  |
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Post by daveh on Feb 17, 2016 17:46:14 GMT
so it looks like i need a fuel sender unit.i have not removed it from the tank so i
don't know what it looks like to avoid buying the wrong sender does anyone have
a part number please for the unit for a mk1a or the mk1 if they are the same
i will just have to keep the tank topped up until i find one i wonder just how much
of a search this will be,
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Post by johnwp5bcoupe on Feb 17, 2016 18:06:22 GMT
You will be lucky part No 503599 if you can manage at least it is a simple screw job to remove it best to have a look first it could be just stuck and will clean?
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Post by daveh on Feb 17, 2016 18:23:21 GMT
You will be lucky part No 503599 if you can manage at least it is a simple screw job to remove it best to have a look first it could be just stuck and will clean? many thanks since posting i have found wadhams have them in stock for p5b and all p5 models but they are closed until the 20th of feb so i will speak to them once they are open again. but i will take your advice and have a look at it and see if i can see any problems with it. this is there info Petrol tank sender Product Code: P5FUELSEND1 there is a extra charge of £4.50 for mk1 and mk1a models |
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Post by johnwp5bcoupe on Feb 17, 2016 18:38:37 GMT
Sounds like a plan at least you have found one if it's past it |
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Post by daveh on Feb 19, 2016 17:54:09 GMT
while waiting to order a new unit my mate called round and told him about the fuel sender failing
and when wadhams are open again i will order a new unit and gasket and 6 new bolts/screws etc:
he looked at it made his own tests and said he will change it for me,he tapped the tank and said it
still sounds very low on fuel, he said put more fuel in and see if that gets the gauge to move off
empty, before we go any further. he wonders if in the past it's had a fuel sender fitted from another rover model
and it needs more fuel to reach the unit float, i did ask about removing the tank with a lot of petrol in it, he say he
can change the unit without removing the tank, i don't know how many gallons the tank holds but i would have thought
putting £30 worth of petrol in it show at least show something on the dash gauge.
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Post by johnwp5bcoupe on Feb 19, 2016 18:27:38 GMT
while waiting to order a new unit my mate called round and told him about the fuel sender failing and when wadhams are open again i will order a new unit and gasket and 6 new bolts/screws etc: he looked at it made his own tests and said he will change it for me,he tapped the tank and said it still sounds very low on fuel, he said put more fuel in and see if that gets the gauge to move off empty, before we go any further. he wonders if in the past it's had a fuel sender fitted from another rover model and it needs more fuel to reach the unit float, i did ask about removing the tank with a lot of petrol in it, he say he can change the unit without removing the tank, i don't know how many gallons the tank holds but i would have thought putting £30 worth of petrol in it show at least show something on the dash gauge. 14 gallons so about 5 galls should indicate Just take it out connect it as it should be and move the sender! |
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Post by p5bdownunder on Feb 20, 2016 12:05:40 GMT
A common fail in those senders with brass floats is for the float to leak. Just give it a gentle shake and you will hear the petrol sloshing around inside the float. Some of the holes are microscopic.... My P5B was always showing half full on the fuel gauge after filling the tank to the brim. Once the level dropped below half, the needle correlated to the level in the tank. The problem? I had a olastuc float on the sender unit which was half full of petrol, so it was therefore too heavy to lift beyond halfway. A new (secondhand) sender unit was fitted with the tank in place and the problem was solved. This probably has no bearing whatsoever on your predicament but I saw an opportunity tell a story that was related to something I actually knew about! And it upped my posts to 61 in the process!  Good luck...! |
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Post by daveh on Feb 21, 2016 16:28:20 GMT
i am thinking now i need a new sender unit, it was removed today
and it looked in a reasonable good order, on the top plate it said Lucas,
so i don't if it's the original unit. the metal float had no fuel inside it, it did have a
squeak where the float arm comes out of the unit top, it was opened looked very clean
and everything looked ok etc: after a good spray of wd it was put back and now it
shows 3/4 full on the gauge and if the wire is removed the gauge shows empty, so it looks
like i still have problem because i dont think the tank is three parts full i would guess it's a good half tank
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Post by johnwp5bcoupe on Feb 21, 2016 16:39:16 GMT
i am thinking now i need a new sender unit, it was removed today and it looked in a reasonable good order, on the top plate it said Lucas, so i don't if it's the original unit. the metal float had no fuel inside it, it did have a squeak where the float arm comes out of the unit top, it was opened looked very clean and everything looked ok etc: after a good spray of wd it was put back and now it shows 3/4 full on the gauge and if the wire is removed the gauge shows empty, so it looks like i still have problem because i dont think the tank is three parts full i would guess it's a good half tank I would run it as is for a while did you test it out the tank? |
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Post by daveh on Feb 21, 2016 16:58:13 GMT
i will run it to see if the gauge drops etc, i did'nt do the job
my mate had it out in a very few minutes and he said it look ok
it was wired up out of the tank with the green wire and the black wire connect
to the battery earth pole, and it only showed empty and full when we moved the float
and as before green wire off the gauge showed empty
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Post by johnwp5bcoupe on Feb 21, 2016 18:12:42 GMT
Your loosing me a bit Dave if the Rheostat/sender is out the tank connected as it should be and provided you have a good Earth? you should be able to go from full to empty moving the arm from one end to the other! |
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Post by daveh on Feb 21, 2016 18:55:55 GMT
Your loosing me a bit Dave if the Rheostat/sender is out the tank connected as it should be and provided you have a good Earth? you should be able to go from full to empty moving the arm from one end to the other! i'm no mechanic so i'm probably explaining this back to front,lol i was watching the gauge and when the float was at it's lowest position it was showing empty then it went from empty to full in a steady move. how fast the float arm was moved i don't know, but now the gauge is not going past showing three quarters of a tank now it was refitted, i just thought it still had problems, the top plate was taken off exposing a coil of copper wire with two arms either side that move when the float lifts and lowers. i just wondered if there was a break in this circuit because i don't think the tank has this amount of fuel in it. |
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Post by johnwp5bcoupe on Feb 21, 2016 20:41:11 GMT
Your loosing me a bit Dave if the Rheostat/sender is out the tank connected as it should be and provided you have a good Earth? you should be able to go from full to empty moving the arm from one end to the other! i'm no mechanic so i'm probably explaining this back to front,lol i was watching the gauge and when the float was at it's lowest position it was showing empty then it went from empty to full in a steady move. how fast the float arm was moved i don't know, but now the gauge is not going past showing three quarters of a tank now it was refitted, i just thought it still had problems, the top plate was taken off exposing a coil of copper wire with two arms either side that move when the float lifts and lowers. i just wondered if there was a break in this circuit because i don't think the tank has this amount of fuel in it. If there was a break it would read empty! give it a bit of time you haven't got anything to loose |
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Post by Warwick on Feb 23, 2016 1:53:55 GMT
Dave, make sure that you never make or break any live electrical connections on the sender (or anything else) within the boot or near tank when the sender is removed and the top of the tank is open, allowing petrol fumes to escape. It is even possible, although unlikely, for a spark to be produced as the rheostat's wiper contact moves across the wire-wound resistance coil. This can ignite petrol vapour which could flash back into the tank with serious consequences. Although the likelihood is low, the consequences are high.
The only reason that this sort of crude (but highly effective) electrical device can be used safely inside a petrol tank is because there isn't enough air in the tank to allow combustion of the petrol vapour. The mixture is extremely rich.
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Post by johnwp5bcoupe on Feb 23, 2016 9:45:15 GMT
Dave, make sure that you never make or break any live electrical connections on the sender (or anything else) within the boot or near tank when the sender is removed and the top of the tank is open, allowing petrol fumes to escape. It is even possible, although unlikely, for a spark to be produced as the rheostat's wiper contact moves across the wire-wound resistance coil. This can ignite petrol vapour which could flash back into the tank with serious consequences. Although the likelihood is low, the consequences are high. The only reason that this sort of crude (but highly effective) electrical device can be used safely inside a petrol tank is because there isn't enough air in the tank to allow combustion of the petrol vapour. The mixture is extremely rich. Unless the gauge is short circuit he will only be drawing μA, a good word of warning though Warwick be careful with an open tank even if you think it is empty I have often wondered Warwick if the gauge went short circuit? now I know it wont go bang no Oxygen knowing what you do for a living I am more than assured it is safe  |
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Post by daveh on Feb 23, 2016 13:58:08 GMT
as always many thanks to all for the help and advice, i have a good friend
who worked as a rover mechanic and he helps me lot with all but basic jobs.
and also gives me advice. i did notice before he removed the sender unit
he disconnected the battery and asked for a plastic bag that he stuffed with
a cloth and blocked the opening where the unit was removed from. at the moment
i'm driving and running the car engine etc: to see if the fuel gauge drops as the fuel
gets used. if not then i will be ordering a new sender,
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Post by Warwick on Feb 24, 2016 10:31:17 GMT
Unless the gauge is short circuit he will only be drawing μA, ... Exactly, John. It's the possibility of a short circuit that is the danger. Unlikely to happen but you're probably dead if it does. ... be careful with an open tank even if you think it is empty ... Spot on again John. It's actually more dangerous if the tank is empty. Petrol doesn't explode. The vapour does. If the tank is full, there's not much room for vapour. When the tank is empty, it's full of vapour. That's why you never cut, solder, weld, or put a flame near an 'empty' tank unless it's been fully purged with steam or inert gas and all liquid petrol residue and vapour has gone. As for those of us who don't have those facilities, the only real option is to fill it to overflowing with water before doing any hot work on it. |
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I had a MK1a and forgot that well it was a long time ago!!!
