V8 1971 P6 - need an electric fuel pump!

[montythemole]

OK new here and my first ever post! Hoping someone can shed some light here on my 'new' 71 P6 V8.

When I got the car the amps on the car meter were down and it was a pig to start without a jump. Fitted new alternator and battery, now starts well.

The old unit was a Lucas 18ACR tag on, which after some searching translates as a factory part No: 54021427, rated at 43Amp. From internet I gathered the same alternator is also known as LRA100, LRA103, LRA106, LRA109, LRA226, GXE2276, 1504563, 1553528, 3900, 3901, 3956, 7060, 7065 and 6071967 by other car manufacturers. (BL, Ford, Landrover). Also found the Lucas LRA460 unit is rated at 55Amp and has better charging characteristics and is a direct swap (according to internet). So I sourced one of these and fitted it.

On initial start the amps read a healthy postive (about half way across on the gauge) but then returns to only just in the + and doesn't move even with electrics on (previously if you sat idling and switched on lights etc you were into the negative side) so I presume the charging is better but maybe ammeter a little low reading?

This is where fun starts:
On way out today - no reading at all from temp and fuel gauge. The tacho seemed about right but would bounce in time to the indicators (?). Figured I must have knocked off the temp sensor whilst fiddling with alternator which would explain the temp. Unsure on the fuel gauge.

On way back, temp and fuel gauge back and working fine. The tacho however started to 'drift' up until it looked like I was redlining even when cruising. Got home now and found that as soon as you turn the ignition to on (even with engine off) it shots across to off the scale.

I'm guessing the car might have a voltage stabiliser (Haynes manual in post!) which could make it erratic, but full deflection seems odd?
I know tacho under-read with poor earth etc but this is just now off or full scale?

Any help appreciated. Once I sort this I can start worrying about releasing some of the V8 burble.

Oh and the car:

 

[DaveHerns]

Re: First Post - Tacho issue and other gremlins on V8

NIce car
I'm tempted to say the new alternator is not related to the faults you have . Your voltage stabiliser would appear to be playing up but that would not affect the rev counter .I think that has just died a death unless anyone else knows differently

Your ammeter is showing a well charged battery and that the alternator is still charging at tickover ,This is what you want ,The old ACR series doesn't seem to charge at tickover and the red light comes on

 

[darth sidious]

Re: First Post - Tacho issue and other gremlins on V8

Just to reinforce what Dave says:-

The initial charge reading after starting will 'jump' to a high-ish reading, then drop down to what the Rover handbook deems a 'slight balance charge'. Unless the battery was in a significant state of discharge, this is normal (so I am told! We had a P6 once, but with no ammeter!)

The alternator charges the battery via what they call an 'ammeter shunt'. The ammeter shunt is, believe it or not, a hefty (able to carry large currents) but very small (ohmic) value resistor! It has what I call 2 'sides'. The one which is connected to the main lead from the battery/starter lead, which I call the 'battery side'. The other side is connected to the alternator feed, which I call the 'alternator side'.

As current flows through this shunt resistance, it develops a very small voltage proportional to the current flowing. If the current is flowing from the alternator end to the battery end, it will develop a very small voltage across the shunt, this is sensed by the ammeter and moves the needle into the positive direction.

According to my wiring diagram from the 'Haynes Book Of Lies', the majority of the electrics take their power from the 'alternator side' of the ammeter shunt. With the engine running (and alternator working, of course!), the current demand of the majority of the electrics comes from the alternator itself and does not pass through the shunt, hence will not register. The only current that would register on the ammeter in this case is the current to the battery (and the electrics that are connected to the battery side of the shunt [horn, interior lights, cigar lighter. hazard warning, (generally the items that are not wired through the ignition switch)], but these are non-constant use items).

In the event of putting on the electrics with the engine not running (or, as you had, with the alternator not charging properly), the current to these items flows from the battery side, through the shunt, to the alternator side. However, of course, the current is now flowing in the opposite direction (to the direction when alternator is charging), so the voltage developed across the shunt will be of opposite polarity. The ammeter registers this as movement in the opposite direction (i.e. towards the - end of the scale)

One point I would make, not meaning to worry you, maybe some of the others here know this answer better. If you have a larger output alternator, there might be a risk that the alternator shunt may get too hot and/or burn out if the larger current draw was flowing through the shunt (taken by the battery [if the battery ever got to a significant state of discharge], or those electrics wired to the battery side). I know the ammeter shows +60 and -60 amps, but the shunt may not be 'comfortable' for that amount of current.

 

[montythemole]

Re: First Post - Tacho issue and other gremlins on V8

OK thanks for assistance! So in conclusion I probably need a new tacho and to keep an eye on the alternator and make sure I'm not frying anything. Now where sells rover tachos?

Very informative description of the alternator. Knew what an alternator did but not in detail!

 

[quattro]

Re: First Post - Tacho issue and other gremlins on V8

If you have several gauges playing up at the same time, I would have a good look at the connections behind your dash.

My car had several wires cut, and many more attached to various extras which caused all sorts of problems. Hence its name, 'Sparky.'

Don't asume that all is as it should be behind there, someone could have had a rewire without knowing enough to do so. Can you take any pics of your wiring, i.e. the fuse box, behind the dash, behind the switch panel in the centre of your car, under bonnet etc, just in case there is something obviously wrong. Look out for any of those horrible little blue connection blocks which people use to attach new wires - not good.

If you still think you need a tacho - http://cgi.ebay.co.uk/rover-P6-3500-tac ... 286.c0.m14

 

[darth sidious]

Re: First Post - Tacho issue and other gremlins on V8

Don't asume that all is as it should be behind there, someone could have had a rewire without knowing enough to do so. Can you take any pics of your wiring, i.e. the fuse box, behind the dash, behind the switch panel in the centre of your car, under bonnet etc, just in case there is something obviously wrong.

Very good idea!

Look out for any of those horrible little blue connection blocks which people use to attach new wires - not good.

I assume quattro is referring to Scotchlok-type connectors! They are meant to be used to tap off power from an existing wire to a new wire. They have a blade which splices through the insulation of the wires, and work on a similar principle as IDC connectors used on telephone and network circuits.

They come in various colours: red for smaller wires, blue for medium/general purpose, yellow for large, brown for splicing a small wire into a large wire, etc. I have actually seen a white Scotchlok-type used in a fog lamp kit.

I am not entirely convinced they are 100% reliable in a car environment, even inside the car (where it's [hopefully!!] sheltered from the elements and heat). I certainly would not advocate using them in the LT ignition circuit wiring!

If you still think you need a tacho - http://cgi.ebay.co.uk/rover-P6-3500-tac ... 286.c0.m14

Two types of tacho-sensing were used on the P6's; Current (RVI) (until ~1972/3)and Voltage (RVC) (~1972/3 onwards), so I would suggest you check this is the correct type for your car before buying it! I know it says it's from a 3500, but it does not say which year of car. The picture does not have sufficient resolution to see clearly if it has "RVI" or "RVC" in the bottom of the tacho face. (But I have to say that after looking at the picture, I tend to think it is more likely "RVC" and than "RVI")

The current sensing RVI tacho senses the number of times the LT current changes in a given time, and is wired in series with the LT circuit. The voltage sensing RVC tacho senses the number of times the voltage across the points changes in a given time, so is wired in parallel with the dizzy.

From the age of your car, I would say it almost certainly has an RVI tacho (unless someone has been changing the wiring, as quattro suggests!)

Take some pictures of the wiring behind the cluster. That would help a lot!

 

[montythemole]

Re: First Post - Tacho issue and other gremlins on V8

OK thanks all for assistance.

Rev counter is an RVI unit (current) so is same as I have in my MGB (which is also playing up but in this instance reading a consistent 2x). Today it appears to be working OK so unsure what is up.

Took your advice and had a look behind (still awaiting my Haynes so only looked where access was possible through gloveboxes etc).

This is on passenger side. Fuse cover removed for photo. Note one scotchlock into loom. Also not number of loose wires on the right. Unsure what these are so have taped up at present to stop any shorts.

The stereo, all seems normal here although have taped around the spades as well as I don't like thinking they could get pulled out.

Passenger glovebox. The plug you see goes straight to the round push button and nowhere else so something has been added and removed at some point. Previous owner had no idea what it was meant to do either. Possibly old stereo install. The rectangle switch on the dash I'm told is the rear window element but yet to prove. The other wire is a speaker wire.

This is the view into the stereo hole, you can see a bunch on connectors. One of the male and one of the female are unconnected but until I know what they are I have now taped around and left disconnected. The wires dissappear off a channel at side of centre consoler and go up to main dashboard. Will remove main dashboard when Haynes arrives.

So overall I have a dead switch that I can remove, one bunch of unconnected wires and one bunch with one unconnected.

The only things not working on car are one of the dipped beam lights and a temperamental tacho that may have now fixed itself.

Incidentally how do you change headlight bulbs, remove the grill and access from the front?

 

[Dave3066]

Re: First Post - Tacho issue and other gremlins on V8

Hi Monty

Nice car you have there.

This is on passenger side. Fuse cover removed for photo. Note one scotchlock into loom. Also not number of loose wires on the right. Unsure what these are so have taped up at present to stop any shorts.

These will be the foglight wires. Search the forum for threads on these. There may also be some associated with the air con. I have a couple of loose wires there marked up as such. Most car manufacturers fitted a standard wiring loom that had the wiring for every option but just used the one's fitted.

No idea what the black push button is but the connector is the type used on the indicators and main beam stalks.

Incidentally how do you change headlight bulbs, remove the grill and access from the front?

Sealed units I think. Lots available on eBay though.

The main problem with wiring that has been altered is that it can be a nightmare to trace circuits due to false earths, concurrent paths and not knowing how the circuit should work. It would be great if people drew a new circuit diagram to show were they'd added bits. Then future users would have a much easier time of tracing circuits.

Pick one function at a time and check the wiring for that circuit, noting any strange circuit branches that appear to be redundant. If all else fails, you could see if you can get a hold of another wiring loom.

Good luck

Dave

 

[montythemole]

Re: First Post - Tacho issue and other gremlins on V8

Hi Monty

Nice car you have there.

This is on passenger side. Fuse cover removed for photo. Note one scotchlock into loom. Also not number of loose wires on the right. Unsure what these are so have taped up at present to stop any shorts.

These will be the foglight wires. Search the forum for threads on these. There may also be some associated with the air con. I have a couple of loose wires there marked up as such. Most car manufacturers fitted a standard wiring loom that had the wiring for every option but just used the one's fitted.

No idea what the black push button is but the connector is the type used on the indicators and main beam stalks.

Incidentally how do you change headlight bulbs, remove the grill and access from the front?

Sealed units I think. Lots available on eBay though.

The main problem with wiring that has been altered is that it can be a nightmare to trace circuits due to false earths, concurrent paths and not knowing how the circuit should work. It would be great if people drew a new circuit diagram to show were they'd added bits. Then future users would have a much easier time of tracing circuits.

Pick one function at a time and check the wiring for that circuit, noting any strange circuit branches that appear to be redundant. If all else fails, you could see if you can get a hold of another wiring loom.

Good luck

Dave

Ta! Haynes arrived today so can have a play soon.

Wiring is on the whole very good, much less messed about with than far younger cars I've had. Assuming one set of spares is fog light, and the round switch is not connected it only leaves me with a unknown scotch lock and and the unknown connections by stereo.

Off on ebay to buy a new headlamp than. Silly sealed units.

 

[DaveHerns]

Re: First Post - Tacho issue and other gremlins on V8

If yours is an "S" 2 of the spare wires may be for the gear selector light you don't have

Has it got a hidden switch as an immobiliser ?

 

[montythemole]

1971 V8 in poo Brown.

Mini update. Decided to take to a local car show so had to get it running. Been struggling to start (turns great but no fuel) which was diagnosed by peeps on retro rides as weak mechanical fuel pump and advised to suck through the fuel myself (mmm tasty) which worked a treat.

Wife drive it to the car show (I was in the MGB) and loved it, took the nearly 2 year old daughter and the -2 month old next baby with her.

Some random shots:

It's up for an MOT now and realised I've driven it a total of 8 times in 9 months of ownership. What a waste!

Torn between selling it as 2nd baby on way, or blowing some of my bonus on getting the odd paint imperfection sorted, adding a new fuel pump (anyone recommend a suitable pump) and possibly going for a big ass carb and filter. Decisions decisions....

 

[SimonG]

Hi,

I was reading through this post and noticed that you had the same tacho problem that I have with my 72 P6B which is yet unsolved, that is, needle constantly full on as shown in your picture. Did you eventually fix the tacho problem?

Cheers...Simon