O1973 tr6 wiring diagram

[John McLennan]

Saffrontr, Elclem1 and kevo_6

Many thanks for your offers of help. I got a 73 CR schedule from matttnz which matches my car.

Problem now is that the new loom does not seem to have all the matching wires in the appropriate branches.

Currently buzzing out any orphan wires to see where they go.

Thanks all

John

[John McLennan]

Hi All,

The new loom is now installed and I have all electrical function. (Thanks Matt for the 1973 wiring schedule)

However I have a problem now associated with the Bosch fuel pump. We all know from many previous posts over many years how sensitive the pump is to less than 12 volts.

With the new loom, I measure 10.05 volts across the pump. Running a dedicated earth to the battery made no difference and running a parallel wire from the fuse that serves the pump only made a minimal difference.

Running a wire direct from the battery gives me 11.8 volts across the pump. Unfortunately I do not have a pressure test guage so cannot provide information on the fuel pressure difference although I am sure many in the forum have graphed this before.

My point here is why a supplier of replacement components for our TRs does not seem to have addressed this well known issue with our fuel pumps.

Stay well all of you.

John

[Waldi]

Hi John,

Have you measured with a running engine?

Also a 1973 car probably has a cut-out switch.

And the full current runs through the ign switch, or do you have a relay installed?

Cheers,

Waldi

[astontr6]

12 hours ago, John McLennan said:

Hi All,

The new loom is now installed and I have all electrical function. (Thanks Matt for the 1973 wiring schedule)

However I have a problem now associated with the Bosch fuel pump. We all know from many previous posts over many years how sensitive the pump is to less than 12 volts.

With the new loom, I measure 10.05 volts across the pump. Running a dedicated earth to the battery made no difference and running a parallel wire from the fuse that serves the pump only made a minimal difference.

Running a wire direct from the battery gives me 11.8 volts across the pump. Unfortunately I do not have a pressure test guage so cannot provide information on the fuel pressure difference although I am sure many in the forum have graphed this before.

My point here is why a supplier of replacement components for our TRs does not seem to have addressed this well known issue with our fuel pumps.

Stay well all of you.

John

Hi John,

In my experience you have to use a 30amp relay with power source direct from the battery to power the pump, s/w through the ign. s/w through 4mm2 wire which is rated at 39amps to guard against volt drop. You do not state the part number of the Bosch pump as some have a running current of 15amps appox. and this my be where your problem lies, down to wire size.

Bruce.

[John McLennan]

Hi Waldi, AstonTR6,

Measurements taken with engine not running since I suspected a fuel delivery problem being the cause of the engine not starting. There is no relay in the system. Before I started the body off rebuild I did have the Bosch conversion supplied with an uprated wire from the inertia switch (after market - not original) and this in turn supplied direct from the battery /alternator via the ign switch (heavy guage wire) and had no problems over many years. 

I had hoped a new loom would have addressed the voltage drop problem but sadly no.

I 'm afraid I don't know the part number of the Bosch pump assembly but it was fitted over 10 years ago.

Currently awaiting the copper washers for the sealing of the head oil supply before trying starting again with a uprated supply wire.

Will update.

Regards and thanks to all.

John

[Waldi]

Hi John,

there is an opportunity for improvement!
loosing 1.75 V (your post above) from battery to pump is not good.

I would install a relay, which also relieves the ignition switch. Also check the voltage drop across the inertia switch (with running pump), it should be very low.

Snd lastly, measure the voltage drop from pump negative earth (on the pump connector) to the battery negative pole, this should also be very low.

Disconnect the ign. Coil while measuring so it does not get cooked.

Waldi

[John McLennan]

Hi Waldi, Astontr6,

Thanks, will take your advice and fit a relay. (Will need to wait until Motor factors etc reopen here)

The continuing story with my fuel pump. Copper washers arrived and engine ready to go. With 11.8 volts across the pump it sounds OK but I do not believe I am getting any significant fuel pressure. Slackening (slightly) the feed to the MU shows some weeping of fuel  but not at 100psi and there is no pressure behind the fuel return to the tank. (If this is to be expected)

If I take off this pipe and fit a length of clear tube the fuel only rises a few inches and if I suck on the tube I get a lot of air along with some fuel which still does not rise up the pipe. I do not know the circumstances in which the MU returns fuel to the tank so any help here appreciated. I have checked all fuel lines and there are no air or fuel leaks and unfortunately I do not have a pressure test set so can only assume I have a pump problem. Other than what I have done, is there go/no go check for high fuel pressure? Given the apparent lack of pressure I am reluctant to invest in a pressure test set up if it likely that a new pump is necessary.  For information both the MU and Bosch pump assembly have been off the vehicle for over 3 years.

So, any further tests before I order another pump?

Waldi - For your information the pump earth is wired to an adjacent body earth point rather than the loom wire.

Thanks

John

 

 

 

 

[Waldi]

Hi John,

it would be good to check the polarity of the pump. Is the white wire connected to + and the black wire to earth? There are often markings on the pump.

If that is ok, next step:

If you would disconnect the discharge line from the pump to prv (this should come out of the “barrel”, not the front cover of the pump), and connect a hose from there to a large can or back in the tank filler opening, make a short start, there should come A LOT of fuel; beware of the risk of fire, this is not a safe practice. Best done outside with a 2nd person and a fire extinguisher near by.

If the pump runs, it should give some fuel at least. If not, check if the nrv in the pump outlet opens (spring loaded), and if ok, check there is fuel flowing towards the pump from tank.

Basically it is a step by step process to rule out possible failures.

Safety: with every step you do, think what can happen before you do it. 
 

Waldi

[John McLennan]

Hi Waldi

Pump has two blue connection but marked + & - so all connections OK.

Output from pump to the PRV is a banjo so I will connect the hose to the PRV to another hose and back to the tank filler.  When working with fuel I always have one fire extinguisher close to hand and if more "risky". somone standing by with another. I echo your safety concerns for anyone working with fuel, high pressure or not.

After this test I will take the pump/filter unit out and check the NRV as you suggest. Got an excuse now for not working in the garden!

Stay well.

 

John

[John McLennan]

Waldi,

Fuel pump delivers what I guess to be about 5 litres a minute through a 5mm ID tube which I don't think can really have 100psi behind it. (I am sure someone has already calculated what 100psi actually translates to in fuel flow terms)

I also discorrected the tank feed and supplied the pump with gravity fed fuel from a fuel can, again through 5mm ID tubing and there was no difference in flow rate so I should be able to discount the tank feed.

For information, the pump is about 12 years old and has about 35k mls under its belt. Any likelyhood that the Bosch filter maybe impeding fuel flow?

I have dug out an old "996" which was donated to me some time ago. None of the fittings came with the pump but will lash something up to see what fuel delivery I can achieve.

Thanks again.

John

[John McLennan]

Waldi,

Fuel pump delivers what I guess to be about 5 litres a minute through a 5mm ID tube which I don't think can really have 100psi behind it. (I am sure someone has already calculated what 100psi actually translates to in fuel flow terms)

I also discorrected the tank feed and supplied the pump with gravity fed fuel from a fuel can, again through 5mm ID tubing and there was no difference in flow rate.

For information, the pump is about 12 years old and has about 35k mls under its belt.

[John McLennan]

Update

I have an old 996 pump donated to me some time ago.

Have connected it up using same set up as above and pump runs quietly and smoothly. Fuel delivery rate is similar but possibly slightly less than the current Bosch set up.

Think I really need to take some pressure measurements to close off this investigation.  (and this slightly hijacked thread!)

Thanks

John

[Waldi]

Hi John,

5 liter per minute equals 300 l/hr.
I agree, you can rule out the tank and flow to the pump.

The flow rate at 105 psi pressure will be less off course.

Here is a curve of the ..044 pump, which will behave similar. You can see the flow  rate reduces by 30-50%, but this would still be ok. A worn pump may however still provide flow at a low pressure, but due to internal leaks quickly reduce in flow rate once pressurized. 

So this test was a good next step, but not conclusive for your pump condition.

Can you connect an air line from a compressor to the prv inlet? Then slowly increase pressure, and see at what pressure it opens? Tge air would be bubbling in your tank, and could potentially overpressure (blow up) your tank, so have the filler lid open!

The prv has a little plastic strainer in the inlet, remove this first and inspect and clean. It is very dirty, that could be the cause of “no pressure” too.

Cheers,

Waldi

Edit: 105 psi equals 7.2 bar.

Edited April 5, 2020 by Waldi

[John McLennan]

Waldi,

Thanks for the information on pump performance but I am not sure about the apparent reduction in flow with increasing power drawn.

When carrying out my test there was a slight bit of weeping from the PRV return but nothing excessive. I will try the air pressurisation test tomorrow. What pressure should the PRV open at?

Thanks

John

[Mike C]

I set mine to open at 680kPag on air  with a calibrated gauge. My CP has always  ran  well at this setting.

[John McLennan]

Waldi, Mike,

My airsupply is a bit unsophisticated so difficult to slowly increase air pressure and know exactly what I am providing. I made up some connectors and tried the exercise on an old prv. (I assume the test process is to blank off the PRV output and wait for the pressure to open the return.) The PRV leaked air at only a few bar so I have parked this test in the meantime before taking the PRV out of the car to check the filter.

What I did do was to route the PRV overflow to a seperate tank where I could see fuel flow. When powering the pump you could hear it pressurise the metering unit and then the pump tone changed and the PRV opened. This suggests to me that the pump is (now?) providing an adequate flow and that it and the PRV are functional although maybe not at optimum pressures.

Some more tinkering tomorrow and I will report progress and think I will invest in some good guages.

Thanks for the help.

John

[Waldi]

Hi John, 

Looks like you are getting good progress. 
For this purpose (getting the car running), the PRV pressure does not need to be very accurate. Target for 6.8 to 7.2 bar. Maybe you can borrow a known good one?

If the PRV is set to low, fuel will get to the MU but never open the injectors. Lower pressure means leaner running, higher pressure rich running, and also a rapid reduction in flowrate. But the simple test would be ok (For me) to see if you can find the issue.

Do not forget the small filter in prv inlet. That would be my first step, easy and no calibration involved.

Waldi

[Mike C]

My old Lucas PRV has only an inlet and an outlet. I hooked it up to an air supply from my garage compressor with a tee to the gauge and it held 680 kPag. The PRV is basically a spring vs pressure force gadget so Reynolds Number effects etc don't come into the setting. When I first did this I even checked for Mach No effects in the throat- there was no chance of these.

If your PRV leaked air at a few bar then it's opening setting is too low.

[John McLennan]

Mike , Waldi,

Firstly, I have ordered the bits I need for a fuel pressure test but expect it will be a couple of weeks till they arrive. I live in a very rural area here and borrowing stuff is difficult even if I knew the French words for it!

Today I checked the injectors and whilst the engine was being cranked, for 10 seconds or so, checked for a spray pattern. No spray from any injector. Bled all injectors and got an initial pulse of fuel from 4 of them and then nothing. So possible confirmation of low fuel pressure. (?)

So before I go further I need to confirm fuel pressure and take it from there. PRV filter is clean. (PS, the battery is new and I keep it on full charge for these tests.)

Thanks again guys and I'll be back in touch in a few weeks most likely on another topic other than wiring!

Regards and stay well

John

[Waldi]

Bon jour John (Jean),

non-pulsing and non-spraying injectors do not give full confirmation that the pump pressure and/or PRV setting is too low. 
Even if everything is as it should be, it will take some time before you can feel pulsing when the system was opened and air entered. The fact you had an initial pulse on 4 lines is in fact positive. 
One thing you could test is the current draw by the pump, but only if you have a current meter that can handle 8-12A. Think my new Bosch pump draws around 11A, but if memory serves me correct, I think someone on this forum measured 8A.
If the pump is worn it will be much lower. Maybe others have current measurements they can share, good or bad?
Best regards,

Waldi

[John McLennan]

Hi Waldi

My injection system has worked faultlessly for 12 or more years and apart from replacing a couple of injectors the lack of problems means I have little experience in the other possible faults other than occasionally bleeding if something gets stuck in the injector tip.

I did feel strong pulses (knocks) in all the tubes just no fuel other than the first pulse.

The injection pipes are new so should I crank more to fill them up.?

Will check current but I think this will be OK as the live wire is mildly warm if I leave the pump running for 5 or so minutes.

John

[Waldi]

Hi John,

I removed all 6 injectors at the same time (number them or make sure the stamped numbers are in correct position before removing). I held them vertical, so any air in the lines could go out. Started the pump, and did short moments of cracking the engine, so the MU would change orientation. I kept bleeding all injectors until they were all dripping a bit of fuel, so no air was in each of them. Then put them all back. Still it did not fire....:( 

Then I replaced the 6 spark plugs (they were new NGK’s but had no clear spark. Installed 6 new NGK’s and now it came to life. Do you have a good blue spark? I had close to nothing with the new but wetted plugs.
Keep battery charged with a good charger (mine is only 6A, which was not sufficient off course).

Besides other issues during my first start, this step took a couple of hrs, the running pump maybe 1/2 hr of that time.

You will get there John.

Cheers,

Waldi

[Mike C]

I bleed the injector lines with the plugs out and the enrichment lever on full choke. Pull the tips with your fingernails if necessary- sometimes the fuel from the MU just bounces back and forth against  a plug of air in the line.

[John McLennan]

Hi Waldi, Mike,

The story today.

Removed all injectors and pulled the tip to bleed. All injectors were still under pressure so if this is normal then seals seem to be good as I have not turned on the pump / cranked the engine for over two days. Have checked all injectors in correct cylinder but have not tried bleeding them tip up so will try that tomorrow. (I have always bled them tip down previously but nothing like trying a new method)

When cranking the engine there is no dripping or cone of fuel from any injector but if tip is pulled then fuel is present.

The spark plugs are new NKG and are all dry. I have not checked the plug spark but have a strobe inline with cylinder one plug whilst trying to start the engine.

So with dry plugs and fuel in all injector lines I have to assume that the pressure is just not quite sufficient to open the injectors.

My pressure test guage is apparently on the way.

All the best guys

John

 

[Waldi]

Hi John,

the strobe tells you there is energy coming to the plug, but does not confirm there is a spark. Better to rake a couple of plugs out. Be careful with sparjs and fuel.

The fact you have no spray but some pressure could mean a too low pressure (the injectors open at around 50 psi) or there is still air in the system.

Waldi