Fuel pump woes

marcus · Post by **marcus** » Sat Nov 01, 2014 7:33 am

Took the car for a quick drive to see friends and their Srs 2 t'other day.

I was about 200 yds from home, pulling out of a junction, accelerating and the car just died on me. Luckily it wasn't a busy road but nevertheless it was just around the corner from a fast bend in the road, of which I was stranded in the middle.

Managed to push the car back 10 yds into a driveway and then looked at my options.

Although I could turn the engine over no problem, it had no intention of firing.Then it started to rain. Moderately.

So I sat in the car, phoned the breakdown guys and whilst waiting, watched with interest where the rain was coming in.

About 45 mins later the breakdown lorry arrived, however, it was impossible to winch the car onto it because of the damage that would be caused to the front underpanel and air scoop.

Another truck was summond which, I was informed, would lift the front of the car up using the front wheels. However, this truck had just been called out to another job and was not expected to arrive for at least another hour.

During this time, the truck driver and myself managed to check that there was at least a spark from the coil. On about the 5th attempt the car started and whilst matey kept pressure on the accelerator to prevent it stopping again, I noticed that the fuel filter glass bowl was almost devoid of petrol. Strange I thought! Surely it ought to be full? I could see fuel pulsing into the bowl albeit at a very feeble rate.

So we decided it would be worth trying to drive it 200yds back to the house. This I managed without stalling by keeping it in 1st gear and at a constant rpm.

Now I'll get to the point.

Having pinpointed it was a fuel starvation issue, one proceeded to take the pump off and dismantle it. On inspection it appears that the rubber diaphragms are fine, however, the electrical points on one half of the pump where not so fine. All very black and grubby and almost destroyed.

When I hooked the pump up to the electrics again, only one of the 2 coils was working, clattering away at a rate of knots whilst the other did nothing.

I'm just about to order new points and diaphragms etc from SNGB to rebuild the coils. However I do have a question.

Do both coils have to be operational for the pump to function and supply adequate fuel pressure? I presume they do.

As I have the pump apart, would it be wise to also replace the valves and O rings etc in the actual pump body?

Thanks.

MarekH · Post by **MarekH** » Sat Nov 01, 2014 8:49 am

Dear Marcus,

It is the carburettor which dictates fuelling. The fuel pump(s) simply supply fuel to the float bowls.

Even a very low pressure ought to refill the float bowls by way of the floats sinking in the float bowls. Pressure to do that is maintained by a ball and spring in the line on the lhs of the engine. Since the system has to produce high flow (still at low pressure) at 5000rpm, under normal running most fuel returns to the tank, so one pump working properly ought to work fine at lower rpms.

I'd check out whether the tank sump has crud fouling the mesh filter preventing you picking up fuel in the first place or have a blocked fuel filter.

You can determine which parts need replacing or cleaning by swapping them from the good pump to the bad pump one by one and testing the bad pump repeatedly.

By way of comparison, the later XJSs had twin fuel pumps - the second pump cuts in at higher rpms only as the amount of flow required is higher to maintain pressure.

kind regards
Marek

PeterCrespin · Post by **PeterCrespin** » Sat Nov 01, 2014 9:07 am

[quote:/]
Do both coils have to be operational for the pump to function and supply adequate fuel pressure? I presume they do.[/quote]

They are both connected to the power supply, soooo ...

[Quote:/]As I have the pump apart, would it be wise to also replace the valves and O rings etc in the actual pump body? [/quote]

Only you can decide. Depends how much you enjoy unscheduled adventures. Some people hate the stifling predictability of modern day life and crave spontaneity at ever turn, or in the middle of the road halfway though a turn. They might pay extra to enter a game of chance, whereas you could enter for free. In fact you'd be in credit as you'd save the cost of your rebuild kit. It's like the Casino at Monte Carlo paying you to gamble.

Wimps would say do the preventive maintenance. Heroes would say PM is the very antithesis of the spirit of adventure ...

D COUPE · Post by **D COUPE** » Sat Nov 01, 2014 9:42 am

Just My thoughts Peter. Fit a new one keep the old one as a spare,

D

marcus · Post by **marcus** » Sat Nov 01, 2014 9:55 am

Marek.

Must say I haven't checked the mesh filter in the tank. Do you have a part number as I can't for the life of me see it on the tank parts diagram?
Thanks.

MarekH · Post by **MarekH** » Sat Nov 01, 2014 1:03 pm

No it doesn't does it but it is the same part as that fitted to the XJS swirl pot so you might check there.

If it isn't clogged up then there isn't an issue there anyway. Either pull the top plate with the twin pipes out from the top or if the tank is near empty, unscrew the sump.

I wouldn't recommend you unscrew the sump unless you have to. It's a rough brass casting which seals via tapered thread into the tank so beware. You are looking for an excess of light brown rusty sediment at the bottom of the tank or in the fuel filter.

I have spares of both you can borrow if you are over here. If you do come over, you can see the new covered headlights which are currently being road tested.

kind regards
Marek

marcus · Post by **marcus** » Sat Nov 01, 2014 2:29 pm

Thanks very much Marek.

I did drain the tank when I got the car and there was a small amount of sediment.

As the tank is now about a quarter full I'll pull the 2 pipes out of the top and have a look see.

Cheers

PeterCrespin · Post by **PeterCrespin** » Sat Nov 01, 2014 3:13 pm

If you have drained the tank comparatively recently and have disovered a burnt set of points I wouldn't touch the tank top plate until you refurb the entire pump and check the result of that intervention first. No point looking for e additional causes which may be illusory until you fix the real one first.

marcus · Post by **marcus** » Sat Nov 01, 2014 4:42 pm

Roger that Peter.

Post by **mgcjag** » Sat Nov 01, 2014 6:00 pm

Hi Marcus.....look in the knowledge base the parts list for tne S3 fuel system shows the sump filtet C29445.......in one of your other posts you mentioned that the car was not running great under load........a friend had exactly the same thing and one of his fuel pumps was not working....car run grear at low revs on one but needs the two once u put your foot down.......have u thought of upgrading to electronic pumps......does away with the points...then keeping the old ones as spares.......handy if u are touring..Steve

AussieEtype · Post by **AussieEtype** » Sat Nov 01, 2014 11:44 pm

Many many years ago I was having trouble with fuel and it was the fuel pump. I had it apart so many times resetting points and it would run fine and then play up - at one stage I even installed a secondary pump next to it and would change the pipes across so I could get home. Not a great arrangement but it did work.

Later in my local club someone posted up a mod to change to "electronic" where the points went onto a low amp circuit and fired a transistor that fired the pump - no more burnt points, the pump works fine and when the pump is in its foam housing looks original.

So if you are having problems with the points the covert to electronic - is worth it.

Garry

marcus · Post by **marcus** » Sun Nov 02, 2014 9:14 am

Steve/Garry.

Thanks for the advice on an electronic replacement pump.

I'll order the service items for the pump I have from SNGB next week and also give Burlen a call re advice on replacement pump options.

Thanks.

marcus · Post by **marcus** » Sun Nov 09, 2014 8:38 pm

Just an update on my fuel pump.

All fully serviced with new points/contacts, diaphragms and valves in pump body.

Road tested satis.

However, I notice that the glass filter bowl by the tank is not always full when engine running.

Is this a concern or quite normal?

Thanks.

christopher storey · Post by **christopher storey** » Mon Nov 10, 2014 3:26 pm

The dual electronic fuel pumps have given problems. Hutsons have had at least one which has gone on fire

marcus · Post by **marcus** » Sun Nov 16, 2014 9:24 am

OK thanks Christopher.

Should the glass bowl be full of fuel with the engine running do you know?

Having overhauled the pump completely, I was expecting the bowl to be brimming all the time, but it's generally about half full with engine running.

However, if I return to the car after shutting it down, the bowl fills up again.

On my previous post I mentioned about my breakdown where I suspected fuel starvation and subsequently set about investigating the pump.

Any advice appreciated, thanks.

christopher storey · Post by **christopher storey** » Sun Nov 16, 2014 12:36 pm

Well, generally speaking in my experience ( not of the Jaguar V12 though ) the filter bowl should be full if everything is working correctly. If it is not, it suggests a degree of fuel starvation/vapour locking or a blocked filter. . Certainly , this applies on Ferrari V12s . It is not perhaps widely known, but a brand new looking filter of the honeycomb type which has been exposed to moisture - probably from water in the tank - is effectively blinded as a filter and will never pass fuel properly again . Whether the same applies to fanfold paper filters I do not know

Post by **Heuer** » Sun Nov 16, 2014 12:48 pm

Have you checked the filler cap? It should have a vent hole which can either be a) blocked or b) missing because a previous owner replaced the cap with the wrong one. The effect is to cause a vacuum in the tank which slows supply varying with how much fuel is in the tank and how long you have been driving. Once the vacuum fades after the car has been standing the fuel can dribble back into the filter bowl. Also suggest you drain the tank and check the sump filter.

marcus · Post by **marcus** » Mon Nov 17, 2014 10:45 pm

OK thanks very much Christopher and David. I'll check out your advice.

AussieEtype · Post by **AussieEtype** » Tue Nov 18, 2014 1:54 am

If you think about it logically, the fuel filter bowl should be full with the engine running. This is because the inlet and outlet is at the top of the fitting so fuel goes in at the top on one side of the metal casting at the top into the bowl through the filter and out at the top of the metal casting on the other side.

If the bowl is not full there will be no or little fuel getting out to go to the carbies.

The simple test is to disconnect the return line (with suitable safety precautions) at either the carbies or the tank and run the fuel pump and see if the fuel is coming back to the tank from the carbs.

I must admit even with new parts,k setting the points etc I could never get my pump to work properly until I added transitors to it and then it was great.

Here is what I used - you might have to save and the zoom to read (us the download function to theright of the page in Photobucket)

Garry[/list]

marcus · Post by **marcus** » Tue Nov 18, 2014 5:52 am

Great thanks Garry. As soon as I get a spare moment I'll take that return pipe off and run the pump.

Obvious test really.

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