SC 308 fuelling issue

I have just got a SC308 with 96,000 miles. Love the car but……

Engine was dying over about 20% throttle; then it would start but not run - was trailered home last Sunday after breaking down.

Fuel pressure is 25 - 34 psi at ignition “on” falling to 10psi after about 5 - 10 seconds of idle then it stalls and pressure falls to almost zero. Replaced filter under car - pretty clogged up and hard to blow through - checked flow from tank to filter connection - seems good. With new filter engine idles for longer but same symptoms and eventually stalls - opening the throttle causes rapid stall.

Obviously the fuel pump/s. But these were both replaced about 3,000 miles ago following identical symptoms suffered by the previous owner - so either the replacement pumps were poor quality or there is another cause.

One unexpected (to me) symptom is that the tank pressurises - on filler cap removal there is a great rush of escaping vapour. Don’t know if that’s relevant.

Before I replace the pumps again I would be glad of any observations/suggestions.


Sounds like the tank vent system is blocked. See if the car runs with the filler cap open. If so then you have your answer.

Tried that earlier today - makes no difference.

I’ll have a look at the wiring if I can find the pump feeds - the electrics checked out OK last time (which is why the PO had the pumps replaced) - worth checking again though.


remove relay for pump 1

the ecu should then run pump 2.

This will rule out a pump issue.

What year car ? in USA ?

1998 UK spec. Daimler Super V8. Engine replaced under warranty at about 25,000 miles now on about 96,000. Reasonable service history.

Will try relay suggestion. The two pump set up is new to me - do they run in series, parallel, or what?


The second pump is activated over ~ 4000RPM to ensure ensure enough fuel flow!

they are in parallel

you need be sure if the tank is under vacume or pressurized.

If pressurized, someone had this issue also, I think it was the rochester valve under the rear left.
Can’t buy new anymore, only ebay part no. cbc7714

Relay for No1 out - engine running OK on the SC pump No2. So I guess that means pump No1 or its electrical connections are down. Will check out electrics first. Relay removal a v useful diagnostic tip - thanks Andy.


Swapped relays between pumps and now running fine on pump 1. Must be a faulty/sticky relay, a bad electrical connection or pump 2 has blown crud out of the pipes in the tank. Will run it for a bit and see what happens……


Drove to fuel station about 5 miles - perfect. Half filled tank and paid. Tried to leave - engine fired but wouldn’t run - same symptoms as before. Removed/swapped and re-swapped relays but made no difference this time. Kept trying and after about 10 minutes engine ran and drove 5 miles home - perfect. Under hard acceleration up to 3,500 rpm - perfect; roads to narrow to try any faster.

Reckon I can rule out both pumps and all filters and fuel lines. I suspect pump/s is/are running at ignition “on”, but the signal to keep them running after engine fires is intermittently lost. If I can reproduce the malfunction I will put a multi-meter on the feeds to the relays to see if voltage to energise the relays is lost as the engine stalls out.


I would suspect its an issue with the tank pressure/vacume you reported.
Problems after filling with fuel suggest this

The evap system on these cars is a nightmare. I wish I had the answer!

I have the single canister system which I think is the simplest of the three alternatives fitted to the 308 model. Having read the manual it seems to be a relatively simple carbon canister vapour collection system purged to the inlet manifold by the ECU and induction vacuum. The ECU adjusts fuelling (presumably via the injectors) to allow for the addition of combustible fuel vapour into the induction system via the purge valve. I do not see any reference to the ECU controlling the fuel pumps in this process.

Running the engine with the fuel filler cap off i.e. atmospheric pressure in the tank makes no difference to my symptoms.

Is there something I have overlooked here?


More results. With No 2 pump relay “in”:- at ign “on” the relay clicks and I can hear the pump priming and after a couple of seconds the pump stops and the relay clicks off - all as it should. At cranking the engine starts and runs. With No 1 pump relay in:- at ign “on” the relay clicks and the pump runs for less than a second and stops - can’t hear a second click (off) from relay. Engine fires but won’t run. Swapping the relays confirms that both relays are working.

Bridging No1 relay switched terminals won’t run the pump at all - so it looks like pump failure after all but why I had all that trouble after filling with fuel I don’t know.


I’m sure you will get to the bottom of it.

Just a bit intermittent at the moment

At IGN on it should only prime one pump

Now convinced pump is the problem here and have bought 2 eye-wateringly expensive genuine Jaguar ones - car goes in to have them fitted Tuesday. The last ones put in c3,000 miles ago were about 1/3 the price “aftermarket” ones.

Have swapped Rochester valve but tank still pressurises when left standing out in the sun all day - pressure reduces once the engine is running and the recovery system draws the vapours into the inlet manifold. Having taken the old valve apart it seems that pressure in the tank is dictated by the force exerted by a non adjustable spring loaded diaphragm in the valve. I see no damage or deterioration in the valve and can only assume Jaguar intended the tank to be pressurised!



Was the 3rd top pipe of the rochester valve connected to anything?

In the pics LH stub connected to pipe from tank, RH stub (with short hose) connected to carbon canister, small dia stub on lid (upside down in pic) connected to vacuum hose (assume runs to purge valve in engine bay). As I understand it, vacuum from small dia stub when engine running opens diaphragm valve to allow purge but when engine not running spring closes diaphragm until tank pressure exceeds force of spring when vapour discharges into canister.


Thanks for that description

I have read somewhere that the Rochester valve is designed to open at +2psi. so it appears that up to 2 psi is an acceptable tank positive pressure with the engine not running. Technical Bulletin 05.1-16 refers to a vacuum test of the valve at 2.94 - 14.7 in. Hg. (1.45 - 7.25 psi) but the text is not clear if that is the acceptable opening range, only a check to see if the valve holds vacuum.

I will get a vacuum gauge on it and report back.


Got the car back today with 2 new genuine Jaguar pumps fitted - goes like the proverbial…….

Fault confirmed as an internal electrical malfunction/incomplete circuit of the old No 1 pump. These were fitted only about 3,000 miles ago for the PO and were from “uroparts” aftermarket supplier. No prizes for guessing who I will be avoiding for parts in the future!

Still to test the Rochester valves - more in a couple of days.