Hi All

Quick question.

Does the fuel pump power really get submerged in fuel?

I am just finding that a little difficult to work and get my head around in terms of safety.

Just fitting a new pump, it's bolted down and plugged in, but it suddenly struck me as very odd having +12V and ground sitting there in fuel. Am I missing something?

Cheers
James

 

When the pump is activated, the pump uses that power and ground to complete the circuit. The pump is cooled by the fuel in the tank. I understand what you’re thinking but the obvious answer is no, there’s no electrical current flowing between the fuel and tank to risk a spark.

 

It does seem a bit dangerous but many cars have submerged pumps these days and I've never heard of one blowing up because of it!

 

Thanks guys. just seemed odd but clearly ok.

I have found another problem.
Before we got the car somebody bodged a fuel pump repair by punching a hole in the evap flange lid... They then passed wires down to the replacement pump which was cable tied to the bracket in the tank.
end result was constant fumes etc.... They also used a cheap pump which was really noisy. However, they wired a new external relay into the space available in the fuse box and I have just found out why.
When the ignition is on the pump only comes on for a second then goes off. End result is it will not start as the ECU seems to be switching the pump off.

The external relay they put in must have supplied 12v to the pump when the ignition was on instead of using the standard wiring. This relay seems to have been powered from the relay location used for supercharged cars and it was working ok, except feeding the cheap pump via random wires floating in the back of the car. So maybe the ECU is switching off the main fuel pump, but keeping the supercharger relay energised.

Please can anybody advise why the pump maybe being powered off after a second?

I guess if we are unable to fix this, then I need to bypass the wiring with another relay as they did, maybe taking the power off the supercharger fuel relay.........

Any advice welcome.
Thanks

 

The pump is supposed to come on just long enough to provide pressure to the fuel system, then shut off until the engine starts.

 

That may be so, I had considered that, but 1 second maybe less?

Also, it will not start at all. So if there is pressure in the rail (will check tomorrow) then it's bore washed.........

Surely if it was dumping that fuel into the engine then the rail would empty and the pump come back on? Not doing any of that.

Thanks

 

The normal operation of the pump is:

- When the key is turned to ignition "on", the pump will run for 1-2 sec and stop
- While the engine is cranked, the pump will run
- If the engine does not fire-up, the pump will stop when the key is released from "crank" position

The described operation of the pump is controlled by the ECM via the pump's relay. During cranking of the engine, the ECM gets the signal from the crank sensor which tells it that the engine is turning and the ECM switches the pump on. If the crank sensor is faulty (or has poor connection), the pump will not be activated during engine cranking.

 

ok that is interesting, thanks.
With the ignition is switched on but not cranked, the pump runs for about 1 second then stops.
While cranking the pump does not seem to run. Are you saying this is a crank position sensor fault?
Surely that would manifest a whole host of other faults? (which are not present if I bypass/jumper the fuel pump relay at the socket), Why would it run when bypassed?

Thanks

 

Look into bore wash. If the pump runs for a second and the engine does not start repeated attempts could easily result in bore wash. While cranking the engine check the tach. It should register a couple of hundred revs if the crank sensor is functional.

 

I suspect bore wash also.
Good call on checking the tach to see if its showing anything on crank.

Update soon.

 

OK an update.
Definitely getting 12V on the fuel pump relay when cranking. So looks like the crank pos sensor is working ok. With that in mind its a bore wash, probably caused by a failed start after changing the pump.

Will update again later.
Thanks

 

I don't think I have run across this issue before. It looks as though the steps to fix the issue is to:
(a) unplug the bad over Fuelling sensor concerned (to prevent excess fuel in the chamber
(b) reoil the chambers by squirting 10ccs of trans or engine oil inside each combustion chamber,
(c) do 3 slow cranks to fully reoil the chambers, then 2 seconds fast crank to expel excess oil,
(d) replace plugs, coils and fp fuse and start the engine.
Does this sound right?

 

That should work. Another method is to floor the accelerator pedal, which shuts off injectors, turn over several 10-20 sec blasts, then return pedal to 1/2 or less and see if it starts. That's from the owners manual.

 

I would do RJ’s method personally but, I might add either having a battery charger or jumper cables from another running car to do the start method. The cranking idea is to 1) clear out the flooded cylinders and 2) heat up the piston rings so they’ll seal up to the walls to create as much pressure as possible. If you crank only with the vehicles battery power, there’s a good possibility that you’ll continue to have the same issue and it won’t run. These cars DEMAND a strong battery to keep all the modules happy while your cranking the engine over with strong voltage AND amperage.

 

Hi All

Thanks for the info.
Anyway, the problem was found. Not bore wash, it was fuel starvation.
Upon pushing the tank back into its normal resting place, we found the fuel feed line was bent over on itself restricting the flow. Weird as we found it ran fine with the tank pulled back 6 inches, but then failed t to start when pushed back into place.

Getting right underneath with a bright light we found the bend in the pipe.
If this is the standard Jaguar pipe (looks like it is) then there is a rubber (teflon cored) hose between the steel line going into the tank and the steel line going into the filter.
The bending seemed to have badly crushed the teflon core, so we swapped out the section between the 2 steel ends with a newR6 fuel-grade hose.

The car coughed and spluttered on start, probably air still in the line, then ran ok.

The return line on the tank looks fine.

See how it goes.
Thanks

 

Good deal. Glad to hear it got started.

 

Please tell us you did NOT try to change the pump by pulling the tank with the lines underneath still connected!!!!!!!!!!!!!
Damaged lines need to be replaced for safety reasons BUT............. New lines are NLA.

Good Luck. (and don't catch fire)

 

Well, partly out.

Lesson learned. Feed pipe and return pipe are both ok now. Not sure if it was before we started actually.
Since buying the car it has smelt of fuel in the boot/trunk, but did not come into the car while driving. But, with the windows open a strong fuel smell was there, especially at low speed.

We found a few things that were wrong and causing the fumes.
Somebody had bodged a fuel pump replacement by doing the following: Pump power harness (with the noise suppressor) was broken, so instead of getting another they decided to run a pair of new wires into the top of the tank by punching a hole into the evap flange. Fumes were leaking out of the hole around the gap by the wires. Hence smell in boot/trunk.
They then ran the wires down to a new relay lose in the space in the fusebox. Due to the lack of parts availability, we sealed over the hole with 2 small metal discs, 1 soldered with lead/tin on each side. Used a replacement pump harness and all original wiring.
The evap valve on top of the flange had been broken and was pumping out fumes the whole time down and into the charcoal canisters. Hence smell under car.
The fuel feed line under the car was damaged and quite rusted. Not sure if it was actually leaking. Repaired with parts from another old XJ8 tank and fuel-grade hose. All seems ok, no leaks.

In the meantime, it's back running, and hope it's going to be ok.

 

Why…. Oh why, do people DO those kind of things? I have rightfully been accused of a few
”southern engineering” fixes, but nothing that would allow fuel fumes to migrate. DANGER,
WILL ROBINSON! The Duchess would surely kick me to Coventry should I try something
like that.

 

Another quick update.
Its fume free.
No leaks.

However, when it starts it needs a rev to get going otherwise there are problems idling as it is hunting about all over the place.
It cracks and pops up through the intake (since the local recovery guy squirted easy start down the intake tube around the MAF, it also pops out of the exhaust. Burping and farting both ends.
The other issue it now has it that it does not like hills, and does not like to go over 50 both it simply struggles on.

Then we had a Restricted Performance error, bank 1 and bank 2 running lean so there is either still not enough fuel, or too much air I guess.
Any thoughts?

Thanks again.