I replaced my fuel pump and filter 3 weeks ago. Car run fine but noticed that its hard to start and hear the fuel pump humming. I replaced the fuel filter and also the sump filter element. I have to crank the key twice (i hear the pump humming..so i figure it is building the line prssure) before starting the car. when the car star..its like that its starving and whenever i step on gas..it dies/no power. i am thinking of changing the pump again. is ther an easy way to chk my fuel pressure ?...thanks

 

That was a long sentence, but I finally sorted it.

I am also going out on a very long limb here and GUESSING its a V12, and a Pre 1989 car, mmmmm??????.

If so read on. If NOT, tell us some details, so we can do the right thing by you and the car.

A few things come to mind.

1) The fuel is not gravity feeding teh sump tank well enough. NOT common, but it does happen.
2) The fuel pump is an elcheapo, and simply cannot keep up. I only use Bosch brand down here.
3) The fuel line under the car, RH side, is crushed/damaged, thus reducing fuel supply to that big V12 beast.

A rather simple test is to turn ON the ignition, wait for the pump to stop humming, press the gas pedal down ONCE, then release (ignition still ON obviously), then proceed to "Start", and see if it fires easier. That pressing of the gas pedal fires all 12 injectors ONCE, giving the engine a pre diet of fuel. Also helps with a heat soak V12 most times.

 

Please add a Signature with vehicle details to help others to give relevant advice.

We can assume you have an XJS but anything beyond that is speculation.

Go to the User CP button on the left of the top menu bar, then Settings & Options under Your Control Panel. Select Edit Signature and enter the details.

Graham

 

the only way to check is to depressurize the system and unhook the supply line from the rail and fit it to a gauge using the appropriate adapters

I've had 2 cheapo 40 dollar fuel pumps and would reccomend against them.

Check all the soft hoses in the back to be sure they are no pinched at all.

If you are sure about your pump and filter I would suspect the regulators. Check that there is vacuum going to the regulators as well

 

Were the filters badly clogged?

I'd check the recently replaced filters....at least the main filter behind the spare tire. Remove it and empty the contents int a clean jar. What you see or don't see might will be important clues.




I had something similar on my '88 XJS. Long story....but it turned out that the inlet regulator was on the fritz.

From earlier postings it looks like your inlet regulator was bypassed (commonly done) but you had a shop reconnect it? Do I have that right?

If so, maybe it was bypassed for good rason?

There's no *easy* way to check the (regulated) fuel pressure. You have to cut the hose that runs alongside the LH fuel rail and install a 'tee' for your pressure gauge....then replace the hose when you're all done. Not a huge problem, just inconvenient. The existing hose can be carefully cut away from the fittings and new hose pressed on.

If you simply want to check pump output pressure, that's not hard. Just disconnect the fuel supply hose....RH side of engine....and attach your pressure gauge.

Cheers
DD

 

Thank you all. Now that i have my fuel pressure gauge, i can check my fuel pump and regulator.

1. What should be the outlet pressure of the pump ?
2. What should be the pressure after my pressure regulator ?
3. Do i have to do that to the RH regulator also ?
3. I read that this from Kirby
The only suggestion that seems to have any benefit comes from Chad Bolles, who suggests disconnecting and plugging the vacuum line to the right side fuel pressure regulator. This will cause the regulator to open up, and the left side regulator will open up to control rail pressure, so that the pressure is nearly unchanged but the flow circulating back to the tank increases significantly.
****Im planning to do this but confused. In the drawing, is this (red arrow)the vacuum that i need to cap off ? what would i do to the hose and what would be the thing to use to cap the hose and regulator ?


Thank you all for the help. I will not give up on this car...

 

okay maybe I am misunderstanding something...but how the !@#$ does the regulator on the left that comes AFTER the fuel flowing through the rail control pressure in the rail??

Letting the right regulator stay wide open would allow waaaay to much pressure into the rail.
Maybe im brain farting or not familiar enough with the regulators on the V12 but that doesn't make sense to me. The regulator operates off vacuum because the car creates more vacuum at idle and needs less fuel. By removing the line you would be provided way to much fuel pressure at idle and wasting fuel

The red arrow is pointing to where the vacuum line is plugged in. You would be removing a hose from that fitting and plugging the hose itself.

 

75 psi or so




Regulated rail pressure....about 36 psi



Do what?


Right.....


I don't understand what's being said. Opening up the RH regulator doesn't inherently dictate what the LH regualtor does, as far as I can tell



Yes, and just plug the hose with a golf tee or small screw or piece of heavy tape or whatever you can drum up

Cheers
DD

 

By controlling how much is returned to the tank.

Low vacuum = closed regulator = less fuel returned to tank = more pressure in the rail

(AFAIK the regulator never *fully* closes....but I might be wrong on that particular point.)




No, because pressure isn't controlled by how much fuel comes into the rail but, rather, by how much is allowed to exit the rail.

The LH regulator controls rail pressure. In fact, the RH regulator can be removed entirely.


True, if you had only the LH regulator.

Cheers
DD

 

ohh I get what you mean doug. The RH regulator would affect FLOW but since the LH is after the rail it can allow pressure to be relieved or built up, thus affecting PRESSURE.
yeah that was definitely some brain farting forgetting how pressure works lolol

that being the case why the hell are there 2 regulators?

 

The inlet (RH) regulator was used to control/eliminate a noise problem. I guess there was some sort of fluid-harmonics-induced hammering noise (or something like that). The inlet regulator changes the flow in some respect (more? less? I really dunno) to keep things quiet.

(I've never noticed any noise problem with the inlet regulator removed, personally)

I remember (this goes back decades) many fuel injected GM cars having a similar problem and a 'fuel damper' device was installed....and later fitted as standard issue.

Cheers
DD

 

ok...i get 40-50 psi after my fuel pump. Is that mean that i have a bad fuel pump ?. Car wont even start. I never had a chance to hook up the pressure gage after the LH regulator. The LH regulator is the one close to the oil fill cap right ? and i should be hooking up my gage to the hose close to the rail ?(by lucas ignition amp) ?

 

That's really low output from the fuel pump. It is enough to start it, but it might have a problem keeping up volume-wise, especially if the LH regulator isn't doing any regulating. You do need to figure out the pressure at the rail so measuring it is still a good exercise.

The LH rail is on the drivers side of a US spec car. Because the car was made for worldwide markets the "side" is referred to as "left" and "right" from the driver's perspective.

 

Yes and yes

Cheers
DD

 

Which, actually, is the correct method regardless of where the car is built or what market it was built for. Left and right is.....er....should be.... always expressed from the perspective of sitting in the car.


Cheers
DD