My 4.0 95 XJS was running fine until a few weeks ago, but now, it will not start. It will turn over strongly, but will not actually start/run. I feel like it's fuel related because I sprayed some starter fluid in the intake, and it ran for a few seconds.

Here's what is happening/what I have done:

1. No fuel at the inlet pipe to the fuel pressure
regulator while cranking.
2. I can hear the fuel pump run for a few seconds
then cut off when I cycle the key. I tried to cycle
the key several times with no joy.
3. Bypassed fuel pump relay. No joy.
4. Bypassed the fuel cutoff solenoid
on the passenger side near glovebox.
5. New fuel filters.

After the first day of no start, it would occasionally start and run perfectly, but the next day, no start. Now, no start for a week.

Can the fuel pump be bad if it comes on and cuts off after a few seconds when I cycle the key?

Not smart enough to go further! HELP!

Richard

 

Hi Richard

What engine have you got in her: AJ6 or AJ16?

 

Yeah what engine? Sounds like fuel related and not CPS. Im sure your speedo bounces when you crank it. This means the CPS is working or not. Fuel pump could be dead. Happened to me.

 

My bad. It's a 4.0.

The tach needle does move when cranking. I can hear the fuel pump come on for about 5 seconds each time I turn the key on;therefore, I know it's at least not dead. Agsin, with all of this, absolutely no fuel comes out of the pipe at the fuel pressure regulator.

 

Did your pump come on for a few seconds when turning the key to start (when your pump was bad)?



QUOTE=Brewtech;2571287]Yeah what engine? Sounds like fuel related and not CPS. Im sure your speedo bounces when you crank it. This means the CPS is working or not. Fuel pump could be dead. Happened to me.[/QUOTE]

 

The initial priming or charging of the fuel line with the initial rotation of the key can be lost in 3 ways

Check valve ( that may be in your pump assembly ) , there is an external to the tank check valve work around without changing the pump

Fuel pressure regulator leaking past the rubber diaphragm , someone was able to pinch off the rubber return line to prove his but the question is how much of a total pinch off

An injector stuck open

The CKPS can still give you a tach gauge but fail in the fuel pump enable phase after the initial fuel line charging

So you would have to place your finger on the fuel pump relay and feel for 3 clicks on - off - on

As the fuel pump fails it will sometimes burn the internal contacts in the relay and burn the sockets on the fuel pump motor connector

So you can swap the relay to help it out a bit and inspect the fuel pump motor sockets

If your engine is an 4.0 liter AJ16 with no distributor and heavy spark plug wires the fuel pressure is regulated to 43 psi trapped in the fuel rail that should hold for days

 

Hi Richard

Before we go down the Wrong Rabbit Hole

Please could you tell us if your Car has an AJ6 or an AJ16 Engine (as it could be on the Cross Over point of 94-95 Spec)

If your Car has a distributor then you have an AJ6 but the AJ16 uses a Crank Position Sensor and as such lots of other different stuff as well

As has been already said it could be a leaky diaphragm in the Fuel Pressure Regulator not holding up the Fuel Pressure when you Switch the Engine off and one of those would cost you about £50 (UK) from British Parts



If the Internal Diaphragm leaks then you could lose Fuel Pressure and that could effect the 'Light Switch' Ignition that these Cars usually have



Hope this Helps as if you need a New Internal Fuel Pump, then it could get very Expensive Very Quickly as it's not so much the Cost of the Pump but more the Cost of the Labor as in order to fit a New Fuel Pump the Fuel Tank may have to come out or at least be pulled back far enough in order to get to it

Make no mistake when I tell you that this is the Job from Hell

Also make sure that you have enough Fuel in the Tank, as 10 Gallons may only be just enough to reach the Sock on the end of the Pumps Fuel Filter and since the Pump is immersed in Fuel to give it Lubrication, you don't want to run it when Low on Fuel or that could burn out the Fuel Pump if you get unlucky

Hope this helps

Alex

Pics are of an AJ16 Engine in a 1995 XJS 4.0L

 

Have you checked the inertia cutoff switch at the passengers door? Your problem sounds like it could be the cause, although I doubt you would hear the fuel pump running. Its a simple check.

When was the last time you checked in on your fuel filter? Could it be clogged?

Pull the small rubber line that connects to the fuel pressure regulator. Does it smell like fuel, if it does, get a new one.

That's all I got right now. I spent $3,000 (mostly labor) to reseal and replace my fuel tank. Without a reseal, you're probably in the low $2,000 range. Just to give you an idea on cost....if you choose to pay someone to do this. If you do it yourself, it's probably $200 in parts.

 

Richard,

Try disconnecting the fuel line feed to the filter (inside the front left wheel arch, at the rear behind the plastic cover) and see if you get a fuel feed when the ignition is cycled and the fuel pump cuts in. Whilst you're in there, change the filter anyway.

Good luck

Paul

 

UPDATE:

The problem was the crankshaft position sensor! After replacing it, the car started immediately (and has ever since)! What is odd is the tach needle would jump consistently while cranking! Has anyone known of a bad sensor when the tach needle moved while cranking?

Before this, I did check the fuel to the filter. The fuel pump did not pump fuel to/after the filter while cranking (even with fuel pump relay bypassed)! I also plumbed a metal line into the fuel pressure regulator with an external Jag pump with no joy!

Sadly, this would have been a 10 minute solution (and not a week) had I just tried the CKPS in the first place!

Thanks to all who took time to help!

Richard

PS Here's the car in question!

 

Looking at the tach for a good CKPS is good troubleshooting but in this case it can fool you