bad running , fuel pump check => no start

Hello,

I'm french, so first, sorry for my english...

I'm tring to solve a problem on my 88 4.0L XJ:

While the cars runs fine (at 50/60MPH), it has some "holes" at stabilized speed... but not on rought acceleration or even "off pedal foot"...

This car has an old alarm+cutoff, from precedent owner, I will remove it (perhaps it's the problem)

I begin to think about a faulty fuel pump, I have removed fuel tank, cleaned it (but was fine), check the pump, it seems to be fine also... so I replace it back... And the card doesn't start now :-( ...

When I turn to ignitition position, I hear the pump doing a small noise for 3 or 4 seconds, and same noise while I trying to start engine. The engine runs but doesn't start :
- I have checked at the valve on the injection ramp and there's some fuel (without any pressure).
- I have about 7 Volts at the pump plugs.

Tomorow I will try to :
-Remove the fuel filter (who has 3000Miles), and check if the pump give some fuel...
-Remove a plug and check for spark.
-Remove the old cut-off/alarm.

Anyone could give me some indications about finding the real problem ?
I'm from france and NOBODY here really knows the 4.0L XJ (only the 2.1 Diesel here...) so I cannot bring it somewhere to repair (it's an exotic car here...) and finding spares is a pity (could you find some Renault Megane parts in USA ?).

Thanks a lot for ANY advice.

Are you saying that the engine runs rough at 50mph, but not under accelleration and decelleration?

The symptoms you describe do not lead me to believe that the fuel pump or fuel system is the problem. 7volts at run is about right and it should run for 3-7 seconds after you turn on the ignition.

It seems more likely that the MAP sensor or throttle position sensor is the problem. The symptoms do not lead me to believe that the crankshaft position sensor is bad. They normally either work or do not work.

Thanks for advice

I'll be checking this also... This morning I'll begin to :
- test fuel circuit (to see If I haven't do any mistake).
- Check Spark
- remove the old "cutoff/alarm"

Thanks for replies

I think your year has a balast resistor: it will be located on the left hand side inside the engine compartment towards the back: it is a big resistor (rectangular in shape) that controls the voltage going to the pump. Sometimes the connection on it goes bad and you have to clean the contacts to make it work.