Hello, my name is Bill. This is my first post here so I wanted to take the time to say "hi" to everyone.

What I have is an 85 XJS H.E. with the V12. It is black with a gray interior. It has 46,507 miles on it. So far everything but the tires seems to be original. I got the car for a very good price because it does not run. So on to the problem.

The engine is flooding. If I pull the injector plugs off it will run on starting fluid. If I unplug the fuel pump and plug the injectors back in, it will idle. It's getting fuel from some place to idle with the pump unplugged, but not enough fuel to run at anything above an idle. If I plug the pump back in with it running it floods and dies. Also the fuel pump relay has been grounded to the battery, P.O. said the shop did that because the fuel pump would not run. I replaced the left bank (drivers side) fuel pressure regulator, as it was leaking fuel into the vac. line.

Any thoughts? I've worked on cars all my life but this is my first step into the world of the Jag.

Thanks for any input, I hope to learn a lot about my new car and maybe help someone else when I know what I'm doing.

Bill

Submitted by zaphod_69@hotm… on Wed, 05/09/2007 - 17:11

Edited on 2007-05-09 17:58:34

Hi Bill
This is my first post also as i have just registered expressly to help you out.

Firstly with the Fuel pump relay thing,this circuit is actually meant to ground through the ECU but can also be cut out by the Inertia switch as i recall ( I may be mistaken on this one as the circuit diagram shows differently) which may just need resetting.( It is in the Left hand footwell under a black plastic cover right by the door hinges)

Secondly the Injectors are powered constantly whilst the ignition is on and the ECU pulses the ground on & off to actually open & close them when it recieves a feedback signal from the ignition amplifier( One pulse of 6 injectors every 3 sparks ).
At the front right corner of the engine bay there is a rectangular multiplug and a silver unit bolted to the inner wing with another plug( Plastic clip type )into it,these are your Injection harness Mutiplug & Power resistor.Unplug the Injection harness & test for any direct paths to ground ( Ignition off ) if there are none then turn on Ignition & test for 4x 12Volt feeds and again check for paths to ground. Any path to ground indicates a problem either in the ECU or the Power resistor pack so if you find one ..remove the Resistor Pack & Test again..if the ground disappears there's a good chance it's the Resistor at fault ...If not then it may be Harness to the ECU ..or the ECU itself ( If the car has had any underbody welding done sometimes the insulation is burned off the harness to the ECU).

Good luck ,Let me know how you get on

Oh by the way ..the Air temp sensor only has a 2-5% enrichment range so that isn't it ..Coolant sensor is much more likely for running rich ..but it cannot hold the injectors open without the engine actually running so that is also unlikely.

Submitted by buck_1one@yahoo.com on Mon, 05/07/2007 - 21:04

I think I may have made a mistake or something. I rechecked some things and I have 2190 ohms on the air temp sensor, off the car in the house at 68 degrees F. The book calls for 300 ohms at this temp. So I'm guessing the sensor is telling the computer it's about 100 below zero. Does anyone think this could be the problem with the flooding?

I'm going to replace it but I'm just wondering if I should get my hopes up or not.

Bill

Submitted by buck_1one@yahoo.com on Thu, 04/26/2007 - 07:05

Edited on 2007-04-26 7:22:48

Yup, deep down I have a feeling it is the ECU also. Not what I really want to hear.

Here is something else I have found strange about this car. With everything hooked up like normal, key on engine not running but in the run position the injectors will flood out the engine,intake,cylinders etc to the point I've had gas running out the throttle plates. I don't know if it is normal for the injectors to be injecting or not. Normaly the fuel pump would shut off and end such a problem but with the pump grounded to the battery it just runs and floods.

Don't know if this info will spark something in someone's mind or not.

Bill

Submitted by dougdwyer1@com… on Wed, 04/25/2007 - 21:37

It *is* beginning to sound like you might have an ECU problem. Not sure how you'd manage checking pulse width on one of these....its not like a modern car where you can use a scan tool to check the data stream. I'm sure there's a way using an o-scope.

I'm not sure what George means by injector "amp", either. There's an injector "resistor pack" on the right hand inner fenderwell, all the way forward. Since the engine *does* run the injectors are obviously getting voltage from the resistor pack but I'm not sure what would happen if the voltage was too high or too low. George?

At this point I'd be hesistant to go any further with w f/p test just to cover the basics.

This is a good one !

Doug Dwyer
Longview Washington USA
1995 XJR

Submitted by buck_1one@yahoo.com on Wed, 04/25/2007 - 17:16

George, not sure what you mean by the injector amp.

If you are talking about injector resistance (ohms), no I have not. My book gives no info on checking injector resistance or what the pulse width should be or how to properly check them. If someone would like to give me the specs and procedure I will go and check them out.

I am really at a lose as to what is going on here, I'd check the battery voltage on my Mustang if I thought it would help :)

Thanks
Bill

Submitted by SE98-32482CJ on Wed, 04/25/2007 - 14:12

Bill I watched a car run once with the fuel pump disconnected--the manifold was full of fuel and somehow it would pull in enough to run--for a while. You are flooding and unless there is another pump hidden somewhere you have regulator problems or the ecu is holding all injectors open---just for fun have you checked the injector amp? George Camp

Submitted by buck_1one@yahoo.com on Wed, 04/25/2007 - 08:02

Hi Doug, thanks for answering. Here is what I have so far.

A: Coolant temp sensor reads 2.14 ohms. Book calls for something close to that with them temp this morning. Connection seems to be fine.

B: The fuel pressure reg vac line goes right to the intake. No switch of any kind. Vac diagram under hood shows it this way too.

C: Vac line at the ECU reads 17 inches of vac at the computer end(fuel pump unplugged engine idling).

D: The enrichment switch does not appear to be stuck shut. It clicks on and off when you move the lever.

Just for ha ha's I checked the air temp sensor and it was reading close to what the book calls for at this temp 300 ohms. I also checked to make sure I had fuel return to the tank. I used compressed air and had air flow into the tank. I wish I had a fuel pressure gage to see what the line pressure is. All the shops I worked at had one so I never got one for myself.

So anymore ideas? Anyone?

Thanks again
Bill

Submitted by dougdwyer1@com… on Tue, 04/24/2007 - 22:23

Hi Bill,

Presumably it won't run for very long with the fuel pump unplugged, or something really, really, weird is going on !

Anyhow, the coolant temp sensor can cause massive over fueling if it is skewed "cold" or the connector is dirty/loose.

Your left hand fuel pressure regulator hose should go to a brown thermo-vac switch on the fuel rail. Bypass the switch and see if that makes any difference.

There's a vacuum hose running clear back to the fuel injection ECU in the boot. Make sure its connected at both ends. At the engine end it attaches to the 1" diamter vacuum balance tube at the rear of the engine.

At the throttle wheel there's a small lever action switch for fuel enrichment....make sure it isn't stuck closed (this only richens the mixture about 10% so probably isn't an issue here, but worth checking on general principle.)

By the way, your f/p relay was grounded right to the battery because the circuit in the ECU which normally takes care of that task is kapoot. Common problem.

Hope this helps a little.

DD

Doug Dwyer
Longview Washington USA
1995 XJR