My money is on the relay, Alex!

 

Hi Greg

I hope you are right!

But how do you Test the Fuel Pump Relay?

Having said that I have found an identical one that I took off a Scrapper (but who knows that could be a dead one as well)

Different make but same numbers

Maybe it could be the Relay as one day the Car was running but the following day She wouldn't Start and wouldn't continually Pump Petrol out of the Tube that I had hanging over the Front Wing when I Cranked her on the Key

 

I'm really hoping Greg is right and the cause of my No Start Problem is the Relay rather than the Fuel Pump, as the prospect of having to Change the
In-Tank Fuel Pump, would not be one that I would be looking forward to

Though if it is the In-Tank Fuel Pump, then I will have to 'Cowboy Up' and do it

So searching through my Box of Spares, I managed to find an identical Fuel Pump Relay that I took off a 'Scrapper' years ago and since I didn't know how to Test either of them

There did not seem to be anything lost by trying the one from the 'Scrapper'

So here's what happened:

First I disconnected the Petrol Feed Pipe that goes into the Injector Rail and then once having done so I got a Piece of Polythene Pipe that was exactly the same size as the Thread from the Main Fuel Inlet, which I was able to screw on nice and tight and had the other end of this directed into a Jar

Although before I did any of this I also disconnected the Plug from the CPS Crank Position Sensor, as when you are playing with Petrol just one Spark can easily turn your Car into a Barbecue, so its best not to attempt this in your Garage

Once having done so, the moment of Truth then arrived where with the CPS still disconnected it was time for me to Turn the Key to see what would happen although with the CPS still disconnected, I was not expecting her to even attempt to Start (No Spark = No Start)

Where never having done this before, I really didn't have any idea what I was expecting to happen

So there was only one way to find out and to say that I was suffering from a fear of failure, must have been the understatement of the Year!

Then Turning the Key to Position 'One' A Full Bore Stream of Petrol shot out of that Tube like a Firehose into that Jar for a Couple of Seconds and did that every Single time that I Turned the Key

Where about 4 ON/OFF Actuations was enough to have that Jar Half Full, which was Totally different from Yesterday, where residual pressure in the line only had a few dribbles of Fuel Coming out

And so I am very Tempted to say that the Fuel Pump is working as it should and hoping that Greg and Grant may jump in to Confirm

Time to take a break for Lunch and then I'll reconnect the CPS and see if She Starts

I was hoping to get a Video or at least some Pics, except instead of Wind and Rain we have Relentless Sunshine, which makes it very difficult to see

 

Good News!

I managed to get a Short Video of Testing the Fuel Pump Relay that I got from a 'Scrapper'

It's looking good although I'm not sure what I was expecting to see

So after Lunch I'll try and Start her up

 

Hi OB,

If you have fuel being pumped on energising of the iginition, then you've confirmed 3 things are functioning:

- The Main Relay. This provides the energiser signal to the Fuel Pump relay. So, if the Main Relay fails, the Fuel Pump relay can't operate, so the pump can't operate.
- The Fuel Pump Relay. Whether energised via Ignition on, or with the starter operating, the Fuel Pump can't run without the Fuel Pump Relay energised.
- The Fuel Pump itself. Petrol spurting out of the pipe indicates that's ok.

Now you mentioned that you had sparks on the plugs with the starter churning. So the CPS is sending a signal to the ecu (otherwise you wouldn't get sparks on the plugs).

The CPS signal also enables the injector signals to be sent by the ecu. So if you've got sparks, there's no reason to suspect that the injector electrical circuit won't also now work.

So, the injectors could still all be stuck, but that's extremely unlikely. And yes, the temp signal could be at fault which impacts the injector duration.

BUT, I think the car is going to start this afternoon. If it doesn't catch after a couple of turns, try completely flooring the throttle whilst churning it and hold it all the way down. You may then find that the engine eventually starts to catch and you can start to lift your foot up.

Fingers crossed, it's going to be a good day!

PAul

 

Hi Paul (ptjs)

Very reassuring to hear that so Cheers!

Maybe that was why She was running the day before I encountered the No Start Problem

Maybe it was a Coincidence that the Fuel Pump Relay went wrong at exactly that time

Also very lucky that I found a Spare Relay with the Same Numbers

Hopefully the Injectors are not blocked as they were Brand New and so I'm really hoping She will Start when I turn the Key

Except that right now it looks if its going to Rain!

Typical British Summer, so potential Start Up on hold for the Time being

 

Cranked her over but still no Start or even showing any signs of Firing and now the Battery needs recharging again, so what could be wrong?

Since I put in the New Fuel Pump Relay, then I would say She seems to be getting Fuel

With the question now being why is She not Firing?

It could be because I put the Old CPS back so may have to put the New one back and see if that makes any difference and also check the Plugs to see if they Spark or maybe the engine got flooded

I really don't know

 

AJ
I think a touch more diagnosis is called for. What about pulling a plug and its coil or lead (I am assuming it is CoP; but as you know I know nothing about the 6 cylinder cars), get the GF to turn the key and see for sure if you have a spark by holding the plug near the block/head.
Also have you verified Grant's point about ensuring there is 12v on the red wire to the camshaft gizmo?

 

Hi Greg

Last time I had a no Start situation, I put on a New Crank Position Sensor and she fired right up!

But this time being unaware that the Fuel Pump Relay had gone bad and WAS the cause of the problem (or most likely was)

I put the Original Crank Position Sensor back on the Car, which could have been a big mistake as that was why I changed it in the first place

So now I know that I've got plenty of Fuel going into the Fuel Rail because of the New Fuel Pump Relay, I am going to put the other Crank Sensor back on, as that was the one that got her running last time

I'll also try and Check for 12v on the Red Wire like Grant Said although its really awkward to get to as you can't see what you're doing

Then I'll try and Start her and in the event that she does Start it's all good

But if She doesn't then I'll pull a Coil over Plug like you said and go from there

Hope this makes sense? as because of the Faulty Fuel Pump Relay, this led me to swapping the Crank Position Sensor which I should have left as it was, as with the benefit of hindsight, it looks as though I may have replaced the Good Crank Position Sensor with the Bad one

 

OB,

You need to know:

- the pump is running when the starter is churning (you've only confirmed to us that it was running in Ign on position, not necessarily when the starter is operating.
- that you have sparks (you told us originally you did, but you haven't said if this is the now the case with whatever CPS is now fitted.

When you absolutely know that the pump runs AND the plugs are sparking when you're operating the starter, and if it still doesn't start, then you'll start looking at the injection electrics or fuel rail pressure retention.

If you approach this methodically and logically, you'll definitely get there!

Cheers

Paul

 

Hi Paul (ptjs)

I never knew that!

Because Petrol only came out under Pressure for about 3 Seconds when I turn the Key to position ONE

But NO Petrol comes out when She's Cranking! and I have no idea why not and didn't know that it was supposed to until the engine was running

If you know the Answer to that one, then I am sure she will start as that seems to be the Missing Piece Of The Jigsaw

If that has got anything to do with the Crank Position Sensor?
This was disconnected during the Petrol Pumping Test you saw on the Video

Should I do the Petrol Pumping Cranking Test again, only this time with the Crank Position Sensor Reconnected?

Or is there something else I need to do?

 

With the Battery Fully Charged, I took off the Original CPS Crank Position Sensor and re-fitted the one that I bought about a couple of Years ago to replace it with and then once having done so I Turned the Key and the Engine Fired up straight away but for only about One Second!

Then I repeated the process and once again the engine only Fired up for a Second and wouldn't even keep going on the Throttle

Putting all this together with what happened Yesterday, when the Ignition is turned on you get a massive jet of Fuel, that comes out Full Bore as can be seen in the Video above

Having said that there was no sign of this to begin with as unbeknown to me, the Fuel Pump Relay had packed up but I luckily had a replacement which is the Silver one in the Photo

As for the other 2 Relays on either side of this, One is the Main Relay (although I don't know which one) and I have no idea what the other one does, so maybe someone who does know will chip in with that info

So now with the help of Paul (ptjs) I think we have identified why the Engine isn't Starting: For although the Fuel Pump will Shoot out a Full Bore Jet of Petrol, every time the Ignition is Turned to Position One (as in the Video above)

It won't Shoot out any Petrol while the Engine is Cranking and if we can solve that mystery, then I'm sure that the Engine will run, so if anyone knows the reason for this, then please let me know




The Silver one is the Fuel Pump Relay and one of the other 2 is the Main Relay, although I don't know which one and I don't know what the other one does either, so if anyone knows then please let me know

Or maybe you know why the Engine doesn't Pump Fuel while its Cranking but only does so when the Key is Turned to Position One

 

Alex
Great progress; nearly there.
A random idea to consider:
On a Lucas V12, the ECU needs a signal from the amplifier in the engine bay to tell it that the engine is cranking; this signal is the ECU's trigger to fire the injectors. I suspect (I do not know) that there is something similar in all injection systems including the AJ16. Once Paul tells us what gives the ECU in your setup this signal, I think that will be a good diagnostic path to follow.
Keep optimistic!

 

Hi Greg

Brilliant thinking out of the Box idea!

As soon as we know where the Signal comes from to Trigger the ECU then we could be on a Winner, it could be as simple as that!

 

OB,

I thought I definitely knew how it worked. My understanding was always that the ECU let the pump run for only 1 second with the ignition on then closed the Fuel Pump relay signal . When trying to start the car, the ecu got a signal from the CPS that the engine was cranking, which opened the relay and the pump then ran continuously.

I then verified that tonight with the Jaguar documentation for the AJ16 which says:

The electrically powered fuel pump is controlled by the ECM via the fuel pump relay. After the ignition is turned on (position II), the pump runs for about 1 second to build fuel pressure for starting. When the ECM receives an engine speed signal from the crankshaft position sensor, it activates the fuel pump relay, which in turn switches on the fuel pump. The fuel pump will continue to run either until the ignition is turned off or until approximately 1 second after there is no speed signal.

So, that has always been consistent with my understanding - that the key input to the ecm to run the fuel pump came from the CPS. Then tonight, in the same documentation for the AJ16, I found the following:

When the engine is cranked (starter engaged), the ECM receives a cranking signal from the starter relay.

So, that slightly confuses things! But, let's assume for now that it's the CPS that provides the signal to the ecu when cranking!


The Fuel pump relay is energised by a signal from the ecu which then enables the flow of current between Terminal 30 (Battery input) & Terminal 87 (output current to Fuel pump).

So, at Terminal 87 (Blue with Red Stripe) you should have voltage output going to the Fuel pump when the engine is cranking. That's Test 1 to measure that.

If you can't see output voltage from Terminal 87, try looking for the input signal from the ecu to the Fuel Pump Relay when the engine is cranking. This is on Terminal 85 and is Pink with a Brown stripe.

IF that test also fails, you need to confirm again that the plugs are sparking when the engine is cranking. If they are, the CPS must be operating ok, as the ignition system only works if the ecu is getting a signal from the CPS.

So, if you've got sparks but no fuel pump running when cranking, it implies that it's an internal fault in the ecu, which is allowing an output for the ignition but not allowing an output to the Fuel Pump Relay when cranking

Let us know how you get on.

Hang in there! We will eventually get there!

Paul

 

Hi Paul

Many Thanks for looking into that

I should hopefully understand all that much better in the daylight when I am with the Car

Since you mentioned the Starter Relay, please could you tell me where I can find that, as maybe I might discover an obvious fault

I've also found the Relays for the ECU that are DAC 7686 though I seem to remember reading about a Service Update where they recommend you swap these out for JA-LHF 6703 AA

These are above the Fuses behind the Passenger Side Knee Panel there are two of these but they don't say what the other one is for or even which one is the Relay for the ECU although one of them must be?

 

Paul, Alex
On the V12s the starter relay does give a signal to the ECU thazt the engine is cranking. Maybe the line concerning the AJ16 is in there by mistake? Or maybe not!
Seer the attached diagram for the Lucas V12, bottom line, first right after the centre.

 

Hi Greg

Many Thanks for your research and that diagram

As for 'The Wizard' and we all know who that is! What he doesn't know about Jags you don't need to know and obviously same goes for 'Greg'

Also Paul (ptjs) who for me is 'The Yellow Pages Of All things Jaguar' 'Better Call Paul!' and I do!

But I'm Cautiously Optimistic, that I may have Sussed out the cause of my 'No Start Problem' but also prepared to be wrong

As after many hours of research, I may have found what I was looking for as I am totally hopeless when it comes to things like following diagrams

Though having said that, here is what I found out

The ECU Cuts off the Fuel to the Engine (which as you know is happening on my 1995 XJS 4.0L) when the CPS (Crank Position Sensor) Fails to send a Signal to the ECU that the Engine is Turning i.e. Not Cranking

Just to Clarify on That: While the Engine may be Turning for instance While it's Cranking on the Starter, if the CPS doesn't send that Information to the ECU then the ECU Cuts off the Fuel

So although I fitted a New CPS a couple of Years ago, they can go wrong or even degrade for all sorts of reasons, even if they are still looking like New

That being the Case I've decided to buy another CPS, as a Failing CPS seems to be a fairly Common Problem on these Cars, as at least from what I have been reading and while I don't like to throw Parts at a Car, even if it doesn't fix it, a spare CPS that you can easily fix at the side of the road 8mm Socket

Is going to be much cheaper than a Tow Truck, assuming of course that this is a Fix that can get her back on the Road

So let's Find Out!

 

OB,

That logic is correct - if the ecu doesn't think the engine is cranking, it won't energise the fuel pump relay and thus the fuel pump.

BUT, if the CPS is not sending the signal, you also won't have the plugs sparking. And you're saying that the plugs are sparking when the engine is cranking? So that implies that the CPS IS sending a signal to the ecu. And that IMPLIES that fault lies in the ecu which is telling the ignition circuit to work, but doesn't seem to be telling the fuel pump circuit to work.

So, before you change the CPS again, perhaps confirm that the plugs definitely are sparking when the engine is cranking.

Cheers

Paul

 

Hi Paul

This may sound like Twisted Logic but I'm thinking that the CPS is Failing, rather than Completely Failed

As Yesterday the Engine Fired but only for One Second

So I think that on Balance I'd rather Spend a few Sovs on a New CPS to find out if the CPS the problem