SORRY. THIS WAS DOUBLE POSTED SOMEHOW... AND, I COULDN'T ATTACH THE PDF 2003XK ELECTRICAL GUIDE.

Morning and Happy New Year to all...

I have a "rescue" thread for this same (beautiful water damaged xkr) and have (thus far) come down to 4 MAJOR problems (JGate adjustment, No Fueling via FPModulation and a terrible Parasitic Battery Drain, intermittent starter issue) and thought I would start individual FOCUS threads on each and update that main thread with findings later.

I have so little time (and sun in these winter months) that every bit of time needs to count - so I like to have something of a plan of attack with the time I do have. This Sat and Sun are my days coming up...

ANYWAYS...Here goes it.

My fuel pump will not run unless I run a ground wire from the YR wire to a ground coming back from the pump. Without it, pump does not run and if running, and ground is disconnected, pump will shut off and car will die, fuel starved. With the temp ground wire to earth, she runs very nicely, considering. Please ignore the circle of the connector in this diagram.





Thanks to folks here I have come to a limited understanding of duty cycle, PWModulation and the controlling unit, FPModule located in the boot and to a degree, the fueling system generally. IF the fuel pump would run and it was over or underfueling, I would get an osilloscope (which I may down the line) to check for pulse and duty cycles. But I get nothing at this point.

There are these 2 White wires going into the FPModule. Running thru different connectors from the ECM to the boot. I can trace all these. They are described this way (see 2nd photo)... IT SEEMS these are all readable positive voltage that,,, for now,,, even if it is a fluctuating DMM value,,, I can just see if I'm getting values, for now??? Will that work? Osilloscope later?



Then,,, and I don't even KNOW what to think about this as I have never seen or checked it,,, the Pressure Sensor on the rail (IP sensor in photo), how it talks to the ECM and how that info is translated and then used to regulate pulse rates... Also,,, where is the PIS1 connector found? It seems like a very important multi-component junction. What should I be looking for in the IPSensor and will a failure here result in a failure of the grounding PWModulation signals from the ECM to the FPModule?


What else do I need to be thinking about?

It's a large file... But I will try and attach the 2003 EG here. All of these diagrams come from sec 4.2 and 4.1,, engine managemanagement.

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If the pump runs when directly grounded then don't waste money on an oscilloscope. Clearly you are not getting any pulse modulation on the ground side (you read 12v there) or the pump would be doing something.

I am curious though as to whether a simple Noid light would show the pulse modulation on a functional system.

 

Curious about the same... Thank you!

In your experience,,, where do I need to go to begin getting a better understand about what is FAULTING in the pulse? Is the signal to pulse, originating from the ECM and rail pressure sensor communication, sent to the FPModule a positive (read) signal. Then understood by the FPM to ground the fuel pump circuit intermittently at rate?

If I were able to read ANYTHING from the ECM,,, or the fuel rail pressure sensor I would be happy. I think I read somewhere that I should find about 5volts going into the fuel rail pressure sensor. Wondering what the signal to the ECM looks like from the rail sensor.

 

Some more complete shots from 4.2 and 4.1 of the EG...

 

There used to be a time when I enjoyed tracing wiring diagrams. Now I see double when I look at them Lol

 

Lol,,, it's not you, hahahaha
They are terrible screen shots, lol

All I know is I need to get this thing sorted.

 

Can you connect an obd scan tool and get a reading? This will let you read the fuel pressure as indicated by the sensor and see if it is a sensible value.

Does your fuel rail have a schrader valve? Seems like some cars (most except for mine) do, which lets you easily connect an external fuel pressure gauge to check the sensor against.

Remember the sensor is referenced to manifold pressure (vacuum) so will read different than an external gauge. At idle (high vacuum) the sensor should be higher than a gauge.

What voltage do you measure on the 2 white wires at connector to the pump module?

 

It does have a valve...

I haven't been able to get that reading at those 2 wires, yet. Will on Saturday. I am trying to go in with a game plan... Making my way (attempting to get any reading at any point, even if it is an DMM average) anywhere I can. Starting at the rail sensor, to the ECU, thru the car interior (if I get anything) straight back to the FPM... Hoping for something.

I had a good set of obd readings,,, then, for some reason, the damn ability to get a connection at the output OBD site was lost and hasn't returned. Don't know why.

With the way that I have been running her, I am sure the pressure is high. Direct running the pump to ground with the 12v +/- that comes from the OE lead at the tank. The FPM won't pulse ground the pump.

Q: of nothing is coming from the rail sensor, a value that the ECM can use to send a corresponding signal to the FPM, will the ECM send a generic/general base signal, or nothing at all?

Below is a few of my pre start and post start obd readings.

First

Second

After running on her own,,, grounded pump lead... Running nicely (all things considered) I might add.


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That list of codes just makes me wince. If you manage to clear all of those, you'll be inducted into the jag rescue hall of fame!

 

If P0603 is right you're going to need the PCM repairing or replacing or have no hope of passing smog / etc tests.

KAM is used for such as OBD monitor status and fuel trims.

If you plan to replace, car is liable to go into anti-theft lock-out unless you replace the other modules involved with matching ones for the replacement PCM and features your car has.

You'll need OBD working so I'd investigate it / some of the above next.

I suspect that splice (PIS1) is inside the fat harness from the PCM. Whether the engine side or cabin side, sorry I don't know.

 

Once running on her own and buttoning everything up in the air intake system (the one clip on hose at back of main filter inlet, air filter clipped in, MAF sensor plugged, and little plug under filter housing - and a couple of other things) DTCs went to two or three...after clearing codes. I was pleased. I was expecting no less after a 2-3 year sit up,,, and starting with fuel in the TB at first... The first two shots are a right accumulation of codes, I think. On thing was,,, I was HAPPY to see that the ECM was functioning well enough to collect them. 2,,, that they fell away after clearing and really, none came back.

Yes,,, the OBD is super important right now and something I will definitely be needing. Gotta figure that out.

And yes,,, the p0603 code scares(ed) the hell out of me...

I get free inspection stickers (MOT) at this point. Thankfully. This is NYC. Not so concerned about that, but, hopefully, lol, I won't be here for ever.

 

I remain optimistic. Lots of learning to do, but optimistic... I love this **** and keep it on the FUN side in my mind. I live in NYC, work in the street in front of my apartment, it's nutts to own a car in NYC in the first place, lol. I now have 4. Allllll, literally, yard finds! One sitting for 12 years. XJS. Small fire, no floors, rear end needing rebuild. It's all good. I have time.

XK8, Porsche 928, XJS, this latest,,,,, thing, lol...

No streessss for fun. And it's all fun. I'll get her going.

 

That 928 is taking time away from your jags . You should ship it to me. 😁

 

Ummm, maybe...?

Not, lol😉

 

Oh yeah, that's definately too far gone. I'd be doing you a favor. 😋

 

So... A quick update - I'm stumped, lol... Need I say more.

I get a fluctuating voltage (DMM) at the number 4 pin, white wire (as if a crude duty cycle reading)... A steady 3.73 voltage from the number 3pin white wire... From the black, I get a good hard earth...

At the fuel pressure sensor on the rail, I get 5v at both the 1 and 3 pins a solid ground on the center 2 pin.

I have a solid 12v at the R going into the fuel pump and what's reading as a ground (make shift) on the YR going into the pump... The plug at the top RH corner of the gas tank.

If I disconnect the make shift ground she starves for fuel and will stall.

I have a "new" FPM (the 3rd) that I can connect ~ have to go pick it up ~ but I don't see what's doing...

Seems like things are right.

What am I missing?

Any suggestions? I am confused...

Rail pressure sensor

 

It ain't good. These are my fueling pressures. Thankfully, obd got its signal back today...

Strange thing is, its reading DTC lean on bank 1...
Looks like an O2 sensor change is in my future... SMHCan't win for trying...

This is engine off...Not running

The p1638 (I think) was due to me messing around with fuses while the car was running. Stupid mistake. It cleared.

 

You probably already know these things, but seems complex. Breaking it down, setting the ground on YR followed by the pump providing pressure probably tells you that something positive is happening on the R side, but it doesn't tell you what is going wrong on YR. It also doesn't necessarily tell you that whatever is happening on the R side is 'correct' for good operation either. Or the fuel pump is taking correct PWM input and will not produce acceptable output unless you ground the negative side (likely substantially increasing full on).

So, ignoring the possible issues with wiring. Either the the pump is bad/inadequate, FPM is giving back bad PWM on at least the low side or it is interpreting its inputs to provide proper output which is cutting off the fuel. Not much help there.

Since these issues are difficult to disentangle without either generous access to replacement parts (I have three XK8s of the same era, can generally swap parts from known good systems), based on the state of the car, I'd try to find a scope. Then at least, you can see the signal on R and YR relative to each other (and then both to B) and work your way back from there.

 

Yes! The disentangling... Spaghetti in my head... And the car.

I have a 3rd module I will try today. eBay.

I could be wrong, but I think the pump is good. Lol, might sound crazy, but I have another OE earlier model Jag pump AND a brand new Walbro pump. I've been holding off on the Walbro until I have things "right". I have made an access hole in the back shelf and can swap things out in 15min,,, it hurt to make the cut but I am very HAPPY with the new ease of access... Can't say that strongly enough.

I will also see if I can get a reading (rather that just testing for ground) to see if I can get a better idea of ground fluctuations at all - on the black wire and,,,,, WHATS the brown and white wire do???? I'd have to go back (and will) but,,, I don't even remember seeing a brown and white wire in the diagrams??? Could be wrong.

Edit ~~~ NW Brown and White is the POWER source. Ok...

 

Yes, BW NW (BT18-5) is the power supply to the FPM and should be at B+ with the ignition switch at ii (on).

Pin BT18-4 is a 1Hz 'heartbeat' from the FPM back to the ECM, so the fluctuating voltage makes sense: you should see a pulse once a second. The FPM varies the duty cycle on this to flag its status to the ECM. I'd expect the ECM to throw a code if there was a problem here, but I don't see anything relevant in your list. If it's pulsing, then it's not 'dead'.

Fuel pressure sensor seems to be indicating max pressure (from JTIS: - "POTENTIOMETER – VOLTAGE INCREASES AS PRESSURE INCREASES" which would imply rail pressure is high enough so would tell the pump to back off - can you disconnect this?

The pump control signal from the ECM is at 160Hz, so measuring the voltage (@ pin BT18-3) on AC range would give you a better indication.

A 'scope is a wonderful tool to help you visualise what is happening with these signals, but sadly won't tell you why.