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2005 xj8. Purchased January 1 of this year. Ran great for 4 days. Than it went into dreaded limp mode.
Did the mechanical work on it over the winter (brakes, suspension etc.). The car ran fine all winter, although not driven as it needed state inspection and I had some obvious issues to address. I was in no rush. About 2 months ago it stopped starting. Just cranks and nothing (smell of gas).
To that end:
Sent the ECU out for testing as I could not read codes and it felt like a good idea to remove that variable; diagnosed and found to be faulty and was replaced.
The MAF replaced.
The crack shaft sensor replaced.
Throttle position sensor replaced.
Replaced fuel filter.
Replaced all of the non-serviceable relays in the front fuse box.
Currently it will start and run for 30-40 seconds and then die. Suspected fuel issue as it feels like it is starving. Did a fuel pressure test on the rail and with the ignition on the pressure goes from low or 0 to about 30~ if I flick the key back to start again it builds to 60+ and than drops back to around 45 psi. When the car starts the engine runs and the fuel pressure drops to zero and dies out. So I thought fuel pump. I accessed the fuel pump which is fortunately very easy to get to in this vehicle… apparently there are two. I accessed the primary and disconnected the fuel line to directly connect the pressure gauge. The pump jumps right up to 45 and if you flick the key, it will briefly jump up to max out the pressure gauge. So I am thinking it is not a fuel pressure issue. I took the gauge off and let the fuel run into a external tank to gauge flow. It pumps plenty of volume. Sooooo now I am thinking that the fuel pump is not being actuated after start. Fuel regulator? So I did the g531332t175 test on the FRP. Pin 1 with ignition on has 5.5volts. Pin 3 To negative terminal with ignition off has 11000 ohms. Pin 3 to positive terminal ignition off 712 ohms. I checked that last one three times. According to the test it should be greater than 10,000 ohms. This could indicate a short circuit… but I have no idea where or what to look for.
To be honest, I do not know what to do next. Replace the FRP, on the premises that it controls the fuel pump? There are 2 codes in the computer for which I cannot clear. One is related to low air flow voltage, and the other is not relevant. This is my first car with this much computer control and I am a bit stumped. I purchased the Jaguar compatible computer scanner in hopes that it would provide a deeper dive into the car but it has not really revealed anything related to the engine and for some reason the only codes I can read are the OBD codes, although I can see the live date. The fuel pressure is indeed being registered and shows what I am seeing on the actual gauge, loss of pressure after start.
I will not be taking this to a dealership, so I would like to head off those suggestions immediately. Thank’s everyone for reading and I hope someone has encountered this issue before.
Last edited by Bluefish001; 06-25-2022 at 08:57 PM.
follow up.
It may not be clear here, the car starts only when the fuel pressure is above 30-psi. As it runs the pressure precipitously drops to less than 18 psi and the car chokes out. Applying the gas pedal increases rpm’s but only reduces the time it runs. The computer running live data reports the same fuel psi drop. It is like the fuel pump is NOT running after the car starts. The fuel pump is working… but “apparently” only when you first key the car on.
Originally Posted by Bluefish001
2005 xj8. Purchased January 1 of this year. Ran great for 4 days. Than it went into dreaded limp mode.
Did the mechanical work on it over the winter (brakes, suspension etc.). The car ran fine all winter, although not driven as it needed state inspection and I had some obvious issues to address. I was in no rush. About 2 months ago it stopped starting. Just cranks and nothing (smell of gas).
To that end:
Sent the ECU out for testing as I could not read codes and it felt like a good idea to remove that variable; diagnosed and found to be faulty and was replaced.
The MAF replaced.
The crack shaft sensor replaced.
Throttle position sensor replaced.
Replaced fuel filter.
Replaced all of the non-serviceable relays in the front fuse box.
Currently it will start and run for 30-40 seconds and then die. Suspected fuel issue as it feels like it is starving. Did a fuel pressure test on the rail and with the ignition on the pressure goes from low or 0 to about 30~ if I flick the key back to start again it builds to 60+ and than drops back to around 45 psi. When the car starts the engine runs and the fuel pressure drops to zero and dies out. So I thought fuel pump. I accessed the fuel pump which is fortunately very easy to get to in this vehicle… apparently there are two. I accessed the primary and disconnected the fuel line to directly connect the pressure gauge. The pump jumps right up to 45 and if you flick the key, it will briefly jump up to max out the pressure gauge. So I am thinking it is not a fuel pressure issue. I took the gauge off and let the fuel run into a external tank to gauge flow. It pumps plenty of volume. Sooooo now I am thinking that the fuel pump is not being actuated after start. Fuel regulator? So I did the g531332t175 test on the FRP. Pin 1 with ignition on has 5.5volts. Pin 3 To negative terminal with ignition off has 11000 ohms. Pin 3 to positive terminal ignition off 712 ohms. I checked that last one three times. According to the test it should be greater than 10,000 ohms. This could indicate a short circuit… but I have no idea where or what to look for.
To be honest, I do not know what to do next. Replace the FRP, on the premises that it controls the fuel pump? There are 2 codes in the computer for which I cannot clear. One is related to low air flow voltage, and the other is not relevant. This is my first car with this much computer control and I am a bit stumped. I purchased the Jaguar compatible computer scanner in hopes that it would provide a deeper dive into the car but it has not really revealed anything related to the engine and for some reason the only codes I can read are the OBD codes, although I can see the live date. The fuel pressure is indeed being registered and shows what I am seeing on the actual gauge, loss of pressure after start.
I will not be taking this to a dealership, so I would like to head off those suggestions immediately. Thank’s everyone for reading and I hope someone has encountered this issue before.
Last edited by Bluefish001; 06-26-2022 at 10:45 AM.
good questions!
It appears to be more prominent on the left bank (facing the engine). Both sides appear to have had oil on the threads. Can not determine how old the plugs are. It is possible that they may be original equipment? NGK IFR5N10. 140,000mph on vehicle. They cleaned up fine and I really have no reason to suspect them as the issue, just a symptom of the fuel related issue, so I am going to put them back for now as the car appears to have run with them just fine. Will order new plugs form Rockauto later in the year or next.
Originally Posted by pkoko
Is it a problem on multiple plugs? Is it on both banks? Which plug #s were wet? Is it repeatable?
I have no idea if any of those questions are relevant or helpful. But maybe someone on this forum can help with further detailed info.
Bluefish,
I am new to the XJ8 platform myself but have a couple of questions for you to try to better understand your issue.
Your profile has you with a 2005 XJ8L
Looking at the schematics (the place I always start being a electronics tech myself), you thought you had two fuel pumps on your car.....I believe only the supercharged engines required two pumps, pump 1 driven from the rear electronics module, while pump 2 is driven by a secondary fuel pump control module.
If you have a single fuel pump it is driven solely from the rear electronics module.
The wet plugs you have observed might simply be from low fuel rail pressure not allowing sufficient atomizing of the fuel before the engine eventually cuts out.
Your starving issue and observed low fuel pressure after start up could be a partially blocked fuel filter or fuel tank vacuum. Have you tried releasing the fuel filler cap to see if there is high vacuum present and afterwards whether the engine will run longer between failures?
When you did your pump flow test, was that pre or post fuel filter?
The injector pressure sensor does share a 5v sensor supply from the ECM to pin one of the sensor plug, and the output from the sensor is on pin 3. As the pressure increases so does the output voltage to from the sensor appearing at pin 3. So if you are seeing pin 3 voltage declining as the car runs and starts its performance decline, then the sensor would appear to be working OK.
The question becomes whether you are seeing the fuel pump being asked to run harder as a result of the declining pressure.
If you meter the voltage to the fuel pump (granted it will be a pulse width modulated supply voltage), do you see any change in the upward direction of the fuel pump drive voltage?
If so, the ECM is telling the rear electronics module to drive the pump harder, so that would tend to rule those out for the time being.
If the fuel pump is being called upon to run harder and it is trying to respond, but if the pressure continues to decline despite the pump working harder, then the issue is either a restriction (fuel pick up or line filter) or the pump is trying to overcome a vacuum in the tank (hence my suggestion to pop the fuel filler cap to depressurize the tank initially).
As stated initially, I am new to this model myself, but lets try to exclude some of the possibilities with some strategic simple tests.
I tend to agree at this point. Did a smoke test and it is tight as a drum. Already replaced the fuel filter and the fuel pressure regulator. Only thing left is the injectors and the fuel pump.
Originally Posted by h2o2steam
Bluefish,
I am new to the XJ8 platform myself but have a couple of questions for you to try to better understand your issue.
Your profile has you with a 2005 XJ8L
Looking at the schematics (the place I always start being a electronics tech myself), you thought you had two fuel pumps on your car.....I believe only the supercharged engines required two pumps, pump 1 driven from the rear electronics module, while pump 2 is driven by a secondary fuel pump control module.
If you have a single fuel pump it is driven solely from the rear electronics module.
The wet plugs you have observed might simply be from low fuel rail pressure not allowing sufficient atomizing of the fuel before the engine eventually cuts out.
Your starving issue and observed low fuel pressure after start up could be a partially blocked fuel filter or fuel tank vacuum. Have you tried releasing the fuel filler cap to see if there is high vacuum present and afterwards whether the engine will run longer between failures?
When you did your pump flow test, was that pre or post fuel filter?
The injector pressure sensor does share a 5v sensor supply from the ECM to pin one of the sensor plug, and the output from the sensor is on pin 3. As the pressure increases so does the output voltage to from the sensor appearing at pin 3. So if you are seeing pin 3 voltage declining as the car runs and starts its performance decline, then the sensor would appear to be working OK.
The question becomes whether you are seeing the fuel pump being asked to run harder as a result of the declining pressure.
If you meter the voltage to the fuel pump (granted it will be a pulse width modulated supply voltage), do you see any change in the upward direction of the fuel pump drive voltage?
If so, the ECM is telling the rear electronics module to drive the pump harder, so that would tend to rule those out for the time being.
If the fuel pump is being called upon to run harder and it is trying to respond, but if the pressure continues to decline despite the pump working harder, then the issue is either a restriction (fuel pick up or line filter) or the pump is trying to overcome a vacuum in the tank (hence my suggestion to pop the fuel filler cap to depressurize the tank initially).
As stated initially, I am new to this model myself, but lets try to exclude some of the possibilities with some strategic simple tests.
How do I test this?
My sense is no but I have not tested for this as yet. I am hesitant to put my meter on the fuel pump wiring with out understanding the circuit. There are 4 wires. Two heavier then the others. The wiring schematic says they are both outputs but does not indicate the polarity or load for each. Also it would appear that they are pulse modulated… I think I might be able to see the pulse on my old analog meter, unfortunately I do not have an oscilloscope yet.
I was going to pull the pump out of the tank next. I suppose I could visually confirm this?
Originally Posted by h2o2steam
As the fuel rail pressure declines, do you see the fuel pump being asked to increase its output before the ECM relents and shuts everything down?
I put back the original Throttle Position Sensor and oddly the car seems more like it should run than with the new one. Testing the two it would appear that the new one only works for one channel? I read about this issue in someone else’s post in this forum.
I cleared the codes and restarted… almost all the codes are still clear. The only ones that Stored are:
P0222 - stored
P0112- pending
P0191- pending
P1000- pending
ignition timing advance for number one cylinder 10°
intake air temperature -40°F
Air flow rate from mass airflow sensor 0.0 lb/min
absolute throttle position 7.1%
Originally Posted by Bluefish001
I cleared the codes and restarted… almost all the codes are still clear. The only ones that Stored are:
P0222 - stored
P0112- pending
P0191- pending
P1000- pending
To answer your initial question regarding measuring PWM with a meter, if is still effectively a DC voltage, just being rapidly chopped, so a DC meter should still pick up an indication of what the voltage is (hopefully somewhat averaging out the result of the high frequency chops).
Single fuel pump models you are slipping some pins into up the back of the plug while it is still connected to the pump and measuring between pin 1 (Yellow) and pin 4 (Red) for primary pump at connector FP2, if you have dual fuel pumps then you have a second yellow wire to pin 2 and a second red wire to pin 5 of the same FP2 connector. They then split at that connector off to two separate connectors to service each pump (pump 1 is connector FP4 (Red pin 4, Yellow pin 2), Pump 2 fed by connector FP3 (Red pin 2, Yellow pin 4).
P0112 - IAT sensor (Intake Air Temperature) located in MAF sensor for normally aspirated engines and a second sensor also on RHS rear of intake manifold if you have must have a supercharged engine. (Still not sure if you have a SC engine so answering to cover both variants)
The sensors operate as negative temperature coefficient sensors, in other words as the air temperature increases, the sensor resistance is decreasing, thus the sensor voltage at both the sensor plug and ECM is falling when air temp rises.
Check what voltage you have on MAF plug pin 4 (Blue wire), pin 5 (Black/Green stripe) should be ground. P0112 would suggest high voltage present at sensor plug (indicating bad sensor) or ECM plug pin 71 is high only (indicating high resistance or open circuit wire to MAF sensor).
If you have a supercharged engine then you are also checking what voltage you have on IAT plug pin 1 (Yellow/Blue stripe wire), Pin 2 should be ground. Looking for high voltage on IAT plug pin 1 or if zero checking pin 72 of ECM plug to see if high then possible bad wire.
If either the MAF pin 4 or the SC model IAT sensor plug pin 1 are reading a voltage of zero or 5 volts (either extreme) then you have either a sensor issue or an open wire.
Your P0222 error is a throttle position sensor error for TP circuit 2.
The TPS sensor is comprised of two variable resistor tracks (TP1 and TP2). Errors of P0122 and P0123 are associated to TP1 operation, and errors P0222 and P0223 are related to TP2 operation. A mismatch between TP1 and TP2 can also bring about a P0121 error code which you are apparently not getting.
Check for voltage at pin 2 of throttle body plug (Yellow wire).this should vary between near zero to near 5 volts depending on throttle body position. That yellow wire goes back to ECM plug P11 pin 076.
Earlier TPS sensors are replaceable but later series throttle bodies have a different TPS fitted which is riveted in place and appears problematic to source an equivalent sensor.
Whether either of these errors will result in fuel pump shut down, I suspect the TPS one could, but ECM generally will insert default values and set the throttle valve to a default position, intimating that fuel pump should not be getting shut off.
Thank you. I now have a raft of tests to perform! This car is the version 4.2L without the supercharger. I will run through your suggestions tomorrow in the light of the day. Already have the back seat out so I think I will start there. Will let you know what I find out.
best regards
— James
It will not work! It is missing a channel as you can plainly see.
Originally Posted by Bluefish001
Thank you. I now have a raft of tests to perform! This car is the version 4.2L without the supercharger. I will run through your suggestions tomorrow in the light of the day. Already have the back seat out so I think I will start there. Will let you know what I find out.
best regards
— James
06-25-2022, 05:30 PM
Starts than di
