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Hi guys!

Hippo needs rescue. Please help!

Freelander 2004, TD4, manual. 93k.

I keep getting the same code P1190- Fuel Rail Pressure Plausibility. Car starts limping usually in second and third gear around 2k revs +/-  

I tried many things already, cleared the code, but so far it keeps coming back when I go for a ride..... UNLESS I disconnect the fuel rail pressure sensor. Without the sensor connected the car doesn't limp anymore.

Code comes with MAF disconnected for example. Injectors are fine.

I do get live readings of 350+Kpa for LP and 26k+ at idle for HP pump, which goes up to 120k.

Can't go past 3k revs in 5th gear, 70MPH. Unless downhill.

I have videos if you need more evidence. But maybe you guys can explain why car doesn't go in MIL limp mode when fuel pressure sensor is disconnected. I checked the cables. They have 5v and 0.5v return at ignition. Can this mean 100% the sensor is broken?

 

Any help sooo much appreciated!! I've been dealing with this for some time and have no idea what can be wrong. And how can I test what is broken.... 


 

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In my experience its usually a cabling or connector fault. Rarely the sensor itself.There is even a replacement overlay harness as a fix from LR.

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11 hours ago, Ally V8 said:

In my experience its usually a cabling or connector fault. Rarely the sensor itself.There is even a replacement overlay harness as a fix from LR.

I wish that was true. The harness was replaced already. The sensor gives readings and the fault P1190 is not about the sensor...it's about the pressure. When I disconnect the sensor I get P1191, which is the sensor itself. But...as I said, I wish it was just the cable. And tests should confirm the cables fault.. However, cables check OK for continuity and voltage.

One interesting thing though: The only thing I can do to avoid getting limps and MIL... is to disconnect the high pressure sensor. The car works fine without it. I mean as good as it gets without the sensor.

I don't just want to replace it based on an assumption. The sensor gives readings after all....

Also I suspect pressure regulator as a possible culprit. If pressure regulator controls the high pressure sensor in any way, or vice versa then, any of the two can be broken . Yesterday for example, I saw something unusual. Just before engine cut off in traffic as I was accelerating, pressure regulator current went to 4V. Then car died. Very unusual high current. The load was not that big.... Most times under high load regulator goes up to 2.5V... Maybe it was an effort to increase pressure.... So that makes high pressure pump faulty....

But then... why is car not limping when common rail sensor is disconnected...

Edited by DreameD
grammar

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I think you are confusing yourself slightly. First off, the engine ecu uses the rail pressure sensor to dictate what to output to the fuel pressure regulator as closed loop control. So when you disconnect it the ecu just uses a default value based on other sensor values such as rpm,coolant temp,airflow and driver demand etc. You are measuring voltages I assume with a multimeter,so are seeing average voltages based on the fairly slow refresh rate of the meter. There are only really two ways to sort this out,firstly the parts shotgun, if I had no choice but to do this I would replace the pressure regulator first,its way more likely to fail than the sensor.

The better way to sort it is to use an oscilliscope,with this you would be able to see the duty cycle of the square wave of voltage applied to the regulator, plus the varying output from the rail sensor.With a decent scope you can then freeze frame the waveforms and see what pressure a duty cycle of say 70% on time produces as a pressure reading at a given rpm. 

The rail sensor should show a voltage output of 0.5v key on,engine off. This should rise rapidly upon cranking,once above about 1.2-1.4v there is enough pressure for the ecu to start firing the injectors.The voltage should then rise to about 4.5v with a wise open throttle and immediately come back down on releasing the pedal. That is the theory,however when I had a problem with a non starting TD6 RR a few years back I found that the ecu would fire each injector 3 times whatever the rail pressure as soon as it was cranking.(Analog to digital converter unit was at fault inside the ecu in that case) But the principle is the same,0.5v raising to about 4.5v max.

The reason you don't get a check engine lamp with the sensor disconnected is because the software in the ecu does not command it for that fault,I don't think LR ever listed,(As they do for later cars) a fault code list that shows command Mil yes/no, plus a detailed description of possible fault causes.

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On 9/13/2018 at 1:04 PM, Ally V8 said:

The better way to sort it is to use an oscilliscope,with this you would be able to see the duty cycle of the square wave of voltage applied to the regulator, plus the varying output from the rail sensor.With a decent scope you can then freeze frame the waveforms and see what pressure a duty cycle of say 70% on time produces as a pressure reading at a given rpm. 

Thanks for your answer. Unfortunately I don't have an oscilloscope. I've already tested the pressure sensor in terms of voltage and I get those voltages you mentioned.  But testing the pressure regulator is harder, especially because it's hard to reach.  Is there any other way to test the pressure regulator, without an oscilloscope? I have a multimeter and a diagnostic tool Icarsoft LRII , thats it. No graphs unfortunately. At most I can connect the multimeter to the regulator, but then...The issue occurs only under load (rarely if I just rev the engine stationary). So how can I test the regulator while driving?:D

 

The only two things left before blaming the HP pump are the pressure regulator and the throttle sensor.  The engine knock/limp and rattle happens not only when I accelerate but also when I release the pedal (sometimes abruptly) and never happens on idle. Also the pedal live readings are very random and don't always show a value based on input. Same goes for the regulator. Sometimes it goes to 4. Sometimes just to 2, under relatively same load. At idle is 0.71.  (Is it ampers or volts for pressure regulator current btw?)

Of course I cant exclude the pressure sensor itself.

But basically with pressure sensor disconnected: I understand why the P code/MIL doesnt come up....because the sensor generates it. What I don't understand is why the engine doesn't rattle or knock under load when it's unplugged. So far it seems the sensor generates that knock. It's either by sending mixed signals to regulator...orrr the regulator can't cope. Any other option?  

 

I still believe this is a very valuable clue. The fact that car doesn't choke if it doesn't know the value of the pressure means something is working at least. Can I know 100% something is not broken (HP Pump) just because car works without high pressure sensor?

Also I see the high fuel pressure values  oscillate alot. Even at idle....the pressure is never stable...they go up and down. 25-28k Kpa.   And under load, it's all over the place. But maybe that's not relevant.

I will try to disconnect the regulator itself and check the O rings as I've heard they go bad sometimes. Can I determine if it's faulty just by looking at it? I suspect the O rings will look normal. Obviously if they are broken I will see, however I doubt car would start if that's the case. If they look normal, I'll just put it back :))

 

 

 

Edited by DreameD

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Without a scope you are just guessing. As I see it you either need to find a decent garage that really does understand Bosch common rail ,(Fail as we call it) maybe even a dedicated Bosch fuel shop ?  Or you can just replace the regulator on the pump. From the symptoms you describe that is the most likely component. Unfortunately a multimeter is of very limited help with what you are diagnosing. Please use either OEM or genuine parts for these repairs,there are some horribly cheap and nasty parts on offer,these will either fail quickly or muddy the waters even more. 

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6 hours ago, Ally V8 said:

Without a scope you are just guessing. As I see it you either need to find a decent garage that really does understand Bosch common rail ,(Fail as we call it) maybe even a dedicated Bosch fuel shop ?  Or you can just replace the regulator on the pump. From the symptoms you describe that is the most likely component. Unfortunately a multimeter is of very limited help with what you are diagnosing. Please use either OEM or genuine parts for these repairs,there are some horribly cheap and nasty parts on offer,these will either fail quickly or muddy the waters even more. 

 

can you recommend any inexpensive scope I can get?  Maybe on Amazon/ebay?

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Sorry, my scopes are Pico 2 and 4 channel - bit much to do a single job. As much as I hate the parts shotgun, I think you might be better of in this case. I see Island 4x4 do a Bosch pressure reg for your car at £85+Vat.

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24 minutes ago, Ally V8 said:

Sorry, my scopes are Pico 2 and 4 channel - bit much to do a single job. As much as I hate the parts shotgun, I think you might be better of in this case. I see Island 4x4 do a Bosch pressure reg for your car at £85+Vat.

Look again at the Island 4x4 listing. They call it the pressure regulator, but the photo shows what looks like the rail sensor to me ? Would need to confirm what you would be getting !

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10 hours ago, smallfry said:

Look again at the Island 4x4 listing. They call it the pressure regulator, but the photo shows what looks like the rail sensor to me ? Would need to confirm what you would be getting !

You are quite right,I didn't look at the photo,only read the part listing - Which is clearly wrong.

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