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Electrical guru's needed, troubleshooting help.

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Old 06-27-2011, 02:29 PM
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Default Electrical guru's needed, troubleshooting help.

I've still got codes: P0134, P0154 (both o2 sensors pre-cat "no activity")
The car is obviously running rich, as in gas mileage worse than normal and you can just smell it. (avg 10 mpg's at best)
I've gone through three sets of new O2 sensors from Atlantic British.
I wised-up and just put in new o2 sensors from BP of Utah (Bosch parts 15175) seemingly OEM sensors.
Still have the same two codes.
Watching live data I can see that the heater element of the sensors works and it goes on and off.
Watching live data I can see that the readings for both front sensors stays at .45, which is the ECU default and "open loop" (hence the sucky gas mileage and overfueling when warm)
I've checked the o2 sensors plugs for power and continuity between the plug and the ECM, both checked out. (multi-meter)

Every LR tech and master tech seems to think these ECU's don't go bad, so what else would be keeping the truck stuck in open loop or keeping the ECU from getting the o2 sensors signal/reading? What else should I check?

Another oddity of note: when I installed the 3rd set of sensors from AB, I watched with live data and the sensors worked, no codes and appropriate readings for a least 30 minutes. This time after I installed the Bosch 15175 sensors the reading didn't budge from the default .45 Curious.

Thanks in advance for any ideas or suggestions,
DIIB
 
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Old 06-27-2011, 02:42 PM
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This may be a stupid question but have you checked your thermostat and verified that isnt stuck open? Because if it is, you wont enter closed loop. ever.

As far as the ECM not going bad, anything is possible. I saw a smart car drive 60 miles with no trans fluid because there was a 3 inch hole in the trans.
 
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Old 06-27-2011, 02:53 PM
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Originally Posted by dgi 07 View Post
This may be a stupid question but have you checked your thermostat and verified that isnt stuck open? Because if it is, you wont enter closed loop. ever.

As far as the ECM not going bad, anything is possible. I saw a smart car drive 60 miles with no trans fluid because there was a 3 inch hole in the trans.
No I haven't checked that. I'm not sure how that would have an effect on the electrical readings to/from the o2 sensor and ECM though. I can see how that would keep the truck in open loop, but my readings from the o2 sensor should still change when the car is revved and warming up, etc.
 
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Old 06-27-2011, 05:59 PM
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Originally Posted by DiscoIIBrandon View Post
No I haven't checked that. I'm not sure how that would have an effect on the electrical readings to/from the o2 sensor and ECM though. I can see how that would keep the truck in open loop, but my readings from the o2 sensor should still change when the car is revved and warming up, etc.

It actually has an extremely large effect of your O2 sensors. You ECM checks your temp sensors to see if the coolant is at proper operating temperature. If not, it will disregard your O2 sensors. The ECM will continously keep checking until it see's proper operating temperature. Once it does, then it will allow the O2 sensor data to become relavant.

You are correct in saying that the readings should change with revving the engine. But I dont know the extent of the system that LR used for engine management. It may completely shut off the O2 sensor until it reads proper collant temperature. Wouldnt hurt to check it though. Obviously, dont go by the guage on the dash, use the scan tool you have and read coolant temp after 10 minutes of runnig the engine.
 
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Old 06-27-2011, 06:02 PM
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Originally Posted by dgi 07 View Post
It actually has an extremely large effect of your O2 sensors.
I think you're misunderstanding what he saw. He's looking at live (raw) data. It doesn't matter whether the ECU is USING that data or not form the O2 sensors. As long as they are working, up to temperature, and available to the ECU (meaning the ECU is working and electrically connected to them) the live data should be accurate as to what they are reading.
 
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Old 06-27-2011, 06:15 PM
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Originally Posted by DarylJ View Post
I think you're misunderstanding what he saw. He's looking at live (raw) data. It doesn't matter whether the ECU is USING that data or not form the O2 sensors. As long as they are working, up to temperature, and available to the ECU (meaning the ECU is working and electrically connected to them) the live data should be accurate as to what they are reading.
I stand corrected . I am no expert on LR systems but I figured it was worth a shot. Well, to the OP, if everything has been tested and tested again, then you just may need to bite the bullet and replace the ECM.
 

Last edited by dgi 07; 06-27-2011 at 06:22 PM.
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Old 06-27-2011, 06:18 PM
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Originally Posted by DiscoIIBrandon View Post
Watching live data I can see that the readings for both front sensors stays at .45, which is the ECU default and "open loop" (hence the sucky gas mileage and overfueling when warm)
I've checked the o2 sensors plugs for power and continuity between the plug and the ECM, both checked out. (multi-meter)
When the engine is running rich, the o2 sensors are going to read rich, and not move from that point, until the engine start running lean. A "normal" engine running close to optimum will have the o2 sensors flopping back and forth from rich to lean. On the last of the carbureted cars in the 90's, a trick would be to use the o2 sensor and a meter to adjust the mixture if you didn't have an exhaust gas analyzer or a propane enrichment setup. You would adjust the mixture until the sensor readings change back and forth.

Perhaps a bad MAF or injectors? Does your live data change at all if you hold the RPM's higher than idle, or perhaps while driving down the road?
 
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Old 06-27-2011, 07:31 PM
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Originally Posted by jafir View Post
When the engine is running rich, the o2 sensors are going to read rich, and not move from that point, until the engine start running lean. A "normal" engine running close to optimum will have the o2 sensors flopping back and forth from rich to lean. On the last of the carbureted cars in the 90's, a trick would be to use the o2 sensor and a meter to adjust the mixture if you didn't have an exhaust gas analyzer or a propane enrichment setup. You would adjust the mixture until the sensor readings change back and forth.

Perhaps a bad MAF or injectors? Does your live data change at all if you hold the RPM's higher than idle, or perhaps while driving down the road?
The maf is new from last year, lr oem and is reading properly according to the live data. And no, the o2 sensor does not change at all. It does not move from the default .45 open loop setting. Not at cold, not while warming, and not while revving. I've watched them adjust under load when functioning properly and under load.

FYI - disco mike informed me on another board that there may have been a TSB on some faulty o2 sensor wiring harnesses...so, that is my best lead at this point. Anyone know the best way to confirm a malfunctioning harness? Multi-meter?
 
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Old 06-27-2011, 08:50 PM
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Originally Posted by DiscoIIBrandon View Post
FYI - disco mike informed me on another board that there may have been a TSB on some faulty o2 sensor wiring harnesses...so, that is my best lead at this point. Anyone know the best way to confirm a malfunctioning harness? Multi-meter?
Yes, use your multimeter in it's "beeper" continuity function. You'll want to make sure you disconnect the plug from the ECU when you check each wire. The continuity function uses voltage to work, my meter generates 2.5 VDC for this. While that shouldn't be enough to damage your ECU, there's no point in tempting fate.

The electric circuit diagrams in RAVE will help you find which wire goes where, page 48 in this case. For example: the front right O2 is connector 0645 with Pin 4 being the white with blue stripe wire, which goes to the ECU on connector 0635, pin 13. Pin 3 on all the O2 connectors is the power from the fuse box. My apologies if you already know how to read the circuit diagrams.

Back probing the connector will test if the wire is good but it won't tell if the connector itself is good. The terminal in the connector could be loose, broken, or corroded. This might be one of those times to stick a paperclip or a thin wire strand in the front of the connector.

I have feeling testing the harness will be frustrating!

JHK
 
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Old 06-27-2011, 09:05 PM
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Any chance you reversed the pre and post cat sensors? If that's done they will go to open loop. Though I would think you'd get codes for the post cat sensors also, if that were the case.

They get power from Fuse 2 in the engine compartment, so if that were the issue then the rears would be faulting also, unless the wiring issue was midstream.
Before replacing the ECM I'd check the wiring with an ohmmeter between the sensors and the fuse and between the sensors and the ECM. The ETM gives you all the pinouts (page 20.5).

Just an FYI, many Bosch sensors are just reboxed NTK, who were OEM for Land Rover.
I've found Amazon to be the best source for NTK sensors in general.
 

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