ECU/Speed sensor question expert required??
Discussion
Following on from one of the other threads with regards problems with the speed sensor. I’ve noted previously that when the Speedo is not working (2% of the time 
, note at this point I’m assuming the problem to be the sensor and not the Speedo itself. The engine will idle erratically and sometimes stall when pulling up to a junction, similar symptoms to a dirty stepper.
I believe that this may be the ECU trying to protect the cats from being poisoned because it doesn’t know the car speed part of the equation for fuelling
.
My problem is in understanding the process that is going on here, with the Hot-wire system the fault memory will log a speed input fault code and the car will behave as above. What I would like to know is when the speed input returns (the other 98% of the time does the mapping in the ECU go back to ‘proper mode’ but still store the fault . I ask this as the erratic idling and stalling goes away but the car seems a little flat, as if it knows there is still a fault . This can be cleared in the short term until the next time if the battery is disconnected resetting the ECU.
How does the ECU work then over to you, shpub/Mark Adams maybe please.
Harry
Btw standard rover/Lucas type hot wire ECU system fitted to the car
, note at this point I’m assuming the problem to be the sensor and not the Speedo itself. The engine will idle erratically and sometimes stall when pulling up to a junction, similar symptoms to a dirty stepper. I believe that this may be the ECU trying to protect the cats from being poisoned because it doesn’t know the car speed part of the equation for fuelling
. My problem is in understanding the process that is going on here
, with the Hot-wire system the fault memory will log a speed input fault code and the car will behave as above. What I would like to know is when the speed input returns (the other 98% of the time does the mapping in the ECU go back to ‘proper mode’ but still store the fault . I ask this as the erratic idling and stalling goes away but the car seems a little flat, as if it knows there is still a fault . This can be cleared in the short term until the next time if the battery is disconnected resetting the ECU. How does the ECU work then
over to you, shpub/Mark Adams maybe please. Harry
Btw standard rover/Lucas type hot wire ECU system fitted to the car
Can you tell me the EXACT system youre running Harry?
Im trying to determine whether the system youre using has on board diagnostics and limp home mode, plus fault code memory, or not.
If it hasnt got fault code memory, then if the input from the sensor goes normal, this would explain the normal running of the engine.
If it has got on board diagnostics and memory, then that would explain the need to disconnect the ecu/battery to erase the fault codes and take it out of limp home mode.
Im trying to determine whether the system youre using has on board diagnostics and limp home mode, plus fault code memory, or not.
If it hasnt got fault code memory, then if the input from the sensor goes normal, this would explain the normal running of the engine.
If it has got on board diagnostics and memory, then that would explain the need to disconnect the ecu/battery to erase the fault codes and take it out of limp home mode.
whilst there I unfurled the snakes nest and the ECU has AMR2175 14CUX on it and a Land Rover badge with 400HC written across it in permanent marker. Does this helpYeah thats fine Harry.
The 14 cux system was indeed fitted on landys with the 3.5 and 3.9 v8.
Ok, test procedure for the speed sensor is as follows:
Disconnect the ECU multiplug (ign OFF!)
Connect voltmeter between terminal 6 (of the disconnected multiplug)and chassis ground or batt neg.
The multiplug will have tiny number markings on it.
Switch ON ign.
Ensure transmission is NOT engaged and roll vehicle slowly forward.
Voltmeter should fluctuate between 0 and 12 volts.
The ecu does include self diagnosis but you will need the dedicated lucas tester to acess the fault codes that it generates(if any).
If you need the fault codes i can post them here for you.
Hope this is of some help.
>> Edited by deltaf on Wednesday 12th February 14:14
The 14 cux system was indeed fitted on landys with the 3.5 and 3.9 v8.
Ok, test procedure for the speed sensor is as follows:
Disconnect the ECU multiplug (ign OFF!)
Connect voltmeter between terminal 6 (of the disconnected multiplug)and chassis ground or batt neg.
The multiplug will have tiny number markings on it.
Switch ON ign.
Ensure transmission is NOT engaged and roll vehicle slowly forward.
Voltmeter should fluctuate between 0 and 12 volts.
The ecu does include self diagnosis but you will need the dedicated lucas tester to acess the fault codes that it generates(if any).
If you need the fault codes i can post them here for you.
Hope this is of some help.
>> Edited by deltaf on Wednesday 12th February 14:14
Thanks for that, so when you say it does 'self diagnose' does taht mean it'll come's out of 'limp home mode' on restoration of the 'out of spec' input and just logs the fault for later reading .
As I've said it only goes to fault 2% of the time so I can't envisage sitting with a multimeter waiting for it to go
.
If the ansewer is yes then it is just an inconvenience whilst the speedo is not working, if you see what I'm getting at.
If however the fault continues to affect performance even after restoration i'll get it sorted now.
What say thee.
harry
. As I've said it only goes to fault 2% of the time so I can't envisage sitting with a multimeter waiting for it to go
. If the ansewer is yes then it is just an inconvenience whilst the speedo is not working, if you see what I'm getting at.
If however the fault continues to affect performance even after restoration i'll get it sorted now.
What say thee.
harry
Well it should come out of limp home mode upon correction of the fault, but not all systems actually work like that.
I personally think it will, as that systems not nearly as sophisticated as some of the jap systems.
Toyotas TCCS management is adaptive, it learns the engines peculiarities and modifies the map to compensate.....but thats another set of problems to play with..lol.
As for yours, id check to see if indeed the sensor is producing the readings it should, maybe a substitution test could eliminate it from the "suspects"?
If it dosent, then id say its the wiring.
I think youll be right to think that itll just store the out of spec parameters, peugeots ecus do this all the time, with steppers and O2 sensors, even if theres not actually a fault!
Correct me if wrong but arent TVRs known for electrical probs?
I personally think it will, as that systems not nearly as sophisticated as some of the jap systems.
Toyotas TCCS management is adaptive, it learns the engines peculiarities and modifies the map to compensate.....but thats another set of problems to play with..lol.
As for yours, id check to see if indeed the sensor is producing the readings it should, maybe a substitution test could eliminate it from the "suspects"?
If it dosent, then id say its the wiring.
I think youll be right to think that itll just store the out of spec parameters, peugeots ecus do this all the time, with steppers and O2 sensors, even if theres not actually a fault!
Correct me if wrong but arent TVRs known for electrical probs?
Harry
if its any use to you i have a code reader, you could borrow it if you wish. As far as intermittant "performance" is concerned, my 99 Griff 500 varies all the time and no codes are stored. Iam not talking day to day but it can vary from one start up to the next within five minutes. I did a rolling road and of course into "dentist" mode it went and was fine when i got there. The exhaust note even changes.
David
if its any use to you i have a code reader, you could borrow it if you wish. As far as intermittant "performance" is concerned, my 99 Griff 500 varies all the time and no codes are stored. Iam not talking day to day but it can vary from one start up to the next within five minutes. I did a rolling road and of course into "dentist" mode it went and was fine when i got there. The exhaust note even changes.
David
David thanks for the offer but its now in with a TVR doctor for a service and MOT....plus anything else 
, I'll see what comes out of it.
I agree with the no two starts seem the same sentiment, sometimes its as tame as a lamb other times it barks when you kiss the throttle, TVRs' who'd ave em eh.
Harry
, I'll see what comes out of it. I agree with the no two starts seem the same sentiment, sometimes its as tame as a lamb other times it barks when you kiss the throttle, TVRs' who'd ave em eh
. Harry
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