Can anybody help its been a while since on. 2003 Discovery 4.6 Bosch engine always in open loop. have been changing Bosch o2 sensors like going out of fashion.
Here's what I have done so far. Engine remanufactured with new improved top hat sleeves finally stopped that annoying tick, tick . the obvious plugs wires coils intake gaskets etc.
checked wiring harness while engine out. found ground faults to o2 sensor 1 bank 1 and repaired. Once installed and started engine runs smooth and a lot more power. have done
around 100km for wear in. On initial start engine smooth as silk starts 1st go had a code pop up sensor 1 bank 1 no response, Changed for another new O2 no problem. ran for about 3 kms
engine light flashing misfire cylinders 2 : 4: 6: 8: checked codes slow response bank 1 sensor 1. No response bank2 sensor 1. thinking possible ECM anybody have any thoughts
any help sincerely appreciated as its spending more time in the shop than driven
Harry

 

Get an ELM327 OBDII reader off of Amazon and an Android torque app - chart the voltages and post here. I did have one ECM go bad where the o2 drivers just quit, but I have to think that is rare. You should check voltage at your plugs to make sure the heater circuits are on, no heaters will kill them fast. Other than that it is pretty simple, the 02's generate their own voltage, the ECM just reads it and adjust fuel based on that.

 

Thanks for the reply Extinct ( hopefully not ) lol I am in the process of obtaining said OBD reader. last night I pulled the plug connectors at ECM pulled the plugs at all four sensors. re checked circuits on all four wires to ECM plug all good. checked pins at ECM cant see any bent etc. checked all four O2 Sensors. One suspect? Bank 2 Sensor 2 heater circuit resistance high. can't see this as the problem though as it is a cat efficiency O2.
Thanks again
H.

 

Hi Extinct got those numbers b1 sensor 1 1.2v on idle jumps between 1.0 to 0.3v at 2000rpm back to1.2 on idle b2 sensor 1 1.2 on idle jumps between 1.0 to 0.2v at 2000rpm
the dashboard noted engine not at temp but was at 105degc. secondary air off or to outside air? basically truck in open loop at idle goes into closed loop at 2000rpm as soon as return to idle back to closed loop HELP""" no sign of misfire codes on bank 2 yet
H.

 

sounds like sounds like it is actually rich at idle, since it seems to be happening on both banks equally I would suspect a stuck idle air control valve. it would probably run pretty rough if that was the case. You might want to try selectively bleeding some vacuum / air into the engine in idle by removing some vacuum lines, start with the smallest ones first and see what that does. Allowing additional air into the engine should lean it out. The other possibility is leaking injectors but if that was the case I would expect it to run lean only on One Bank, not both

 

I took note of what you said. Just happened to have another used Idle Air motor from the used motor I installed while having the other re built so I swapped it out.
lo and behold within a matter of minutes closed loop on idle O2s alive & kicking ran for about 3 minutes after then started kicking random misfire bank 1 then stalled out started again engine smooth then starts to drop rpm like hunting for fuel. runs smooth rpm normal but in open loop. switches to closed loop runs like a bag of scrap.
codes come back lambda sensors bank one and two. checked for vacuum leak because I can hear suction through intake probably normal however put my hands close to air elbow hose from IAC to intake sound to changes without touching it. I wonder if these could be porous allowing air in
H

 

sorry missed this but in closed loop Both O2s ranging from 8.2V to 0.3V

 

Let's make sure I understand:


"lo and behold within a matter of minutes closed loop on idle O2s alive & kicking ran for about 3 minutes



after then started kicking random misfire bank 1 then stalled out



started again engine smooth then starts to drop rpm like hunting for fuel.



runs smooth rpm normal but in open loop. switches to closed loop runs like a bag of scrap. What causes it to switch?


codes come back lambda sensors bank one and two. Might have a bad MAF? That usually is the only thing that cause erratic running.



checked for vacuum leak because I can hear suction through intake probably normal however put my hands close to air elbow hose from IAC to intake sound to changes without touching it. Does engine running condition change?



I wonder if these could be porous allowing air in

 

Yes. Starts up runs from cold. Air pump running. Air pump stops as warming up. Engine drops to normal idle around 750rpm runs smooth. Within a few minutes goes into closed loop now with the replaced ( Used) IAC. looking good so far.. Cycles from closed to open loop and back. At normal running temp. Now cycles to closed loop engine starts to hesitate as though running out of fuel. Within a few seconds cycles back to open loop engine running smooth. No misfire codes but both upstream O2 sensors kick codes. Guessing because of the switch back to open loop. The sound from the hose is throwing me as why changing tone / sound when I put my hand near it.

 

Maf but I'm guessing... What does the maf read on the ultragauge