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Generation 2 Pajero NH - NL Models 1991 - 2000

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  #1  
Old 17-11-12
Lazyc Lazyc is offline
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Default NJ ECU Issues

Mate of mine has a 94 3.0 NJ auto, LPG lift kit etc.

Loaded up last Monday for a few days away with kids and family friends.

2 km down the road it dies, bit of a flick on the tacho and that's it.
Few phone calls and racq, he gets it towed home.

No spark, no volts on sensors.
Replace 20amp ECU fuse, car starts but runs very bad.
Pours fuel out the rear.
After working out the ECU fault codes and that takes its time to get them. As nothing was straight forward.
All fault codes, really....
the common thing was the earth was shared by all the sensors.
Open the ECU we found the earth track was wide open, quick track repair, while he was there he replaced all the caps with new high voltage units.
So with that in hand we had to find the reason for the fuse and track to pop.
Narrowed it down to the oxy sensor very quick.
Pic to follow, but it had melted down the core and fused all the wires together.
Replace sensor, replug and road test.
Shudder to think what that would have cost in a shop, oxy sensor was $104 from autobarn. Some 4 wire stock item.

Was a little surprised when he pulled the dead one out, i did the testing but never had to look at it to know it was rubbish.

Repaired his remote locking, forward park lights as well...
Big day.

LC
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Last edited by Lazyc; 17-11-12 at 08:05 PM.
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  #2  
Old 17-11-12
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t-rex1995 t-rex1995 is offline
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Hi mate when my paj got put on fuel bout 1 month ago run like shit on petrol chewed it and smell it out the exhaust badly but run on gas fine sound fine but C/E light stayed on on petrol only as when all set up C/E light would show up when on gas as a fault would come up when on gas cause the injectors are closed hope this makes sense but found out why was running like shit the complete tip of the O2 sensor was gone found abit of it in the catalylic convertor now the C/E light briefly comes on for a second once the injectors are open and all working it goes off
they cut the C/E light harness when was on straight gas as a code would come up cause injectors not working but now shes all good running fine.
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Old 17-11-12
Lazyc Lazyc is offline
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He has some box that fakes the ECU with fuel injector feedback.

But really just a nasty fault that would have cost mega bucks to fix in a workshop.

LC
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Old 17-11-12
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t-rex1995 t-rex1995 is offline
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sounds like mine it's a feedback system its a sprint gas system has its own ecu starts on petrol then flicks to gas but can make it start on petrol and stay on by just pushing the button but fuel pump keeps pumping to keep fuel system fresh its own ecu just shuts the power to the injectors and fuel just flows through the lines and injector rails and makes it start on petrol then flick over like blink of an eye.
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Old 17-11-12
captain_paj captain_paj is offline
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My Pajero is the offending vehicle.

To start with, I couldn't get fault codes from the diagnostic connector. I had to take the shroud off the ECU and connect directly to C1 and A1 (ECM ground) to get my test light to flash codes.

Fault codes showed MAP, MAF, AFT, CT fail.

As these were all on the same ground (Sensor Ground at ECM) we guessed there was a ground fault.

Voltage potential between Sensor Ground and ECM ground was 12.25V - so this indicated that Sensor Ground was floating.

I traced the two Sensor Ground pins at ECM and found the copper track had blown.

Soldered in jumper wire to bypass broken track. While I was at it, replaced the three capacitors in case they would generate a fault as this is a known issue with them leaking. Mine hadn't leaked or bulged at all, but replaced them for the $1.15 it cost me.

As SOMETHING must have caused the more than 20 amp draw (as ECM fuse had blown) we de died the only thing that could draw that much power would have to be the O2 sensor earthing out - and as we never got an O2 sensor fault code it must have been a catastrophic failure.

Lazyc put a multimeter on the O2 sensor and the heater wires were earthing to the chassis. OK - so O2 sensor was faulty.

Unplugged sensor, started car, ran perfectly. As soon as it got to normal running temp, using the accelerator would make it cough and splutter. Ok, no probs, that's expected with an unplugged O2 sensor.

Down to Autobarn and a new 4 wire sensor, crimp on the existing connector, and unscrew the existing one. That's when we saw the carnage.

With a new O2 sensor and the track repaired in ECM, it runs better than it EVER has. Definitely more power, and I was able to retune the LPG system.

The LPG system is crap, a mixer ring system. Very el cheapo and I hate it. I'll convert it to injection at some stage - about $500 worth of bits and a days work and I'll have it done. Some day...at least the system has injector simulators...
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Old 18-11-12
Lazyc Lazyc is offline
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Quote:
Originally Posted by captain_paj View Post
That's when we saw the carnage.
Understatement of the day.

LC
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Old 18-11-12
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hootnah hootnah is offline
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lazyc and Captain paj, a very logical fault finding proceedure indeed and great work, thanks for the great write up.
Cheers, Jim.
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Old 18-11-12
Rendrag Rendrag is offline
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Quote:
Originally Posted by captain_paj View Post
Unplugged sensor, started car, ran perfectly. As soon as it got to normal running temp, using the accelerator would make it cough and splutter. Ok, no probs, that's expected with an unplugged O2 sensor.
Wait, what? As I've mentioned in a heap of threads, I've never found the O2 sensor on my NJ to make any real difference..? I saw a *tiny* increase in fuel economy when I replaced mine (the one it had when I bought the car was wired backwards (so it was going between -0.2 and -0.6v, not 0.2 and 0.6), and swapping the sensor wires over never made much difference), but the car ran fine without it..? Now you've got me wondering if it'd be worth finding someone in the area with an NJ, and swapping ECU's with them for a week to see if my economy changes drastically, incase the backwards wiring on mine blew something on the ECU? Hrrm!
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Old 19-11-12
captain_paj captain_paj is offline
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I don't remember where I read it, but I was reading that the ECU when it gets to proper operating temp and other conditions are met, will check the O2 sensor and if it is happy with it, will go ino closed loop mode.

Unplugging my O2 sensor completely results in my Paj running perfectly until warm enough, and then when I put the accelerator down it revs up, then drops off in revs and runs rough, and I have to put the accelerator down harder and all is good.

I didn't try it while driving, this was just in the driveway. I tried it a number of times though with the same result. Switching to LPG and doing the same thing didn't have the same result, indicating it was a fuel trim issue.

This makes sense to me - light throttle to round 2-3000 RPM brings it up to those revs, then the ECU tries to trim the fuel using the O2 sensor. Heavy throttle means "run the sucker rich, bugger the O2 sensor" - a heavy foot while under load would result in the O2 sensor not being used - but a long run at cruise would use the O2 sensor to trim the fuel for economy. So Rendrag - I would spect that it would entirely depend on your driving style and the topology of your driving scope to dictate whether the O2 sensor makes any difference to your fuel economy.

I would be interested to know exactly WHAT constitutes an O2 sensor error that results in a generated fault code. My original O2 sensor (which I thew away when I replaced it with the one that just fried) was stuck showing a lean condition no matter what - I could screw the LPG mixture so rich the engine would blow black smoke and the LPG "ECU" (I use the term loosely as its such an el cheapo mixer ring system) would read lean no matter what...

I have no idea if my ECU is doing the right thing. I find it interesting that an "O2 sensor completely unplugged" condition doesn't generate a fault code...

Re wiring an O2 sensor backwards causing damage to an ECU - without researching it, and I don't have the electronics background of Lazyc (to whom this stuff comes as naturally as breathing) but - a voltage as low as that output by the sensor, even backwards, I wouldn't have thought enough to damage anything. Piss the ECU off? Yup, I reckon...

I personally would be measuring the voltage fom the O2 sensor signal pin at the ECU with the engine at around 2000RPM, and also following the copper track from the pin to the first solder pad it goes to in the ECU and checking the voltage to Signal and ECM ground.
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