Thread: OBD2 fault code question

I assumed even the simplest LPG systems would have a simple emulator to simulate the operation of the petrol injectors to ensure the vehicles ECM detects no change to its injector circuit. I thought the majority of LPG systems had a slave ECU to do this job.Obviously not with glenhenry,s car.
However,If there was an LPG slave ECU then such faults might occur with poor electrical work. So glenhenry does not have one and I assume you do not have one as well.
Sorry about the misinformation..

You are right, they do have emulation, but the THOR ecu is too clever, it is not fooled by the emulator. Also, the O2 sensors get emulated by the LPG, but the THOR ecu sees through that too, it tries to tell the engine ECU that the lamdba is 0.45v (not rich or lean) and keeps the real value for its own mixture measurements, but the THOR ECU gets suspicious and throws faults. I even went to the LPG ecu manufacturer folks and we changed the type of emulation, there are several (square wave, flat line, etc) and it still expects to see more 'real looking' changes in the signal and eventually throws O2 faults and injector faults, eventually it goes into open loop mode.

I can clear the faults and all is good again, but for the last 2 yrs I have abandoned LPG entirely, and just use petrol. I must add, that LPG systems better than mine, may well do a better job of fooling the THOR.

The LPG system taps into the O2 sensor wire and the earth for the fuel injectors, and I have often wondered if the extra wiring and connectors are affecting the signal coming back from the (sensitive) O2 sensors, and causing my rig to have LTFT of ~+18% on both banks. I have chased every air leak, and replaced the sensors.

Thanks to all players...I have run a few tests over the last few trips to work...I did a fault check...none, started on petrol and switched to lpg and back during a run, fault check...still none. the obd2 has a different vacuum value every time i drive..last time was 7.9...Hoges, I tried the fuel trim thing...stays on 100, probably got the wrong one. Glenhendry could you please give me a guide to which apps to add as there are a few. My MAF reading goes from .1 at idle to .4 at cruise at 100kmh.Peter51,I will endeavour to go through the wiring now that the switching doesn't seam to give the faults.Mine is a 96 GEMS as well, might be different to set up for a THOR.O2 sensors stay at zero and not working.loving the journey though, having to run on petrol is a pleasure to everything but my wallet...

Cheers

We need some units for those MAF values.

GEMS o2 sensors are 0v-5v. Wideband.
THOR o2 sensors are 0v-1v. Narrowband.

MAF sounds way wrong, mine goes from ~5->~100 (I thing grams/sec). Like I said, any popping or backfiring (even once) is possible to damage the delicate MAF. Strange that you are not seeing MAF faults tho. Here is all the MAF values you need to test.

Text your number to 0414 678 88eight and I will shoot you a torque screenshot. I will try to add a screenshot of all the value later tonight.

deano2469
My advice deano is to get a obd pid parameter recorder. They are on the internet for PC. GLM software is good - Australian company you can call.
You need to record a data stream as shown below. Forget about codes. They dont show the full story. They just cause false conclusions. You need the data steam to do the detective work as to why the ECU " thinks" it has the correct code.

This data stream below shows a bad MAP. You will get the idea by following the clues. look at the MAP voltage, and you see it is far lower than it should be. 0.4 instead of 1.0 I know you have MAF but it is the same principle.And remember how important the load sensor is when setting the basic injection pulse width? So with a low value for MAP, the whole computer calculation would give us a lean mixture all the time. Even the O2 wouldnt be enough influence to fix it. Although it may try, and you may see the LFTRIM go rich to try to help. This is a very common problem to fix by the way, and if you dont know the exact values for the MAF sensors you are working on, you wont be able to catch it. Check RAVE. By the way, the easiest and most reliable way I have found to catch a bad MAF sensor it to check the value with the key on, engine not running. Compare it with what the value should be with no vacuum or the throttle wide open, and you can get the first clue. Anyway hopefully you get the idea and maybe someone can post normal values for you from their vehicle for you to compare.
Please post you O2 values. Are they swinging rapidly from .45 to .8.
BTW I am on the sunshine coast and may be able to help out next week - but in the interim get yourself a data stream to investigate- you will work it out.

MAF Readings

At Idle...................... 20 kg/hr (5.5 g/s) ± 3 kg\hr (8.3 g/s) (^)
At 2500 rpm............... 61 kg/hr (16/9 g/s) ± 3 kg\hr (8.3 g/s) (^)
At 3000 rpm............... 90-100 kg/hr (25-27.8 g/s) (*)

22-25kg at idle,90-100kg at 3000rpm in neutral,engine hot all loads off.

At Idle 20 ± 3 kg/hr
At 2500 rev/min 60 ± 3 kg/hr ..

Steve

Originally Posted by TheTree

MAF Readings

At Idle...................... 20 kg/hr (5.5 g/s) ± 3 kg\hr (8.3 g/s) (^)
At 2500 rpm............... 61 kg/hr (16/9 g/s) ± 3 kg\hr (8.3 g/s) (^)
At 3000 rpm............... 90-100 kg/hr (25-27.8 g/s) (*)

22-25kg at idle,90-100kg at 3000rpm in neutral,engine hot all loads off.

At Idle 20 ± 3 kg/hr
At 2500 rev/min 60 ± 3 kg/hr ..

Steve

There is an error in these values, I created them and screwed the maths. Please find the correct values here.

At Idle...................... 20 kg/hr (5.5 grams/sec) +/- 3 kg\hr (0.8 g/s) (^)
At 2500 rpm............... 61 kg/hr (16.9 grams/sec) +/- 3 kg\hr (0.8 g/s) (^)
At 3000 rpm............... 90-100 kg/hr (25-27.8 grams/sec) (*)

Bibliography:
(^) - RAVE & MAF Values
(*) - P38A P38 4.0 HSE MAF SENSOR DATA Is it working? Whats wrong? Please help. - Page 2 - Land Rover Zone

hi again all, merry xmas. I get a bad reading when MAF is plugged in and no reading at all when its not. It runs the same either way...i will have to get a good used or cheap new MAF in the new year, bit short currently. thanks for all info guys, I will reassess when I get the new one.