P0171 Driving me Insane!!!

[Ecomike]

I'm wondering if the LPG ECM doesn't spoof an o2 sensor signal during LPG operation to prevent unwarranted DTCs. That would explain the need to run the LPG electronics in series.

An internal disconnect type of system? (signal passes through in petrol mode. In LPG, it is interrupted and a dummy signal gets sent to the Petrol pcm to keep it happy.) :dunno:

If the LPG ECM is spoofing the Petrol PCM in LPG mode, then the problem may be in the spoofing process itself. But that only answers the Petrol PCM O2 data problem while running on LPG. Neither explains the excess use of LPG.

But if the LPG ECM is getting biased data from the O2 sensor (and the Petrol PCM is getting accurate data), due to excess wire/connector resistance (like a extra few ohms) in the LPG ECM contacts, that would explain the LPGs poor MGPs, and the petrol PCMs reported fuel trim problems.

 

[four_shot]

If the LPG ECM is spoofing the Petrol PCM in LPG mode, then the problem may be in the spoofing process itself. But that only answers the Petrol PCM O2 data problem while running on LPG. Neither explains the excess use of LPG.

But if the LPG ECM is getting biased data from the O2 sensor (and the Petrol PCM is getting accurate data), due to excess wire/connector resistance (like a extra few ohms) in the LPG ECM contacts, that would explain the LPGs poor MGPs, and the petrol PCMs reported fuel trim problems.

Thats what I was thinking. It's either that, or the LPG is adjusted too lean @ cruise rpms. What is the tank regulator supposed to be at, and is that the actual pressure?

 

[XJSteven]

Well I've just done a 560 mile round trip over the Easter long weekend. The LPG economy was still bad on the way there (approx 22 litres per 100km) but on the way back a couple of days later it was back to normal usage (18 litres per 100km)! I don't know what's going on but this is typical because I'm taking it back to the LPG specialist tomorrow so he might not be able to see the problem?

On the return trip I was doing a fairly constant speed of 68 miles per hour.

I recently calculated the petrol consumption and it was normal so it's definitely an LPG problem. And just to confirm the P0171 code did not come on running petrol, only on LPG.

 

[XJSteven]

I'm leaning twards the stepper motor not opening the valve enough and leaning out the system at cruise speeds. It may be just an adjustment issue?

There is the off possibility that the LPG ECU is faulty.

The most frusterating thing for me is that its halfway around the world and I can't look at the d@mned thing myself...lol!

I'll mention this possibility to the LPG guy tomorrow...unless you are planning an overseas trip in the near future so you can take a look for me.

 

[four_shot]

You buy, I'll fly!

 

[four_shot]

Waiting with baited breath...lmao!

 

[XJSteven]

If the price of fuel gets any higher I might be able to pay for a flight out of the savings I make when I get the problem fixed. Better yet, I'll ship my Jeep over there instead and go for a driver around the US.

I took it in to the LPG mechanic today and he asked me to leave it with him overnight. He was booking it in for a dyno tune as I left.

 

[XJSteven]

Just had a call with an update...it ran perfectly on the Dyno Tune but then he got some irregular readings driving back to his workshop. Finally someone has picked up on a problem! He suspects it is either the Converter (which I'm sure he told me he checked last time I was there) or the LPG ECU itself (apparently they don't handle the heat under the engine bay too well, especially on Jeeps, and I'm sure I read somewhere they should be installed inside the car).

Anyway I think there has been some progress this time! Tomorrow should be interesting...I'll update this thread when he's completed further testing.

 

[four_shot]

Now mike and I can say "Told ya!" to the lpg installer.

 

[XJSteven]

Now mike and I can say "Told ya!" to the lpg installer.

Maybe!

The first thing he did was check the fuel trim on petrol and confirmed it was normal. Then during (or after) the Dyno run on LPG "the stepper motor operation began to run abnormal paths". He pulled the LPG converter apart and replaced the damaged diaphragm. He then found a loose earth wire at the negative battery terminal for the LPG ECU.

Apparently the ECU was freezing (and I think he said reverting back to default settings?) once the engine got hot. He hasn't come across an intermittent fault like this one before so he's not sure if the loose earth wire has fixed the problem. He reset the ECU but if the LPG economy doesn't come good now he suspects the LPG ECU will need replacing.

So I won't know if the problem has been fixed until after I've filled up a few times over the coming weeks and rechecked the LPG consumption figures. Fingers crossed!

 

[Ecomike]

Where is the LPG ECU located, exactly? Picture????

It is always a good idea to stay well grounded!!! LOL

Electrons behave much better when grounded!:guitar:

And if the ECU is getting too hot, this was a poor choice of verbs!!!

"Apparently the ECU was freezing"

 

[XJSteven]

Where is the LPG ECU located, exactly? Picture????

It is always a good idea to stay well grounded!!! LOL

Electrons behave much better when grounded!:guitar:

And if the ECU is getting too hot, this was a poor choice of verbs!!!

"Apparently the ECU was freezing"

It's too dark to go out and take a picture right now but looking at the Jeep from the front it's in the right hand back corner of the engine bay, just before the firewall and bolted onto the side panel.

I'll try and rephrase my last post then...it was seizing up when it gets too hot. Is that better?

The LPG gauge has 4 lights; 4 lights means full and 1 light means almost empty (not very accurate compared to a needle gauge). Anyway, I've traveled 110km so far on this tank of LPG and I still have 4 lights showing. Previously it would have been down to 3 lights by the time I'd done 100km so it's looking promising. Maybe the grounded electrons are happy now.

I was told that if I have to disconnect the battery it's best to remove the negative lead first and put it back on last, that way the LPG ECU should hold it's settings. Is this the same for the petrol ECU and anyone know why it would make a difference which one comes off first?

 

[Ecomike]

That sounds like the worst possible place for an ECU to me. Hottest spot under the hood, short of attaching it to the exhaust manifold.

They may have some kind of capacitive charge protecting memory that is discharged by ground the positive cable to the negative cable AFTER disconnecting both cables from the battery.

 

[four_shot]

updates?

 

[four_shot]

Steve, Im going to go out on a limb and say this got fixed. :cheers:


I would like to know where th fault was though.

ooroo