P0171 Driving me Insane!!!

[Skreed]

I don't agree with that a good o2s will fluctuate voltage between about .3 and .7v reguardless of rpm.

 

[Ecomike]

I don't agree with that a good o2s will fluctuate voltage between about .3 and .7v reguardless of rpm.

Have you actually tested one? Hmm, I have!

.1 to .9 is typical at idle, and at a steady 2500 the range gets real tight on a properly working engine and system.

Here is some more info on O2 sensors.

http://www.aa1car.com/library/o2sensor.htm

 

[XJSteven]

Can I rule out a vacuum leak at least?

 

[Ecomike]

A vacuum leak before the combustion chambers should cause a high idle, after the combustion chamber, but a leak before the O2 sensor (after combustion chamber) can cause a false rich reading by the O2 sensor.

 

[casm]

I didn't mention this earlier but I also replaced the fuel pump and filter but I doubt it has anything to do with fuel pressure or fuel delivery because as I said before it happens on LPG too.

Something I mentioned earlier in the thread:

One other possibility is that something in the LPG conversion has an air leak that's showing up under normal running. I'm no expert with LPG by any means, but from what little I remember of how it plumbs in there are a couple of potential points of failure.

It's been a very long time since I've dealt with anything LPG-related (and even then not extensively, nor on an XJ), but from what I recall of the conversions there's typically a valve that controls LPG feed into the fuel system. If there is a leak at whatever seal exists between that valve and the stock fuel system, air could be being sucked in which would explain why this happens under both fuels. However, that's not to discount any of the earlier suggestions as it really is a shot in the dark on my behalf.

Also, I can't find any mention of fuel pressure numbers in this - I may have missed the answer in reading back, but has it been tested at the fuel rail under gasoline-only operation?

XJSteven, do you have any photos of the LPG conversion? It may be worthwhile to see how it plumbs in to the fuel system - not to place blame on it immediately, but rather so that we better understand how it all ties together.

 

[Skreed]

Have you actually tested one? Hmm, I have!

Sure all the time! I am not just pulling this stuff outta my ass.

I was just looking at one today, thats why I posted up.

The information in the in the link you posted I already know, not to mention it doesn;t back up any of the facts you stated.

The O2s voltage peaks will come closer together when RPM increases, meaning the voltage is flip flopping more.

That being said I am just trying to help someone out, thats all.

 

[Ecomike]

Sure all the time! I am not just pulling this stuff outta my ass.

I was just looking at one today, thats why I posted up.

The information in the in the link you posted I already know, not to mention it doesn;t back up any of the facts you stated.

The O2s voltage peaks will come closer together when RPM increases, meaning the voltage is flip flopping more.

That being said I am just trying to help someone out, thats all.

What are you using to measure the voltage with?

I am using a high impedance analog volt meter. A Micronta 22-220

 

[Skreed]

OTC oscilloscope.

 

[Ecomike]

OTC oscilloscope.

That explains the difference. On the analog volt meters the response time is too slow at 2000 RPM to see the entire range, but it does see it at 750 rpm, the digital voltmeters are useless even at idle, much less higher rpms.

Few people have a scope and scope skills to test their O2 sensor with, and they are not cheap (yet).

Interesting to here that it still spans the range at 2000 rpm on a o-scope! Thanks for the info!

Is OTC a brand?

 

[Skreed]

Yeah OTC makes some good high end stuff...I cant afford one for myself yet, but soon enough.

I think its the OTC 3840, the prices are coming down below a grand.

If you can afford one of these it makes diagnosis a snap, once you learn all the basics of the scope.

 

[Ecomike]

May not be long before we do it all with an App, bluetooth and I-phone.

I bought a set up for $20 last week that gives me live OBD-II for $20, straight from HK, using USB. They had a bluetooth version also. Free software that gives live sensor, fuel trim, etc data.

 

[XJSteven]

That is good...O2 sensors have a voltage of 1 volt. .5v is "perfect" mix so to say, but thats not how the computer works. It will fluctuate between about .2v and .8v to "keep" the mix at or near the target of .5v

A bad reading would be constantly high or low. Lean=low voltage Rich=high voltage

So you are saying my 02 sensor appears to be working fine at 2000 rpm but what about my 'bad reading' at idle (i.e. - the high voltage of .940v steady)?

 

[XJSteven]

It's been a very long time since I've dealt with anything LPG-related (and even then not extensively, nor on an XJ), but from what I recall of the conversions there's typically a valve that controls LPG feed into the fuel system. If there is a leak at whatever seal exists between that valve and the stock fuel system, air could be being sucked in which would explain why this happens under both fuels. However, that's not to discount any of the earlier suggestions as it really is a shot in the dark on my behalf.

Also, I can't find any mention of fuel pressure numbers in this - I may have missed the answer in reading back, but has it been tested at the fuel rail under gasoline-only operation?

XJSteven, do you have any photos of the LPG conversion? It may be worthwhile to see how it plumbs in to the fuel system - not to place blame on it immediately, but rather so that we better understand how it all ties together.

Hi casm,

Here is a photo of the LPG conversion. Looks like the LPG feeds into the system in the same place as the air does:

It is a 'vacuum inducted' system and I found some info here:

http://www.xfalcon.com/forum/showth...How-do-they-work&p=52428&viewfull=1#post52428

No, I haven't yet tested the fuel pressure under gasoline-only operation.

 

[XJSteven]

Check the wires to see if they touched the exhaust manifold and got shorted or damaged.

There are no damaged or shorted wires. It might be too soon to speak but 3 days ago I cleared the error code twice and at this point it hasn't come back on (fingers crossed!). All I've done in that time is disconnected the oxygen sensor a couple of times during testing so if I'm lucky I might be able to put it down to a loose connection at the plug, even though I've had it disconnected before. I will continue checking for the error code over the next week or so and whether there is an improvement to my fuel economy!

This one is puzzling. I am going to say the computer thinks the engine is running lean, and is adding fuel to compensate, but that the computer is not seeing the rich fuel mix data from the O2 sensor. Sounds like a signal voltage drop between the sensor and the PCM to me, bad wiring or connections between O2 sensor and PCM.

As a 96 you have an OBDII system that doesn't have a 60 way connector at the PCM, you will have 3 connectors at the PCM.

OK stupid question but if I were to check the wiring at the PCM how would I locate and unplug the 3 connectors? Here's a few photos of the PCM...I can't see any connectors and I can't feel any underneath the PCM either. If I shove my fingers down there and feel around, the bundle of wires seem to join the PCM through a hole:

 

[Skreed]

So you are saying my 02 sensor appears to be working fine at 2000 rpm but what about my 'bad reading' at idle (i.e. - the high voltage of .940v steady)?

Was this reading when fully warmed up?

 

[XJSteven]

Yes I think so. I'd just got home from a 30 min drive in the afternoon and had it sitting there for no more than 15 mins before I started it back up to take the readings. I let it idle for 5 mins before I hooked up the voltmeter.

I might check it again tomorrow when fully warmed up to confirm readings.

 

[Ecomike]

Was this reading when fully warmed up?

Good question. Did we check the heater resistance and voltage on the O2 already? I forget.

I think the readings at higher RPM indicate the O2 is working, but is getting cold at long idles?

 

[casm]

Here is a photo of the LPG conversion. Looks like the LPG feeds into the system in the same place as the air does:

Makes sense, and isn't completely dissimilar to how I've seen the conversion done in the past. It looks like the the neck on the throttle body was drilled to act as an inlet for the LPG, then sleeved to accept the hose from the LPG tank. The LPG valve should be somewhere between there and the tank, probably at the tank itself.

Given this, I'm now doubting that the LPG system is the culprit. It really doesn't get much more simple than this setup and is pretty much how I remember it working the last time I saw one on (IIRC) a carburetted Range Rover. Everything is plumbed in at the wrong spot to cause a lean condition - if that LPG hose were to detach or not seal properly, it would be roughly-equivalent to running the throttle body with the air tube detached (i.e., fully-open), and that alone wouldn't trigger what you're seeing.

No, I haven't yet tested the fuel pressure under gasoline-only operation.

Might not be a bad idea. Also:

OK stupid question but if I were to check the wiring at the PCM how would I locate and unplug the 3 connectors? Here's a few photos of the PCM...I can't see any connectors and I can't feel any underneath the PCM either.

Remove the airbox and it'll all become much clearer. My memory is that there's basically one wiring trunk (the one you're probably feeling) that comes into the PCM where it subsequently splits out to three separate connectors. Can't recall if you have to remove the black cover over the PCM to see them or if they're visible once the airbox is removed (it's been years since I've been in there), but it should be apparent once you've made some room in there.

 

[90xj06]

i would suggest getting a drb2 to read what the readings of the
O2 are from the pcm.

if you where close to me i could plug my reader in and go through the tests

 

[XJSteven]

Good question. Did we check the heater resistance and voltage on the O2 already? I forget.

I might not have posted this but I tested the 2 ground wires and they were good so I cleaned the G101 bolt up anyway. There was 13.8V power going to the heater and I got a reading of 5-6 on the ohmmeter when I checked resistance across the two white wires to the sensor.

Remove the airbox and it'll all become much clearer. My memory is that there's basically one wiring trunk (the one you're probably feeling) that comes into the PCM where it subsequently splits out to three separate connectors. Can't recall if you have to remove the black cover over the PCM to see them or if they're visible once the airbox is removed (it's been years since I've been in there), but it should be apparent once you've made some room in there.

I'll give this a try and see how I go.

if you where close to me i could plug my reader in and go through the tests

Thanks for the offer 90xj06 but I'm a bit too far (other side of the planet ).