P0171 Driving me Insane!!!

Hello all. I've had this "too lean" error code for months now and haven't been able to find the cause of the problem. It is affecting my fuel economy and driving me crazy trying to resolve it.

Here's what I've done so far:

1. The spark plugs and leads were replaced approx 12 months ago.
2. Replaced the distribution cap and rotor 6 months ago.
3. Put in a new air filter 6 months ago.
4. Replaced CCV valves and pipes 2 months ago.
5. Replaced upstream and downstream oxygen sensors 2 months ago.
6. Replaced ignition coil 2 months ago.
7. Replaced TPS and installed throttle body spacer 2 months ago.

Finally put it down to an air leak because I had cracked exhaust headers so I've installed extractors only to get the same P0101 error code again!

AAAAARRRRHHHH!!!

I don't think it's the injectors because I mainly run on LPG and get the P0171 code on both petrol and LPG. I'm not sure but it might only come on after a certain speed (???) because I can clear the code and drive around the local area and not see the code reappear until I've driven longer distances (at a higher speed).

Any suggestions?

After reading a few posts I went out and had a look for the MAP sensor. There is no vacuum hose coming off it and I can't find a loose hose hanging down anywhere. Where's it supposed to go to and could this be my problem?

I don't know if it's ever had one (while I've owned it) so it might not explain the sudden change in fuel consumption and the error code.

What year xj? earlier xjs , map sensor mounts on the firewall just above the valve cover, has a small hose that runs to the throttle body

It's a 96 model and the MAP sensor is mounted on the throttle body itself, not on the firewall where I was initially looking for it. I can't see where a small hose would fit the throttle body?

I'm still at a loss with this. Anyone got any ideas or suggestions on what to try next?

Check your ECT (coolant temp sensor)

You may also want to check you batt voltage and charging voltage are up to spec. You could also check for AC ripple from the Generator.

Is the LP system totally seperate from the Gasoline System? Did you have to change anything in the Gasoline system? What I know about LP systems is next to nothing, but as far as the Gasoline system goes, have you checked for Vacuum leaks? I would at least put an ohmmeter across the injectors and look for and check for uniform readings in all of them.

Thats a start atleast.

Skreed said:

Check your ECT (coolant temp sensor)

You may also want to check you batt voltage and charging voltage are up to spec. You could also check for AC ripple from the Generator.

Is the LP system totally seperate from the Gasoline System? Did you have to change anything in the Gasoline system? What I know about LP systems is next to nothing, but as far as the Gasoline system goes, have you checked for Vacuum leaks? I would at least put an ohmmeter across the injectors and look for and check for uniform readings in all of them.

Thats a start atleast.

Click to expand...

Thanks Skreed.

I took your advice and checked the Engine Coolant Temp sensor and it was a little under 1000 ohms. The battery voltage is 12.5V and 13.75V when charging.

I checked for AC ripple by starting the engine and letting it idle and got a reading of 0.028V so that seems fine too.

Yes the LPG system is completely separate to the gasoline system but I put an ohmmeter across the injectors anyway and they all showed approx 17.5 ohms (with and without the ignition turned ON).

I took a few other readings while I was at it:

1. MAP sensor - ignition on with engine off was 4.75V, engine running at idle was 1.85V.

2. Throttle Position sensor - the center terminal gave a reading of 812 milli-volts at idle (throttle closed) and 3.8V at wide open throttle.

3. Intake Manifold Air Temperature sensor - approx 2300 ohms.

4. Also checked for damaged vacuum hoses and the one on the manifold next to the Manifold Air Temp sensor (that comes up into a T junction) was split around the base so I will replace it. What is it for?

Oh, and I solved the mystery about the missing vacuum hose on the MAP sensor...apparently there is no vacuum connection on mine, it only has an electrical connector which makes sense I guess since it's mounted directly on the throttle body.

Looking through the owners manual there are a lot of voltmeter tests that can be done at the PCM terminal to eliminate the wiring harness (for ECT, MAP sensors etc). The only problem with mine is it doesn't seem to have a "60-way electrical connector" like shown in the book that I can unplug to check the terminals. My wiring goes around the firewall in a big bundle and straight into the bottom of the PCM. Is this normal?

Given that nothing above looks out of the ordinary I have booked it in for a vacuum leak test next week. Does anyone have any other ideas before I potentially waste money on a mechanic?

That is not a map sensor on the throttle body, there is TPS sensor and an Idle air controller on the throttle body.

See the MAP sensor here:

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

What is an extractor?

Cracked header will cause the error code, if crack is before the O2 sensor.

Hi Ecomike, thanks for posting.

Ecomike said:

What is an extractor?

Cracked header will cause the error code, if crack is before the O2 sensor.

Click to expand...

Sorry, different terminology...by extractor I mean headers and yes my old header was badly cracked but I have replaced it now (including a new manifold gasket only last week) and it made no difference to the P0171 error code.

Ecomike said:

That is not a map sensor on the throttle body, there is TPS sensor and an Idle air controller on the throttle body.

Click to expand...

I definitely have nothing resembling a MAP sensor on my firewall so here are a few pictures of my throttle body.


1. This thing sticking out of the throttle body to me looks similar to a MAP sensor and co-incidentally gives off the same voltages expected of a MAP sensor:




2. This photo shows the Idle Air Controller and TPS sensor on the throttle body as well as the "MAP sensor" or whatever it may be:

XJSteven said:

Hi Ecomike, thanks for posting.



Sorry, different terminology...by extractor I mean headers and yes my old header was badly cracked but I have replaced it now (including a new manifold gasket only last week) and it made no difference to the P0171 error code.



I definitely have nothing resembling a MAP sensor on my firewall so here are a few pictures of my throttle body.


1. This thing sticking out of the throttle body to me looks similar to a MAP sensor and co-incidentally gives off the same voltages expected of a MAP sensor:

2. This photo shows the Idle Air Controller and TPS sensor on the throttle body as well as the "MAP sensor" or whatever it may be:

Click to expand...

That is a MAP sensor.

If you look under the MAP sensor there is an 'L' shaped rubber tube that goes from the sensor to the TB.

DTC P0171, Fuel System Lean, is a lean air/fuel mixture indicated by an abnormally rich correction factor. I see you changed your upstream O2S. It's heater may not be working, causing the O2S not to work properly. If you remove the connector from the upstream O2S harness, you can check for heater voltage at the connector. I believe the two pins are the gray and white wires to the connector. With the ignition switch in run/engine off position, you should read battery voltage at the connector. If not, the circuit fuse may be blown.

po171 check your fuel pressure. if you have a weak pump or clogged filter you'll have low volume and pressure. them the computer is trying to compensate by opening the injectors longer and you ll result in poor economy and poor power that code also.

I had this same problem about 2 months ago. The issue with mine was my upstream o2 sensor. I replaced it with a Bosch and it was bad out of the box. Exchanged it and reinstalled the new one and it's been running great.

FYI, these are things that should be checked if a P0171 code is set:

RESTRICTED FUEL SUPPLY LINE
FUEL PUMP INLET STRAINER PLUGGED
FUEL PUMP MODULE
O2 SENSOR
O2 SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
O2 SENSOR HEATER OPERATION
TPS VOLTAGE GREATER THAN 0.92 VOLTS WITH THROTTLE CLOSED
TP SENSOR SWEEP
MAP SENSOR OPERATION
ECT SENSOR OPERATION
ENGINE MECHANICAL PROBLEM
FUEL FILTER/PRESSURE REGULATOR (HIGH)
PCM

Is the P0101 code posted in post #1 and mistake, or are you getting both codes?

That looks like a Map sensor all right, but is non-OEM, custom.

Time to pull out an analog volt meter, high impedence, and start testing each live at the sensor, and at the computer.

Might be a leaking intake manifold.

That is a stock oem map sensor

green95xj said:

That is a stock oem map sensor

Click to expand...

Did they change the MAP sensor location in 96?

XJSteven said:

1. This thing sticking out of the throttle body to me looks similar to a MAP sensor and co-incidentally gives off the same voltages expected of a MAP sensor:

Click to expand...

That is definitely the MAP sensor.

The hose coming off of it should make a 90-degree bend directly into the throttle body. If that's missing, I'm (almost) willing to bet that that's your problem, or at least a good part of it.

Can you remove the MAP sensor and get a photo of the surface that it mounts to? I'd like to verify that it is as it should be; the fact that there's apparently nowhere obvious for that vacuum line to go to bothers me a bit.

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.

Ecomike said:

Did they change the MAP sensor location in 96?

Click to expand...

Yes, that is the MAP sensor. And yes, they did relocate it. The change happened with the introduction of OBD!!.

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.

I hate to say it, but you may want to look at a 97 service manual. I own a 96 and I know that aftermarket service manuals don't state that a 96 is different than a 95. It is closer to a 97 on the PCM operation side.

I would suggest checking the fuel pressure first. 50 psi is normal, no return line on this system. Try driving it with the pressure gauge connected and see of the pressure drops significantly.

Check for vacuum leaks at the intake manifold. Get some Carb cleaner and spray it where the head and intake meet. The RPM should change if there is a leak.

Next I would find someone with a computer scan too, not just a code reader. I bet by looking at the information displayed you should be able to find the source of the lean condition.

Sidewinder CC said:

DTC P0171, Fuel System Lean, is a lean air/fuel mixture indicated by an abnormally rich correction factor. I see you changed your upstream O2S. It's heater may not be working, causing the O2S not to work properly. If you remove the connector from the upstream O2S harness, you can check for heater voltage at the connector. I believe the two pins are the gray and white wires to the connector. With the ignition switch in run/engine off position, you should read battery voltage at the connector. If not, the circuit fuse may be blown.

Click to expand...

Just a quick question before I do some more investigating and answer some of the replies...is the 02S heater voltage supplied by the same circuit as the power to the fuel pump? If so, there would only be power to the O2S connector for a few seconds when the ignition is turned ON, is that right or am I on the wrong track?