OK thanks, the P0171 code was back today so I installed the new IAC. The valve on it was shorter than the one I pulled out. I started it up and the revs were very high (2000-3000 rpm at idle) so I reset the ECU and the idle dropped back to normal. I'm yet to go for a drive.
P0171 Driving me Insane!!!
- Thread starter XJSteven
- Start date
- Location
- Waukegan, IL
any news on the scan tool front?
Nothing yet, it's probably still in China.
- Location
- MilkyWay Galaxy
I still go back to it sounding like a defective heater (or heater ground) on the O2 sensor. I don't have the FSM, etc for your year, but testing across 2 white whites to the test the sensor heater does not sound right. One end of the heater should be a black wire (ground wire)? If you have 8 ohms across the two white wires, that sounds like a bad sensor?
Can you take your meter to the parts store and see if they will let you test a new sensor? I would expect the two black wires to be sensor grounds, the other end of the sensor and other end of the heater if you will.
At room temp I would expect one white to black wire to read 8 ohms, the second black to white wire to read in the meg ohm range, or infinite, and the two black wires might read about 1 ohm between them (but I am not sure of that, I don't recall if they use a common ground). All tests above are on a bare sensor, not connected to the wiring harness.
Hi Ecomike,
From the '95 FSM (I don't have the '96):
Oxygen Sensor Heating Element Test
With the sensor at room temperature...disconnect the 02 sensor connector. Connect the ohmmeter test leads across the white wire terminals of the sensor connector. Resistance should be between 5 and 7 ohms. Replace the sensor if the ohmmeter displays an infinity (open) reading.
When I performed this test my O2 sensor was within the correct range. I had already replaced the O2 sensor and it didn't fix the fault before but I do have a new O2 sensor now that I can hook up to be sure.
Note: I also ran the ohmmeter across the two white wires on the previous O2 sensor that I took off the car and that passed the above test too.
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- Location
- MilkyWay Galaxy
Well what ever odd gremlin your have, it seems to be playing its games at idle, based on your live O2 sensor data. I guess you are down to maybe looking for a vacuum leak or cracked manifold.
I forget, is it running lean or rich at idle? You mentioned that you ruled out leaking fuel injectors because it does it running on LPG fuel as well, but does the gas fuel pump run while it is running on LPG? If the fuel pump is still running, injectors, or the fuel pressure regulator can still leak fuel into the intake.
Edit: OK I rescanned the entire discussion here. The PCM says it is running to lean (at some point in time, when, at idle or cruise, we do not know yet). The O2 sensor says it is running rich at idle, very rich, but normal (not lean or rich) at cruise. Rich at idle sounds like too much fuel to me since you seem to have ruled out the O2 sensor and sensor circuit as OK.
Hopefully your scanner will arrive soon and get you live PCM data soon!!!! This one is a real puzzle! It may be wiring to the PCM or the PCM itself?
I am wondering if one them is wrong, the O2 sensor or the PCM, or of both are right, how that can be? If the PCM is getting a signal loss in the wiring from the O2 sensor, rich could look normal to the PCM, and normal could look lean to the PCM! I think?
I am not an engine guru, but have you check all the plugs, checked their condition for any signs of mechanical issue like valves?
I forget, is it running lean or rich at idle? You mentioned that you ruled out leaking fuel injectors because it does it running on LPG fuel as well, but does the gas fuel pump run while it is running on LPG? If the fuel pump is still running, injectors, or the fuel pressure regulator can still leak fuel into the intake.
Edit: OK I rescanned the entire discussion here. The PCM says it is running to lean (at some point in time, when, at idle or cruise, we do not know yet). The O2 sensor says it is running rich at idle, very rich, but normal (not lean or rich) at cruise. Rich at idle sounds like too much fuel to me since you seem to have ruled out the O2 sensor and sensor circuit as OK.
Hopefully your scanner will arrive soon and get you live PCM data soon!!!! This one is a real puzzle! It may be wiring to the PCM or the PCM itself?
I am wondering if one them is wrong, the O2 sensor or the PCM, or of both are right, how that can be? If the PCM is getting a signal loss in the wiring from the O2 sensor, rich could look normal to the PCM, and normal could look lean to the PCM! I think?
I am not an engine guru, but have you check all the plugs, checked their condition for any signs of mechanical issue like valves?
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This gremlin is definitely giving me a headache.
I have just been out and installed the new 02 sensor now so will see what happens over the next few days.
Something very interesting - when I filled up with LPG today and calculated the fuel consumption for the past week it appeared to be back to normal usage levels. It's been using 25% more fuel for the past 6 months which has been the only negative effect of the P0171 code. Other than the bad fuel economy it has been running very well. One tank of fuel probably isn't very accurate so I will recheck the figures next time I fill up. It doesn't explain the cause of the P0171 error but I'd be very happy to get the fuel economy back!
I have just been out and installed the new 02 sensor now so will see what happens over the next few days.
Something very interesting - when I filled up with LPG today and calculated the fuel consumption for the past week it appeared to be back to normal usage levels. It's been using 25% more fuel for the past 6 months which has been the only negative effect of the P0171 code. Other than the bad fuel economy it has been running very well. One tank of fuel probably isn't very accurate so I will recheck the figures next time I fill up. It doesn't explain the cause of the P0171 error but I'd be very happy to get the fuel economy back!
- Location
- MilkyWay Galaxy
Did you check the intake and exhaust manifolds for flatness, before replacing the shared gasket between the two?
I had some non flatness between the inner 2 and out four ports on the E-manifold when I did the head job on our 89XJ. I had to add a copper shim gasket to the middle exhaust ports on mine to get true flat seals. Of course mine is an 89 (all Renix era) but I read here about routine problems with cracked E-manifolds even on HO engines.
No I didn't check that, would the result be a vacuum leak? The vacuum test I did showed no leaks.
- Location
- MilkyWay Galaxy
Absolutely, if it was warped or not all on the same flatness plane! It could cause an exhaust leak or intake leak or both, with one feeding the other. I had a crack in the exhaust on the 89 joint area, fixing it (welding) warped it a little, so I had fix that with sanding the faces, and a extra hand made copper shim gasket on mine, as the two outer ones could not be over sanded without creating a problem for the intake/exhaust shared bolts on the top side.
You can check for intake leaks with aerosol as I understand, looking for an idle speed change. Stethoscope works too following the sound for and I or E leak.
The vacuum leak may be too small to show up on a vacuum test.
While an exhaust pipe is pressurized, the manifold part sees pulses, and between pulses it can draw in fresh air (scrubbing effect of the pulses) that confuses the O2 sensor to believe the engine is leaner than it really is.
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Thanks Ecomike.
This is one of the many things I've already done and there was no change to idle speed.
Well I've driven around with the new upstream 02 sensor installed (the second one I've tried) and it made absolutely no difference so here's a summary of the problem so far:
FAULT:
Intermittent P0171 error code using 25% more fuel (on dual fuel systems). Code only appears on longer drives, possibly only at higher speeds or higher running temperatures?
PARTS REPLACED:
Spark plugs and leads - replaced 12 months ago.
Distribution cap and rotor
Air filter
CCV valves and pipes
Upstream and downstream oxygen sensors
Ignition coil
Fuel pump
Exhaust headers & manifold gasket
TPS
IAC valve
Upstream oxygen sensor – replaced for the second time.
TESTED (with ohmmeter/voltmeter):
Engine Coolant Temp sensor.
Battery voltage.
AC ripple from generator.
Fuel injectors.
MAP sensor.
Throttle Position Sensor.
Intake Manifold Air Temp sensor.
Tested continuity of wires between sensors and PCM.
Vacuum leak test (with vacuum gauge).
Checked for vacuum leaks by spraying carby cleaner.
FAULT:
Intermittent P0171 error code using 25% more fuel (on dual fuel systems). Code only appears on longer drives, possibly only at higher speeds or higher running temperatures?
PARTS REPLACED:
Spark plugs and leads - replaced 12 months ago.
Distribution cap and rotor
Air filter
CCV valves and pipes
Upstream and downstream oxygen sensors
Ignition coil
Fuel pump
Exhaust headers & manifold gasket
TPS
IAC valve
Upstream oxygen sensor – replaced for the second time.
TESTED (with ohmmeter/voltmeter):
Engine Coolant Temp sensor.
Battery voltage.
AC ripple from generator.
Fuel injectors.
MAP sensor.
Throttle Position Sensor.
Intake Manifold Air Temp sensor.
Tested continuity of wires between sensors and PCM.
Vacuum leak test (with vacuum gauge).
Checked for vacuum leaks by spraying carby cleaner.
And with great timing the USB OBD Diagnostic Interface for my laptop has just arrived from China today!
The software I will be using is ScanTool.net v1.13:
ScanTool.net OBD-II Software for ElmScan is free software that allows you to use your computer and an inexpensive hardware interface to read information from your car's computer. Current version allows you to read trouble codes and see their descriptions, clear the codes and turn off the "Check Engine" light, and display real-time sensor data such as RPM, Engine Load, Vehicle Speed, Coolant Temperature, and Timing Advance.
Sounds simple but I noticed under the Freeze Frame heading it says "This feature is not implemented in this version". Will I still be able to capture the live data I need? Can somebody please tell me how to use this software or recommend some different (inexpensive) software to try? Thanks.
OK please ignore my last few posts, I was going to delete them but I can't figure out how to! I am now using EasyObdII and can see the Live Data on the screen. The "Show Freeze Frame" heading is grayed out but I assume I will be able to click on this once a code is thrown and it has taken a freeze frame of the data.
Is it as simple as driving around with the laptop hooked up and waiting for the software to take a freeze frame? This is all new to me so what live data am I actually looking for?
Is it as simple as driving around with the laptop hooked up and waiting for the software to take a freeze frame? This is all new to me so what live data am I actually looking for?
- Location
- Waukegan, IL
What I'm interested in is what the "fuel trim" #s are. There will be two numbers the 'short term' (many times condensed into STFT) and long term (LTFT). They may give us a clue as to whether the lean condition is intermittant or constant.
The freeze frame data is a helpful tool because it gives you many of the operating parameters necessary to recreate the fault in the shop.(engine temp,engine speed, fuel trims,vehicle speed,things like that)
From what I gather, your software doesn't provide this. Hopefully I'm wrong.
As for test driving, Yes drive it with the laptop connected. If it's available use the software's "snap shot" or "movie" or whatever data logging functions it has to look at the failure after the fact. Otherwise you'll need someone to drive while you watch. Good luck and keep us in the loop.
The freeze frame data is a helpful tool because it gives you many of the operating parameters necessary to recreate the fault in the shop.(engine temp,engine speed, fuel trims,vehicle speed,things like that)
From what I gather, your software doesn't provide this. Hopefully I'm wrong.
As for test driving, Yes drive it with the laptop connected. If it's available use the software's "snap shot" or "movie" or whatever data logging functions it has to look at the failure after the fact. Otherwise you'll need someone to drive while you watch. Good luck and keep us in the loop.
