Another P0171 thread - LotusTalk - The Lotus Cars Community
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post #1 of 16 (permalink) Old 05-07-2018, 03:54 AM Thread Starter
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Another P0171 thread

My new-to-me Elise throws P0171 most (but not every) time that I drive it. The CEL often comes on in the first 30 seconds after I start the car; and the car idles poorly for the first 30 seconds (often requiring that I give it some gas to prevent it from dying). It hunts a little at idle (varying +/- 100 RPM). It seems happy when on the road.

I have attached some screen shots. I removed and inspected the MAF sensor, which was perfectly clean.

Any thoughts?
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post #2 of 16 (permalink) Old 05-07-2018, 06:03 AM
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Do you know if it is the stock cat? Have you looked for air leaks prior to AND after the O2 sensors? What year and how many miles? In other words, how likely is is that the sensors are dying.

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post #3 of 16 (permalink) Old 05-07-2018, 07:03 AM Thread Starter
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I have not looked for leaks. 2005, 22,000 miles, non-stock intake manifold...
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post #4 of 16 (permalink) Old 05-07-2018, 08:18 AM
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Maybe check to make sure your O2 sensors connectors are not swapped?


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post #5 of 16 (permalink) Old 05-09-2018, 06:08 AM Thread Starter
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If I try to clear the codes while the engine is running, I am warned that this could damage the engine. Is it true that clearing the codes with the engine running is not good practice?
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post #6 of 16 (permalink) Old 05-10-2018, 04:34 AM
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The ECU should be passive (engine off) when you clear error codes.

With the engine running, the ECU is active (full input-output mode). Clearing codes in that state could disrupt the ECU and cause negative feedback to the engine, but I've never heard of this happening.
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post #7 of 16 (permalink) Old 05-21-2018, 05:54 AM
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Quote:
Originally Posted by jon_bondy View Post
I have not looked for leaks. 2005, 22,000 miles, non-stock intake manifold...
Its a stock CAT and stock intake maniford AFAIK ...just a snorkel delete. Unless Tim changed the intake somehow.

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post #8 of 16 (permalink) Old 05-21-2018, 07:26 AM Thread Starter
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The intake manifold and air cleaner are not stock at this point. They seem easier to access than the stock one.

I took the car in, they sprayed carb cleaner everywhere, and there were no air leaks detected. They pulled the air cleaner and blew it clean with a compressor. The throttle plate was dirty, so they cleaned that.

I have not tried a cold start yet, but I did get another P0171 afterwards, and the idle continues to hunt, although not as badly. Perhaps the Techron is helping, but if so, the change is not striking. I suppose I could put more in every tank for a while. Seems more like voodoo than science or engineering. And Tim (the previous owner) was surprised at the P0171, implying that this was not happening last summer and fall, so why would the injectors get dirty over the winter in a garage?

Still looking for a cause. If I start the car and goose it for a minute, it then idles without stalling. If I then clear the P0171 code, I can drive the car for an hour without any further codes and with good performance (no hesitation, no backfire). So the lean mixture problem is only on a cold start. My temptation is to keep clearing the codes and only invest more time and money if it starts to code during normal driving.

Not sure what to consider next.
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post #9 of 16 (permalink) Old 05-21-2018, 02:41 PM
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Mine was solved with a new Mass Air Flow Sensor, do not get a generic sensor. Bought a refurbished and two after market new ones and only ran normal with original MAF sensor.
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post #10 of 16 (permalink) Old 05-22-2018, 03:52 AM Thread Starter
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My MAF looks like it came straight out of a factory box. Was yours that clean? How do I identify whether the MAF is original or not? Thanks!
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post #11 of 16 (permalink) Old 05-24-2018, 01:29 PM Thread Starter
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I have been assuming, since the CEL only comes on right after I start the car, and never comes on while driving, that there only is a lean condition when I start the car. But then I read this from @charliex :

The ecu internally stores two sets of codes, one readable with all working OBD II reader, one not so much, it then counts for a preset number of times/starts that the condition exists, if it does it'll throw the code and the light comes on, theres also the 'just happened' codes, and the happened on a previous run codes, pending vs stored. Usually if there is something amiss it registers the code internally within 10 seconds, monitoring the STFT to see if its >17% will give you an idea.

This implies that I might have been running the engine lean for hundreds of hours, which worries me.

And then there is this from @Westrock :

To answer one of your questions, yes the O2 sensor determines if the engine is running lean or rich. But the ECU is programmed to believe that a certain amount of air flowing through the MAF will require a certain amount of fuel. So if extra air is introduced (or lost) then the O2 can certainly compensate in real time, however the ECU knows that it is having to add more fuel then what is to be expected for the metered airflow. If my understanding is correct, a P0171, does not mean that car is actually running lean in the sense of what's actually being burned. What it means is that ECU is "seeing" through the O2 sensor that it has to add more fuel than is to be expected and so in corrected form the car runs ok, but if it were to run blindly based of calculations, it would be running lean. So it's like the ECU saying "Hey something is wrong with your system and it would be running lean, but I am able to compensate to get it back on track, but you should know something is whack". This of course is under closed loop, once you go to open loop (full throttle) and its all calculation based that's where the problem rears its head. When you least want to run lean.

And this implies that the P0171 code does not mean that the engine is actually running lean at all.

So. I am not at all sure what to think now
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post #12 of 16 (permalink) Old 05-24-2018, 01:45 PM Thread Starter
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And this, also from @Westrock , implies that the problem might be my non-stock K&N intake manifold and air cleaner:

To answer your other question, yes the cross sectional (diameter) of the intake pipe is critical in a MAF based system. Think of the MAF measuring one molecule of air. It says ok, one molecule has just passed by and I believe this space I am in to be 2.5" in diameter. So I can surmise that at that moment 100 molecules of air just passed by me (not factual), but if the intake pipe was increased to 3", then maybe 120 molecules might pass through that same space. But the MAF will have no way of knowing that. So more air is flowed then what is metered. Which leads to the O2 making corrections, leading to a P0171.

I am not sure whether the diameter of the K&N is different than stock.
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post #13 of 16 (permalink) Old 06-19-2018, 05:58 AM
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The K & N filter / snorkel delete was done less than 2 weeks after the car was delivered and I never had a problem with it ( regular yearly cleaning and re-oiling ) I would get a MAF sensor cleaning kit and go that route....the 2005's had a habit of becoming dirty even though they looked clean......a good cleaning and they cleared themselves out.

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post #14 of 16 (permalink) Old 06-19-2018, 06:00 AM
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Unless Tim did something I don't know of, it was a simple swap of stock air filter to the K&N....I did not change anything else, except the snorkel delete.

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post #15 of 16 (permalink) Old 07-02-2018, 10:39 AM Thread Starter
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The P0171 has been resolved. We "smoked" the intake, and found a crack between the MAF sensor mount and the tube on which it was mounted. The mount was attached to the tube with epoxy (rather than welded) and the epoxy had come loose. We replace the entire assembly with a plastic tube with the MAF sensor mount as an integral part. The ID of the new tube was a bit larger than the ID of the stock air intake, so I 3D printed a polycarbonate sleeve to correct the ID. The car no longer shows the P0171 errors.
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post #16 of 16 (permalink) Old 07-10-2018, 06:45 AM
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Strange...... "It wasn't me !" no idea who might've done that.....

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