Long Term Fuel Trim

[Sacha Rosenthal]

Have recently replaced cats and threw a P0172 code. I replaced a seal on the throttle body and the code has not yet returned; been about 50 miles. The ‘issue’ (and I’m not sure it really is one) is that my LTFT is still fairly negative and I cannot figure out why. It looks like all sensors are working well and I took some screen shots. One at idle and two driving around 25mph. Would love feedback.

The one thing I see is that System B does not enter closed loop. Could that be dumping more fuel than necessary into the engine?

The PO installed (or said they did) 4 hole injectors. I have no idea when nor what brand. Could that also be a problem?

They also said they replaced a thermostat, but again, I have no idea what/when.

The Jeep has a little stutter in idle, but not too noticeable. It occasionally surges in reverse on idle or will stall. Otherwise it drives well.

What else should I be looking at? I’m at a loss and I don’t want to take to a shop to ‘clean the engine’ or replace the intake manifold (which was the last conversation I had with this particular mechanic) unless that is the potential solution.

I’ve replaced O2 sensors, TPS, spark plugs, put a new MAP sensor and reverted to original.

Thanks!

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[whitrzac]

I would bet the injectors are larger than stock.
Keep driving, see if it eventually gets better, or swap in a set of stock injectors.

 

[Chris]

My bet is on the injectors as well.

 

[mots]

Yep, very likely the cause. The PCM is pulling as much fuel as she can to compensate for rich mixture. short term trims also show it pulling fuel.

 

[Sacha Rosenthal]

Thanks guys.

This has been driving me bonkers.

Now a silly Q. Where would you recommend I buy the injectors and are they easy to change?

I’ll give it a bit more time before I do anything, but that is looking like an option.

Thank you!


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[Sacha Rosenthal]

One other Q.

The PO also installed an aftermarket throttle body and apparently it’s not sealing all that well to the intake manifold. Could any extra air getting in cause a rich fuel condition or is it more likely to cause a lean error?

Is it worth replacing with OEM? They’re tough to find and I’m fearful either it or the intake is a little warped...

Thanks!


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[pagrey]

Your system "B" is open loop because your Jeep doesn't have a system "B"

Your fuel trims are fine, mine are 9 yours -20. No codes, who cares?

Injectors will change your fuel trim because they require shorter or longer pulses to get the same fuel but in the end it doesn't matter.

If the intake is warped sand it smooth and put it back together or use some RTV.

 

[Sacha Rosenthal]

Your system "B" is open loop because your Jeep doesn't have a system "B"

Your fuel trims are fine, mine are 9 yours -20. No codes, who cares?

Injectors will change your fuel trim because they require shorter or longer pulses to get the same fuel but in the end it doesn't matter.

If the intake is warped sand it smooth and put it back together or use some RTV.

Thanks.

The code is now ‘pending’ (as of last night) so will assume it will ultimately come back. If there were no codes, I’d be fine. This is the third time it’s come back after a variety of things changed; O2, cats (different code), TPS, MAP etc... I’ve clearly missed something!

Things left would be an OEM throttle body (if necessary) and/or new injectors; both having been changed out in the past.

The throttle body was put back on by the mechanic using Indian Head gasket maker, so am hopeful that does the trick. Would RTV have been better? Are they similar?

I’m the 8th owner so have no clear idea on all the other mods that have been done.


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[pagrey]

Anything that'll seal the leak will be fine, RTV wont be any better.

You're right, if you cleared the code and it's now pending I'd consider it the same as getting the code.

 

[mots]

One other Q.

The PO also installed an aftermarket throttle body and apparently it’s not sealing all that well to the intake manifold. Could any extra air getting in cause a rich fuel condition or is it more likely to cause a lean error?

Since we don't have a MAF sensor (TJ uses MAP), it won't be seen as non-metered air. Still best to get it sealed up, but that tiny leak should not cause any problems with mixture per se. Like pagrey stated, IF it isn't' throwing a "rich" code or any other related codes, then the PCM is able to pull enough fuel to make the PCM happy with the mixture based on the O2 feedback.

However, if you are still popping the p0172 (System Too Rich) periodically, then either the O2 isn't working or perhaps the PCM can't pull enough fuel to compensate for the injectors you have.
https://www.fixdapp.com/blog/p0172
Modern ECU's are pretty amazing in being able compensate for these types of fueling changes in closed loop, but all ECU's will reach a limit at some point to how much fuel can be pulled (or added) via fuel trims. If you are under this fairly generous range of compensation, then all should be well if you aren't popping any codes.

 

[Sacha Rosenthal]

Since we don't have a MAF sensor (TJ uses MAP), it won't be seen as non-metered air. Still best to get it sealed up, but that tiny leak should not cause any problems with mixture per se. Like pagrey stated, IF it isn't' throwing a "rich" code or any other related codes, then the PCM is able to pull enough fuel to make the PCM happy with the mixture based on the O2 feedback.

However, if you are still popping the p0172 (System Too Rich) periodically, then either the O2 isn't working or perhaps the PCM can't pull enough fuel to compensate for the injectors you have.
https://www.fixdapp.com/blog/p0172
Modern ECU's are pretty amazing in being able compensate for these types of fueling changes in closed loop, but all ECU's will reach a limit at some point to how much fuel can be pulled (or added) via fuel trims. If you are under this fairly generous range of compensation, then all should be well if you aren't popping any codes.

Thanks. I was really hoping all would stay as is and not pop a code. This does not appear to be so, unfortunately; pending P0172 code has shown up.

I am in closed loop and all O2 sensors are operating well, I think. They all show a range of 0.1-0.9 (ish) volts. The upstream fluctuate rapidly. The downstream are flat (close to 0) until accelerating, then they tick up closer to 1V.

I’ll go ahead with new injectors and pause on the throttle body replacement for the time being, but will see if I can run a new rtv bead/replace gasket if needed.

Appreciate the information and help as always.

Once injectors are replaced, I’ll see if that does the trick and report back. Typically takes 30-50 miles of driving and a few starts to pop the code.


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[Sacha Rosenthal]

Replaced the fuel injectors this morning with OEM Mopar. Code gone! Watched the fuel trims for a few miles miles and all looks normal.

Finding the injectors proved to be a challenge. Back ordered until October. First order in for 6 weeks before I found a place on eBay to buy from and had in hand 3 days later. Only had 6 in stock. Was refunded from the original vendor.


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[Daryl]

Replaced the fuel injectors this morning with OEM Mopar. Code gone! Watched the fuel trims for a few miles miles and all looks normal.

Finding the injectors proved to be a challenge. Back ordered until October. First order in for 6 weeks before I found a place on eBay to buy from and had in hand 3 days later. Only had 6 in stock. Was refunded from the original vendor.


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For future reference, what are your fuel trims?

 

[Sacha Rosenthal]

The short term were ranging from +3 to -9. Long term were close to 0 vs -20. To be fair, that was for a 5 mile test run post install.

If you like, I’m happy to keep an eye on them for the coming weeks and let you know what happens.


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[Daryl]

The short term were ranging from +3 to -9. Long term were close to 0 vs -20. To be fair, that was for a 5 mile test run post install.

If you like, I’m happy to keep an eye on them for the coming weeks and let you know what happens.


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Yes, that would be great if you could. This thread would be a great reference for what a normal, good running engine fuel trim ranges should be.

 

[Sacha Rosenthal]

Here’s a series of shots ranging from idle to 25mph, 35mph and up to 65mph. All pretty similar!

Still had a stall once I got to work and was reversing under hard lock into parking space. Will clean IAC and see if that solves it.

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[lindsey97]

To check for leaks on your engine, get Berryman's B12 and spray in very short burst around base of throttle body, intake gaskets, and vacuum lines, with the engine running. If the engine revs up or changes tone, then you have just found your air leak. Be careful, Berrymans is flammable.

 

[Dominic Maionchi]

I am unable to get my fuel trim on my 06 wrangler within the proper range.

I am negative at idle but it goes to 0 when I’m driving. If I let it idle too long I’ll get a code indicating rich mixture on both banks. I’ve replaced all the sensors.

Any thoughts on what could be causing this? Is it a valve problem?

 

[DWR]

I am unable to get my fuel trim on my 06 wrangler within the proper range.

I am negative at idle but it goes to 0 when I’m driving. If I let it idle too long I’ll get a code indicating rich mixture on both banks. I’ve replaced all the sensors.

Any thoughts on what could be causing this? Is it a valve problem?

Following the K.I.S.S. method.... first things first, go check your intake filter to make sure it isn’t crazy dirty/clogged.