[FIXED] Fuel Trims Analyzing - Pending Lean Codes

Hello. At the 850 mark I start to go WOT. MY short term is climbing 20% on both banks which tells me its a rich command for a lean condition and its happening at the moment of WOT not long term memory. If its a lack of fuel delivery why is the O2 going rich not lean? Could it be ignition misfire? Thanks.

Under sudden WOT acceleration close loop control is ignored
When the throttle suddenly goes wide open a huge gulp of air enters the inlet, the pressure in the manifold rises close to atmospheric, the mass of air entering each cylinder increases, the compression pressure increases as a result the engine computer has to compensate very quickly.
Back in the days of carbs this correction was done by device in the carb called an accelerator pump that squirted a surprisingly large amount of fuel into the intake venturi when the throttle was moved.

a sudden WOT is a good way to test the ability of an O2 sensor to react to a deficiency of oxygen.

Ok. Can I rule out fuel delivery by the O2 sensor going rich? Also A couple of things I noticed. During idle fuel trims get better or worsen when I raise the rpm. The same thing happens when I put it in gear. i smoked the intake and there was smoke coming from the PCV grommet and the rear end seal of the lower intake. This means both lower and upper manifold need to be removed. I'll update this thread once i'm finished.
BTW my truck is a 1999 Mountaineer 5.0 with 191k miles.

MAF engines show big changes in fuel trims at idle speed with an kind of vacuum leak "pirate air" the trims add a lot of fuel at idle to compensate, but much less extra fuel at 2,000 rpm
MAP engines are more immune to the effects of vacuum leaks, with a MAP engine high or erratic idle speed tends to be the most prevalent symptom, On a MAP engine looking at the IAC position with a scantool if the valve is closed or nearly closed it is a sign of a potential vacuum leak.

You can learn a lot about the fuel system and the cat and pre-cat exhaust system by just watching the upstream and downstream O2 , how long the sensors take to come alive after a cold start, how quickly the cat starts to work, by any of the various test that drive the exhaust rich and then lean you can get an idea how much life is left in the cat. Paul has a great couple of video's and book section on tasting cats using the reserve oxygen test.

EricGoodrich wrote: a sudden WOT is a good way to test the ability of an O2 sensor to react to a deficiency of oxygen.

Yes - Just repeated very quick fluttering the the throttle at idle only moving the pedal 1/4" to 1/2" can drive the upstream O2 rich and give you a good idea if the sensors are working and the CAT is up to the job.

On road test if you have a suitable road to do it safely holding full throttle, then completely lifting off to get injector cut off is also a good test.

Don't worry at all about the 20% short term trims at WOT - most Ford's I've seen from that era behave the exact same way. This '02 Crown Vic, for example:



I think you can absolutely rule out fuel delivery for now, with the O2's going full rich at wide open. The MAF going over 4.0V also suggests that the MAF is OK, and there are no volumetric efficiency issues. I also see that the long term trims improve slightly around frame 835, when you first get on the throttle, so I think you're on the right track with your vacuum leak diagnosis.

UPDATE

So yesterday I finished installing lower, upper, front and rear seals gaskets. Smoked the intake and no smoke visible except for smoke coming out under port holes from the EGR valve. I reset the KAM and and started the engine. My LTFT went up to 23 & 28% immediately. At idle and at 2500 rpm I could not get the trims to improve.Yet driving and giving it some throttle the trims improve. I smoke the intake again to make sure I didn't miss anything the first time. To rule out the EGR valve I sprayed carb clean into it and the O2 and STFT didn't go rich at all. Upset about putting all those hours spent installing those gaskets I packed it in and took my family in my truck to drive 20 miles to a party.
This morning i setup my scan tool and do a cold engine start and noticed a 4% trim improvement at idle. Woohoo LOL! Again I could not get the numbers to improve at higher rpm at idle but improve when I drive as the image capture will show.

Did a compression test

Took a fuel pressure reading and it was at 64 psi and within spec. Snap throttle and idling held at 64 psi even though I have a bad check valve when the engine is off the pressure bleeds off.
Idling trim data is telling me fuel delivery. Driving trim data is telling me vacuum leak. O2s going rich at WOT. No smoke coming from the intake and PCV crankcase. I know this computer is going to throw me a pending lean codes soon and inspection sticker due next month. Can't diagnose the problem.

Man, that's disappointing. I don't suppose you tried pinching off the brake booster hose at idle? Or, putting smoke into the booster with your machine? Just trying to think of vacuum leaks that don't show up normally with a smoke test.

Looking at your data, and I still think it looks like a vacuum leak issue. I suppose it could be a MAF issue where it's only misreporting airflow at idle rates, but reads correctly otherwise? I'd be surprised, 'cause your 4.37V at WOT definitely suggests the MAF is doing OK.

I'll try the brake booster test. Thanks

Update

So I removed the brake booster hose and plugged the hose with a vacuum gauge. As you can see the image below I have 28% and 25% at engine startup with no improvement with the brake booster disconnected.



Snapping the throttle long term goes down indicating vacuum leak.



I then blipped the throttle and noticed after doing so the short term goes negative at both banks. Otherwise I think and I might be wrong ,no reaction in the short term would've not happened if I didn't blipped the throttle.



While the short term is negative the long term doesn't react until seven or eight minutes later.



Look at the trims now. A vast improvement.



This is short lived because when i turned off the engine and started it up again 10 minutes later my long term was 23% and 18%. idling for five minutes the long term was not changing until I blipped the throttle several times in which the short term reacted bringing the long term to 14 & 10%.
Don/t know if it's coincedence or not but fuel trims improve while blipping the throttle during idle, Done it twice now. What could be cause this? Thanks.

At idle my STFT was fluctuating between -3 to +3 when i noticed a 3% increase when I depress the brake pedal. When I release the brakes the STFT goes back to baseline. Depress the pedal once all the way, release and the same happens. Then I started to pump the brakes repeatedly and STFT rises with every pump. I got it to go up as high as +45 and +35 on both banks. As it rises there is a slight rpm change. Stop pumping the STFT went back to baseline even though LTFT were in the 20's. Maybe I'm wrong but the brake booster shouldn't affect the STFT the way it did?
I wished I graphed it with my laptop. Used my iPhone instead and i haven't smoke test the brake booster yet.

A vacuum servo works by having two chambers under vacuum separated by a diaphragm When the pedal is depressed a controlled air leak is introduced into one side to boost to reduce the vacuum on the pedal side of the servo to add to the pressure you put on the pedal. ---- when you push the pedal the whole booster unit becomes a controlled vacuum leak but it isn't an issue because the brakes are used when the vehicle is slowing down when the inlet is under very high vacuuum or at idle where the IAC and O2 sensor correct for the tiny ammount of extra air introduced. You will also see tiny changes in IAC postion and fuel trims when you turn the steering or switch on the AC or headlights.

The official way to test a servo iswhile stationary to run the car at idle, then switch off and count how many hard presses of the brake pedal it takes to exhaust the reserve vacuum ---- normally should be able to still feel some vacuum assistance on the third press.

I didn't diagnosed my problem yet but I guess being persistent has it's rewards. My check engine light came on three days ago with my inspection sticker due this month. Yesterday at my son's indoor practice I'm out in the parking lot with my scan tool trying to find out my lean condition. I'm looking at my fuel trims in the upper 20's on both banks when all of a sudden the fuel trims dropped on its own to a stunning 8% and 3%! Stunning because I never seen it this low before. If I play my cards right I could take advantage. When my son's practice finished I erased the codes and did a drive cycle on the highway. All the readiness monitors passed even the EVAP and no pending codes!! Made a beeline to the auto shop and got my inspection sticker! When we arrived home I turned off the truck for just five minutes when I turned it on again the fuel trims are in the upper 20's again. The joke is I have a whole year to figure this out lol but I'm still going to troubleshoot. That's my short story.

I'm still trying to figure out this lean condition when not busy from work. I bought the VE calculator from AES wave. Don't know if I'm understanding the help file. It says high RPM and high MAF g/s at WOT. I've also seen Paul's video. So before I plug in these numbers I'll show two captures and tell me which data to put in. Purple graph is MAF and green is RPM.

Is it A:



Is it B:



Or C:
Do I take the highest MAF from one capture and the highest RPM from another capture and put them in the calculator?

Thanks.

EDIT - I didn't realize this thread continued further. Well maybe there is info in my post that will help if its not figured out yet.

I'm concerned about smoke coming from the EGR. That should be shut completely when smoking the intake. If it were me I would take a closer look at the EGR or the EGR Gasket. I know you mentioned spraying carb clean around it but I don't always have 100% success with that test, in fact, maybe only a handfull of times I have had success with that. Prime example on a 07 Corolla 1.8L. No change to AFR Sensor at all or even idle speed when spraying brake clean everywhere. Though replacing intake gasket, cleaning o-ring and matting surface on throttle body and cleaning matting surface for intake tube to t-body and cleaning throttle body brought the fuel trims back down around 7% instead of +14,+18 & +20 I was seeing at random times during idle between ST/LT FT

You mentioned your LTFT went to 23-28% immediately even after resetting the KAM. How soon after startup? How long was STFT high and how high was STFT after LTFT learned new trim numbers? I am wondering if the fuel trims never were erased for some reason. I remember a ford I was working on years ago, the scan tool offered a "fuel trim reset" option on a I think 99 or very early 2000s F150 with a shorted stuck rich O2. Maybe try that or disconnecting the battery and shorting out the NEG and POS leads together.

Little story about the corolla case I've been working on and to emphasize on the fuel trim reset, this 07 corolla I have been working on through me in the wrong direction for the first day of diag. Fuel trims were high at idle, 7-10% but increased as RPMS and/or LOAD increased to around 14-18% between Long term and short term... this lead me to a fuel delivery issue. After various checks and everything looking normal, I decided to disconnect the battery today (2 days later) to reset the fuel trims, and here its winter and 20s. After connecting the battery back up and starting the car, curious about stone cold startup trims, Initial STFT went up to 7-10%, after snapping the throttle about 10 times trying to piss it off, idle STFT became 14-22% and actually IMPROVED with RPM and LOAD down to 5% and 6%. Completely Opposite of what it was originally showing me. This lead me to a vacuum leak. So far my trims are better but not where I want them. Long term is 7% which is better than 14%. Toyota also says +35% & -35% thresholds between LTFT and STFT is the malfunction zone so it seems I got some head room even at 7-10% between current ST/LT FT. They still improve with increased RPM / LOAD, I hope it stays that way haha so I can continue my diag. direction.

Looks like you are putting a lot of emphases on your long terms. If you reset the fuel trims so long term is 0, it takes time for long terms to react usually so STFT should be the one your look at closer after an initial reset.

You could also do some snap throttle tests with your MAF on a scope. Mr. Danner has some great videos about this on youtube and his premium channel. MAF can cause all kinds of weird fuel trim numbers when there is really no problem other than the MAF.



Could you grab a video of LIVE scan data? Best would be after disconnecting the battery and shorting the leads, have live data up before starting the vehicle and recording with your phone or camcorder. Let it idle for awhile and allow us to watch the trim numbers along with other parameters. Then hold engine around 2000, then 2500, then 3000 so we can really see the reaction. I would customize your data list for faster parameter updates. Any PIDs releated to MAF g/s and MAF Voltage, O2 Sensors, Fuel Trims, Throttle, rpm, load...maybe thats it. We should be able to see LTFT at 0 for a little while, especially during initial open loop after a reset.

I'm not to concerned about the fuel trims under heavy acceleration. Once the O2s are pegged rich, not much the pcm can do for fuel trims other than looking at a fuel map table.If the PCM was looking the the O2s for fuel trims at WOT or heavy acceleration, it would probably try removing fuel to get them switching again which would be a bad thing under heavy load. I recently watched a video about a GMC 6.0 I think it was that, by design, stayed in closed loop under WOT and the O2s kept switching. My guess is they were Wideband or AFR sensors.

In your screen capture linked below, I see very negative STFTs with High LTFTs. Its correcting for awhile, not completely but its correcting partially. This is where a fuel trim reset would come in handy to whip out long terms.

www.scannerdanner.com/media/kunena/attac...hot18_2017-11-29.png

Thanks for your input graywave! I had the battery disconnected for a full day but didn't touch the posts together. So perhaps the KAM didn't reset. After awhile I did another reset using the scan tool. On the first startup the trims were low for the whole day. As the days pass the trims get higher and higher. I'm at 21 and 18 on the LT on idle and and when I put in gear 18 and 14 on LT. The ST has corrected on all instances. While I'm driving on part throttle the the LT raises a couple of percentage points. They never improve. I'm sure I fixed my vacuum leak issue.

I'm thinking I have an injector issue but I can't rule it out yet. That's because I have a bad check valve in my fuel pump. In order to do injector balance test I have to change the pump first. Is it possible with one injector partially clogged or failing , the other seven injectors can provide the O2 with a rich signal at WOT as I've shown many times?

The following test have been done since changing the upper and lower intake gaskets.
Smoked intake
Isolated purge valve hose from intake. Isolated brake booster from intake. Isolated vacuum line to dashboard HVAC from intake.
Fuel pressure at 64 psi at idle and snap throttle. No pressure loss when changing gear in rev or drv
MAF above 4 volts and grams p/s high at WOT
Clamped breather hose and PCV hose with vacuum gauge at dipstick. Pressure rose to 1 psi
Engine breathing at 82% using DECS VE calculator

Test not done yet:
Fuel pressure gauge connected while driving
Injector balance test

MAF plugged, unplugged then plugged.

Fixed