Correct diagnosis? P0171 Toyota Corolla ZZ series engine

Hi all at ScannerDanner,

Big fan of the videos and thankfully the SD video on a Chevy Prism misfire issue helped me to narrow down my issue a lot. Hoping some of you can help me understand If I've diagnosed the issue correctly and/or suggest any extra tests to do. Here is the most recent log, you can zoom in on parts of the graph and can see the sensor values below the graph: datazap.me/u/timoc33gmailcom/full-maf-te...g=0&data=0-2-4-10-12

The car is a 2000 EUDM toyota corolla, with a 1,6 litre version of the 1zz-fe called a 3zz-fe. They are identical except for crank and rods, my 1.6 has a shorter stroke.
Car sat for a year almost, and once it entered regular service again it was running fine, until the last refill. Filled the tank with Euro 95 (10% ethanol) and one or two days later, p0171 fun begins.

The fuel trims are high across the rev range, but they are lower on idle than higher up the rev range (About 16% at idle, 35-40% at 3000 rpm). I just filled the tank with premium unleaded and there has not been any significant change in trims, so that leaves us with vacuum leak, MAF, or fuel delivery.

The car is hard to start for the first start, but on the second or third attempt starts fine and will start fine after that until it's sat overnight. Driveability is good EXCEPT on WOT. past 70% throttle position, the car goes back into open loop and the 02 readings do get pegged lean. However, if you put your foot down and stay out of open loop the car accelerates well to redline.

I have narrowed this down to fuel system needing overhaul due to sitting for a year, or MAF needing replacement. Already cleaned the MAF which made a temporary improvement, and have a bottle of injector cleaner in the tank now. Which way would you go with this?

Also, at cruise I get a VE calc of 75%, but at closer to full throttle this drops to 52% - Does this point to an underreading MAF?

This seems like a fuel delivery issue i would hook up a fuel pressure tester and see if fuel pressure drops below 40-45 psi or what ever your regulator regulates it to while idling and at 1500, 2500 rpm. This could be a weak fuel pump from what i am seeing. I also did notice maf value a bit low on the first rpm rev curve past 2500 rpm it dropped down to where is was at 1300 rpm and fluctuated there for a bit. So cant rule out maf yet either.

Any chance you are willing to attach your CSV? I find it painful to use DataZap. I would like to upload it to ScanShare so I can more easily select and manipulate PIDs and get the extraneous stuff out of the way.

I can also add VE to your graph

I believe you're also using OTC's VE calculator. Besides ignoring BARO, the math has been demonstrated to be wrong. VE, in this context, has no value outside of peak torque at WOT.

www.scanshare.io/Tools/VeCalculator

sorry I didn't reply sooner, busy week! Thanks for helping. I can't attach a CSV here so it's in my google drive instead: drive.google.com/drive/folders/1znA-1sj1...drdV5ypp?usp=sharing

There are two MAF log spikes to look for that are near full throttle. The first one was in closed loop, the second was in open loop and the car went lean on that one. You could tell from the drivers seat too. I did find a VE calculator with baro correction ( atgtraining.com/atg-volumetric-efficiency-calculator/ ) and got a max reading in the mid 70% range with about lines up with fuel trims mostly being around the 30% range. Sounds like replacement MAF would be a better step than fuel injectors?

With fuel trims getting more positive with higher rpm i would say u definately need to put a pressure gauge on fuel line and see if pressure drops with higher rpm this seems like a fuel pump. Maf numbers dip here and there but not drastically though a graph versus a chart would help covering a road test. But i would start with fuel pressure first

e11nl wrote: sorry I didn't reply sooner, busy week! Thanks for helping. I can't attach a CSV here so it's in my google drive instead: drive.google.com/drive/folders/1znA-1sj1...drdV5ypp?usp=sharing

I may have missed it? But I can't see that you went WOT for more than a couple seconds. :huh:

To get a useful reading, you really need to stay at WOT from a stop or slow roll through 1st gear, and preferably through 2nd as well. An uphill highway on-ramp is ideal. That gives the engine every chance to breathe as well as it can, and it gives the scan data ample time to capture the problem.

Thanks!

Here is a link for the ScanShare data plot. I personally like it's layout better. I had the programmer get rid of all the "pretty" stuff. IOW, technicians typically just want the data to be clearly displayed and arranged. That is why Toyota TechStream is so good. Along with SO as well.

ScanShare also graphs Snap On files. Nobody else is ever likely to do that. That may sound a little bold, but I was involved with the parsing project and SCM files are a nightmare. PIDS files are easy, but those are produced by Windows based SO tools.

Pick your pids, I left it blank.

www.scanshare.io/share/ywXw9EMpa06yvCANp7GRKA

I was also a bit disappointed in a couple things. One, I only saw one WOT. Your data rate seems really slow as well.

This picture might be the most useful. I made a scatter graph in Excel from your data. To the group, what do you see?

I see an underreporting MAF.

Nice pic though, what if the trim wasn't scatter?, is this pic implying less FT correction at Higher MAF?

I like the use of total trim!!! been doing the same for over 2 years now!!

Thanks Flatrater

SCanshare seems pretty sweet, I love Manipulating Data in Excel. I uploaded a CSV but Scan share doesn't like it, is there a way to delete the file. I just have a basic membership?

I agree, wish they hadn't stopped putting schrader valves on the fuel rail when they went returnless. I am more concerned with fuel flowrate than pressure though, as it may be clogged filter/injectors rather than pump going bad (apparently these corollas are known for being outlived by their fuel pumps, little less so for injector filters).

I plan on testing another MAF next and if no bueno I will look for somewhere that has the fittings to test fuel flow and pressure.

I was from coast most of the way to redline. Funny story, I am in the Netherlands and there are little to no inclines to use for long WOT pulls near me for hundreds of km. I have looked, believe me.. I also got back out on the second pull because the car was clearly running lean and I didn't want to hurt it in the course of getting a log.

Looking for a way to limit the number of sensors being read so I can get a better refresh rate instead. Thanks for the guidance!

I agree, progressively higher correction with airflow.. But I am mostly concerned first with understanding whether airflow is getting reported correctly, before diving into the fuel system.. expecting that every rubber hose and seal I disturb would have a high chance of needing replacement and I have no fuel or vacuum leaks now!

That is a nice tool, I will make use of it from here on out.

Next time I will try to just sample the points I need to so the refresh rate is better. I will also look for the longest on ramp I can find to get through the whole rev range. So make sure to log MAF, throttle, LTFT, STFT, IAT, 02, anything else?

Weycraze wrote: Nice pic though, what if the trim wasn't scatter?, is this pic implying less FT correction at Higher MAF?

Trim is best thought of as a band or range. Using very specific values can lead to a faulty diagnosis. This vehicle is quickly reaching max adaptation so you see it flatten out quickly. Given the curve and the extreme correction, I'd want to get a WOT capture.

Here is a scatter graph of a vehicle that had the MAF replaced and trim cleared. It was then taken out on a test drive. The values flatten out when the system moves into OL operation. That region is zero because it hasn't had time to learn any LT values.

Note the large variation for the same airflow. Once again, this is a "fixed" system. This was part of an industry presentation I did about 15 years ago. Another thing to consider when looking at trim vs airflow is that the MAF output is not linear. It is more of an exponential and the most resolution is found between 0 and 50 g/s (rough numbers). That will affect the scatter graph as well

Thanks for the explanation, I fully understand the specific trim thing, you want an overall picture.

But Again, I'm looking at this picture and I see FT +-15 at lower Maf g/s, and at higher MAF g/s there is no Trim.; Are the scatter MAF or FT?

My Brain is not seeing the diagnostic value of this here. I always use Calc.LD and ABS Ld with trim and MAF pids to determine if there's an Air/or Fuel issue.

Could you please explain this in a lot more detail?

Thanks

Paul

Weycraze wrote: I always use Calc.LD and ABS Ld with trim and MAF pids to determine if there's an Air/or Fuel issue.

How would I do this? just for seeing how trims relate to loading or..?

e11nl wrote: Next time I will try to just sample the points I need to so the refresh rate is better. I will also look for the longest on ramp I can find to get through the whole rev range. So make sure to log MAF, throttle, LTFT, STFT, IAT, 02, anything else?

Only log what you need to perform a V.E. calculation. RPM, MAF and IAT are must haves. BARO is good to have if the vehicle has that PID. TPS is another nice to have but isn't really needed so long as you keep the pedal floored during the run.

Some of my old notes to self lol!!!



This one came from Tyler,

Well, I finally got to take another log, this time with the number of sensors being logged reduced. Turns out the view I was using was logging all sensors.

With an actual WOT pull in second, I saw more normal MAF values, and calculated between 85%-91% VE depending on which weather site I get barometric data from. I would expect this to be a decent calulator: atgtraining.com/atg-volumetric-efficiency-calculator/

So it does in fact look like a fuelling issue, it currently has injector cleaner in the tank and I have a new fuel filter on the way. Will look for somewhere to test my fuel pressure next.

Thanks for the help!

Weycraze wrote: This one came from Tyler

That one was actually from Flatrater. :blush: Though I didn't know it at the time. Credit where it's due!

I just shared this with Chad, might as well put it here, its relevant:

It is a good guideline as well: