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Discussion Starter · #21 · (Edited)
Thank you very much Matt and Brandon for the little lesson on fuel trims. I read that twice and am digesting it as we speak.

JimInVirginia thank you for looking, I really do appreciate it. Also for your experiences with MAFs

Al, I have a bluetooth scan tool and have been checking for codes that way. That is a legitimate thought, the light being burnt out. It didn't even cross my mind but now that you mention it, I've had that happen on a different car I owned in the past. Catless exhaust = O2 sensor code forever = burnt out light. That car ended up having like 15 codes though lol. I ripped out the EVAP system among other things. It was fully gutted. I wanted to cage it and race in the Champ Car series or something like that, maybe even dirt track it. Life happens though and the car is no longer with me. I had forgotten what it's like to only have one vehicle, bleh. Might start looking for a '03-'04 Powerstroke to daily and start really modifying the TBird. Anyways, I got off topic there lol. I was actually already thinking about Delphi so I'll probably order one of those. I wish I could find Hitachi or Motorcraft but oh well.




Now, onto my data log. It lists "oxygen sensor short term fuel trim" separately from "short term fuel % trim". Based on what was said above, I saw some pretty wild numbers. I will post the logs here if anyone feels like digging through them, it's a nightmare of data lol. I saw as high as 42% and as low as -21% all in the same drive. If anyone wants to give me an overview of what to look for in the data instead of having to dig through it themselves, I'm more than happy to learn. On my phone app I can put the data in graph form and it's a lot easier to look at. If you want to look though, by all means, please do lol.

One thing I did do was I charted throttle position and MAF air flow rate on the same graph. They follow a pretty similar path, although there are a few instances where it looks weird to me. But I have no idea what I'm doing! So suggestions on what to look for in the graphs is much appreciated. Sorry for the lengthy post. Thanks again.


Well crap, when exporting the data it turns into an Excel spreadsheet and it's just a mess. I can post screenshots of specific graphs though, just let me know what you want to see. Or what I should be looking at.

The fuel trims seem to be all over the place. Up down up down up down. Both long and short term. I have reset the EEC several times over the past few days though.
 

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Feel free to post what you have and I can take a cursory glance at it. A lean code could mean a dirty MAF, a bad MAF, a vacuum leak or bad O2s. Given your observation that the car runs much better with the MAF disconnected, that's as good a start as any.

Fuel trims are capped at 25% adjustment (IIRC) so perhaps your software is extrapolating STFT and LTFT to display fuel trims in an absolute fashion relative to what the MAF sensor is reporting. If the software doesn't show long term and short term trims independently, it might be worth a KAM reset (just unhook the battery for a minute or two then drive it in mixed city/highway for 5-10 miles while logging data). When you do that the LTFTs are reset to 0. Be sure you log MAF counts, RPM, load as well as the other things. If your MAF counts relative to the RPM and load are way off relative to known real-world values (I can refer to old logs of my car for that), that would be a surefire way of knowing that the MAF is bad.
 

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You have a vaccum leak. Do a smoke test; that's the least dangerous.
I'm betting the egr hoses. :) I'd do that first. there are 8 small pieces of hose there. :)
There are some other pieces that will be rotted by now; the elbow on the front of the vb for one. :) I went to Advanced and bought a foot of every vacuum hose they had, and went thru and replaced everything that looked old. :)

To get a good datalog for us, Take it for a drive long enough to get fully warm; then plug up the maf and drive home, logging both ways.

I think I'm going to print B's post and tape it into the logbook I use. :) I bought some 39lb injectors the last time I forgot that stuff, lol. oh well, if I can find the rest of the stuff I need for this eaton blower, I'll use them. :)

for the datalloging I do, you have to save the data as a csv file, then import it into excel, IIRC.
That should show everything. as Brandon said, MAF counts, RPM, load short and long fuel trims, engine temp, the open loop flag helps too if you have it.
 
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Discussion Starter · #24 ·
Feel free to post what you have and I can take a cursory glance at it. A lean code could mean a dirty MAF, a bad MAF, a vacuum leak or bad O2s. Given your observation that the car runs much better with the MAF disconnected, that's as good a start as any.

Fuel trims are capped at 25% adjustment (IIRC) so perhaps your software is extrapolating STFT and LTFT to display fuel trims in an absolute fashion relative to what the MAF sensor is reporting. If the software doesn't show long term and short term trims independently, it might be worth a KAM reset (just unhook the battery for a minute or two then drive it in mixed city/highway for 5-10 miles while logging data). When you do that the LTFTs are reset to 0. Be sure you log MAF counts, RPM, load as well as the other things. If your MAF counts relative to the RPM and load are way off relative to known real-world values (I can refer to old logs of my car for that), that would be a surefire way of knowing that the MAF is bad.
It shows STFT and LTFT independently. The file format isn't supported by TCCOA so it won't let me upload the logs. It logs 36 different parameters all at once, including the ones you listed. I am looking at the graphs now for MAF vs load vs rpm based on your post. The graphs follow a similar path but there are some irregularities. In this screen shot I've uploaded, this is when I first started the car this morning and it was running terrible. It actually died while I was in R backing out. I'm sorry if I'm misunderstanding, I really am in over my head here. This is a great learning experience though and I've been wanting to learn about this stuff for quite a while. Thank you for your patience.
 

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Discussion Starter · #25 ·
You have a vaccum leak. Do a smoke test; that's the least dangerous. I'm betting the egr hoses. :)
Honestly in my mind at this point it's either a vacuum leak or the MAF. My thinking is this though: if it was a vacuum leak it wouldn't be intermittent would it? There are times where the car runs completely normal for a few mins then goes back to stumbling. If it was the MAF though, surely I would have a code for that unless it's not "bad" per se but failing. That would explain the random changes between running fine, and running poorly, right? Correct me if my logic is wrong. I'm off work Thursday so I'm going to spend the day inspecting the vacuum lines, spraying carb cleaner and such. If I find nothing then I'll just bite the bullet and order an MAF. This is tentatively my plan.

I also want to learn as much as I can about this data I'm collecting while I have the experts here though, lol.


I will look into the smoke test instead of carb cleaner. Thanks for your recommendation.
 

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What were the conditions of the logging screenshot you posted? Can you include RPM in the display? With the car idling in park at 800 RPM, it should have a load of about 16-18% and air flow of about 0.8 lb/min or 6 g/s.

Under no circumstances will an N/A engine reach or exceed 100% load unless it's shut off, lol.
 

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Al, I have a bluetooth scan tool and have been checking for codes that way.
Out of curiousity, what bluetooth scan tool and app are you using?

I purchased a cheap elm327 obd module that works poorly (when it works at all) with the few included apps and am looking for something better.
 

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Discussion Starter · #28 · (Edited)
What were the conditions of the logging screenshot you posted? Can you include RPM in the display? With the car idling in park at 800 RPM, it should have a load of about 15-16% and air flow of about 0.8 lb/min or 6 g/s.

Under no circumstances will an N/A engine reach or exceed 100% load unless it's shut off, lol.

I wondered about the load, lol. This is when the car died while I was backing out this morning. If there something specific you want to see, I will get it for you! Here is the graph you requested. I could do them all three on the same graph but I figured this is easier to read.

I can zoom out to show a longer time period but the graph gets harder to read the further you zoom out, ya know.

I can create specific conditions tomorrow and log that if there something you want to see. I do have more from today though, I logged about a 14 mile trip.



Out of curiousity, what bluetooth scan tool and app are you using?

I purchased a cheap elm327 obd module that works poorly (when it works at all) with the few included apps and am looking for something better.
I am using BAFX Products WiFi OBDII Scan Tool with the app called Car Scanner. With how little I know about this stuff I honestly can't tell you if it's good or not, lol. I bought it to be able to read codes, didn't even realize it could do all this. It has reliably pulled/cleared codes for me for about 2 years though. I just started branching out into the other functions literally days ago.

Here it is


EDIT Wow I just realized I am not using the app that they reccomend for it...smh
 

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There are a few spikes on there of load getting to about 80%. At those points were you hard on the throttle?

Load is volumetric efficiency. In other words, the volume of the air entering the engine relative to its displacement. A load of 100% would mean 4.6L of air entering for every 2 revolutions or 4 strokes. 50% means 2.3L of air, and so forth.
 

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Discussion Starter · #30 ·
There are a few spikes on there of load getting to about 80%. At those points were you hard on the throttle?

Load is volumetric efficiency. In other words, the volume of the air entering the engine relative to its displacement. A load of 100% would mean 4.6L of air entering for every 2 revolutions or 4 strokes. 50% means 2.3L of air, and so forth.
I was not hard on the throttle. This was pulling out of my driveway and driving on a narrow residential street. I have updated the graph to include throttle position.

That makes sense now, what you said about a N/A car never hitting 100%, lol.
 

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Discussion Starter · #31 ·
I was sitting here digesting everything you have said and it just clicked. The load is high but the throttle position is low. So air is entering the engine somehow. Vacuum leak!

If my logic is sound anyways...
 

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Load is calculated based on the MAF airflow data and RPM, so if there was a vacuum leak (unmetered air - air entering the engine not measured by the MAF) the PCM wouldn't know about it, and load wouldn't reflect it. If the MAF knew about unmetered air, it would report that to the PCM and it would properly deliver fuel and no lean codes would ever show up for a vacuum leak. :)

I dunno, it's hard to draw conclusions with the data I can see thus far. It looks a little off but the best thing to do is just hold it at idle for a while, then do something like 2nd or 3rd gear at low throttle up to 3000-3500 RPM or so to make sure the data curves are smooth and without jitter or spikes throughout the range.

I'm used to logging data like this, lol.

42753
 

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Discussion Starter · #33 ·
Load is calculated based on the MAF airflow data and RPM, so if there was a vacuum leak (unmetered air - air entering the engine not measured by the MAF) the PCM wouldn't know about it, and load wouldn't reflect it. If the MAF knew about unmetered air, it would report that to the PCM and it would properly deliver fuel and no lean codes would ever show up for a vacuum leak. :)

I dunno, it's hard to draw conclusions with the data I can see thus far. It looks a little off but the best thing to do is just hold it at idle for a while, then do something like 2nd or 3rd gear at low throttle up to 3000-3500 RPM or so to make sure the data curves are smooth and without jitter or spikes throughout the range.

I'm used to logging data like this, lol.

View attachment 42753
Wow yeah that looks just a tad bit more useful than what I'm working with, lol. Very nice. At some point I'm going to look into something like that, with some tuning software.

I will definitely do that. Idle for a while. Second or third gear, low throttle to 3500. Will report back with more graphs.

I've done some reading about all this stuff but it's just overwhelming, one of those I don't even know where to start. Every single paragraph just goes way over my head, really quickly. Your info has been enlightening though and interesting too!

Thanks again, I know I keep saying it but people like you are an invaluable resource to humble shade tree "mechanics" like myself. Love this forum and this community. I bought the TBird on a whim, never been a Ford guy, didn't know anything about them other than it was a V8 coupe and it was cheap. Looked to be in great condition. I lucked out though, love the car, love the community. I'm dying to have a project car again and the TBird is a strong contender. It suprised me how well this thing handles. I mean theres a ton of body roll and squishy springs/shocks which I've never liked but it's so easy to control while sliding around. I love driving it in the rain, lol. It has a lot of steering angle too, which I like. The open diff HAS to go at some point though. bleh. Poops on my party.
 

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They all work together. The computer adjusts the pulse width of the fuel injectors based on the volume of air flow going into the intake as measured by the MAF sensor and amount of air/fuel mix in the exhaust based on voltage readings from the O2 sensors. Throw temperature sensors in there, too. Lean means what, I forget. Vacuum leak or low fuel pressure? Too much air, not enough fuel. Could be a leak in the exhaust diluting the O2 sensor reading, too. Could be an O2 sensor itself. I always wonder... if it was a problem with the MAF sensor why aren't there codes for both banks? The freeze data on the data logger may show an anomaly with O2 sensor voltages.
 

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Yeah, fueling codes come when the PCM reaches the adaptive limits for adjusting to keep fueling at stoich in closed loop as reported by the O2s. As you said it requires all the pieces working together properly. The MAF and IAT sensors are primary for determining air mass entering the engine, with some minor scalars for desired mixture when in open loop based on ECT and IAT. In closed loop the sensors are on the back burner for fueling control since the O2s are providing mixture feedback.

If the PCM has to add or subtract 25% (again, IIRC) fuel on top of what is considered normal, given the feedback from all the sensors, it will those the rich/lean code(s). Old O2s respond differently as they age so that could be a contribution for why one bank throws a code, but not the other. I suspect though that in time they'd both throw the code.

An easy trick (well, easy in terms of saying it - not so easy with the impossible-to-get-at passenger side upstream O2) to see if the sensors are the cause of a single-side code is to just swap the O2s between sides, and see if the code follows the sensor or not.
 

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Lots of good information here .. Just the tip of the iceberg. Best way to learn is ask questions.

Reminds me of how much fun all of those advanced electrical diagnostics classes were. Something about a "false lean" on an over-rich condition .. 🤔
 

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Oh boy. :)

Fuel delivery looks like this:

The MAF sensor voltage is converted to an airflow rate using the MAF transfer function (a table of airflow vs. MAF voltage) in the PCM.

The PCM computes the needed injector pulsewidth next. This is based on the injector flow tables, calculated air charge from the MAF and desired lambda (lambda is AFR, independent of fuel type, and is always 1.0 (stoich) unless in open loop). The STFT shows you the commanded lambda; if the STFT is lower than 1, it increases the fuel charge. If it's over 1, it reduces fuel charge. Then it's multiplied by the LTFT for the final fuel delivery pulsewidth.

In closed loop the PCM is using O2 feedback as a bit of a "reality check" for the MAF sensor data to fine-tune and maintain perfect stoich - or 1.0 lambda. It does that by constantly "switching" the commanded lambda from ever-so-slightly lean to ever-so-slightly rich (about 2% in each direction), within the limits of the responsiveness of the narrow-band O2 sensors (their AFR reporting range is only within a few percent of stoich, otherwise they are 5V for much richer or 0V for much leaner than that). This switching as monitored in data logging software indicates the PCM is successfully maintaining the perfect AFR for your fuel - 14.08:1 for E10 and 14.64:1 for E0. If the MAF is slightly off or if there are mechanical deficiencies, the commanded lambda might be rich or lean to compensate for that. If this is the case, your STFTs might switch between .92 and .96 if you're running 6% lean and it needs to add that much fuel to compensate. If this remains consistent for a long enough period, adaptive fueling will set the long term fuel trim to 1.06 for that spot on the MAF transfer function so the STFTs stay right about 1.0.

In open loop, the PCM isn't using O2 sensor feedback to maintain stoich - it's commanding the desired lambda based on fuel delivery tables (there are a few; depending on driving conditions different tables are used). Since the O2s can't being used to fine-tune commanded mixture to actual mixture, only ECT/IAT/MAF sensor data is being used. Open loop is used at WOT (high TP over about 60%) or for a few moments after cold engine starts.

To summarize, if the MAF is off, the O2s will make up for it - but only in closed loop. And as you've learned, MAF sensor data is how the PCM calculates load, which are your cylinder pressures during combustion. Spark delivery is based on load vs. RPM - so as you can see, the MAF sensor really is about the single most important sensor on the car aside from, maybe, the crankshaft position sensor.

All this is why you CAN NOT change or modify the MAF sensor without a tune. Changes to the MAF sensor or housing mean the MAF transfer function is no longer a reflection of reality, and since fueling and load (spark) depend on it, well...

Oh, and I finally found my dongle, so I can fire up Advantage again to see what the stock calibration does, instead of just relying on memories of it from 8 years ago, lol. :D
 

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SRB - That open loop piqued my curiosity, so I took my bone stock 95 LX 4.6 around the block, ran good. Then swapped out my "good" MAF sensor to the one that gave me double digit fuel trims. Still double digit fuel trims but never came out of closed loop. So I still don't have any suggestions for you why your car comes out of closed loop, other than a loose electrical connection or loose sensor.

Like stated above, in open loop the computer should default to a set of preprogrammed settings for air/fuel mixture rather than the MAF and O2 sensors. It shouldn't run bad just because its in open loop. I don't know if there could be a problem with the resident fuel delivery tables but If it was me, I would disconnect the battery for a few hours, reconnect then drive it hard but not rough. Try to teach it how to run again. Sorry, I'm all out of ideas. Give it another hard look for vacuum leaks and loose electrical connections. Good luck with it. - Jim
 

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in open loop the computer should default to a set of preprogrammed settings for air/fuel mixture rather than the MAF and O2 sensors.
Mostly correct; the PCM uses a table of commanded lambda based on load and RPM feedback. The MAF is still used to calculate the load for fuel delivery calculations. With a failed MAF sensor, there is a table defining load based on TP and RPM.

This is the factory MBE3 base fuel table. This is what the PCM uses under most circumstances whenever it's in open loop. There is a separate table for cold start lambda. There are also a few adders/modifiers for various conditions encountered while driving, such as ECT and ACT variations. As you can see, from the factory the PCM is commanding a lambda as rich as .7 - for E10 that's an AFR of only 9.8:1!

42785
 

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I am a Motorcraft guy thru and thru but for MAF's, I am NOT impressed with the Motorcraft. They do not last, and/or get out of range enough to cause WOT pinging. I've replaced them on every MN-12 I've owned and also chased WOT pinging issues on every single one.

On my latest T-Bird, I wasted at least $100 for a year or so of 89 octane use until I finally replaced it with a Delphi unit. Now I am back to good 'ol 87 octane, and the MAF will pay for itself after about a year, then it's gravy after that.

I even had great luck with a Cardone unit on my old '95, plus gas mileage went up 2 MPG.

Al
 
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