Fuel Rail Pressure vs Intake Manifold pressure - Here is the skinny

[landtank]

Are you saying another MAF sensor from Toyota that fits in your MAF housing?

BTW--it's cool to see this kind of tech interchange.

Toyota actually makes a few sensors with the same foot print. I bought this one by accident and plugged it in to check it out. It immediately read a higher air flow and the ECU began to lower the FT% to compensate.

I never left it in long enough to see how much of a difference there was so I don't know how compatible it is with the line attached.

I looked last night and again this morning and can't find it. We cleaned for Easter and it might have been thrown away. I'm heading to a dealer to get some AC parts later on and if they have one in stock I'll grab it and at least do a quick test on it.

 

[landtank]

From re reading and studying Slee's info I think I have a fueling issue with my truck.

By disconnecting the line and monitoring the FT% I saw a 6% drop in what Slee indicates as an increase of 7.5 psi in fuel pressure. I then applied 8 psi to the FPR and expected to see the FT% to further drop again if it indeed was designed to and it did but only by a little. Since his tests shows it should have and I have all original parts it looks like it is time to clean house on my system

 

[knorrena]

Fascinating. Can we change the header for this thread to something less intriguing so Sco$$ does not read it and molest the learnings?

 

[fzjconvert]

So what does this mean for all of us that have been previously enjoying the LT MAF?

• Continue to use as-is?
• Continue to use but reconnect hose?
• Discontinue use?
• Don't do anything until Rick tests the new sensor and lets us know if we should be swapping it out?
• Send Christo a frosty one for being a rapid pit bull and settling the discussion?
• All of the above?
• None of the above?

I tell you this! If anything with LT's, mod my truck is running on the rich side. I have nothing scientific to back this up. I'm going by the old fashioned way. My olfactory senses! You see before you had all of these fancy gizmo's for testing. A guy would have to tune by what you could see, smell. I have had my share of hot rods, rice rockets, vw's and the like, making at times some respectable HP and quarter mile times. I have never blown up a motor from running to lean! That said LT's mod is staying on my truck. It just plane runs better than it did before!

 

[sleeoffroad]

For those of us who are running the LT MAF...................

What happens if the little rubber hose is just refitted?
The fuel line would see higher pressures - OK.

But then what??? If this means extra fuel was injected because of the higher pressure, surely the O2 sensor would 'smell' this and amend the fuel trim, via the ECU, accordingly (I'm talkng closed loop and not WOT open loop).

Yes, and it will adjust up to the point. however if the fuel trim goes out of prescribed spec it will throw a code. This is a clear indication that the sensor is not calibrated for the truck's systems. IE, bore diameter, response curve etc etc. We have said this all along. The amount of air is incorrectly reported to the ECU. The disconnect of the reference line was a band aid to keep the idle FT in check without understanding and discounting the importance reference signal on the fuel pressure regulator.

Rick stated that it was there to accommodate a MAF that was "inaccurate" at low air flow. That is simply incorrect.

There was a number of assumptions made and 'facts' posted about this mod that were incorrect. When we tried to point those out, we were accused of being on a witch hunt.

I sincerely hope if Rick is going to test a new sensor it is done the correct way and not just by observing fuel trims that is merely a feedback system to accommodate for minor changes that happen when the motor runs or sensors ago. It is NOT the be all end end all of how the system works.

I can also post voltage results taken at various RPM ranges for both the stock MAF and the LT MAF to show that the stock MAF does not saturate. Again something that was stated as fact and never proven or shown. It was concluded from observing fuel trim values that were reported as 0's, or as Shaun and Rick stated the 02 sensors went off-line. Well, that turned out to be merely a function of the Autoenginuity software that posts 0 for fuel trim when the truck is in open loop.

 

[sleeoffroad]

Just to add fuel to the fire, pun intended, remember that with my wideband and around 8psi boost I never saw a lean condition in open loop operation including in prolonged periods of WOT. I don't think that the danger is "dangerous" leaning but obviously as I've measured and shared all along all our rigs are all "leaning a little" with this LT MAF MOD, and, as I've measured and shared all along "that's what makes it so wonderful".

My question to you is to check if you get the same behavior with the FPR disconnected with a stock MAF. My feeling is that the drop in fuel pressure is the source of your lean condition vs the MAF readings. Again, little more lean might be a good thing in your case, but Toyota tunes motors rich for a reason.

We have many more questions to ask and answers to answer though. And also as I've stated so many times I hope that we will all stick to scientific methodology and let the data deliver answers instead of what we want to be true.

That is all I have asked for all along. Proof of the statements made.

 

[Romer]

Thanks Christo for doing the testing, gives us info to ponder.

I hope this doesn't make Rick decide to give up on creating products. This is all part of development.

It seems more of an issue for my Boosted truck than Sarah's stock truck.

Rick's housing provides much better airflow for a boosted truck, finding a sensor to meet specs there would be something worth pursuing.

Christo, if you want I can bring my truck by and you can run the same tests or others you might think of on a SC truck with the LT MAF and with the Stock MAF. I will likely swap them before Moab so I can see how the Stock MAF does on the way to Moab. May leave Sarah's in though . . need to ponder.

 

[Romer]

It was suggested to me that I should try and just put the FPR hose on and see how she runs before I swap them. What are your thoughts on this?

 

[sleeoffroad]

Rick's housing provides much better airflow for a boosted truck, finding a sensor to meet specs there would be something worth pursuing.

There is no evidence that the stock MAF is restricted other than peoples perception when they look at the design. Yes, Rick's is more open, but that does not mean the stock one is restrictive in any way based on the vehicles air requirements. There is also no calibrated air flow numbers to support the claims that the sensors flows better or reads better.

Christo, if you want I can bring my truck by and you can run the same tests or others you might think of on a SC truck with the LT MAF and with the Stock MAF. I will likely swap them before Moab so I can see how the Stock MAF does on the way to Moab. May leave Sarah's in though . . need to ponder.

Thanks for the offer, but as it is, we have devoted quite some time to this. Not sure what else if would help if we spent more time on it. I just wanted to point out the facts we posted and subsequently considered to be incorrect.

 

[TrickyT]

...
Photo 1. - Fuel pressure at idle. All systems Stock. FPR connected to intake manifold, so it would be receiving a vacuum signal at this point. Pressure ~ 37.5 PSI...

Christo,
If we had one more data point, the vacuum manifold pressure when the FPR was connected to the intake manifold, we could make a simple three-point graph of manifold pressure versus fuel rail pressure for low-speed and high-speed fuel pump settings. Such a graph would help indicate if the FPR behaves linearly. Would you be willing to remeasure the "all systems stock" configuration again but with a vacuum gauge connected this time around?

 

[sleeoffroad]

Christo,
If we had one more data point, the vacuum manifold pressure when the FPR was connected to the intake manifold, we could make a simple three-point graph of manifold pressure versus fuel rail pressure for low-speed and high-speed fuel pump settings. Such a graph would help indicate if the FPR behaves linearly. Would you be willing to remeasure the "all systems stock" configuration again but with a vacuum gauge connected this time around?

It is not needed. The factory regulator is a 1:1. You can see that if you connect pressure to it and gradually increase the pressure. How close to linear I do not know but that is the intent. Unlike a rising rate that has different ratio's. Also not sure what it would matter if it is linear or not. The point is that the reference port is there for a reason and that the system is designed to have constant pressure differential between the fuel rail pressure and the manifold pressure.

 

[turbocruiser]

I can also post voltage results taken at various RPM ranges for both the stock MAF and the LT MAF to show that the stock MAF does not saturate. Again something that was stated as fact and never proven or shown. It was concluded from observing fuel trim values that were reported as 0's, or as Sean and Rick stated the 02 sensors went off-line. Well, that turned out to be merely a function of the Autoenginuity software that posts 0 for fuel trim when the truck is in open loop.

That's not really right; if it was the Auto Enginuity would show 0's on open loop with Ricks MAF as well. Anyways for posterity purposes I never stated (AFAIR ... R= Remember) that the sensor's went off line. That wasn't my mistake; my mistake was thinking that open loop equalled 0's. I only thought that with the Stock MAF; as soon as I placed the LT MAF I then thought that the 0's equalled the stock MAF "saturation". Anyways, posting voltages would help us here but I just wanted to correct these two things. Signed, SHAUN.

 

[landtank]

as far as the statements about the MAF sensor. it stopped increasing in air flow at around 23lbs and at that same point the O2 sensors stopped reporting also. With my MAF installed I don't ever remember seeing that on any of the log files regardless of how hard Shaun pushed the truck. We also saw the same thing when Romer data logged his truck.

I don't see how this could be our engenuity software. How would that software know there was a different sensor?

In my field of work when a sensor stops reporting data it's considered being saturated, sorry if that term doesn't transfer over here.

 

[landtank]

I tried the other sensor today and while it reported a higher level of air flow it wasn't enough to bring the FT% back in line with the vacuum attached. To do so I would need to decrease the ID of the housing with a sleeve and right now I'm heading out for a trip and can't do anything on that until afterwards.

The other option would be larger injectors if they came in the correct size.

 

[sleeoffroad]

as far as the statements about the MAF sensor. it stopped increasing in air flow at around 23lbs and at that same point the O2 sensors stopped reporting also. With my MAF installed I don't ever remember seeing that on any of the log files regardless of how hard Shaun pushed the truck. We also saw the same thing when Romer data logged his truck.

I don't see how this could be our engenuity software. How would that software know there was a different sensor?

02 sensors never stop reporting. The ECU might not use the data but they do not go off-line. We have a Toyota Scan Tool and I can assure you that never happens.

Here is an extract from a file Shaun sent me. Shaun can verify, this is line 72-81 in the Excel file he sent me. - First Run STOCK MAF.XLS

STFT % LTFT% RPM B1S1 (V) Throttle Position %
-3.9 3.12 4579 0.82 57
2.34 3.12 4166 0.1 57
5.46 3.12 3173 0.73 68
0 3.12 3320 0.92 73
0 3.12 3607 0.92 74
0 3.12 3704 0.93 75
0 3.12 3931 0.935 75
0 3.12 4026 0.94 75
0 3.12 4273 0.94 69
0 3.12 4432 0.94 56

(Sorry can't get the columns to format)

This is a part of the file where the truck was under WOT (probably highest airflow, but can't verify since the file did not have air flow logged), so that is open loop. The 0's are the fuel trim as calculated, but the 02 sensors are on-line as can be seen from the 02 sensors voltage readings. The only places in the files where the 02 Sensor voltage goes to 0 is where the throttle position sensor is 12% with RPM"s higher than idle. (ie, foot of the throttle and you have a fuel cut situation).

I have both LT MAF and stock MAF files and in both there are places where the FT is 0 but nowhere is the O2 sensor voltage 0, except for the times when you are in fuel cut. I can post the files to my site if Shaun is OK with it.

As for reported airflow. What is the voltage produced by the stock MAF vs your MAF at WOT under load? Not the reported air flow volume as calculated by the ECU? Did you graph the voltage during the RPM band to show that the voltage curve flattens out or saturates?

 

[landtank]

Everything was read through the OBDII port.

With the stock MAF the airflow would increase to @24lbs (from memory) and since the display for RPMs were still increasing we assumed that the air flow was also.

Simultaneously when the air flow value would become stagnant the O2 sensors would stop displaying any value and display a 0.

With my MAF the air flow would continue to display a value up to 36 lbs (from memory) and the O2 sensors would continue to display a value.

Unfortunately you need to be boosted to see this happen so Shaun would have to be the one to run it again or Romer who also saw the same thing.

 

[sleeoffroad]

Everything was read through the OBDII port.

With the stock MAF the airflow would increase to @24lbs (from memory) and since the display for RPMs were still increasing we assumed that the air flow was also.

Simultaneously when the air flow value would become stagnant the O2 sensors would stop displaying any value and display a 0.

As in the voltage was 0? or the fuel trim was show to be 0? I looked at the one file Shaun sent me and there are no 0's except for fuel cut situations. 02 sensors does not and can not switch off.

With my MAF the air flow would continue to display a value up to 36 lbs (from memory) and the O2 sensors would continue to display a value.

The air flow value is calculated from the voltage (of the MAF sensor). The calculated value means nothing, unless you know the voltage and if it is calibrated to the housing diameter. So for all intents and purposes 36 could equal 24. That is what I have been saying all along. How do you know 36 means 36? You have to read the voltages and not the air flow calculated value to see what is happening. That is the whole sensor calibration part.

Unfortunately you need to be boosted to see this happen so Shaun would have to be the one to run it again or Romer who also saw the same thing.

 

[landtank]

0 as in the value on the display was 0, I don't know any other way to convey this. I took it as being off line since it didn't look like a voltage value, just a 0.

I guess 36 could be equal to 24 but the vacuum line was removed because it was reporting too low of air flow. Also on stock trucks the air flow in pounds was rather close (2lbs from memory) at WOT which is just a couple of pounds short of that point where the boosted trucks would flat line. That would mean a spike in air flow just after entering boost which I don't remember seeing.

The accuracy of the air flow aside, the O2 sensors where definitely displaying a voltage well beyond the rpm point when the stock MAF was in place. And the voltage was within the expected range.

 

[turbocruiser]

Well, I think that I came to this after-party "fashionably late" . Christo you are welcome to post the logs if you would want although I remember you were wanting calculated load as one of the variables and I don't think that any of the logs I sent to you took load into consideration. I know I have some Stock MAF and LT MAF runs with those on them as well as with airflow on them. Might be better to find those first and post apples to apples.

Again, I want to emphasize that with the LT MAF the rig never read the 0's as with the Stock MAF; IOW I was never able to find the "saturation point" as I called it commonly even when it was reading 36.6 lbs air (off of my memory here so several grains of salt are recommended ) at 99% calculated load and over almost 5K rpms.

I also again want to emphasize that when we were running the stock MAF and saw the 0's we assumed that was open loop operation and it closely correlated with what was obviously open loop on my wideband. It wasn't until we swamped to the LT MAF that I realized I was in open loop on my wideband but the MAF was still reading strong.

Whether it is saturation of the Stock MAF or something else, one thing that is completely clear to me is that I couldn't find that point through LT's MAF. The calibration concern is a whole other worry and I cannot conclude anything on that without testing on some sophisticated equipment. Anyways again with the LT MAF there was no "saturation point" and there was no leaning past the point of 10.8 AFR at prolonged periods of WOT. That to me and to Rick was an amazing achievement considering that the Stock MAF the rig was reading 0's at around 60% load, getting stinkin rich and all the other things it definitely does do in terms of the shiftpoints etc.

All it took was one little look at the tests that you did (and thanks again for that truly) to see the relationship with the Fuel Pressure Regulator and boost and vacuum and the reference to Intake Manifold but as I've stated time and time again we still have many more questions to answer. Still, as you told me time and time again, the wideband has wisdom and so does scanner technology to a proper point and I can say with complete certainty that we never found the true "saturation point" or a truly troubling "lean point" with Ricks MAF. Is this the end of our equation, no clearly not, so, let's keep learning ... I love it all.

 

[Buckru]

Nothing but good, open dialogue between all posters in this thread.

Thanks,

Buck