You know he's right Harold...

 

But I'm learning some things....

1. airflow through the MAF sensor is all-important to amount of delivered fuel, closed-loop or open-loop.

2. increased airflow of 3.5 through stock MAF accounts for 3.5s running very rich.

3. slight changes in airflow through MAF sensor has major effect on A/F. Laminar airflow through the 3" MAF needs serious improvement.


I don't want any add-ons I don't need, and nothing that might change timing. I find that the A/F is independent of RPMs and throttle opening, once above idle. Since I'm not late for anything here, I'll continue to explore while I build my newest Shift_Fast_3 and install the dual-stage dual-bottle NX spray. I'm not adverse to technology if properly applied - but I need to feel it's necessary.

 

Yeah, from one viewpoint he (and you) are right. But I felt the need to explore the 3" MAF some more, and I find that airflow through mine is not laminar, especially at low RPMs.

At least I know now why all 3.5s into 4th gens are rich, and why changing the fuel pressure on my car did not affect A/F - it's the sensor air-flow that matters.

 

How about looking into retrofitting an A33 MAF into your car? Reason I state this is because if laminar flow is important to you, there are more MAF housing options for the A33 sensor which have honeycomb + screen combos.

My LRMAF has a very nice honeycomb layers (15-18mm thick, AND the normal MAF screen we have all seen (a la A32 MAF)

It be nice to see the air flow differences using the same MAF on different engines (gm / s on 3.0L vs 3.5L)



I also agree, that it greatly affects idle AFR (larger MAF housing ). I have to add 5-8% fuel when in a drive gear, and 12-15% in P or N.

But normal driving (clsoed loop / open loop / low load), it runs just fine (14.2 - 15.0) using the correction factor for the Q45 MAF.

 

Well lookee there - just the honeycomb I was visualizing..... I think I will track down one of those to look at. Thanks.

 

It dawned on me today that the real problem with trying to lean up the 4th gen car/MAF with the 3.5L engine is that I need to have a way to slightly reduce the airflow through the hotwire sensor "tunnel". Duh..

So tonight I took out the airbox/stock-MAF-with-screen combo one more time and wiped the back of the sensor post with a dab of acetone, then laid a piece of Gorilla tape up above the sensor hole coming out the back of the sensor stalk, just covering the hole with less than 1/16" of material. Bingo - starts and runs normally, and when you really nail it and go for fuel-cut, the A/F is about 12:1 through 2nd gear and drops into the 11s in third and pulling hard. Next will be some logging with the PLX and review on my notebook, but I think I've got the first solution. Normal driving is just that - normal. Tuning with tape - how weird...

It just takes a little bit of coverage over the rear of the sensor hole, and then you own the A/F/.

 

Aren't you afraid of the tape coming off and going into the motor?

 

Short-term solution. You're not joining the ankle-biters ***-ociation, are you?

 

If you're really confident on this method, a permanent solution would be to remove this tape, sand the back of the hotwire tunnel with a rough-gritt sandpaper, and apply the equivalent amount of JBWeld to cover the same area that the tape did

 

Now that's a good suggestion! I may not be able to get the tape off, though. The acetone wash and Gorilla tape adhesive make a really sticky combination. Of course the gasoline fumes will dissolve the tape sticky pretty soon...

I was floored when this method worked so well - and the amount of blockage required is so little and so sensitive to tunnel area covered up, it confirmed my feeling that the airflow sensor is critical for A/F control. I gotta do a flash photo of the tape before making this mod more permanent.

How did you handle your MAF install? Details welcome...

.

 

Maybe.

 

Wait though, by altering the airflow going through the maf it's essentially doing the same exact thing that an AFC would do afaik? If you don't want to use an afc to alter the maf voltage because of the timing effects, well in essence altering the airflow over the maf is doing the same thing except it's 1000X more complicated.

As I understand it, the less air the ecu thinks is going through the engine (whether that be affected by altering the air passing over the film, or by the actual signal, see how they are the same thing yet?) Than the less fuel and more timing the ecu is going to run, using an afc to tune is going to put you in the same map's that altering the actual maf is no?

The alternative, to the e-blue, would be to actually lower your fuel pressure as much as possible and get the thing to run chicken lean instead of pig rich, than you can alter your maf voltage the other way so it thinks more air is going in therefore reducing timing and adding fuel! You'd have to tune your nos jets differently obviously for the lower FP, and at some point you will max out the duty cycle of your injectors (adding de-k/Z ones would help), so you would need to see the duty cycle of them first. But someone more knowledgable in the SC section is going to have to comment on when you are going to be pushing the limit's of the maf.

Regardless though, I'm under the assumption that you are doing with the maf the same thing you would be with an afc, or am I wrong?

 

FYI: If you get the additional injector harness, Eblue doesn't alter MAF signal, it alters / uses actual injector signals.

 

^ By default it does. If you get the optional injector harness you can increase duty cycle, but can't alter the pulse width directly like you can with the EU.

 

My intention was to get the A/F back to the 3.0 values (or close, anyway). Since the pig-rich A/F was being caused by the excessive air flow being sucked into the 3.5L, eventually I tried blocking off just a little of that airflow as it exits the hot-wire sensor tube in the MAF.

I tried various forms of a 3" MAF and got all sorts of lean readings, even put a collector horn on the sensor tube - which helped some - played with the fuel pressure a lot - which didn't change anything, and my little piece of tape is still the best A/F mod I could create. It starts and drives well, the A/F and timing is back to normal WOT values, the engine seems to run stronger now, and I can still tune-by-tape. Remember, the ECU, MAF, internal engine timing stuff, and everything else is stock 1999 parts for a 3.0.

Now I can get back to spray. and not have to worry about what weird things piggybacks are going to do to complicate my life. I don't need to change injectors - or fuel pressure - or duty cycle - and timing is back to a normal WOT 3.0. And nitrous jet sizes are back to normal... Not bad for a piece of tape, eh?

Of course I'm not done here - but this tune-by-tape mod lets me go on with the re-installation of the dual-NX nitrous setup.

.

 

I can guarantee you that your car isn't running rich because the 3.5 "swallows" more air. The larger VQ35 injectors and/or higher base fuel pressure are likely to blame. VQ35's don't flow that much more air than 3.0's (except maybe at high RPM), and certainly not without a functioning CVTC system.

 

Let's see ... the fuel pressure is normal - usually 43 psi, and I did lower it a lot with no discernable change in A/F, as have others here. The 3.5L has a 70mm intake tract from air box through TB, the intake is SSIMed. Betcha the air flow is a lot higher than a 3.0 w/MEVI - especially at high RPMS, which is what I'm concerned about. The 3.0 didn't have CVTC either, and my 3.5 has the clone S1 cams as well. Since the displacement is higher, the engine will need a larger injector to compensate for the 3.0 stock injector map at WOT.

The actual WOT air flow at any RPM is at least 16.7% higher than the 3.0, due to the increased displacement size. The other intake mods just make it higher than that. And the stock MAF sees it all...

IMHO....

 

http://forums.maxima.org/showthread....4568&highlight=

The higher airflow could be by virtue of the cams and/or intake mods and not necessarily displacement alone. Either way, moot point.

 

Interesting thread -it goes in a lot of different directions with varying conclusions...

For WOT open-loop conditions, up to stock fuel cut, does anyone really believe that the 3.5L will not move appreciably more air through a stock MAF than a 3.0? Due to the 16.6% larger displacement? Let alone the differences between the 3.0s 60mmTB and smaller IM passages vs. the cammed 3.5s 70mm intake passage and TB and SSIM? Both using the stock MAF?

.



.

 

My MAF readings change when I toss a new intake on (rightfully so).

Both MAF's are 70mm ID. (A32 / A33B)

A SAFCII could tell you that, if you ran it w/ both engines, vaguely .

All we need is flow rates documented for both engines using the same TB / MAF housing.

W/y stock MAF housing, I was seeing nearly 75% airflow, now, w/ the 82mm, I rarely get 52%. 58% w/ a JWT POP.

 

16.6% greater displacement does not necessarily equal 16.6% greater airflow @ every RPM.


Besides that, the 3.5 has larger injectors. I simply don't see how the slightly higher mass airflow rate on its own would make the car pig rich. The VQ35 makes the majority of its increased HP and TQ over the 3.0 by virtue of it's geometry, not necessarily by significantly higher mass air flow alone when compared to a similarly equipped 3.0.

 

1. I didn't say it did - just that the larger displacement will move appreciably more air through the MAF. And I think that at WOT my 3.5 inhales a LOT more air than a 3.0 does. Especially a stock 3.0, which the MAF and ECU was designed for.

2. Skipping the "HP and TQ" arguments, I found that blocking a very small amount of air passing through the sensor tunnel had major effects on the A/F. The extra airflow makes a huge difference in how the MAF sensor - and ECU - interprets the extra airflow. I really gotta photograph the tape I installed - its very small, but has a huge effect. The first tape patch covered a little more area, and the A/F went very lean - even in closed-loop. Weirdness.

How many people that have done the 3.5L/3.0-timing conversion have complained about being extremely rich? Most, I think.

 

This I will respectfully disagree with. An engine's mass airflow rate at a given RPM has as much to do with cam profile and valve timing, intake and exhaust port design (and the interport flow relationship therein), intake manifold design, rod/stroke ratio and other things as much as it has to do total engine capacity.


I guess we'll have to agree to disagree. The displacement increase alone is not responsible for your richness, IMO.

Besides, how could increased airflow over the MAF cause a rich condition anyway? If the MAF sees more air, more fuel will be added. Sure. But more air over the MAF equals more air into the engine to go along with the added fuel. So I don't get it...


That can be easily explained by larger-than-stock injectors and higher base fuel pressures that are typically run methinks.


Either way, it's great that you thought outside of the box and found a cheap and easy solution to your ends.

 

Yeah, and I've been shopping for E-U 's as well.....

Something about extended rev limits, I hear.

Thursday EDIT: I just downloaded a logging file from the PLX and ran it - It was a 2nd-gear blast up to nearly 6K, and the A/F held at 12.5:1 all the way! Yes!

.

 

Here is the PLX graph from the one highway on-ramp WOT run I made. The second peak is 2nd gear.





Shows how well the tape can work to tune the A/F... No more pig-rich 3.5L. Next will be a WOT 1st-2nd-3rd-gear run...

 

took me a minute to figure out how to read the 2 graphs together, but now that I fugred it out, not bad at all. Actually, 12.5:1 is leaner than what the 3.0 ECU usually does on the 3.0s (I saw constant 11.9-12.1 WOT before ever tuning the old 3.0.

I think your a/f is perfect enough for some good ol laughin gas fun (to your its good, I still prefer my Boeing turbine ) .... I say you boost it 8psi on top of a 100shot..... OMG thats an 11 second run guaranteed!

 

Well, at least you figured out the graph! Clever South Floridians.... Yeah, the A/F looks much better now. I was out terrorizing tourists this afternoon and got three more PLX logs. Looking good in 1st, 2nd and 3rd.

I'm starting another thread in All Motor for Tune-by-Tape, so join me there...

(and yes, RMT turbo + spray would be a monster )

 

dont tempt me grey, Im not selling this car until i graduate in another year.... means i have a whole other year for Maxima fun before I turn over to the dark side of BMW lol. Some spray may just take place before I let her go, lol That turbo sure would love a 75 shot :-X!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

Yes it would, iv done it a couple of times. 35shot on top of 10psi, and it was rather scary lol. Tried with 50 and it was useless (on the street at least), no traction whatsoever, on any gear lol, well only tried 1st and 2nd, it just felt like i was doing a burn out lol.

 

Wow, the gearheads have spoken ..... I, too, have a PLX data log too. ...

 

I remember seeing one of your posted log files - that's what sold me on the PLX.

And I always though of you as a gearhead too ...

 

Good ole lankshark burrrr

 

I spent all of today building the 5-solenoid and 3-relay rack for N2O (one solenoid/relay pair for purge solenoid). Two heated 15lb bottles as well. Just need to design a common manifold for the two bottles to regulate pressure.

The LandShark is getting ready to go hunting....