maftpro or lexus afm????

[moorman]

So you are saying that fuel cut is ONLY because of too much intake air? That is not correct. What if he was hitting fuel cut because the fpr was disconnected? What if he was hitting fuel cut because he had a big boost leak? What if it was running too rich because of incorrect afc settings? There is a lot more to it then you are implying. And furthermore, the ecu triggers the fuel cut because it can not supply enough fuel for the air metered going into the engine (injector duty cycle maxed out) , so if he gets a maft he still has the problem and still gets fuel cut.

Running too lean will not trigger fuel cut, the ECU isn't smart enough for that (what a shame too...what a life-saver that would be!). I have run too lean. A good example...... I was diagnosing a vacuum leak some time ago, and in troubleshooting I decided to plug all vacuum ports.....absent-mindedly including the one going to my fuel pressure regulator. No FP increase with boost (16psi), NASTY detonation, but no fuel cut.

The function behind the Lex AFM changing the point where fuel cut happens is *entirely* because the ECU believes there is less air. (NOTE: this isn't to say more values don't contribute to when & where FC happens, but that Karman frequency is a very LARGE factor)

If you're hitting fuel cut and drop in a Lex AFM and do nothing else at all, you'll run deathly lean, but you'll stop hitting fuel cut. (for the kids watching at home: "deathly lean" means "don't do it")

 

[bigaaron]

Exactly, you can:
1 "fix" your fuel cut "issue" by running way lean, and blow up the engine.
2 buy bigger injectors and not get (or need) fuel fuel cut because everything is right.

Something IS wrong with the fuel system if you hit fuel cut, you don't have the correct injectors.
Fuel cut is just stopping major engine failure.
Fuel cut is when the "stupid meter" hits 10 the car makes the right decision for you and shuts itself off for a sec.
When I had the stock injectors the karman freq was 1500hz+ at 15psi and it would hit fuel cut. Now with a maft and 550cc injectors the freq is about 1250hz at 21psi at 11 to 1 afr and no fuel cut. One time my stock fpr vacuum line popped off at 20psi and thank god the fuel cut kicked in. When I get my bigger turbo on there I bet the karman freq will be 1250hz at 15psi because there will be more air flow at lower pressure.

 

[Allan_MA70]

if you got cams/head work/manifolds you would flow more for the same pressure.

IJ's is an ideal example at only 18psi the thing hauls ass like other 7m's at 25psi

The one major issue the lexus and other AFM replacments fail to address is ignition side of things the stock ecu still thinks 1200hz is like 80% throttle and still has the ignition advanced as such.

 

[moorman]

Exactly, you can:
1 "fix" your fuel cut "issue" by running way lean, and blow up the engine.
2 buy bigger injectors and not get (or need) fuel fuel cut because everything is right.

Something IS wrong with the fuel system if you hit fuel cut, you don't have the correct injectors.
Fuel cut is just stopping major engine failure.
Fuel cut is when the "stupid meter" hits 10 the car makes the right decision for you and shuts itself off for a sec.
When I had the stock injectors the karman freq was 1500hz+ at 15psi and it would hit fuel cut. Now with a maft and 550cc injectors the freq is about 1250hz at 21psi at 11 to 1 afr and no fuel cut. One time my stock fpr vacuum line popped off at 20psi and thank god the fuel cut kicked in. When I get my bigger turbo on there I bet the karman freq will be 1250hz at 15psi because there will be more air flow at lower pressure.

Our points are crossing paths somewhere, but missing eachother. I run 440s. I've run 23psi. Fuel injectors will not affect when fuel cut happens. If need be, I can go out and re-tune so that I'm hitting FC at my daily 16psi, yet still have AFR of 11:1. The wideband can log so you can see my results.

If fuel cut was based on AFR, it would be impossible to run too lean, you'd just hit fuel cut. In your circumstance, when a hose pops off (especially at 20psi) you get a boost leak and boost pressure falls. When your boost controller sees boost pressure fall, it allows the turbo to spool more to keep boost pressure at 20psi.....this sucks in more air past the AFM, increasing Hz into FC range (but boost gauge will still read only 20psi). Same thing happens when you have an IC piping leak, except you aren't losing fuel pressure at the same time, so you run rich & hit FC instead of lean.

In my example, there was no boost leak....there was only lean since my FPR port was capped rather than open. KV freq remained the same as usual, so no fuel cut, despite there being an obvious problem with my fuel system.

I really wish the ecu behaved as you say, because it would be much more fool proof.

The one major issue the lexus and other AFM replacments fail to address is ignition side of things the stock ecu still thinks 1200hz is like 80% throttle and still has the ignition advanced as such.

Ya. If you've got a way to keep detonation at bay, the extra timing is good. Without detonation suppression of some form, I think it's best to adjust FC such that turning up the boost a few psi will push you into FC. That way you retain *some* form of protection against a faulty wastegate, and minimize the timing advance at the same time.

 

[Nick M]

What if he was hitting fuel cut because the fpr was disconnected?
--------------------------------------------------------------------------------

A manifold leak will raise the airflow meter reading. And it raises fuel pressure.

What if he was hitting fuel cut because he had a big boost leak?

Then the air flow meter meter reading will rise.

What if it was running too rich because of incorrect afc settings?

If you alter the airflow reading to the ECU and make it think to more air is coming in, your mixture will richen. And eventually boost cut will be the result. If you trim it lower, you will raise boost cut becuase the ECU thinks the airflow reading is less.

There is a lot more to it then you are implying. And furthermore, the ecu triggers the fuel cut because it can not supply enough fuel for the air metered going into the engine (injector duty cycle maxed out) , so if he gets a maft he still has the problem and still gets fuel cut

Yes, the ECU triggers boost cut because too much air for the fuel system Toyota gave the car is inadequate. Yes, your points overlapped. The AFM is the main input to the ECU.

 

[bigaaron]

I was replying to this:

i wouldnt necessarily say something's "wrong" with the fuel system... it kindof sounds misleading.
-shaeff

I was making an arguement for my reasoning behind saying something is wrong with your fuel system if you are hitting fuel cut. If you take everything I said out of context it is easy to argue with.

Fuel injector size WILL affect the afm reading when running a maft. Why, because it scales the output frequency to match the injector size.

I can go out and re-tune so that I'm hitting FC at my daily 16psi, yet still have AFR of 11:1

Right, you don't have big enough injectors! Are you saying that you have it now tuned at 14:1 so you dont hit fuel cut? Everything I have been talking about is with reguards to running a maft. I can run 20psi and be at 10 to 1 with no fuel cut, with a maft and 550cc injectors. And that is at full throttle in any gear under any load situation at any rpm. You have run 23psi on 440cc injectors. That's nice....and why would you want to do that? Push stock components to the limit to see how far you can go without blowing up on your own engine, but don't recommend that to others who may not have a full understanding of what the concequences could be. I would rather do it right then do it cheap.

I made 4xx whp on 440's
I run 2x psi on 440's
I run xx to 1 afr and it didn't blow up

All those statements would make me say: WHY?

 

[suprahero]

WOW!!!!!Some of you guys should own a dang T.V> show on how to thorughly confuse the already confused. I really do appreciate all of your help and suggestions, but I'm not any closer to knowing what to do about my fuel cut. I guess there is no miracle answer, because it can be one of a hundred problems causing it. I think I'm just going to order the maft pro and try it out. If I need to I will then buy some 550 injectors. Does that mean that I need a walbro 255 fuel pump? Will I need bigger injectors? I'm really not trying to run more than around 13 pounds of boost. If I buy the Maft pro, do I still need the gm afm? Would I do away with my safcii? Thanks alot guys.

 

[bigaaron]

All arguing aside, I don't think anyone in their right mind would say that it is not a good idea to get a set of bigger injectors to go with your maft for higher boost, if you can afford it.
You don't need them for 13psi but it gives you a safety margin. As soon as you see what 13psi is like you will want to know what 15 is like, then 17....
You don't have to have a afc with a maft or maft pro. The maft pro is more tuneable, the maft is very basic, but both have afc-like adjustments.
Upgraded fuel pump would also be a good idea, if you have the money. My origional point relating to what SUPRAHERO said was that if he had fuel cut before, the maft will not really fix that, unless you use it WITH 550cc injectors.

 

[suprahero]

Thanks Bigaaron, money is not a deciding factor in all of this. I'm going to get what is best for my car. I need 550's and a new fuel pump. Do I need to go ahead and buy the maft pro as opposed to the maft? I'm sure it will help me later on if I decide to upgrade some more. Thanks for your help.

I also want to order an intercooler from you. I will email you what I need and you can tell me how much I owe you for a few couplings and odd items. Thanks.

 

[bigaaron]

Thanks Bigaaron, money is not a deciding factor in all of this. I'm going to get what is best for my car. I need 550's and a new fuel pump. Do I need to go ahead and buy the maft pro as opposed to the maft? I'm sure it will help me later on if I decide to upgrade some more. Thanks for your help.

I also want to order an intercooler from you. I will email you what I need and you can tell me how much I owe you for a few couplings and odd items. Thanks.

The maft pro sounds really cool, I am ordering one myself. The map sensor option is the way to go. Any type of air flow meter will not be as reliable as a map based system. If you pop a ic pipe, it still runs. A small vacuum leak will not be a big problem. No more stalling from your vented bov. It's around $600-ish for the whole setup from Dr Jones or www.fullthrottlespeed.com

Sorry if it got all complicated but obviously everyone has their own opinion and experiences. I don't want want to come off as a know-it-all, I just give my best advice and you can take from it what you will. If my advice is wrong them I am sorry but I only speak from personal experience.

 

[shaeff]

wow. there's so much information in this thread, that i bookmarked it. kudos to you all for A) good info, and B) keeping the discussion very calm and cool. thanks.

by the way, i'm going MAFT pro, too.

-shaeff

 

[MKIIITrbo89]

Just wondering, how does the maftpro rank against something like the Greddy E Mange Ultimate. Haven't really heard of many people using this and was just wondering.

 

[bigaaron]

Larger fuel injectors will affect your maft tuning which will lower the karman freq which will affect the point when fuel cut happens. So fuel injector size will determine how much boost you can run before fuel cut. Riddle me that!:icon_razz
Anyhew, I rarely get mad about Supra arguements :rant:,
I come here because I enjoy the discussions. :nuts:

 

[moorman]

Are you saying that you have it now tuned at 14:1 so you dont hit fuel cut?

No, that isn't what I'm saying at all, because AFR has nothing to do with fuel cut. My current AFR's are 11.5:1. The time I ran 23psi, AFR was 10.8:1. However, let's not turn this to a discussion on what can and can't be achieved w/ 440's. I was offering up a means to factually demonstrate that FC can happen....or not happen....with the same injectors, the same boost, and the same AFR. The KV frequency is the value that will change between the two scenarios.

Everything I have been talking about is with reguards to running a maft.

Everything I have been talking about is regarding fuel cut. The method you use to meter the air is irrelevant, because the ecu doesn't know the difference. It understands a KV frequency, either from the actual KV meter, or from some other meter that translates its output into the voltage that corresponds to the KV freq. It's all about manipulating that particular signal when your intent is to manage fuel cut.

 

[moorman]

Larger fuel injectors will affect your maft tuning which will lower the karman freq which will affect the point when fuel cut happens. So fuel injector size will determine how much boost you can run before fuel cut.

WOOHOO! We have the merging of points! :bigthumb:

...and agreed. Nobody's mad, we just lack the communication skills to make our points mesh.

 

[bigaaron]

It understands a KV frequency, either from the actual KV meter, or from some other meter that translates its output into the voltage that corresponds to the KV freq..

What does Kilovolts have to do with this, this is low voltage stuff. :biglaugh: :icon_razz :icon_bigg :naughty: :nono:

 

[Nick M]

I dont see any arguing. It is just information.

Arguing is "hey dumbass, you dont know what you are talking about"

I think the MAFT-Pro is a great idea. Some of the older ones here know how much a Vein Pressure Converter, PFC-Fcon with FCD, graphic control computer for trimming the signals and the 550's, you had a few grand just in electconic parts. And there wernt many alternatives like now. Now is the good times.

 

[Allan_MA70]

lucky ignition is not important! :slap:

but your car wont stall with your venting BOV :bling:

love peoples priorities! :aigo:

 

[moorman]

What does Kilovolts have to do with this, this is low voltage stuff. :biglaugh: :icon_razz :icon_bigg :naughty: :nono:

:icon_bigg Not sure....I just posted up what that Karman freak told me to type.

 

[bigaaron]

lucky ignition is not important! :slap:

but your car wont stall with your venting BOV :bling:

love peoples priorities! :aigo:

Most car owner priorities: (i'm not totally excluded either)
1: looking cool
2: being "different"
3: buying lots of aftermarket stuff
4: being fast
5: looking cool
6:
7:
8:
9:
10: functionality of aftermarket cool looking stuff
:biglaugh: