Max voltage for KA24DE MAFS?!? And ignition timing question

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MarkEmark
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I tried searching for the exact specs but couldn't find it on this forum...

I hear many people speaking of "maxing out" the MAFS...I want to know at what voltage this ocurrs. Because I think I am maxing my MAFS out past 5000 RPM in first, second, third and fourth gear....

My Blitz R-VIT measures the airflow as 5.11 volts past 5000 RPM in all these gears.

If I am "maxing it out," what's the negative effects of this? By the way, I am only running 9 psi, and past 5000 RPM (when the MAFS is showing 5.11 volts), my boost is only around 7-8 psi MAX, and this is from a T3 super 60.

Also, I'm running a JWT ECU and some of the timing measurements I got don't seem to make sense...the timing is retarded more @ 5000 RPM than it is at 6000 RPM and 7000 RPM, in every gear...BUT, there is more boost at 5000 rpm than their is at 6000 rpm and 7000 rpm...but I didn't think the JWT retarded timing based on boost....

For those of you interested, here's some specs on the timing...

1st gear 4000 RPM (full boost), 13 BTDC1st gear 4500 RPM, 13 BTDC1st gear 5400 RPM, 15 BTDC1st gear 5850 RPM, 17 BTDC1st gear 6787 RPM, 17 BTDC

2nd gear 5000 RPM, 15 BTDC2nd gear 6000 RPM, 17 BTDC2nd gear 6762 RPM, 18 BTDC

3rd gear 5000 RPM, 14 BTDC3rd gear 6000 RPM, 17 BTDC3rd gear 6762 RPM, 18 BTDC

4th gear 5000 RPM, 12 BTDC4th gear 6000 RPM, 17 BTDC

Timing at idle is 20 BTDC.

I was going to advance it to 22 BTDC at idle because i've heard the timing for the JWT is real conservative, so everyone of those numbers would be advanced 2 degrees...is that safe or should I leave it at 20? I mean I could always go back to 20 if after advancing it to 22 it started to ping, but the engine has NEVER pinged to date.

Anyway, help is appreciated, thanks.

PS--Can anyone find a graph or chart showing o2 sensor voltage v. air/fuel ratio? The only one I can find is on http://www.splitsec.com, but a few days ago I found an autometer graph showing 02 voltage v. a/f ratio and now I can't find it.


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klattr1
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thats some good info and researching you are doing. the timing maps on the jwt ecu seem about right. im sure you could get away with 3-4 more degrees advance effectively but i dont want you to learn the hard way (set timing according to full service manual).Im getting 14-15 degrees WOT on my JWT ecu and I now run 4 degrees advance at 17 psi daily driven on pump gas.Well, if you are getting more than 5V as a reading then its time to switch to a Z32 MAFS (N62? i think)Do you have the JWT stock mafs/370cc injector program as of now? I'm sure you could account for the Z32 mafs with a SAFC or something similar but I couldnt imagine you boostin more than you are with those 370cc injectors though.Air Fuel Ratio/Voltage 17.1:1/.10 16.5:1/.20 16.0:1/.30 15.4:1/.39 14.9:1/.49 14.4:1/.59 13.8:1/.69 13.2:1/.78 12.7:1/.88 12.1:1/.97

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MarkEmark
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I think I'll advance it to 22 deg BTDC @ idle and see how it performs....if I hear a single ping I'll just back off...I hope it doesn't ping because my air/fuel ratios seem rich enough, and along with 93 octane, an efficient intercooler, and alcohol injection it should be good.

I'm running the JWT + 370cc turbo program, stock KA MAFS.I don't have SAFC or anything to account for the larger MAFS...I'm just very surprised that I'm maxing it out at no more than 9 psi (past 5000 RPM when I am maxing it out, the boost is around 7.5 or 8 psi).

What exactly is the harm in running a MAFS with the voltage maxed out past 500 rpm????

According to that chart my a/f ratio is mostly around 12.5:1 past 5000 rpm, which seems pretty good. The lowest it is is .80 volts (probably 13:1) @ 5000 RPM in 4th gear, but the timing at that RPM is also a very conservative 12 BTDC so I won't worry about that. The richest it is is 12.2 or 12.3:1, which is all of second gear past 5000 RPM...but overall it seems to be close to 12.5:1 which everyone says is safe...so I guess I'm good.

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klattr1
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well since you have that Blitz device, setting your base timing correctly is easy. warm the motor up, pull the TPS and stabilize idle. Then have someone keep telling you your timing readout from your Blitz device. If your crank pulley shows the same timing number as the Blitz readout, then your timing will be stock. If you want 2 deg. more advance, then make your crank pulley show 2 degrees higher than what the Blitz readout shows. After you do all this, plug the TPS back in and haul butt. The 4 deg. advance on my car made me pick up 4mph in the eighth mile trap speed. So im guessing it picked up some horsepower. it also makes the car a little more "driveable" in a way (especially down low).I just want to make sure you set your timing correctly because too many people do it the wrong way and it ends up being like 10 deg. advance by accident.Dont trust only your 02 sensor voltage readout though. Its somewhat accurate but it doesnt show sharp changes like air fuel ratios do on a wideband (dyno). So get that thing to a dyno as well to make sure. Have fun and good luck!

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MarkEmark
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klattr1 wrote:well since you have that Blitz device, setting your base timing correctly is easy. warm the motor up, pull the TPS and stabilize idle. Then have someone keep telling you your timing readout from your Blitz device. If your crank pulley shows the same timing number as the Blitz readout, then your timing will be stock. If you want 2 deg. more advance, then make your crank pulley show 2 degrees higher than what the Blitz readout shows. After you do all this, plug the TPS back in and haul butt. The 4 deg. advance on my car made me pick up 4mph in the eighth mile trap speed. So im guessing it picked up some horsepower. it also makes the car a little more "driveable" in a way (especially down low).I just want to make sure you set your timing correctly because too many people do it the wrong way and it ends up being like 10 deg. advance by accident.Dont trust only your 02 sensor voltage readout though. Its somewhat accurate but it doesnt show sharp changes like air fuel ratios do on a wideband (dyno). So get that thing to a dyno as well to make sure. Have fun and good luck!


I'm a bit confused about that...I want the Blitz to record and show the exact timing...I don't want it to be two degrees off from the crank pulley (actual) timing...I want the blitz to show the timing that the crank pulley shows...Why does the TPS need to be unplugged? I figured to myself since I had the Blitz I wouldn't need to mess with a timing light and I'd just need to read what it was from the Blitz display.

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klattr1
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to correctly set your timing to stock (20 deg. with TPS unplugged), your ignition timing being displayed on your Blitz readout should be the exact same as the timing number coming off of your crank pulley. If they are not in sync, then you are either retarded or advanced the base timing.Unplugging the TPS and setting the timing and then plugging it back in kinda locks the ecu in place. Its in the FSM and its the correct way to do it.You said up above that you were toying with the idea of advancing your base timing to 22 degrees. So to correctly advance the base timing without having to idle down exactly to 700 rpms would be to use the method i have described above. So if you pull your TPS and your Blitz readout shows 12 deg. total timing at whatever rpm its at, then you would offset your timing on the crank pulley from rotating the distributor until your timing light shows 14 deg. Understand?

There's two ways to set your base timing to stock:1. idle down to 700 rpms with TPS unplugged and shoot timing light and rotate distributor until it shows 20 deg.2. make sure that your CONSULT timing readout device is in sync with the timing readout from your crank pulley with TPS unplugged.After you have set it, plug TPS back in and boost away.

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MarkEmark
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Damnit, what the hell's up with Nico? I posted a reply last night to this post and now it ain't there.

Anyway, I followed the FSM procedure, advanced the timing to 22 deg BTDC (according to a timing light) with the TPS unplugged...My blitz stilll shows 20 deg BTDC...Does this mean because the TPS was unplugged the blitz will never show the advancement in the timing? In other words I'd always have to add 2 to whatever number I get on the Blitz? I don't really how it won't show the exact timing anymore...I guess the only way the Blitz will show the exact timing is if the crank pulley is set at the standard 20 deg BTDC. But WHY? Does the Blitz automatically assume a base of 20 deg BTDC and then make all of its measurements off of that, so that if it were actually 22 deg BTDC then all of the other measurements would be correspondingly shifted as well?

I know the FSM doesn't say anything about this, but what if I set my timing back to 20 deg BTDC so it was synchronized with the blitz unit, then adjusted the timing to 22 deg btdc WITH the TPS plugged in...would the Blitz adjust accordingly then?

Anyway...I'll take the car out today see if it made any difference...hopefully it cured some low RPM hesitation/stumbling....

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MarkEmark
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Also, anyone care to expound upon my initial question?

What exactly happens with the MAFS is "maxed out..." is this detrimental? I assume it just means the MAFS cannot read any more air...so it thinks 5.11 volts worth (if you will) of air is going through the MAFS when it's really more....which would create a leaner situation, if I'm not mistaken (it thinks there's less air, so there's less fuel...) But according to to those 02 readings I'm not running lean at all in the upper RPM range when the MAFS is maxed out, so i think I'll just leave it be for now. I'm leaving for college in a week anyway, so all this stuff is going to have to wait :(

And does anyone know what function of the fuel injector would be measured in ms (I think milliseconds?)? Would that be the pulse-width or something? And what does this parameter tell me about the fuel system (anyone have any numbers as to when an injector is "maxing out" as well?)

Anyway, I'd rather know the answer to my timing question first :)

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klattr1
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your Blitz readout is displaying what your ecu is programmed for. There are timing maps programmed which will run certain numbers based on load (airflow) and water temps and rpms.So if your Blitz readout shows 20 degrees and your crank pulley shows 22 degrees, then you just effectively advanced your base timing by 2 degrees. So basically whenever you are in full throttle now and your Blitz shows a timing number, then add 2 to it and thats what the true number is. It kinda tricks the ecu or offsets in a way (ecu wont show your base timing advance or retard).Well, if your air fuel ratios are good then i wouldnt be too worried about it. Basically you will not be able to boost much more without the ecu being to adjust the fuel based on your airflow numbers.Injector pulse width is the amount of time the injector stays open. From that number and the correlating rpm, you can figure out duty cycle. The equation for it is: (inj. pulse width in ms x rpm)/1200= duty cycle %.Hope this helps.

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MarkEmark
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Yes that does help...

Although it kinda sucks not being able to read the exact timing right on the Blitz display...

I took the car out for a nice long ride today and the timing advance made a noticeable increase in performance...it runs better all around, and smoother too...especially in the lower RPM range where before it kind of hesitated before.

Now that I know the formula for duty cycle, I'll see what my injectors are running at. Thanks

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klattr1
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MarkEmark wrote:I took the car out for a nice long ride today and the timing advance made a noticeable increase in performance...it runs better all around, and smoother too...especially in the lower RPM range where before it kind of hesitated before.
im glad you are able to fully monitor your car now. the timing advance on my car made it feel like it should be like that in a way.I was getting 14-15 degrees timing WOT and for example, Scott at Secret Services programmed a turbo ka ecu to 21 degrees WOT at almost 11 psi on pump gas so you know it really should be fine. Just dont push the timing any further than it is.

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MarkEmark
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Did some injector pulse-width monitoring and found out that the highest duty cycles my injectors ever were at was 89.03%, at 5212 RPM in 4th gear...they were mostly around 85% though in all gears...Which is good, it means I'm not really that close to maxing out the injectors, but the MAFS is maxed out every gear past 5000 rpm...hmm...

This is around 8-8.5 psi of boost (past 5000 it drops off). Man I wish my boost didn't drop off...Too bad it will be a loooong time before I can upgrade my turbo to a nice T04/get a digital boost controller...

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Aaron_9349
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klattr1 wrote:Air Fuel Ratio/Voltage 17.1:1/.10 16.5:1/.20 16.0:1/.30 15.4:1/.39 14.9:1/.49 14.4:1/.59 13.8:1/.69 13.2:1/.78 12.7:1/.88 12.1:1/.97


I didn't fully understand this chart, and I was wondering if you could explain it better. This voltage is the voltage rating of the MAF sensor or my incoming air voltage according to the emanage right? And is this at idle? Also, is this voltage in the 0-5 range, or are you refering these voltages as being over 5, since he said he was running over 5volts @5000rpm? I'm trying to translate this in order to better understand my air fuel ration to voltage relationship, so that I can better understand it and tune better on my emanage. Sorry if the question sounds dumb, but my idle incoming air voltage rating was just over 2.10, which may be also helping add to my idle problem.

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klattr1
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the voltage listed in the table is 02 sensor voltage correlated to actual measured air fuel ratios from a wideband 02 sensor.our little conversation about mafs voltage was to see if he's maxing out his stock mafs and sure enough he is.

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Aaron_9349
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ahh, got ya. Yeah I was wondering why it was so low compared to the MAF voltage. THanks

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MarkEmark wrote:Also, anyone care to expound upon my initial question?

What exactly happens with the MAFS is "maxed out..." is this detrimental? I assume it just means the MAFS cannot read any more air...so it thinks 5.11 volts worth (if you will) of air is going through the MAFS when it's really more....which would create a leaner situation, if I'm not mistaken (it thinks there's less air, so there's less fuel...) But according to to those 02 readings I'm not running lean at all in the upper RPM range when the MAFS is maxed out, so i think I'll just leave it be for now. I'm leaving for college in a week anyway, so all this stuff is going to have to wait :(

And does anyone know what function of the fuel injector would be measured in ms (I think milliseconds?)? Would that be the pulse-width or something? And what does this parameter tell me about the fuel system (anyone have any numbers as to when an injector is "maxing out" as well?)

Anyway, I'd rather know the answer to my timing question first :)


When your MAF "maxes" out, the electronics that are metering the air flow hits its voltage supply, which, in this case, is 5.1V. Ultimately, any more air that flows through the MAF will be unregistered since the electronics cannot put out more than 5.1V.

It is possible to modify the electronics in the MAF by lowering the gain stage (if there is such one), but I don't know anything about the circuit inside that black box.

Anyhow, long story short, any air that goes through the MAF once it reaches 5.1V will be unmetered, so the engine will squirt the same amount of fuel based on 5.1V. However, if you have access to the fuel map, you can add more fuel in each point in the rpm band where the MAF is maxed out.

For example, my MAF maxes out at about 5000-5500rpm @ 0.5bar, but since I have access to the fuel map via a piggyback, I can extend the fuel injector pulsewidth when the maf is maxed for rpms between 5000-6500. This isn't as eloquent as I would like, but it works for now.


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