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Maf & injector calibrations with standard ECU, is it rig 

 

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 Post subject: Maf & injector calibrations with standard ECU, is it rig
Posted: Sun Apr 24, 2005 11:53 pm 
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The spark and fuel tables are tables for the amount of spark to deliver and the a/f ratio to command if you are NOT open loop. Open loop is when you are richer than 14.64:1 a/f raito and no longer using the O2 sensors for feedback. The PCM uses load in calculating spark and fuel. If your MAF transfer function is off (this is the input voltage from the meter to the PCM and what the flow is at that voltage) VE will be calculated incorrectly and hence so will timing and fuel be calculated incorrectly. This is why the MAF is so critical to making the engine work right. VE gets an input into almost everything, even what the trans feels like when it is shifting.

Most will say that you can get a MAF calibrated for a given size injector and not change the PCM. This is right and wrong. Let's say you have 19# injectors and some MAF. You want to put in 38# injectors. You purchase a MAF calibrated for 38#ers. What they do is TRY to make it so at every voltage point the output from the MAF is original injector size divided by new injector size, in this example, 19/38 or 1/2 of the original value. The PCM now thinks there is a lot lesse airflow into the engine. Let's say before at 2 volts it was 12#/min, now with the "new" MAF, to get that same 12#/min you are at 1 volt. So, you now running at 1 volt with 12#/min of air and the PCM thinks you are running much lower flow, thus giving you a lower fuel pulsewidth. If the air meter was set up correctly, you would have 1/2 the pulsewidth and the amount of fuel going into the engine will be correct. This is the part that's right.

Now the wrong part. Load is calculated incorrectly, in this example, it's 1/2 of what it should be. So, the PCM uses the wrong values out of the spark and fuel tables. This typically ends up in knock (also known as detonation, or pinging) on some cars, since the car is leaner with more spark.

The correct way to calibrate for injectors is ALWAYS to make changes in the PCM via a chip or flash.

 

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Posted: Thu Apr 28, 2005 2:52 am 
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Correct however most agree that going from 19lb to 24 or even 30lb won't hugely effect the load calculations, well at least not to the point of detonation (the V8 can actually do with a bit of leaning up and more timing anyway). Obviously the best way is to reprogram the EEC but unless you have an EB/ED V8 its not easy to do.
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Posted: Thu Apr 28, 2005 11:21 am 
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The load calculations are done using the throttle position sensor and that wont change by changing you injectors. You still need the same amount of pedal to make the same power. The only thing that can do what your talking about by putting more load on that the motor thinks is by putting a huge TB on, even then you may just have to retard your timing a tiny bit to compensate (for those of us with pre AU V8's).

 

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Posted: Thu Apr 28, 2005 11:56 am 
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AXR88U wrote:
The load calculations are done using the throttle position sensor and that wont change by changing you injectors. You still need the same amount of pedal to make the same power. The only thing that can do what your talking about by putting more load on that the motor thinks is by putting a huge TB on, even then you may just have to retard your timing a tiny bit to compensate (for those of us with pre AU V8's).


I think what he is saying... is that when people change injectors, the common workaround for EEC is to change the maf/sampling tube. Make the MAF see less air, therefore shorten injector pulse as the larger injectors will flow more fuel per sec/min/hour. Load is a function of MAF/RPM with throttle positition used for acceleration enrichments. By "fooling" EEC you are forcing it to use incorrect load calcs as the MAF signal is bogus. It's a crude workaround - but I agree with EDXR8 that the results are not too dire. Tens of thousands of 80s/90s Mustang owners will testify to this.

 

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Posted: Thu Apr 28, 2005 12:43 pm 
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AXR88U wrote:
The load calculations are done using the throttle position sensor and that wont change by changing you injectors. You still need the same amount of pedal to make the same power. The only thing that can do what your talking about by putting more load on that the motor thinks is by putting a huge TB on, even then you may just have to retard your timing a tiny bit to compensate (for those of us with pre AU V8's).


Load calculations are not done with the throttle position sensor, they are done with the MAF sensor.
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Posted: Thu Apr 28, 2005 12:45 pm 
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EDXR8 wrote:
AXR88U wrote:
The load calculations are done using the throttle position sensor and that wont change by changing you injectors. You still need the same amount of pedal to make the same power. The only thing that can do what your talking about by putting more load on that the motor thinks is by putting a huge TB on, even then you may just have to retard your timing a tiny bit to compensate (for those of us with pre AU V8's).


Load calculations are not done with the throttle position sensor, they are done with the MAF sensor.


Efficiency calculations take the TPS into account though, dont they ?

 

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Posted: Thu Apr 28, 2005 12:50 pm 
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Why is it when you look at an ignition curve, that throttle position is one of the axis' ?

 

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Posted: Thu Apr 28, 2005 1:04 pm 
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AXR88U wrote:
Why is it when you look at an ignition curve, that throttle position is one of the axis' ?


Where exactly are you looking at this table ?

 

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Posted: Thu Apr 28, 2005 1:22 pm 
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The base fuel and spark tables are RPM vs LOAD... TPS would be used for accelarion enrichment wouldnt it?

I believe load is a raw value from MAF... i.e. the amount (read: MASS) of air being drawn into the engine would change depending on the position of the throttle plate... hence no need for TPS to be applied?


http://www.kvitek.com/ford/

Check out eectch98 document.

 

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Posted: Thu Apr 28, 2005 1:30 pm 
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there would be efficiency tables for fuel, and load tables for spark.

 

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Posted: Thu Apr 28, 2005 1:34 pm 
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I said it wrong. Back many years ago when playing with a crummydoor v6 with a Haltech system on on the dyno, I noticed that the load was directly proportional to the throttle position.

 

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Posted: Thu Apr 28, 2005 1:41 pm 
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AXR88U wrote:
I said it wrong. Back many years ago when playing with a crummydoor v6 with a Haltech system on on the dyno, I noticed that the load was directly proportional to the throttle position.


Yeah a lot of aftermarket ECUs have this function... you can calculate load/VE based on MAP and RPM (speed-density) or TPS and RPM (Alpha-N)

http://www.fuelairspark.com/Information ... dalpha.htm

 

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Posted: Thu Apr 28, 2005 1:45 pm 
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On a basic stock engine, the TP closely matches the load curve because it is used as a backup system should the MAF (V8) or MAP (I6) fail (very rare). Once modified however, the TP can be way out. All fuel tables in the EECIV/V are load vs engine temp and timing tables are load vs rpm. Raw Load is calculated using the MAF reading, air charge temp and rpm. The EEC then calculates a load percentage using pre-determined maximum raw load vs rpm.
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 Post subject: gonna do it , why not properly?
Posted: Fri Apr 29, 2005 9:58 pm 
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But, if you want to do a job ,isn't it best to have even the "little things" set properly?
From experience the advance curve is quite important to be set as good as possible to get a broader power/torque curve.
"when I state good, I mean to suit the engine's individual requirements"
thats the main reason for all the different size springs available for aftermarket distributors with mech advance.

 

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Posted: Fri Apr 29, 2005 10:22 pm 
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Yeah thats true, but the factory settings are extremely safe so there is plenty of room to move there. Ideally you want to custom tune the EEC with any mod you do but it is a complex process to get everything right.
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