tuning programmable engine management systems

[safe]

Sal, thanks for the Euro map.
What unit are the fuel-map values, anything comprehensible?

[scarceller]

Originally Posted by dfink

Now for the twin plug question. Several posts through out my searches found that 24-25* was the max for a twin plug system. I and others have not found this to be the case. There was about a 6hp loss going from 30* to 24* at WOT 7000rpm. I found that under WOT I got the best results from a rather linear ramp up peeking at around 5000-5500 rpm. Jumping up too soon also caused a loss in the lower to mid ranges. So for my setup 30* appears to be the best. I tried to go to 32* and also experienced a loss of power. I never did get any hint of knocking. This was with a 12.5:1 A/F ratio and 10.5:1 compression ratio.

dfink,

You have the best approach to tuning, simply any Ign map or Fuel map we discus is simply a ballpark idea and should only be used as such. The only way to know what WOT ign/fuel map works best in your car is simply via dyno time. And it's great to share such results with others that may have similar setup but even then what works in one motor may not in another even if built the same.

But if you are starting with nothing in a custom EFI then having some ballpark ideas would be very helpful.

[scarceller]

AFR vs Intake Air temps?

The motronic factory setup is designed to enrich mixture at load and WOT as intake air temps go up. In my car I have set my AFR to about 13.0AFR (WOT AFR) on a cold 30F day and then this same exact chip setup on a 95F day will run a WOT AFR of about 12.8. By design the motronic has a compensation map based on Intake Air Temp that richens mixture as temps go up.

I think the richer AFR is designed to help keep CHTs cooler as Air Temps increase.

Now for how the IntakeAirTempFuelCompensation map works:
First let's set some basics:
- Cold air is more dense and thus needs more fuel
- Warmer air is less dense thus needs less fuel

So, to maintain the same AFR regardless of air temp you must decrease fuel as temps increase. And the Motronic does indeed do this but it just does not decrease fuel enough to keep the same AFR it simply only decreases fuel slightly as temps increase and thus results in AFRs actually getting richer as temps increase. Kind of hard to understand but in the end the engineers decided to simply let AFRs get slightly richer as temps increase.

If the system did not compensate for Air Temp then you would be in trouble because if you tuned on a warm 90F day and set your WOT AFR to 12.8 and then used this same map on a cold 20F day your AFR would be in the low 13s maybe even 13.3 and you just went lean! Detonation!

So here is the IntakeAirTempFuelCompensation from the motronic:
10F = 146 fuel trim, more fuel
58F = 136
88F = 128
147F = 121 less fuel
You can see how they take fuel away as temps go up. But they just don't take enough away and thus AFR goes down as temps go up.

Also keep in mind that these 3.2L cars use a AirFlowMeter (not a MAF) and the AFM does not measure Mass of air but simply volume and does not account for air temp and this is why they must include air temp in the fuel trim. MAF devices account for air temp and thus don't need to trim as much based on air temp but often they also do some trimming as well.

[scarceller]

Originally Posted by safe

Sal, thanks for the Euro map.
What unit are the fuel-map values, anything comprehensible?

Sort of, the digital value is some number between 0 and 255 and they are simply fuel trim values. Where the number 128 means apply no fuel trim and means FuelTrim=1 then if you require extra fuel for the given cell the numbers go up and less fuel numbers go down. Here are a few examples:
128=1.0
255=1.99 (not a realistic fuel trim)
0=0 (also not realistic)
141=1.1 (this is a realistic fuel trim, 10% more fuel)
115=0.9 (also realistic fuel trim, -10% less fuel)

So values higher than 128 mean extra fuel and less than 128 mean less fuel. It's rare to see numbers higher than 150 or less than 110.

If you are trying to figure out what the AFR is for a given cell GOOD LUCK you can't do it! You simply need to use a WBO2 for this, so I look at what I have with the WBO2 and then tweak the map, very time consuming! This is why the modern EFI systems are great, you can setup a ballpark map and then setup the desired AFR table. Then the EFI system monitors the WBO2 and fine tunes the fuel trims on the fly, great stuff if you have a system with this auto tune ability.

[911st]

I suspect:

"Load" for a Motronics system is different from a more advanced aftermarket or race style system. Motronicis only knows of load in two ways. If the WOT switch is triggered or if the "advanced algorithms" conclude such.

On a more advanced EFI system load is measured in different ways. It can be measured by changed in manifold pressure (MAP) or by looking at the throttle plate angle (TPS) relative to motor speed.

What we seem to be calling "load" on the Motonics map is the rate of air flow as measured by the AFM. If the throttle is opened significantly but not enough to trigger the WOT switch, we may reach for different cells in the cruse map that are more conducive to acceleration. However, the WOT map will not be triggered.

So again, with Motronics "load" the output of the AFM. With an add on EFI it is the throttle angle or manifold absolute pressure.

Dose this make for different strategies between the two types of systems?

[safe]

Originally Posted by scarceller

Sort of, the digital value is some number between 0 and 255 and they are simply fuel trim values. Where the number 128 means apply no fuel trim and means FuelTrim=1 then if you require extra fuel for the given cell the numbers go up and less fuel numbers go down. Here are a few examples:
128=1.0
255=1.99 (not a realistic fuel trim)
0=0 (also not realistic)
141=1.1 (this is a realistic fuel trim, 10% more fuel)
115=0.9 (also realistic fuel trim, -10% less fuel)

So values higher than 128 mean extra fuel and less than 128 mean less fuel. It's rare to see numbers higher than 150 or less than 110.

If you are trying to figure out what the AFR is for a given cell GOOD LUCK you can't do it! You simply need to use a WBO2 for this, so I look at what I have with the WBO2 and then tweak the map, very time consuming! This is why the modern EFI systems are great, you can setup a ballpark map and then setup the desired AFR table. Then the EFI system monitors the WBO2 and fine tunes the fuel trims on the fly, great stuff if you have a system with this auto tune ability.

OK.
So does 128 correspond to 50% duty cycle of the injectors or something like that?

How large are the injectors by the way, do you know?

I'm not trying to figure out AFRs, just a rough baseline. My EFI will adjust it self, as you say, with the help of a wideband.

[scarceller]

Originally Posted by 911st

I suspect:

"Load" for a Motronics system is different from a more advanced aftermarket or race style system. Motronicis only knows of load in two ways. If the WOT switch is triggered or if the "advanced algorithms" conclude such.

On a more advanced EFI system load is measured in different ways. It can be measured by changed in manifold pressure (MAP) or by looking at the throttle plate angle (TPS) relative to motor speed.

What we seem to be calling "load" on the Motonics map is the rate of air flow as measured by the AFM. If the throttle is opened significantly but not enough to trigger the WOT switch, we may reach for different cells in the cruse map that are more conducive to acceleration. However, the WOT map will not be triggered.

So again, with Motronics "load" the output of the AFM. With an add on EFI it is the throttle angle or manifold absolute pressure.

Dose this make for different strategies between the two types of systems?

You are close on 'load' for motronic but not exact. Load is not just AFM signal, it's the combination of given AirFlow vs RPM. The motronic has an algorithm to calculate load that uses the RPM vs AirFlow to come up with what Load row to use from the PT tables. It really does calculate load for a give RPM. But I never did exactly figure out the formula yet and it's on my wish list.

[scarceller]

Originally Posted by safe

OK.
So does 128 correspond to 50% duty cycle of the injectors or something like that?

How large are the injectors by the way, do you know?

I'm not trying to figure out AFRs, just a rough baseline. My EFI will adjust it self, as you say, with the help of a wideband.

Not really sure about the duty cycle question.

The stock injectors are 24lb injectors at 3bar FP. But these are run in Batch injection mode that squirts fuel 2 times per crank rev. If you are using some new breed EFI system then you may be using Sequential injection that times the fuel delivery to the opening of the valve and in this mode sequential systems tend to use higher flow injectors like in the 30-40lb range because the really want to get the fuel in quickly right at the exact valve time. Also as RPM increases the amount of time to get fuel delivered will decrease meaning that at some RPM sequential starts to look a lot like batch. Many folks say that sequential is most useful for hi-torque lo-RPM engines and that it really is not that beneficial to hi-RPM engines. In the end sequential injection works best with larger injectors and not driving them much over 65% open. Hope this makes sense.

[Trog]

Gents,

The roads cleared up yesterday so I took the P-car out for a spin. Wasn't planning to do any tuning, just enjoy the sunny day for a couple of hours.

I noticed that I've picked up an annoying idle oscillation. The oscillation cycle is about 2-seconds. The engine would idle fine, then it would jump about 100RPM, and then settle back down. While watching the VE and timing maps, it appears the fuel mixture and timing maps are fighting each other at idle.

It was a pretty cold day and MAT temperatures never got much past 2degC.

The idle AFR is approx 14.0.


T...

[scarceller]

Originally Posted by Trog

Gents,

The roads cleared up yesterday so I took the P-car out for a spin. Wasn't planning to do any tuning, just enjoy the sunny day for a couple of hours.

I noticed that I've picked up an annoying idle oscillation. The oscillation cycle is about 2-seconds. The engine would idle fine, then it would jump about 100RPM, and then settle back down. While watching the VE and timing maps, it appears the fuel mixture and timing maps are fighting each other at idle.

It was a pretty cold day and MAT temperatures never got much past 2degC.

The idle AFR is approx 14.0.


T...

Trog,

How much headroom do you allow before you try to correct idle with ign or fuel? Meaning: if your target idle is 850RPMs then I would not try to correct the idle till it got at least 50RPMs or more off target (>900 or <800) I also found that simply correcting idle with ignition works best and maybe you should not try to correct with fuel. If you wish to also try fuel then kick the fuel in later but don't do both at same time.

So does your setup try to correct with ignition and fuel?

Also when you say it jumps 100RPMs does it jump 100 above target or does it also drop below target. For example 850-950-850-950-...

My car sometimes hunts for idle as you describe but only for few moments during cold start, never once warm.

[psalt]

Sal wrote,

The stock injectors are 24lb injectors at 3bar FP. But these are run in Batch injection mode that squirts fuel 2 times per crank rev. If you are using some new breed EFI system then you may be using Sequential injection that times the fuel delivery to the opening of the valve

Sal,

"Batch" mode is two injections per engine cycle. OEM's time Sequential Injection to the closing of the intake valve. The OEM acronym is based on injector closing X degrees before intake valve openning. For them, it is all about emissions and economy, the idea about firing the injector when the intake valve is closed is about having consistent puddling. Injecting into an open valve has less consistent results because of vaporization issues. Above 40% load it is close to irrelevent, injectors are sized to 85% duty cycle so they are spraying for most of the time available in the engine cycle (2 crank revs), intake valve open and closed.

[Trog]

Originally Posted by scarceller

Trog,

How much headroom do you allow before you try to correct idle with ign or fuel? Meaning: if your target idle is 850RPMs then I would not try to correct the idle till it got at least 50RPMs or more off target (>900 or <800) I also found that simply correcting idle with ignition works best and maybe you should not try to correct with fuel. If you wish to also try fuel then kick the fuel in later but don't do both at same time.

So does your setup try to correct with ignition and fuel?

Also when you say it jumps 100RPMs does it jump 100 above target or does it also drop below target. For example 850-950-850-950-...

My car sometimes hunts for idle as you describe but only for few moments during cold start, never once warm.

The jump is +100RPM.

Currently I'm not using ignition to correct for idle drift (hasn't been a problem). The AFR values around idle may be the problem. I've limited the closed-loop O2 range to 10%. I may be hitting the limit.

T...

[scarceller]

Originally Posted by psalt

Sal wrote,

The stock injectors are 24lb injectors at 3bar FP. But these are run in Batch injection mode that squirts fuel 2 times per crank rev. If you are using some new breed EFI system then you may be using Sequential injection that times the fuel delivery to the opening of the valve

Sal,

"Batch" mode is two injections per engine cycle. OEM's time Sequential Injection to the closing of the intake valve. The OEM acronym is based on injector closing X degrees before intake valve openning. For them, it is all about emissions and economy, the idea about firing the injector when the intake valve is closed is about having consistent puddling. Injecting into an open valve has less consistent results because of vaporization issues. Above 40% load it is close to irrelevent, injectors are sized to 85% duty cycle so they are spraying for most of the time available in the engine cycle (2 crank revs), intake valve open and closed.

Paul,

Thanks for catching my error: for batch it injects the fuel in 2 shots per complete cycle (2 crank revs not 1).

So the 85% duty cycle seems compatible with Batch Mode, this means that you really don't need larger injectors for sequential?

I'm not that familiar with these new EFI systems or sequential injection but am very interested. I'm thinking of toying with a megasquirt install in the near future.

[scarceller]

Originally Posted by Trog

The jump is +100RPM.

Currently I'm not using ignition to correct for idle drift (hasn't been a problem). The AFR values around idle may be the problem. I've limited the closed-loop O2 range to 10%. I may be hitting the limit.

T...

Trog,

You may have found your issue: very cold air usually needs more fuel even if the engine is fully warm. If your base fuel map is a bit to lean for the cold air intake temp then the WBO2 target AFR of 14.0 may simply be outside the 10% range.

Does the EFI system have intake air temp compensation maps? to allow more fuel for very cold air? If so you may need to add more fuel into those compensation maps. Don't simply add more fuel to main fuel map as this may work now for you in these cold temps but later in warmer weather it will run rich.

[Trog]

Originally Posted by scarceller

Trog,

You may have found your issue: very cold air usually needs more fuel even if the engine is fully warm. If your base fuel map is a bit to lean for the cold air intake temp then the WBO2 target AFR of 14.0 may simply be outside the 10% range.

Does the EFI system have intake air temp compensation maps? to allow more fuel for very cold air? If so you may need to add more fuel into those compensation maps. Don't simply add more fuel to main fuel map as this may work now for you in these cold temps but later in warmer weather it will run rich.

Sure does, currently set at 0 for all MAT temperatures below 20degC.

[scarceller]

Originally Posted by Trog

Sure does, currently set at 0 for all MAT temperatures below 20degC.

What about at other higher temps? Is it 0 across the board? The idea is to get more fuel at cold temps less as Air Temps go up. In the end you want to achieve a Intake Air Temp compensation scheme that keeps AFRs about the same as AirTemps change. I say about the same because in general you want your AFR (like at WOT) to get slightly richer as air temps increase. Read prior post I did on this in this thread.

[psalt]

Sal,

Injecting half the fuel once every revolution goes back to the old analog systems that ran off the coil pulse rpm signal. Four injections per engine cycle would be twice as many opening and closing times and they get in the way. Sequential injectors are not twice as large, big injectors are too hard to control below 2ms. For road cars, the emphasis is emissions, economy, and drivabilty. With batch injection, different things, some good some bad, are happening in different cylinders when the injectors all fire. Sequential allow the good and bad events to at least be consistent. Firing at a closed valve heats the fuel more consistently.

[Trog]

Originally Posted by scarceller

What about at other higher temps? Is it 0 across the board? The idea is to get more fuel at cold temps less as Air Temps go up. In the end you want to achieve a Intake Air Temp compensation scheme that keeps AFRs about the same as AirTemps change. I say about the same because in general you want your AFR (like at WOT) to get slightly richer as air temps increase. Read prior post I did on this in this thread.

Minor reduction of fuel at higher ambient temperatures:

[911st]

Originally Posted by scarceller

You are close on 'load' for motronic but not exact. Load is not just AFM signal, it's the combination of given AirFlow vs RPM. The motronic has an algorithm to calculate load that uses the RPM vs AirFlow to come up with what Load row to use from the PT tables. It really does calculate load for a give RPM. But I never did exactly figure out the formula yet and it's on my wish list.

Sal, You are a great resource on Motronics, thank you.

So are the two axis on the map RPM and AFM voltage or postion? Or are you saying the second axis somthing other than AFM voltage?

I understand some type of correction factors that take the active cell and modify it for O2, temp, etc. But is sounds like there is somthing else going to degermin the second axis???

Not getting it I guess.

If the cell value is just RPM by AFM voltage I can understand how we could set a line of cells that represent cruse load at cach RPM level. Then the cells just past that line where the AFM voltage is a bit higher could be a more aggressive settings. Then again eventually approaching values to achive max TQ levels as on the WOT map. How fast the cell values approach aggressive values would have an impact on part throtle response.

[jpnovak]

Sal, thank you for the ignition maps.

Does the Motronic WOT ignition map differ much from the high-load sites on the part throttle map?