When the question is simple enough, I just go into stupid mode and design a circuit. Investigating whether the customer is asking for what he NEEDS is a whole 'nuther conversation...which I usually don't bother with. In this case, I wouldn't know whether he's right if he explained it to me.

As a multidisciplinary tinkerer I can't ignore the larger picture when dealing with a complex system and poorly defined want.

Especially so given how many people that come to these types of forums wanting something that wont actually do what they think it will do and it takes 50 - 100+posts to get to that realization.

In this case wanting to swap between a MAF and MAP (two completely different sensor devices) on the go and then limit one's output draws my immediate attention to there being a lot more to the story than was initially given.

Same with wanting to increase a fuel injectors volume capabilities. There's more to the reasons why than 'just because I want to'.

 

Guy's I'm simply running the MAF for off boost drive-ability and the map sensor for boost control. I have re-engineered the software calibration data in the stock ECU to accept these hardware changes.

Thanks for the help everyone

I still don't follow the need being things don't add up for me.

If you have the capability to change the programing then by default the MAF or MAP sensor units should be able to give you the correct input signals through whole range of throttle and load conditions all by themselves.

That and the injector PWM trim limits should be able to be adjusted as well along with the A/F ratio values the system should be aiming to achieve based on O2 sensor signal values.

My guess is you have added a turbo or higher boost than stock turbo to the engine and need extra fuel to make it work at the higher capable HP range hence the need to put more fuel through the stock fuel injectors which if so that should be easily done in the software unless they are already running at 100% of the softwares injector duty cycle limits which if so changing input signal parameters will still not expand the PWM duty cycle limit beyond what the programing allows for as is.

That's the scenarios that come to my mind in this endeavor that make me question the validity of your wanted approach to your problem.

 

My guess is you have added a turbo or higher boost than stock turbo to the engine and need extra fuel to make it work at the higher capable HP range hence the need to put more fuel through the stock fuel injectors which if so that should be easily done in the software unless they are already running at 100% of the softwares injector duty cycle limits which if so changing input signal parameters will still not expand the PWM duty cycle limit beyond what the programing allows for as is.

See? I told you I wouldn't understand!

 

Now if we could just get the other 99% of the population to be as honest as you!

 

This site is the best thing I ever found to remind me of how much I don't know!
Really. Often enough, I complain that I'm surrounded by idiots. I look good among average people!
On here? Not so much.

 

Guy's I'm simply running the MAF for off boost drive-ability and the map sensor for boost control. I have re-engineered the software calibration data in the stock ECU to accept these hardware changes.

Thanks for the help everyone

I feel like if you can modify software calibrations you shouldn't need to build what you think you are needing to build. You where asked what kind of car you are working on and said simply BMW. How about you give us your VIN or make, model, and year. If you are the mad car hacker you say you are then you should only need a stock MAF and stock MAP and modify your fuel tabels with HP tuneres or what ever software your working with. Unless your Bemmer was N/A and your doing a custom turbo set up. If so I'd suggest you have a professional with a dyno and gas analyzer do it for you.
$0.02
-Jason

 

How could you run an injector at 100% duty-cycle?
Isn't it on only when the intake valve is open?

Simple answer, no. The injector fires slightly before the valve opens, to get fuel in the air stream, but does stay open as the vale does. In modified engines they change injector sizes (pounds of fuel per hour is the rating) to keep from needing to use such high duty cycles on the injector.

 

To get more fuel through a smaller injector takes either more on time or higher fuel rail pressures which for the fuel rail pressure that can be cheated by modifying the fuel pressure regulator unit in one way or another which will be limited by whatever the fuel pumps own bypass valve limit is which could be as much as 150 - 200% of the nominal fuel rail set pressures you may have quite a bit of headroom to play with.

The only problem with increased fuel rail pressure in a gas engine is, while the duty cycle can be kept low, the actual opening distance of the pintle is less and more heat is made in the injector solenoid coil due to having to overcome the increased pressure. This is because of the higher pressure than the injector is designed for.

 

The only problem with increased fuel rail pressure in a gas engine is, while the duty cycle can be kept low, the actual opening distance of the pintle is less and more heat is made in the injector solenoid coil due to having to overcome the increased pressure. This is because of the higher pressure than the injector is designed for.

How so being they have a fixed resistance value of something like 15 ohms for most BMW injectors?

If the the duty cycle was say 5% of the programmable limit at idle Vs 100% how would that create overheating then that does not occur at the high duty cycle end of things?

Do explain the thermodynamics of your reasoning being in my books any fuel injector that fires uses the same electrical power regardelss of whether it's internal solenoid valve moves or not given the same supply voltage and PWM duty cycle.

 

From what I can find online in the BMW tuner forums the stock fuel rail pressure is ~3.5 bar (~51 PSI) but many guys are cheating their stock fuel injector volume limits by using aftermarket or modified fuel rail pressure regulators that push things into the 5 - 6 bar (72 - 87 PSI) range for moderately modified and higher than stock turbo boosted racing engines and they have no injector issues with running at that pressure.

If it was me I would have no issues with raising the stock fuel rail pressure by 50 - 60% over the stock settings to cheat the stock volume limits.

 

From what I can find online in the BMW tuner forums the stock fuel rail pressure is ~3.5 bar (~51 PSI) but many guys are cheating their stock fuel injector volume limits by using aftermarket or modified fuel rail pressure regulators that push things into the 5 - 6 bar (72 - 87 PSI) range for moderately modified and higher than stock turbo boosted racing engines and they have no injector issues with running at that pressure.

If it was me I would have no issues with raising the stock fuel rail pressure by 50 - 60% over the stock settings to cheat the stock volume limits.

Im no BMW engineer but I agree with that. There are multiple manufacturer that use PWM on the fuel pump to lower and raise fuel pressure. If your familiar with direct injection you are well aware of this as pressure may be between 500-2500psi depending on load. That is done with the High pressure pump but the injector still deals with low and elevated pressures.

Edit :you will have rich codes from raising your fuel pressure because your fuel trims will be excessively negative especially at idle. This can cause catalytic converter damage over time.

 

The only problem with increased fuel rail pressure in a gas engine is, while the duty cycle can be kept low, the actual opening distance of the pintle is less and more heat is made in the injector solenoid coil due to having to overcome the increased pressure. This is because of the higher pressure than the injector is designed for.

I think the moment the pintle begins to move may be later but the amount of flow through the injector until it closes will be more. If you had a lab scope hooked up and watched both the amperage of the injector and the voltage at overlayed on each other you can see the moment the pintle begins to lift and the moment in begins to close. I can post pictures or screen shots if anyone is interested? I don't think the heat is a big factor, its already about 190* F in that area anyway.

 

How so being they have a fixed resistance value of something like 15 ohms for most BMW injectors?

If the the duty cycle was say 5% of the programmable limit at idle Vs 100% how would that create overheating then that does not occur at the high duty cycle end of things?

Do explain the thermodynamics of your reasoning being in my books any fuel injector that fires uses the same electrical power regardelss of whether it's internal solenoid valve moves or not given the same supply voltage and PWM duty cycle.

By not allowing the the core to go full distance into a coil. The core is part of the heat transfer process.

A injector running at much less than 100% is going to create less heat than one running at close to 100%, just due to the on/energized time being lower.

 

Possibly yes but as I stated earlier given what the BMW tuner forums are saying they obviously handle running at far higher line pressures than stock without any issue so I have doubt that any delay is significant enough to matter.

That and once the tiny needle valve head comes off the seat the piston no longer has any force differentials between either end freeing it up to move the full designed stroke length.

 

Never worked on a BMW so what your saying may be true for them.

 

I'm a Ford guy myself and I know Ford injectors can take substantial overpressure and still function fine. I've played with old 3.0 V6 injectors that normally ran around 30 - 40 PSI up to around 120 PSI just for curiousity sake to see what their spray patterns looked like and had no firing issues.

All my BMW info came from reading BMW tuner forum threads related to boosting fuel rail pressures. If they are doing it with success I have no reason not to believe them.

 

So did he run away or is he lying dead in some garage with a MAP or MAF sensor embedded in his head?

 

Traded for a Mercedes...

 

Yea, that'll make things better.

It's like trading your town poofter for the one from the next town over.