The 944's AFM is not likely to be playing a part while on boost. Due to the nature of its design it would be too restrictive to measure high air flows and as such porsche used other parameters to inject at high air flow such as on boost. Even on a lux the output of the AFM maxes out at about 3500rpm. I would look elsewhere especially if it is metering correctly at low rpms and off boost.
Need help fixing a fueling problem
- Thread starter rickware
- Start date
Green is referring to the size/flow rate of the injectors. The ammount of fuel you get through an injector is down to the pressure behind the injector and the size of the injector. Bigger injectors flow more fuel than little ones at the same pressure.
As mentioned you should be using a 3 bar or more fuel pressure regulator for your application.
As the 944's injection is a of a very early design your engineer might not be aware that it is fuel pressure that is giving the additional fuel that is required under boost not a change in injector pulse width. Injector pulse width is the electronic signal sent to the enjector that is usually used to regulate fuel flow. Changing the fuel pressure also regulates fuel flow.
As mentioned you should be using a 3 bar or more fuel pressure regulator for your application.
As the 944's injection is a of a very early design your engineer might not be aware that it is fuel pressure that is giving the additional fuel that is required under boost not a change in injector pulse width. Injector pulse width is the electronic signal sent to the enjector that is usually used to regulate fuel flow. Changing the fuel pressure also regulates fuel flow.
is there a way that i can check the pressure out of the fpr to see if it is 3 bar? also are you saying that i need to upgrade the fpr as it won't reach 3 bar in the standard form. sorry but as you can tell i'm getting a bit above my knowlege, would you know of a good person around surrey/london area who i should take it to.
Diver944
Active member
Guys I'm sorry to rain on your parade but there are a number of errors here. Firstly can I ask if the seller of this equipment knows anything specifically about 944 Turbos? Some years ago AET had a stand at the major club shows and in talking to them it was very clear to me they had no specific knowledge of the 944T (apologies if they do now ).
First of all the fuel pressure does not change in any way whilst the car is in operation, the standard FPR is rated at 2.5 bar, but most aftermarket kits for the 944T use a 3bar FPR to deliver more fuel. The map on the chipset has to be written specifically for a 3 bar FPR, if you simply connect up a 3 bar FPR then you will be 20% rich everywhere. The map simply injects more fuel by opening the injectors for longer as the revs increase. It is not intelligent or dynamic in anyway, it has to match the airflow from the turbocharger
Secondly I would not connect anything into the vacumn line that serves the FPR, you don't want anything to interfere or possibly disrupt the fuel pressure, especially when you are on full boost. I too have the GReddy EBC and the picture below shows how mine is attached to a TiAL dual port wastegate from the banjo bolt on the intercooler pipe. Yours may differ because some wastegates have the side and top ports completely reversed, ie the Lindsey wastegate works totally opposite to the TiAL
You need to determine what rate your FPR is, what size your injectors are and how much air this particular turbocharger flows dependant on RPM. Then you either need a custom map to match that all or have a kit that is ready made for a 944T. I am suspecting the hybrid AET turbo is flowing far too much air than the map on the BBR chip is expecting. My other suspicion is that connecting the EBC into the FPR is possibly reducing the flow of fuel into the injectors, hence you are massively and dangerously lean.
Drive the car gently off boost (or not at all) until we get to the bottom of this [
] Once sorted and safe you should be able to enjoy the boost once more [8D]
First of all the fuel pressure does not change in any way whilst the car is in operation, the standard FPR is rated at 2.5 bar, but most aftermarket kits for the 944T use a 3bar FPR to deliver more fuel. The map on the chipset has to be written specifically for a 3 bar FPR, if you simply connect up a 3 bar FPR then you will be 20% rich everywhere. The map simply injects more fuel by opening the injectors for longer as the revs increase. It is not intelligent or dynamic in anyway, it has to match the airflow from the turbocharger
Secondly I would not connect anything into the vacumn line that serves the FPR, you don't want anything to interfere or possibly disrupt the fuel pressure, especially when you are on full boost. I too have the GReddy EBC and the picture below shows how mine is attached to a TiAL dual port wastegate from the banjo bolt on the intercooler pipe. Yours may differ because some wastegates have the side and top ports completely reversed, ie the Lindsey wastegate works totally opposite to the TiAL
You need to determine what rate your FPR is, what size your injectors are and how much air this particular turbocharger flows dependant on RPM. Then you either need a custom map to match that all or have a kit that is ready made for a 944T. I am suspecting the hybrid AET turbo is flowing far too much air than the map on the BBR chip is expecting. My other suspicion is that connecting the EBC into the FPR is possibly reducing the flow of fuel into the injectors, hence you are massively and dangerously lean.
Drive the car gently off boost (or not at all) until we get to the bottom of this [
] Once sorted and safe you should be able to enjoy the boost once more [8D]thanks paul, and i have turned of the boost and not driving it either as above 0.7 bar it was dangerously lean. i will connect the ebc as you suggest tomorrow and i do have a lindsey dual port wastegate and a standard fpr but bigger injectors. i have just purchased a 3 bar fpr so will fit this shortly.
Paul, how does the 944's ecu know what the boost is then? If what scott is saying is true and that the dme does not know what the boost pressure is how does it know to add more fuel when boost kiicks in.. also how does feeding boost to the FPR not change the regulated pressure?
Edit:
Thinking about it further, the thing I didnt realise last night is that the pressure in the manifold is working against the fuel flow through the injectors. The FPR must be maintaining the pressure differential between the fuel pressure and the manifold pressure at 2.5/3 bar. Surely then the absolute fuel pressure must increase to maintain the pressure differential. That does mean that its not the FPR delivering the extra fuel under boost then.
It does still mean that if your not feeding the right pressure to the FPR you will alter AFR under boost, as the pressure differential between manifold and fuel rail would change thus altering the flow through the injectors. Specifically if the pressure sent to the FPR was lower than boost pressure the pressure differential between fuel rail and manifold would decrease, this would reduce the injector flow rate and lean out the AFR.
Edit:
Thinking about it further, the thing I didnt realise last night is that the pressure in the manifold is working against the fuel flow through the injectors. The FPR must be maintaining the pressure differential between the fuel pressure and the manifold pressure at 2.5/3 bar. Surely then the absolute fuel pressure must increase to maintain the pressure differential. That does mean that its not the FPR delivering the extra fuel under boost then.
It does still mean that if your not feeding the right pressure to the FPR you will alter AFR under boost, as the pressure differential between manifold and fuel rail would change thus altering the flow through the injectors. Specifically if the pressure sent to the FPR was lower than boost pressure the pressure differential between fuel rail and manifold would decrease, this would reduce the injector flow rate and lean out the AFR.
Diver944
Active member
At full throttle the ECU simply has a lookup table to work out how much fuel to deliver depending on what the RPM is. For example at 4000rpm it may open the injectors for 0.001 of a second, at 5000rpm it may be 0.002 of a second and at 6000rpm it may be 0.003 of a second (they were arbitrary figures to give you an idea). If the boost has increased, or started coming on earlier then the ECU will not know this and will continue to open the injectors for the same amount of time, thus causing the fuelling to be incorrect.
The role of the FPR is to supply a known constant fuel pressure to the fuel rail, so that when the injectors open they deliver the correct amount of fuel before they close again. If you vary the fuel pressure without varying the time the injectors are open then once again the fuelling will be incorrect
A 'one size fits all' chip will have been written with a specific boost pressure in mind as well as a known boost curve. The aftermarket kits out there need to be used in conjunction with the other parts they were written for to keep the fuelling safe. The alternative with an AFM car is a custom map written on the fly on a rolling road (or out on the real road).
I'm hoping that Ricks problem is being caused by the way the Greddy is plumbed in, maybe the pulses from the solenoid are affecting the FPR's ability to deliver the correct fuel. Whatever the problem is, I've not seen one on a 944 Tee'd into the line to the FPR.
I think his wastegate is connected properly because he is able to vary the boost
The role of the FPR is to supply a known constant fuel pressure to the fuel rail, so that when the injectors open they deliver the correct amount of fuel before they close again. If you vary the fuel pressure without varying the time the injectors are open then once again the fuelling will be incorrect
A 'one size fits all' chip will have been written with a specific boost pressure in mind as well as a known boost curve. The aftermarket kits out there need to be used in conjunction with the other parts they were written for to keep the fuelling safe. The alternative with an AFM car is a custom map written on the fly on a rolling road (or out on the real road).
I'm hoping that Ricks problem is being caused by the way the Greddy is plumbed in, maybe the pulses from the solenoid are affecting the FPR's ability to deliver the correct fuel. Whatever the problem is, I've not seen one on a 944 Tee'd into the line to the FPR.
I think his wastegate is connected properly because he is able to vary the boost
Thanks for the info on how the DME maps, not a very advanced system is it!
About FPR again! Injectors flow rate comes from duty cycle and the pressure differential between the fuel rail pressure and manifold pressure. Differential is the key point as it is the difference in pressure not absolute pressure that matters. Say my fuel rail is at 3 bar and the boost pressure in the manifold is 1 bar the differential would be 2 bar and you would get the flow rate of the injectors at 2 bar. If you didnt compensate for that you would have 3 bar fuel pressure off boost and 2 bar on boost. This is backwards as you will need more fuel on boost than off! By feeding boost pressure into the FPR you increase fuel pressure by the boost pressure thus maintaining 3 bar pressure differential and getting the fuel flow rate you expect.
Edit:
With regards to the problem here, say you put the EBC on the line with the FPR. The EBC varies the pressure in the line to some unknown value used to control the wastegate to regulate boost. This pressure will not always represent the pressure in the manifold. This would mean the pressure differential will also be at some unkown value and you loose control of fuel flow as you dont know the flow rate.
edh
New member
did all these components come as a package? (turbo, chips, injectors)
the injectors should have a specific rating (mine are 72lb) which the new ECU chip needs to be set up for. If you're trying to make a set of components from different suppliers work, then I think you will struggle. Hope I'm wrong though
the injectors should have a specific rating (mine are 72lb) which the new ECU chip needs to be set up for. If you're trying to make a set of components from different suppliers work, then I think you will struggle. Hope I'm wrong though
so the diagnosis on here was spot on and ithas been remapped to 280hp at 1 bar. Thing is I now have a dilema as the technician told me he should have been able to get much more out of it but my engine is tired (bottom end) as the bores are worn and rings. so do i a. leave it as it will run fine for what i do on 280hp, b.rebuild my bottom end with new bores and some nice pistons on the way, c. exchange mine for a reconditioned. d. any other suggestions?
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