AFPR Tuning Tips

[sweet97]

Finally got a full throttle AFPR today. I would like to hear how you guys use your AFPR's to tune. Raise the base and then tune for a good idle and cruise but have fuel for WOT with extra timing? Lower the pressure so the ECU will run closer to the stock timing curve. What's your tricks? mark

 

[HighPSI TSi Guy]

i just use mine to skew the timing curve to my liking.. beyond that it's useless..

 

[sweet97]

Can you be specefic? What do you have the base pressure set to? Mark
PS: How does this affect the timng curve? Thanks, mark

 

[awdLaunch16g]

Basically the only purpose to the AFPR is to tune down the fuel pressure when running a larger pump, and get basically a rough fuel correction for your setup. For example, if you switch from a stock pump to a 255lph pump, the stock fpr is not going to be able to regulate all of that fuel, making it run extremely rich. therefore you get the afpr to put the suel pressure back down to a reasonable, preferably stock level. Now, you can also use it to adjust the flow of your injectors, if you have smaller injectors that arent flowing enough you can raise the pressure to squeeze every ounce out of them to get the fuel you need. Now the problem with that is you will be running at a dangerously high duty cycle. On the other hand oyu can also use the fp to make larger injectors flow less, however larger injectors do not like to flow too little, they become inefficient.

 

[sweet97]

Something seems missing. I just don't see guys spending $200.+ to bring their pressure back to stock. There must be a way to tune with the adjustments in pressure that are possible. The way i see it the regulators are on a 1:1 ratio. Therefore if the base is 35 psi and i run 20 psi then I will hit 55 psi. If my base is 40 and irun the same 20 psi i get 60 psi. Those 5 pounds difference must be the tuning FACTOR. Anyone else? Mark

 

[1LE]

Don't think of it as spending $200 to bring it back to stock. Think of it as spending $200 to set the proper pressure... Which just happens to be the same as stock

Yes, you can play games with the AFPR to help skew your timing curve. However, the value is limited. There's only a small range of pressure you have to work with before you get yourself in trouble. Not the appropriate tool for the job.

 

[HighPSI TSi Guy]

Something seems missing. I just don't see guys spending $200.+ to bring their pressure back to stock.

haha... unfortunately, you do.. DSMers are pretty dumb these days!

basicly, the idea is, you up the FP, and pull fuel on the SAFC = more timing, or subtract fuel pressure and add fuel on the SAFC = reduce timing.

also, it can come in handy when running strange setups.. i.e. injectors just barely being outflowed, turn up the FP so they can flow more.. or when i had my gutted 1G MAF, the car wouldnt idle at less than 47ish PSI FP.. haha

 

[98spydert]

, what's dumb? spending the money to bring your FP back to stock or spending the money and having no clue what to do with it :laugh:


Some people can't get a tune at a certain psi so they raise or lower their fp and start over. For some reason I've heard many success stories doing that.

You can use it to gain a little timing if you're on stock injectors or using a chip to compensate for injectors. The same way you gain timing with larger injectors and compensating with a piggy back. You up the injector size and have to remove fuel(IPW) via piggy back witch results in the wrong timing maps and an excess of timing. Same idea, you add fuel ressure and have to remove IPW.

Adjusting the fuel pressure has the same result of adjusting the base settings on a MAFT. One mass adjustment.

 

[HighPSI TSi Guy]

Adjusting the fuel pressure has the same result of adjusting the base settings on a MAFT. One mass adjustment.

incorrect! MAFT makes all adjustments through airflow signal, whereas AFPR is independent of airflow signal

 

[sweet97]

That's correct HIGH_GUY! That's why I am thinking I can use the AFPR to tweak the MAFT settings to let the translator set the fuel and timing and then be able to either lessen or increase the fuel ever so slightly to aid in tuning. Say the translator setting is going to set the fuel at "X" and the timing will be set at let's say "Y" due to the air the ECU "sees". This setting may knock due to being too lean for the timing the ECUis allowing. I add to the base a few psi of fuel and perhaps the knock stops! Sounds good doesn't it? Anyone agree with my line of thought on this? mark

 

[98spydert]

incorrect! MAFT makes all adjustments through airflow signal, whereas AFPR is independent of airflow signal

I should have clarified. The END RESULT is the same. You can loose X% fuel via maft base settings (viea base knob adjustments) or you can drop a X psi on your adjustable fuel pressure regulator. Both result in less fuel for the entire rpm range, not just one range or point... sheesh, talk about nit picking.

 

[HighPSI TSi Guy]

I should have clarified. The END RESULT is the same. You can loose X% fuel via maft base settings (viea base knob adjustments) or you can drop a X psi on your adjustable fuel pressure regulator. Both result in less fuel for the entire rpm range, not just one range or point... sheesh, talk about nit picking.

but the end result is NOT the same!

one still results in a timing shift where the other does not!

 

[98spydert]

but the end result is NOT the same!

one still results in a timing shift where the other does not!

Look at my original post


Edit: also, before you continue to nit pick. They're two different examples, I explained the first one which we seem to agree on; add fuel pressure and remove IPW via piggy back in order to gain timing. The second example; having no mention of timing, is removing FP in order to lean your a/f. Please interpret them as two different examples and not a reason to argue. Thanks.

 

[sweet97]

That's correct HIGH_GUY! That's why I am thinking I can use the AFPR to tweak the MAFT settings to let the translator set the fuel and timing and then be able to either lessen or increase the fuel ever so slightly to aid in tuning. Say the translator setting is going to set the fuel at "X" and the timing will be set at let's say "Y" due to the air the ECU "sees". This setting may knock due to being too lean for the timing the ECUis allowing. I add to the base a few psi of fuel and perhaps the knock stops! Sounds good doesn't it? Anyone agree with my line of thought on this? mark

OK HIGH-GUY then do you agree with what I wrote? I can use the translator for a particular setting which will affect fuel and timing. With the regulator the same setting will have the same timing curve but either more or less fuel depending on where I set my base fuel pressure. If true I could eliminate knock if it is due to a lean condition without changing the MAFT seting, just by changing the base fuel pressure. If this is correct I have learned some good info for tuing with an AFPR! Mark
PS: There's a difference between dumb and uneducated! I'm slow and uneducated but not dumb!!...

 

[pboglio]

I have no experience with aftermarket AFPR's. But, I've measured my fuel pressure at 18 psi and it was 58 psi dropping to 55 psi by redline on a stock T25 and stock injectors.

My mods are way past that now. Unless you are running a HIGH flow fuel pump (liters per hour) and know the fuel pump peformance chart for your fuel pump, you are likely going to crush its ability to FLOW the necessary fuel volume at high rpm with high fuel pressure. I have 660 injectors and my 150 lph DENSO fuel pump is a GONNER by 24 psi of boost pressure in the intake manifold. I can see my A/F ratio just drop off the cliff, even though calculated A/F is good and the injectors are WELL below 90%. I'm limited to race gas/24 psi/bigger fuel pump etc. The fuel pump is flowing LESS fuel under HIGHER fuel pressure, how much less you can find at www.roadraceengineering.com etc.

Do yourself a favor, buy a fuel pressure tester that you can tape to the windshield or buy a permanent one. Set it to factory specs at idle (35-38 psi) and that plus boost under WOT. Then tune using your SAFC.

 

[sweet97]

Gene I am using a MAFT for tuning. If I set my WOT knob on a particular number the eCU sees "X" amount of airflow and adjusts fuel and timing from that. Doesn;'t my logic make sense that if I adjust the base pressure I would have the same timing curve but different amounts of fuel or does the amount of fuel set the timing?
The ECU does not know what size injectors I have or what the base pressure is.
If I click the WOT knob 1 click counterclockwise I would end up running leaner with more timing. I am hoping if I adjust the base pressure a few lbs. higher I might be able to run the additional timing but with more fuel?>! Or would I have to be able to adjust the fuel on the fly to acheive what I want? More timing without knock? mark

 

[pboglio]

Gene I am using a MAFT for tuning. If I set my WOT knob on a particular number the eCU sees "X" amount of airflow and adjusts fuel and timing from that. Doesn;'t my logic make sense that if I adjust the base pressure I would have the same timing curve but different amounts of fuel or does the amount of fuel set the timing?
The ECU does not know what size injectors I have or what the base pressure is.
If I click the WOT knob 1 click counterclockwise I would end up running leaner with more timing. I am hoping if I adjust the base pressure a few lbs. higher I might be able to run the additional timing but with more fuel?>! Or would I have to be able to adjust the fuel on the fly to acheive what I want? More timing without knock? mark

Maybe I got screwed up. You want to add fuel via MAFT (i.e. less timing) and drop the fuel pressure to balance out, theoretically this would work. The engine knows how much fuel you have based on 02 feedback. Fuel pressure will ALWAYS be low, but the 02 sensor will fight the MAFT for control of the fuel injectors at part throttle. If you pull back fuel pressure to reduce FUEL by 0.8333% (550/660) of normal via fuel pressure (i.e. reduce fuel pressure to .694% of stock), the 02 sensor will hit its fuel trim limit. You add +120% (via the MAFT) fuel to make 660 injectors look like 550 injectors to the computer. Remember, the MAFT gets knocked out of control during part throttle, your fuel pressure is low, and the computer 02 can only add +120% fuel and then it runs out of adjustment at part throttle. You are basically 1% fuel away from always running lean at part throttle, pray your fuel injectors don't clog or you're screwed. You have the capability of running LEAN at part throttle, even with the MAFT. WOT works because YOU and the MAFT are the computer in this case, take out a little fuel pressure & add a little fuel, everything SHOULD balance, but only at WOT. Part throttle the MAFT gets knocked out of control. Don't do it, set the fuel pressure to factory specs and dial in WOT using the MAFT. The timing adjustment is a tuff one, your kinda screwed both ways. Last option is 550cc injectors, it by far is the safest method short of DSMLINK for your 1G.

Wait, I got a great Idea, this question is best answered by Tom Dorris and Dave Mertz @ www.dsmlink.com/forums , just join up and post. These guys are Fuel injection gurus (DSMLINK creators). Post in the aftermarket fuel injection forum section or whatever and they will be nice to you.

 

[1LE]

I have 660 injectors and my 150 lph DENSO fuel pump is a GONNER by 24 psi of boost pressure in the intake manifold. I can see my A/F ratio just drop off the cliff, even though calculated A/F is good and the injectors are WELL below 90%. I'm limited to race gas/24 psi/bigger fuel pump etc.

Wow, we could swap pumps I use a 290lph pump to supply fuel to 550's at 14psi of boost

 

[sweet97]

Gene I am talking only WOT. I will check out the contacts you gave, thanks. There must be a way to tune using the AFPR. Otherwise it becomes spending $150. to $275. just to allow the use of a big pump and bring the base under control and set it at stock. The 02 voltage is not controlling anything under WOT. What I'm saying is set the MAFT a click lean for the timing advantage and compensating with the higher base pressure to NOT run lean when I click the MAFT to a lower setting. Could just be junk to throw out the window but I have to try or at least know for sure! Thanks as always. Mark

 

[Darksyne]

Wait, I got a great Idea, this question is best answered by Tom Dorris and Dave Mertz @ www.dsmlink.com/forums , just join up and post. These guys are Fuel injection gurus (DSMLINK creators). Post in the aftermarket fuel injection forum section or whatever and they will be nice to you.

Only people who own DSMLink may join the forums

 

[sweet97]

Perhaps someone will be kind enough to ask them if a 1G owner using a MAFT can use an AFPR to tune his motor.
Like leaving the WOT setting on a particular setting and then adjusting the base fuel pressure. I am only interested in WOT operation at this point as far as tuning with an AFPR goes. Mark

 

[AL92]

From everything I have read Mark you can raise fuel pressure and then turn down maft so you gain timing.Lots of guys run past stock fuel pressure it don't make the injectors go 100% faster it extends their flow capabilities.They are rated at a certain pounds per pressure normally..say 30 pounds..I am used to v8 injectors but same deal and say at 42psi base..raise it to say 50 and you all of a sudden have like 36 pound injectors.I am just pulling numbers out of a hat but thats what happens.They flow more at higher pressure but at way higher pressure than stock then its not good and you need bigger ones.For our turbos Sweet the afpr should be ample with our present 650 and 660 injectors.Remember you run leaner without knock on race fuel and on the street our injectors will easily do 20psi or so on pump.No worries mate..turn up the afpr and turn down the maft..I have done lots of reading on this lately.Don't ask me to link posts ..
just trust me..!! Of course once you change base pressure your base maft settings for injectors will change too and you will have to lean it out more if you raise base pressure.
But thats what you usually want anyway.

 

[1LE]

Keep in mind though, the FPR raises pressure 1:1 with boost... If you're running lots of boost you may end up with pressure that's too high for the injectors work the best...

 

[sweet97]

Stock injectors are usually good to 60 PSI. mine are from buschur so i will find out what they recommend for max pressure. Mrk