fpr or richen with maft???

[91-gsx]

now i just had a question for you tuners, when you tune how do you know when to increase your fuel pressure, or to just richen using something like my maft? i am currently running about 26 psi on my fpr becuase they tell you to take the vacuum hose off and set the pfr to 36psi and then put the vacuum line on and it shoudl drop by a few psi and that is what i did, and it as 26 psi. should i increase it?

 

[sweet97]

I would richen with the AFPR. Richening with the MAFT will cause you to run less timing and possibly hit fuel cut. You may have a no fuel cut burned into your EPROM you would lose timing. I run up to 43-45psi on my FPR with the line off. You can increase boost a couple of lbs. and increase the fuel pressure a couple lbs. then check the timing and knock, and possibly raise both again or back the boost a lb. to rid knock if there is any. The AFPR is another tuning tool. Mark

 

[91-gsx]

so if i am knocking up top by lets say 10 knocks but i am getting full timing, which is like 22 degrees right? anyway would i just increase the fuel pressure a little to get rid of the knock? and do i have to take the line off when i adjust it? becuase mine can go up without taking the vacuum line off.
thanks mark

 

[99gst_racer]

Always adjust your fuel pressure with the vac. line pulled - otherwise you're adjusting blind. I'd turn the pressure up a little more (2-3 psi) if it were me, but I would make my tuning adjustments from the MAFT, not the afpr. The MAFT is a tuning tool, so use it for what it does. If you need to add fuel, then do it with your tuning tool. Do you have any recent logs?

PS - 26 PSI seems kinda low. I don't think it is supposed to drop 10 psi after you reattach the vac line. I have my fuel pressure set at 42-43 psi and after I reattach my line, it drops to about 37 psi.

 

[sweet97]

The AFPR is a tuning tool also. Adding fuel with the maft could result in fuel cut because the ECU may see too much air. I would pull the line as that is what the pressure is at WOT as vavcuum is no longer applied, boost is. Uop the pressure 2 lbs. at a time and see what happens to the knock. You may need mto lower your idle knob if you increase the base pressure enough. Mark

 

[99gst_racer]

The AFPR is a tuning tool also. Adding fuel with the maft could result in fuel cut because the ECU may see too much air. I would pull the line as that is what the pressure is at WOT as vavcuum is no longer applied, boost is. Uop the pressure 2 lbs. at a time and see what happens to the knock. You may need mto lower your idle knob if you increase the base pressure enough. Mark

Yes, but increasing the base fuel pressure will send an increase in fuel across the entire RPM band. Unless he is evenly lean across the entire band, that could make him run rich at some points. Whereas, with the MAFT, you can add or take out fuel in fine increments across specific points on the RPM band. If you could tune out knock with a small twist on the afpr, then sales in DSMlink, S-AFC, etc... would plummet.

 

[sweet97]

Paul you are correct as am I. Depends on the situation and the amount of change that is needed. The problem with adding 5% of fuel at WOT will also let the ECU see possibly too much air resulting in fuel cut and a timing decrease. Adding a couple psi of base fuel which can be taken out at idle and at the MID point may solve 91-gst problem. He can try both and see which works best. I got the AFPR tuning method from a guy running in the 11's. base timing can also be adjusted, backed off a couplke defgrees. There is more than 1 way to tune. I just offerec something that I use. I also have a maft. mark

 

[GPTourer]

PS - 26 PSI seems kinda low. I don't think it is supposed to drop 10 psi after you reattach the vac line. I have my fuel pressure set at 42-43 psi and after I reattach my line, it drops to about 37 psi.

But because he is a 1G, his pressure should be a lot lower right?

I have mine set at 41.5 or so (on my 2G). I think if you have injectors that are a little bigger then you need them to be, you might lower the pressure a bit so you can get your duty cyle up a bit higher. Course I have no idea what that is, but it keeps you from having too pull so much out with an SAFC2 giving you more timing and thus more power, no?

 

[99gst_racer]

The problem with adding 5% of fuel at WOT will also let the ECU see possibly too much air resulting in fuel cut and a timing decrease.

Normally, yes. But the thread starter is using 750cc injectors and a stage 3 chip. So, I would think it's safe to say he doesn't have to worry about fuel cut. But even if he didnt have the chip, he would be taking out fuel for the 750's, so he would just take out less to richen it up. And taking out fuel rasies the point in which you hit fuel cut because the ECU see's less airflow. Also, the MAFT v2.01 allows adjustments in 2% increments, so he wouldn't have to add a full 5%.

Adding a couple psi of base fuel which can be taken out at idle and at the MID point may solve 91-gst problem.

Yes, that may work. It's definitely worth a try.

I think the biggest question is if he even needs more fuel. Like I said, I'd like to see a log. I'm rich and I still get knock sometimes. More fuel isnt always the solution......

 

[91-gsx]

so i first understand that i have to disconnect the vacuum hose to raise the base fuel pressure. not whe you guys raise boost do you also raise the base psi?
thanks

 

[sweet97]

Normally, yes. But the thread starter is using 750cc injectors and a stage 3 chip. So, I would think it's safe to say he doesn't have to worry about fuel cut. But even if he didnt have the chip, he would be taking out fuel for the 750's, so he would just take out less to richen it up. And taking out fuel rasies the point in which you hit fuel cut because the ECU see's less airflow. Also, the MAFT v2.01 allows adjustments in 2% increments, so he wouldn't have to add a full 5%.


Yes, that may work. It's definitely worth a try.

I think the biggest question is if he even needs more fuel. Like I said, I'd like to see a log. I'm rich and I still get knock sometimes. More fuel isnt always the solution......

I agree with you 100%. I am just stating that the AFPR is an additional tuning tool.
There ARE GUYS WHO THINK ALL AN afpr DOES IS STOP FUEL OVERRUN. tHAT IS WRONG AND IT COULD BE DONE FOR LESS THAN WHAT SOME OOF THESE afpr'S COST! Sorry for the caps, mistake.
Say a motor was knocking a little or had no knock but you wanted to run a couple psi of additional boost. Adjusting the base pressure a couple of lbs. may do the trick. I use mine as a tuning aid, thats all. Mark

 

[TSIfreek]

so i first understand that i have to disconnect the vacuum hose to raise the base fuel pressure. not whe you guys raise boost do you also raise the base psi?
thanks

Not nessasaraly. Your AFPR is a 1:1 rise in pressure. As boost rises fuel pressure rises with it.
When you set the BASE fuel pressure have the vacume line off and pluged. Adjust it until you have 40-43 psi and your done put the vacume line back on and it will drop. I would go more on the low side with the 750s. The chip you are running is programed for 750s right?? MAFT program will also help. Play around with tuning the MAFT and FP and see what the engine likes the best. You want to shoot for very little knock. Also check for boost leaks every now and then.