fuel pressure drop after 6k rpm

[s2k_suprchrgd]

I went to get my car tuned today but for some reason my fuel pressure drops after 6K rpm. I thought it was a bad fuel pump so I changed it to a new walbro 255 but still having the same problem. I dont know what else to check or look for??


FYI I'm runing:

Fullrace gt35r kit
aem ems
oem FPR
RC 1000cc injectors
relocated battery in the trunk
9:1 comp built motor

[dc_35]

i'm guessing you start building quite a bit boost at 6k also....it's the boost pressure "pushing" back on the fuel...i think a non-oem FRP is the only/best solution. The oem isn't made to raise pressure during boost.

[dc_35]

http://www.youtube.com/watch?v=E2fLKOtchso#t=1m43s

^ the hondata guys explains some of it.

[Sideways]

I had a similar problem and it turned out the be a clamp on little hose the pump is inserted into in the tank. The silly clamp would only tighten so much and then pop it would be loose again. That hose does require clamps to hold higher pressure.

[Stratocaster]

How are you monitoring the fuel pressure ? You have a gauge installed on the fuel rail?

[repiv]

http://www.youtube.com/watch?v=E2fLKOtchso#t=1m43s

^ the hondata guys explains some of it.

That guy's way too smart for me, but what he says does make sense. If fuel pressure drops, add more fuel.
The problem with using the OEM FPR (and not an aftermarket fuel management unit that ramps up fuel pressure in response to boost pressure) is that it won't hold back any more pressure from a higher output fuel pump. It's designed to act like a dam and maintain a certain amount of pressure. If you put in a "bigger" fuel pump, that dam will just release the excess pressure anyway. You need a bigger dam in order to take advantage of the bigger pump. That's why Vortech and Comptech can get away without tuning for more fuel on their stock kits. They give you a bigger pump and a bigger dam (FMU) to keep the pressure up. If you tune for more fuel, you don't need a bigger pump or dam.

[repiv]

As we've hinted in your other thread in "Xviper's Den", you may not need to worry about the fuel pressure drop if you tune for fuel. If you can get the A/F ratios to where you need them to be, you should be fine so long as you're not over taxing the pump or the injectors, but it looks like you've got the big injectors and pump now anyway.

[s2k_suprchrgd]

i'm runing a greddy fuel pressure gauge that sits on top my dash...

xviper after 6K rpm my car start to run really lean so the tuner cannot add any timing or tune it properly.

[s2k_suprchrgd]

Sideways i had a original 255 walbro fuel pump that came with the VTSC kit and i had no problems with it. My problems just started after I installed my turbo kit. how did you fix the clamp problem?? i just replaced my fuel pump but the clamp wasnt loose according to AMS.

do you think the fuel line has something clogging it?? maybe O ring??

oh ya i also have a greddy fuel pressure gauge with a sensor tapped into the fuel rail..

[repiv]

Sideways i had a original 255 walbro fuel pump that came with the VTSC kit and i had no problems with it. My problems just started after I installed my turbo kit.
Did you retain the Vortech FMU? That might help.

[dc_35]

Did you happen to look at the video i posted at all???

Is this an actual problem is your car leaning out because of the fuel pressure or do you just think it shouldn't be doing that?

[karno]

I went to get my car tuned today but for some reason my fuel pressure drops after 6K rpm. I thought it was a bad fuel pump so I changed it to a new walbro 255 but still having the same problem. I dont know what else to check or look for??


FYI I'm runing:

Fullrace gt35r kit
aem ems
oem FPR
RC 1000cc injectors
relocated battery in the trunk
9:1 comp built motor

I have the same AEM EMS CPU as yours.. and I didn't watch the youtube dingy yet, but I just go ahead and jump in;
How did you know that the fuel pressure droped? Was is bogging before the transition to VTEC? Base on the fuel map that is on the higher RMP; especially, before VTEC that the fuel ratio is dramtically decrease versus the build up before 6k rpm.. I believe you may be experiencing the opposite of low fuel pressure but instead too much fuel.. It would help if you have the Fuel/Air ratio gauge and sensor installed and have the car tuned live on the road with the AEM EMS.. That how I got my tuned.. :thumbsup:

[4U2NV]

Merged redundant threads.

[s2k_suprchrgd]

^^^ thanks...

[s2k_suprchrgd]

Did you retain the Vortech FMU? That might help.


no i'm not using the FMU anymore...

[s2k_suprchrgd]

I have the same AEM EMS CPU as yours.. and I didn't watch the youtube dingy yet, but I just go ahead and jump in;
How did you know that the fuel pressure droped? Was is bogging before the transition to VTEC? Base on the fuel map that is on the higher RMP; especially, before VTEC that the fuel ratio is dramtically decrease versus the build up before 6k rpm.. I believe you may be experiencing the opposite of low fuel pressure but instead too much fuel.. It would help if you have the Fuel/Air ratio gauge and sensor installed and have the car tuned live on the road with the AEM EMS.. That how I got my tuned.. :thumbsup:


I dont have a A/F ration gauge but my tuner has one that he plugs into my car. i'm not sure if i'm getting to much fuel but another s2000 like mine had no problem with the tune, his fuel pressure was steady through out the rpm. Do you think I might have a kinkedor clogged line?? oh ya my fuel pressure drops after 6k but it really drops after 7k thus runing really lean.

[repiv]

no i'm not using the FMU anymore...

Without the FMU, you can't really take advantage of the higher fuel pressure the Walbro puts out. Like I said before, the OEM FPR just releases any excess pressure over the stock requirements. The FMU provides a stronger dam.
However, if you tune the injector pulse and duration, you can still use the extra volume the Walbro puts out. If you can't have pressure, you take volume.

[karno]

I dont have a A/F ration gauge but my tuner has one that he plugs into my car. i'm not sure if i'm getting to much fuel but another s2000 like mine had no problem with the tune, his fuel pressure was steady through out the rpm. Do you think I might have a kinkedor clogged line?? oh ya my fuel pressure drops after 6k but it really drops after 7k thus runing really lean.


It seems like you are running rich instead of lean, because the fuel ratios after 6k rmp is like 10% versus 100% at 3k rpm.. Also, the plug-in F/A only work if you still using the stock MAP sensor.. So, make sure that sucker is clean. But tuner alsways use the one that stuffed into the exhaust only and that is not very acurate. Have one installed around the CAT area, that is the best place to read the A/F... ;) And when this is done do a live tune on the road and go through the RMP ranges on every single gear on lite and heavy load, and the A/F gauge will come in very handy, don't read the F/A from the computer. That is the best way to tune the car...

[dc_35]

I dont have a A/F ration gauge but my tuner has one that he plugs into my car. ....oh ya my fuel pressure drops after 6k but it really drops after 7k thus runing really lean.

so did your tuner say you are leaning out? what was his solution to this? or did he tell you to go home and fix your fuel pressure? Fluctuations in fuel pressure should be able to be tuned out by increasing injector pulse, i'm not sure why your tuner would not just do that, unless of course you were running out of fuel. but i don't think that would be the case.

I guess what i'm asking are you 100% for sure leaning out when your fuel pressure drops or are you just looking at the pressure and assuming less fuel pressure = less fuel = lean?

IMO it looks like you are worried about something that isn't really a problem.

and once again...

Did you happen to look at the video i posted at all???

Is this an actual problem is your car leaning out because of the fuel pressure or do you just think it shouldn't be doing that?

[s2k_suprchrgd]

so did your tuner say you are leaning out? what was his solution to this? or did he tell you to go home and fix your fuel pressure? Fluctuations in fuel pressure should be able to be tuned out by increasing injector pulse, i'm not sure why your tuner would not just do that, unless of course you were running out of fuel. but i don't think that would be the case.

I guess what i'm asking are you 100% for sure leaning out when your fuel pressure drops or are you just looking at the pressure and assuming less fuel pressure = less fuel = lean?

IMO it looks like you are worried about something that isn't really a problem.

and once again...


I'm sorry i didnt reply to you your post but i was at work and i cannot watch the video. I just watched the video it does make sense but my car is dropping fuel pressure drastically after 7k and the car starts to run really lean therefore my tuner cannot tune it. My tuner is chris black at AMS he knows this stuff he has tuned quite a few s2k in chicago area and he said he has never seen any s2k drop fuel pressure like my car. to answer your question my cars is running lean becasue of fuel pressure and it is a problem.

[dc_35]

How low does your fuel pressure drop?

[repiv]

running lean becasue of fuel pressure and it is a problem.
What was the a/f number? Fuel pressure doesn't dictate a lean condition alone.

[dc_35]

http://i476.photobucket.com/albums/rr128/aznasinine/1000ccinjectors.jpg

Here i made a little chart to try and show how losing fuel pressure doesn't mean you are losing the ability to fuel your engine.

As you can see from the chart Fuel pressure is PSI from 10-60psi, the corresponding cc/Min measurements for your 1000cc injectors are also shown as related to fuel pressure.

Now on the far right are theoretical HP numbers when using those flow rates at 80% duty cycle (a safe %), the equation to get these numbers is
(Flowrate lb/hr * Duty Cycle) / BSFC.

as you can see even if your fuel pressure drop to 20psi you still have the capabilities to support 460HP.

Now you haven't answered yet but i would assume that your not dropping that low, so any loss of fuel pressure can be corrected in the EMS.

[s2k_suprchrgd]

My tuner tried to correct the fuel pressure in the EMS and yes my fuel pressure is dropping that low.

[s2k_suprchrgd]

i'll get the exact numbers this weekend and post them

[s2k_suprchrgd]

it was a stupid washer by the fuel pressure regulator causing problem. its all fixed now. i made 535whp and 360trq. thanks for your help guys...