I think I'll pull the hat tomorrow and check everything.
Fuel rail pressure dropping
- Thread starter zquez
- Start date
I think I'll pull the hat tomorrow and check everything.
Your tuner should be able to tell, I know my tuner let me know when it looked like one of mine was going out. I got oem style replacements from rockauto.com for a decent price, believe the brand is denso or something like that.
I trimmed the hose about .25 to .5 of an inch and replaced everything. Took it for a drive today and its worse. I was watching the screen the whole time to make sure I didn't max out the pump but today it was erratic.
I got 100% dc while maintaining a constant 3500 rpm. It held delta psi until 62% dc then dropped to 28 psi before building back up around 35 psi. Then at 94% dc it drops down to 17 psi. It hits 100% at 3491 rpm (NOT WOT) and drops to 11 psi, 6, then 4 psi. ALL AT 3500 +/- 50 RPM!!!!!
at 100% dc the volts are 13.10.
Im about sick of this shit.
Whats next boys? GT500 pumps? Going back to stock? Blowing a motor? ughh.....
I was looking at boost a pump, but it seems to make the pump work harder by giving it more voltage. If my pump is 100% dc at 13 - 15 volts how does adding more help?
I got 100% dc while maintaining a constant 3500 rpm. It held delta psi until 62% dc then dropped to 28 psi before building back up around 35 psi. Then at 94% dc it drops down to 17 psi. It hits 100% at 3491 rpm (NOT WOT) and drops to 11 psi, 6, then 4 psi. ALL AT 3500 +/- 50 RPM!!!!!
at 100% dc the volts are 13.10.
Im about sick of this shit.
Whats next boys? GT500 pumps? Going back to stock? Blowing a motor? ughh.....
I was looking at boost a pump, but it seems to make the pump work harder by giving it more voltage. If my pump is 100% dc at 13 - 15 volts how does adding more help?
05yellowgt
Senior Member
Who's tune are you running? Lito's, or are someone else's and he is helping look at logs?
W3bb3r04
Slow 3v Member
Dan @ Pro Dyno tuned my car. I actually took it to him and sit in the car with me while we drove around logging and he didn't see anything wrong except that the tps counts seemed to be low. Lito found the fuel issue for me in the logs.
05yellowgt
Senior Member
It almost sounds like to me that the fuel pump voltage tables and other tables associated with the return fuel system aren't calibrated for the pump you are running. It can result in incorrect fuel pump duty cycle calculations, erratic fuel pressures as the computer tries to learn on the go. You'll see erratic and and rapid swings in fuel pressure as the system tries to anticipate where it needs to go to stablize your DeltaV @39psi or whatever is being commanded by your tune.
It has been several years since I did any SCT tuning, and I don't pretend to be anything other than an amateur enthusiast who had the opportunity to learn a bit and apply that to tuning my own car, which I stopped once I got into more than basic bolt on's.
It has been several years since I did any SCT tuning, and I don't pretend to be anything other than an amateur enthusiast who had the opportunity to learn a bit and apply that to tuning my own car, which I stopped once I got into more than basic bolt on's.
But would the computer not be able to realize on the fly that its losing pressure and leaning out and try to fix it? I assumed thats why i got the throttle body codes, because the computer was limiting the incoming air flow to stabilize the a/f ratio. The tune commanded more air but the computer said no.
I put it back to stock and reloaded the tune so we'll see if that makes a difference.
ill also give dan a call and see if he has any ideas.
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05yellowgt
Senior Member
The computer will try to learn as time goes on, but if the tune is really off it is going to have a really hard to compensating.
one eyed willy
Pizzle fo shizzle
compare fuel pump volts to actual fuel pump volts and see if they are close to matching, the pump will start out at the volts in the table and then correct its self...the closer they are to being correct the faster or less correction needed....for the problems you are having thou, the tables would have to be really out of whack to be that bad IMO......sound slike a physical issue
BAP wont do anything for you.
have you tried blowing out the fuel lines? you said something ruptured...exactly what was it and how did you fix it?
BAP wont do anything for you.
have you tried blowing out the fuel lines? you said something ruptured...exactly what was it and how did you fix it?
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The line going from the pump to the hat burst. It was really only a rip and there wouldn't be much debris if any and the filter would have caught it, which I replaced.
I just logged it again with the re-loaded tun and it didnt feel erratic but it did not feel 100%.
@ 100% dc
FPUMP_ACT_VOLTS 13.65
FPUMP_FLOW_RATE 1.48
FPUMP_VOLTS_TAB 8.02
I have seen the fuel pump act volts @ 14.53 and volts tab @ 9.78
one eyed willy
Pizzle fo shizzle
FPUMP_ACT_VOLTS 13.65
FPUMP_VOLTS_TAB 8.02
So your ECU thinks it should be 8.02 volts but its actually taking 13.65. This may be why the DC is so high, the ECU knows it is having to give it more voltage than what is commanded.
You need to do some normal driving, and get the tuner to correct the voltage table based on the data logs, your fuel pump tabel should almost match your actual voltage....it will never be exact but it should be ALOT closer. 5 volts is a huge difference.
FPUMP_VOLTS_TAB 8.02
So your ECU thinks it should be 8.02 volts but its actually taking 13.65. This may be why the DC is so high, the ECU knows it is having to give it more voltage than what is commanded.
You need to do some normal driving, and get the tuner to correct the voltage table based on the data logs, your fuel pump tabel should almost match your actual voltage....it will never be exact but it should be ALOT closer. 5 volts is a huge difference.
W3bb3r04
Slow 3v Member
Think it could be the wire upgrade?
I don't know. I wouldn't think so because it is giving more power to the FPDM which regulates the voltage going to the hat to control the pump. Right? The thought had crossed my mind of having the wire upgrade going to the fuse box instead of straight to the battery but I don't know that that would make a difference. It seems like its in my tune based off of what One Eyed Willy is saying.
The FPUMP_TAB seems to max out around 8 but the actual voltage keeps increasing.
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I just got off the phone with Dan and I'm gonna bring the car by tomorrow afternoon for him to look at it. He says that the Walbro 405 isn't a variable speed pump and he's had issues with them before (?). 
But basically that that pid is a learning table and that there may be something weird going on with how and what the car is learning. Hopefully we make a breakthrough.
But basically that that pid is a learning table and that there may be something weird going on with how and what the car is learning. Hopefully we make a breakthrough.
W3bb3r04
Slow 3v Member
Let me know what they find out!
Of course! What kind of power are you making? Are you maxing at the top of the RPM range?
W3bb3r04
Slow 3v Member
Never had it dyno'd. I will be at the Pro Dyno meet next weekend. And mine is reading maxed out at 5800 rpm but the Air fuels dont change like you would think and it definitely makes it to 6000 without fallin on its face.
Mine makes it that far on warm days and the pressure never drops far enough because I shift at 6k. Strange. What do you think you're making? 400?
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