please look at this xfi log

[asloan5]

I have a stumble off the line. I believe it to be a fuel delivery issue. Pay attention to 1.1 to 1.9 seconds launch was pretty hard. The fuel pressure is ramping up with boost then at 1.4-1.7 seconds the pressure drops then starts to recover as boost is rising the whole time. Pressure should have kept rising with boost. The wheels lift up drop down due to a stumble in the engine and lift back up again. The fuel pressure is ramping up with boost at launch then dips when the stumble happens then picks back up. Is that fuel pressure drop enough to be the cause of my stumble. It this possible just from the inertia of the launch pulling the towards to back of the car ? Pump is a fuelab with a ss prefilter and post filter which both are clean with a fuel cell baffled and with foam and #8 aeroquip teflon line to the fuel rail and a fuel lab regulator coming off of the fuel rail with a #6 teflon line back to the cell. The fuel pressure readings are not 100% accurate I'm fiddling with the settings in fast to make it more accurate but the pressure drop is for real. Don't pay any attention to the log after this time I broke traction and spun then had to get out of it.
Fyi We retraced all the fuel lines from cell to fuel rail and back there is not pinches tight spots questionable areas where the line is routed. 100 % sure of this.

 

[Otto J]

take another log launching much easier and see if it does the same thing.
I see you are running a #8 up front,what size do you run from the cell to the pump?

 

[asloan5]

2 #8's from cell to a Y fitting #10 from Y to the prefilter and the prefilter is connected directly to the pump inlet all inline.

 

[asloan5]

41402 Prodigy Fuel Pump High Efficiency EFI In Line

here is a link to the pump with a pressure / flow chart for the 41402 pump

 

[norbs]

Looks like the pump is keeping up fine after the launch, but it looks like it picking up air on the launch. Why is your battery voltage falling so much during the run?

 

[asloan5]

Looks like the pump is keeping up fine after the launch, but it looks like it picking up air on the launch. Why is your battery voltage falling so much during the run?

battery voltage poss fan coming on because my temps are over 160 at the end of the track
car has a 15 gallon cell with 7-8 gallons in it the cell is baffled and has foam in it with a rear bottom sump. I cannot imagine that its a fuel starvation from the cell.

 

[S2V6RACER]

You need to get the voltage up. The pump isn't keeping up IMHO.

 

[asloan5]

how accurate does xfi report battery voltage I recall seeing threads about that

 

[Boost231]

it depends on how its wired. i have 14.* volts coming from the alternator while the car is running. im getting this same power to the inlet of the caspers adapter box. on the outlet side of the caspers box it drops the power off to 12.* volts which is also showing on the xfi. now i was told i could either hotwire the xfi or try changing the ground out to a better ground. this is what john spina told me about the box.

Regarding voltage drop, it is usually a function of excessive load at the XFI ECU. Check the voltage with the ECU unplugged, then check it plugged in. IF the drop is apparent when plugged un, either the unit draws too much current, or there is excessive resistance at one of the connectors. Look at the black connector from the car’s harness for any signs of corrosion for starters.



The 12 volts can be seen at the pink/black wire in the engine harness connector, and flows through to the B connector, terminal B17.



Other things to consider, take a look at the fuse panel for any signs of corrosion as well, and look at your bulkhead under the hood (C100, the one under the power brakes system). It is common to see corrosion at the power feeds in this bulkhead. This is the source of your ECM power.



John


now if i have the car running and check the voltage at the pump i see 14.* volts but the xfi is showing like high 12's to low 13.'s

i have yet to fix the voltage problem as far as what the xfi reads but i will by the end of the year i hope. i just dont have the car here with me in cally so i cant fix it to give you a answer of what i did to fix it either hotwire or ground.

 

[asloan5]

whats all of your opinion on the drop in fuel pressure in relation to the car nose diving am I in the right line of thinking. and on a hard launch 1.4 60 foot time are any of you logging a drop in pressure like I did from the inertia ?

 

[S2V6RACER]

No, my fuel psi and voltage are rock solid. Are you sure your fuel pump is operating properly and what size fuel cell are you running?



What is your E.T. and MPH goals with your combo?

 

[asloan5]

No, my fuel psi and voltage are rock solid. Are you sure your fuel pump is operating properly and what size fuel cell are you running?



What is your E.T. and MPH goals with your combo?

Fuel pump just came back from fuel lab with flow charts they say it's fine.
15 gallon cell with approx 8 gallons in it. Cell is baffled and has foam.
et goal is a high 9's @136 ish

 

[asloan5]

You need to get the voltage up. The pump isn't keeping up IMHO.

I ordered the 240amp alt from the other tb board. I should have it in time for test and tune thursday nite. I'm also upgrading the size of the fuel pump relay from a 30 amp to 75 amp to make sure the it can handle the current, The requirements of the pump say 30+ so I will be on the safer side instead of the minimum.

 

[norbs]

Here's something you can do the math with voltage drop. Try different awg sizes watch the voltages drop quick.

Voltage Drop Calculator Tool

your running 10 awg i assume?

 

[asloan5]

your running 10 awg i assume?

10 awg from my cutoff switch to the relay for the pump
4 awg from alternator to battery side of cutoff switch

 

[Reggie West]

If you dont have one get a volt booster. These cars have ground issues the only we cured it was a 16 volt system.

I cant read the file you attached but if the FAST is seeing anything below 12.5 volts at any point, it will affect the FAST unit and bog it. They are very finnicky about that.

Good luck.