erratic fuel pressure under WOT......

[one eyed willy]

Im getting closer and closer to having my tune dialed in 100%.......doing some datalogging this weekend and noticed my WOT A/F was a bit up and down and not constant. It appears the fuel pressure is causing it? it should be at 38PSI but it is anywhere from 32 to 45 when im at WOT.Duty cycle looks great and no where near topping out.

my fuel setup is gt500 pumps with FRPP harness and modules, KB BAP, stock returnless lines with Fore fuel rails, 80# SD flow matched injectors, 10k miles on the fuel filter, 10K miles on the fuel rail sensor.

im not sure if its a tune issue or a hardware issue at this point, figured id throw it out there and see if anyone has any more experiance with a issue like this.

I have attached a datalog, hopefully that works OK.

 

[JeremyH]

I would go ahead and replace the fuel filter Paul and go from there. I replace my fuel filter once a year every 8-10k miles or less.

I didnt look at rpm but fuel pressure based on voltage and duty cycle looked to be normal as I would expect it though.

So your noticing a fluctuation in afr?

How old is the wideband sensor?

 

[one eyed willy]

15k-20k miles maybe on the sensor.ill grab a filter for shitz and giggles.

 

[one eyed willy]

i think i see a trend going on with the "fpump act volts".....voltage seems to dip with each dip in the a/f....

also when browsing thru the "fuel injector">"injector comp batt volt for pressure"...i see this chart..notice how at 50.029 it actually dips down? I don't think that's normal so I plan to fix that first!

 

[BruceH]

I just sent a value file from when I had those injectors. The big difference I see is the 30 psi value.

 

[one eyed willy]

Well that's very strange because I loaded that file already.ill check the one you sent and see what it does,lol

 

[one eyed willy]

I just loaded it again and get the same thing....

 

[one eyed willy]

I was reloading the same one as before, I can't open the last one you sent me because we have different ecu codes

 

[JeremyH]

I looked closer and see an issue. It starts at line 2429 on your datalog.

Your fpdm duty cylce all of sudden locks in and dispalys a .75 (75%) reading which is one of the trouble codes for when the fpdm/pcm senses an issue with the system. Also at the same time you fuel pump voltage goes negative/goes away.

This leans me towards a wiring issue, intermitent ground or power through the relay to the pump etc. Maybe the relay skipped a beat, you could try replacing the relay for the gt500 sysytem. How often does it do this?

 

[one eyed willy]

i think its always done that when i let off the gas, i think the pressure builds from the WOT and when i let off the pedal my pressure jumps to 75 for a breif milisecond and then it cuts the pumps to get the FP back down to 40...i dunno. but thats after the WOT and from what i remember its done that for awhile now.


what i have discovered is.... when i load the value file for gt500 pumps, its ALOT different than my current tune, meaning that the gt500 file looks like it was never loaded on the original tune.....or they have changed the file?

 

[JeremyH]

Yeah that doesnt sound right none of my setups or ones I have seen have done anything like that a spike from 39 to 75psi when letting off the gas is really weird. When I let off it dips to like 25psi then stabilizes at delta. Mine spikes when I go wot to like 60psi for a second then adjusts down not the other way around.

I point out the dc trouble code as it was the same one Matt(mindifIsmoke) was getting when he was having overpressure issues. His issue was seeing 60-70psi of pressure even though voltage was down to like 4-5 volts and should have been alot less pressure. On a normal log where pressure is fine be it tune or hardware you dont see those fpdm dc codes at all. When you let off the gas voltage and pressure should drop together, your voltage actualy goes away while pressure spikes. That seems off to me. I have a bunch of different datalogs from different fuel setups saved if you want one to reference.