I am running the Ptuning fuel return system on my 05 tC. Ive been trying to set a good tune on my car but its a little hard when my fuel pressure keeps changing. I have my base fuel pressure set to 50psi. On a morning start up my fuel pressure will be at 72psi. After driving around for about 10mins. My fuel pressure will go to 58psi. Once i actually start driving for about 30mins itll finally settle to 50psi. Is this normal? how are you suppose to set a good tune if 30mins later my fuel pressure drops by 22psi?

 

its normal bro

 

whats happening is the car is warming up and it will start to pull more vac, higher vac drops the pressure. also heat will cause the spring to "soften" so to speak.

for instance i just put my dezod fuel return system on yesterday and set pressure to 45psi...did a few tuneing runs and checked pressure afterwords, it was now sitting at 40psi. so I cranked up the pressure again this morning back to 45psi after the car was warm, after a few tuneing runs i checked again and its now at 43psi (which was my goal).

 

oh btw if your set on 50psi and you drop to 20psi then you got issues, fuel leak either intank or downstream.

 

I figured it would be something like that. But why would it make such huge changes on mine. You have a litte 5psi buffer while mine is making 22psi changes.

 

well there arnt any leaks outside so if i do have a problem i guess its internal in the tank.

 

its possible..but have you ever looked at what the stock fuel system does on a cold start up? I have and when cold your looking at anywhere between 45psi-50psi...after the car has been running for a bit it drops to 43psi. not sure how thats really possble for the stock fuel system to have that much variance but if i were to guess it would prolly have something to do with the fuel pump heating up the fuel and inturn warming up the stock fpr spring, or underhood temps heating up the lines. Cant say for sure cause I didnt engineer this stuff...lol

 

Still a small change as opposed to my changes. Guess for now till i figure it out im just gonna have to drive till my car decides to settle on 50psi before i do any tuning or racing

 

maybe the fpr's valve is sticking when its cold.

 

Im really thinking that whatever the problem is it has to be at the FPR. I am sertain that i hooked everything up right. I mean the kit is almost dummy proof from messing up.

 

Where did you connect the FPR vacuum line?

 

^^good point

 

to my vacuum block were everything else is connected to such as my boost gauge, AEM FIC, electronic boost controller, water/meth vacuum source. Everything else works great off this source just my FPR is giving me trouble

Oh yea and vacuum block is coming off my intake manifold were the pcv use to be. I deleted the PCV a long time ago and now just vent to the autmosphere

I dont think vacuum source is the problem. The changing pressure issue still happens even with the Vacuum disconnected off the FPR

 

Make sure you used the red block off plug in place of the factory reg. Only other thing I can think of is that a line is pinched between tank and floorboard. Make sure lines route towards rear of car coming off sender assembly... and go through tunnel area.

 

The red plug is in. I have full adjustablilty of the fuel pressure. The lines arnt pinched. They have enough clearence between tank and floor board. Im 99% its got to be something with the FPR.

 

i notice some changes in fuel pressure too, between cold start and when its hot.. i could barely notice a change in afrs though but mostly on idling.. running on boost, i see just a bit and im not even sure its fuel pressure related.. i might need to recheck pinch line too, but when i installed it i checked it over 5 times making sure it not pinched

 

that is NOT supposed to happen.

base fuel pressure is supposed to be set without a vacuum line connected to the FPR

One of the lines may be kinked at the fuel tank (its a tight fit) or you could have a faulty regulator.

I would also inspect the OEM fuel pump assembly make sure all of the wires and hoses are tight

 

I thought it was best to connect the FPR to a boost-only reference source like the compressor housing? This way the FPR is reading constant atmospheric pressure and maintaining constant pressure when in vacuum and then raises 1:1 with boost pressure. Are you running a check-valve in-line so the FPR only sees boost? If so, check to make sure it's not sticking.

If you're no longer scavenging combustion blow-by gasses with engine vacuum and fresh air via the PCV valve, you should probably change your oil a lot more often. Better yet, reconnect the PCV side. My 2 cents.

 

Well actually I have my boost source connected to my intake manifold. Didn't know it was suppose to be a boost only refrence. Ill make the change but its not gonna make a difference on my end. The chang in pressure happens even with the vacuum disconnected.

As for the pcv. Iv been running like that for the last 15K miles like that with no problems. Plus I already change my oil every 3k miles. I believe that's a good enough change in oil.

Again for those asking about the lines there all good. Iv already checked them all and they are all fine.

 

I wish I could be more help. Good luck Brother.