Return Guys: Fuel Pressure Drop when hot?

[MTBSully]

Had my return system installed for 600 or so miles now with no issues thus far. I was sitting in traffic the other day though and it seemed like my fuel pressure was dropping when the car got hot. Gauge was reading around 20PSI. At first this was concerning, but I was keeping an eye on my wideband the whole time and it was dead on. Once I got the car moving to highway speeds again fuel pressure seeming to increase back closer to the value I set it at at the regulator (40PSI). When I was in traffic, it was around 20PSI.

Is this normal? Anyone else experienced this?:beer:

 

[GodStang]

Mine always stayed at 50psi until I went into boost.

 

[DSG2NV03]

mine always stayed at 50psi until i went into boost.

+1

 

[nonliberal]

Had my return system installed for 600 or so miles now with no issues thus far. I was sitting in traffic the other day though and it seemed like my fuel pressure was dropping when the car got hot. Gauge was reading around 20PSI. At first this was concerning, but I was keeping an eye on my wideband the whole time and it was dead on. Once I got the car moving to highway speeds again fuel pressure seeming to increase back closer to the value I set it at at the regulator (40PSI). When I was in traffic, it was around 20PSI.

Is this normal? Anyone else experienced this?:beer:

Sounds like a fuel pump issue. Are you running multiple pumps? If so do you have them set to all run at once or do the other kick in when in boost?

 

[03redfirevert.]

might check the batt voltage at idle

 

[CCM]

I've had the same issue before, stopped after driving 70+ on the highway and was stuck idling for 15 minutes at a railroad crossing. I watched it slowly drop from 30 to 20 while I was sitting there. I parked the car and checked the wiring in the trunk and the boost a pumps were both really hot (I have one for each pump to regulate the voltage). Getting back on the highway did nothing to fix it. By the time I got the car home, I was only showing 12 psi. Of course I stayed out of boost the whole time, and for the most part my AFR on my wideband stayed good. I let the car sit overnight, and the problem was gone when I fired it up the next day :shrug:

 

[triple-s]

Mine idle's at 44 psi then goes up with boost.

 

[mustang john]

You know I have mine set to 40psi base with the boost/vacuum reference line disconnected, of course when I plug the boost reference line back in the psi drops due to the vacuums affect on the regulator. It only reads 40psi if I am driving and have the vacuum/boost at 0.

All you guys saying your pressure is steady until you go into boost, you don't see any psi drop with vacuum from normal idle or cruising?

 

[itSSlow98]

Mine is set at 39 and it NEVER changes except for when it increases with boost. I would check voltage at the pumps when its dropping or it could also be the fuel overheating.

 

[mustang john]

Mine is set at 39 and it NEVER changes except for when it increases with boost. I would check voltage at the pumps when its dropping or it could also be the fuel overheating.

Did you set yours with the boost line disconnected? Still not getting how guys are saying the psi is rock steady until boost then it rises. With boost the psi rises of course but with vacuum it also drops from the set base pressure.

 

[itSSlow98]

Did you set yours with the boost line disconnected? Still not getting how guys are saying the psi is rock steady until boost then it rises. With boost the psi rises of course but with vacuum it also drops from the set base pressure.

Mine was set with the vacuum line attached.

 

[mustang john]

Mine was set with the vacuum line attached.

What is your base pressure? I set my base to 40psi with the boost reference line disconnected (that's a true base pressure) and with it hooked back up and car running the vacuum pulls the psi down to around 35psi give or take a few psi. I watch my psi fluctuate quite a bit during normal driving as the car goes from vac to boost.

I have an Autometer Cobalt digital fuel pressure gauge so I watch the fuel pressure all the time.

 

[speeddemon2000]

I had a similar issue. I found that it was caused by heat. If you let it sit a while the fuel pressure would go back up once the fuel cooled. Then once the fuel heated back up the issue returned. To illustrate this better I had just drove about 50 miles on the highway at around 75 mph. I watched on my gauge as the pressure dropped from the low 40s down to around 29 psi. As soon as I got off the freeway I added 1/2 tank of gas to my tank. If you don't know the gas at the pump is usually pretty cool even in the summer time. If you have every filled up a motorcycle in summer time you will immediately notice how cool the gas tank gets during the fill up. So what did I do to alleviate the issue. I talked to Fore performance and they suggested staging the pumps. I purchase a hobs switch from lsxtune (http://www.lsxtune.com/shop/product_...roducts_id/576). It helped the issue a lot. It didn't completely eliminate the issue but pretty close. The next thing I did was run my fuel system in a dead head configuration. I did not see FP pressure issues after that.

 

[y2k2gt]

Maybe you need a larger return line.

 

[MalcolmV8]

Pressure should drop from vacuum to the regulator. Mine is set to a base of 39 PSI with pumps on and engine off. Or engine on and vacuum/boost hose removed from the regulator. When the hose is connected the engine vacuum causes fuel pressure to drop as it should. I forget exact numbers off the top of my head but an engine warmed and idling sees around mid to low 20s fuel pressure. Pull the vacuum line off and it jumps back to 39. This is normal operation. Remember the idea is to keep a pressure differential of 39 PSI across the injector which means if the manifold side goes into vacuum you need to lower the fuel pressure to keep that constant 39 PSI pressure differential across it. In boost fuel pressure should go up 1 PSI per additional lb of boost.

Also note 39 PSI is just the Ford default. You can adjust the tune for other differential pressures and then adjust your FPR accordingly but don't just pick a new pressure for your FPR without adjusting the tune to match.

 

[mustang john]

Pressure should drop from vacuum to the regulator. Mine is set to a base of 39 PSI with pumps on and engine off. Or engine on and vacuum/boost hose removed from the regulator. When the hose is connected the engine vacuum causes fuel pressure to drop as it should. I forget exact numbers off the top of my head but an engine warmed and idling sees around mid to low 20s fuel pressure. Pull the vacuum line off and it jumps back to 39. This is normal operation. Remember the idea is to keep a pressure differential of 39 PSI across the injector which means if the manifold side goes into vacuum you need to lower the fuel pressure to keep that constant 39 PSI pressure differential across it. In boost fuel pressure should go up 1 PSI per additional lb of boost.

Also note 39 PSI is just the Ford default. You can adjust the tune for other differential pressures and then adjust your FPR accordingly but don't just pick a new pressure for your FPR without adjusting the tune to match.

Lol thank you, I said as much already (several times) and no one seemed to take note. All their fuel pressures are rock steady untill they see boost... :bored:

 

[CCM]

I had a similar issue. I found that it was caused by heat. If you let it sit a while the fuel pressure would go back up once the fuel cooled. Then once the fuel heated back up the issue returned. To illustrate this better I had just drove about 50 miles on the highway at around 75 mph. I watched on my gauge as the pressure dropped from the low 40s down to around 29 psi. As soon as I got off the freeway I added 1/2 tank of gas to my tank. If you don't know the gas at the pump is usually pretty cool even in the summer time. If you have every filled up a motorcycle in summer time you will immediately notice how cool the gas tank gets during the fill up. So what did I do to alleviate the issue. I talked to Fore performance and they suggested staging the pumps. I purchase a hobs switch from lsxtune (http://www.lsxtune.com/shop/product_...roducts_id/576). It helped the issue a lot. It didn't completely eliminate the issue but pretty close. The next thing I did was run my fuel system in a dead head configuration. I did not see FP pressure issues after that.

When you say dead head, you mean that you put the regulator in line before the rails instead of after, right? I was considering doing that to try to avoiding unnecessary fuel heating but I kind of shied away from it when I saw that no one else on here did that. How long has it been since you made the switch, and have you had any issues?

 

[FastyJohn03]

When you say dead head, you mean that you put the regulator in line before the rails instead of after, right? I was considering doing that to try to avoiding unnecessary fuel heating but I kind of shied away from it when I saw that no one else on here did that. How long has it been since you made the switch, and have you had any issues?

I had a similar issue. I found that it was caused by heat. If you let it sit a while the fuel pressure would go back up once the fuel cooled. Then once the fuel heated back up the issue returned. To illustrate this better I had just drove about 50 miles on the highway at around 75 mph. I watched on my gauge as the pressure dropped from the low 40s down to around 29 psi. As soon as I got off the freeway I added 1/2 tank of gas to my tank. If you don't know the gas at the pump is usually pretty cool even in the summer time. If you have every filled up a motorcycle in summer time you will immediately notice how cool the gas tank gets during the fill up. So what did I do to alleviate the issue. I talked to Fore performance and they suggested staging the pumps. I purchase a hobs switch from lsxtune (http://www.lsxtune.com/shop/product_...roducts_id/576). It helped the issue a lot. It didn't completely eliminate the issue but pretty close. The next thing I did was run my fuel system in a dead head configuration. I did not see FP pressure issues after that.

Bring it the thread back.. Did you ever had issues with this or in anyway you notice a difference in a good way?

 

[speeddemon2000]

Bring it the thread back.. Did you ever had issues with this or in anyway you notice a difference in a good way?

I have not seen any issues so far. I have been running e-85 with this setup since the summer. The only thing I will change in the future will be the injectors. I will run ID1300s once I find some money for them. Since this change I have not seen any heat related fuel pressure drops.

 

[speeddemon2000]

When you say dead head, you mean that you put the regulator in line before the rails instead of after, right? I was considering doing that to try to avoiding unnecessary fuel heating but I kind of shied away from it when I saw that no one else on here did that. How long has it been since you made the switch, and have you had any issues?

The reason I went this route is Lethal runs their fuel system in this manner. You can download the PDF from their website that shows how they install it. The only difference is they tap into the the front of the fuel rails instead of the back. I went to the back because I wanted my fuel line to stay away from the the front snout of the blower.