Is it abnormal for fuel pressure to bounce around at the rail? Video posted.
07-11-2016, 09:30 PM
#1
Is it abnormal for fuel pressure to bounce around at the rail? Video posted. I'm having issues getting my engine startup idle tuned. They didn't have a problem with the dyno and street tuning. The tuner says he thinks it might be a fuel issue, possibly faulty injectors. It's a cammed LS1 with stock fuel rails, Ford Lucas 38# at 3 bar injectors, factory fuel lines and evap, Racetronix 255 fuel pump, and Racetronix hotwire kit. Heads are milled 243s. Cam is a 226/234 .612/.595 112+2. Intake is LS6. Throttle body is a POTZ ported stock tb. Maf is stock. Lid is SLP. It also has long tube headers and high flow cats.
I brought the car back home and put a mechanical gauge on the fuel rail port and I get 60psi prime, 46psi key on engine off, and 62psi with the engine running. Wot the fuel pressure drops a couple psi. When the car is off pressure doesn't bleed off for a very long time. When the car is started, and for a little while after, the fuel pressure gauge bounces like crazy. After the engine settles into an idle the gauge is more still but still bounces a fair bit.
I'm getting ready to send my injectors off to have them flow tested and cleaned if need be. They all ohm'd out the same but that doesn't mean they aren't clogged or something.I'd like to make sure I'm not missing anything else so I'm checking everything. The injectors are a few years old now with about 40k on them. The fuel filter is new. The fuel pump has about 3k miles on it. The regulator in the tank is the original with 122k on it. It started and ran fine on the old tune and factory pump. It started and ran fine on the old tune with the current fuel system but it was running super rich due to being tuned on the factory pump. I then tore the car apart to refresh the motor and swap heads, leading to needing the new tune, and it hasn't been right since. The tuner theorizes that the excess fuel covered up the problems as they developed. Now that the fuel is in line in the new tune, the problems are more apparent.
I've attached a video of startup and another after it finds it's idle and settles down. Can anyone tell me if this is normal or not?
http://vid1288.photobucket.com/album...pssk5y7fb6.mp4
http://vid1288.photobucket.com/album...psvhgee8sv.mp4
I brought the car back home and put a mechanical gauge on the fuel rail port and I get 60psi prime, 46psi key on engine off, and 62psi with the engine running. Wot the fuel pressure drops a couple psi. When the car is off pressure doesn't bleed off for a very long time. When the car is started, and for a little while after, the fuel pressure gauge bounces like crazy. After the engine settles into an idle the gauge is more still but still bounces a fair bit.
I'm getting ready to send my injectors off to have them flow tested and cleaned if need be. They all ohm'd out the same but that doesn't mean they aren't clogged or something.I'd like to make sure I'm not missing anything else so I'm checking everything. The injectors are a few years old now with about 40k on them. The fuel filter is new. The fuel pump has about 3k miles on it. The regulator in the tank is the original with 122k on it. It started and ran fine on the old tune and factory pump. It started and ran fine on the old tune with the current fuel system but it was running super rich due to being tuned on the factory pump. I then tore the car apart to refresh the motor and swap heads, leading to needing the new tune, and it hasn't been right since. The tuner theorizes that the excess fuel covered up the problems as they developed. Now that the fuel is in line in the new tune, the problems are more apparent.
I've attached a video of startup and another after it finds it's idle and settles down. Can anyone tell me if this is normal or not?
http://vid1288.photobucket.com/album...pssk5y7fb6.mp4
http://vid1288.photobucket.com/album...psvhgee8sv.mp4
Last edited by RebelExtrm02; 07-13-2016 at 01:47 PM.
07-11-2016, 11:13 PM
#2
when I had a FP gauge on the end of my stock rail the pressure held steady at 58 psi and didnt budge the whole time the car was on. then again my fuel system is completely stock (changing soon)
I would suspect your in tank regulator is showing signs of failure now that you have a new tune that needs more fuel.
I would suspect your in tank regulator is showing signs of failure now that you have a new tune that needs more fuel.
07-13-2016, 01:34 PM
#3
I received my injectors back today. They all passed. The shop said two of them were a percent further out on flow than the rest but otherwise functioned normally. Looks like the fuel pressure regulator is the only thing left in the fuel system as a variable.
I received this information from the tuner when I updated him on the injectors:
"I can't think of anything outside of fuel on the start up issue as the file you came up on originally the car started fine, but was also pulling 25% or more fuel to maintain stoich. As soon as the maf is turned back on and within +/- 2% trim it has this issue. I have often heard of issues with cavitation in the tank on the stock system with bigger pumps, but that shouldn't happen with start up, just under high loads or fuel demands. It's only on start up is the issue. Everything else is peachy with it."
Did you have a stock or aftermarket camshaft?
I received this information from the tuner when I updated him on the injectors:
"I can't think of anything outside of fuel on the start up issue as the file you came up on originally the car started fine, but was also pulling 25% or more fuel to maintain stoich. As soon as the maf is turned back on and within +/- 2% trim it has this issue. I have often heard of issues with cavitation in the tank on the stock system with bigger pumps, but that shouldn't happen with start up, just under high loads or fuel demands. It's only on start up is the issue. Everything else is peachy with it."
when I had a FP gauge on the end of my stock rail the pressure held steady at 58 psi and didnt budge the whole time the car was on. then again my fuel system is completely stock (changing soon)
I would suspect your in tank regulator is showing signs of failure now that you have a new tune that needs more fuel.
I would suspect your in tank regulator is showing signs of failure now that you have a new tune that needs more fuel.
07-13-2016, 06:01 PM
#4
9 Second Club
Dont see anything wrong there. What exactly is the problem ?
Gauge vibration could simply be due to an undamped gauge, but nothing you're showing will have any noticable effect on the engine.
Gauge vibration could simply be due to an undamped gauge, but nothing you're showing will have any noticable effect on the engine.
07-13-2016, 07:09 PM
#5
I'm trying to figure out if there really is anything wrong with my fuel system before I make a third 360 mile round trip the tuner to have them work on the idle some more, if they even will at this point. I've never tested the fuel pressure on a cammed car so I didn't notice if what I saw on the gauge was normal or not.
The tuner can't get my car to idle right at first start up. He said it acts like there is a sudden rich spike shortly after startup that causes the engine to stumble that eventually lines out and the car is fine. If you shut the car off and turn it immediately back on, he says there doesn't appear to be an issue. If you wait a few seconds and try again the start is all over the place again. They wanted to pull my injectors and test them because they said most of the time if they have this much trouble tuning idle on the car is because there is something wrong with the injectors or elsewhere in the fuel system. I couldn't stay any longer so I brought my car home and I sent my injectors off to a different company for an unbiased opinion and they flow tested them and said they were fine. The only thing left, mechanically, in my fuel system is the regulator. Everything else is new or replaced and verified working.
There is also a lingering problem of the idle surging up when you're coasting to a stop in neutral with the clutch out. It doesn't happen all the time. I have smoke tested the motor and there are zero vacuum leaks. The IAC and TPS are new (other parts I replaced when they first couldn't get car to idle at startup).
The tuner can't get my car to idle right at first start up. He said it acts like there is a sudden rich spike shortly after startup that causes the engine to stumble that eventually lines out and the car is fine. If you shut the car off and turn it immediately back on, he says there doesn't appear to be an issue. If you wait a few seconds and try again the start is all over the place again. They wanted to pull my injectors and test them because they said most of the time if they have this much trouble tuning idle on the car is because there is something wrong with the injectors or elsewhere in the fuel system. I couldn't stay any longer so I brought my car home and I sent my injectors off to a different company for an unbiased opinion and they flow tested them and said they were fine. The only thing left, mechanically, in my fuel system is the regulator. Everything else is new or replaced and verified working.
There is also a lingering problem of the idle surging up when you're coasting to a stop in neutral with the clutch out. It doesn't happen all the time. I have smoke tested the motor and there are zero vacuum leaks. The IAC and TPS are new (other parts I replaced when they first couldn't get car to idle at startup).