high fuel pressure?

AaronTG04

Member
I'm having an issue with my car. In general the car works fine but the rpms hang sometimes between 1500 and 2000 rpms and do not drop until the car is completely stopped, then the car idles normal. I searched for vacuum leaks using the carb cleaner method but I couldn't find any. So, I controlled the hanging rpms using a IAC restrictor plate, now the car is unable to idle beyond 1300 rpms.

I just got a notebook and I decided to try datalogging using my sct x3 and livelink. I data logged several parameters but the ones that concern me are the fuel rail pressure, fuel pressure drop across the injectors, and the actual voltage at the fuel pump.

I started with the engine cold so I let it idle for a few minutes. During this time livelink showed fuel rail pressure and fuel pressure drop across the injectors at about 40 psi which I think is normal. But after 8 minutes, when the engine got warmed, both values raised to 65 psi. The pressure at the fuel injectors should be around 40 psi, right? I also noticed that the voltage at the fuel pump was constant at 12.44 volts at all times. In a returnless style fuel system the voltage at the fuel pump should not be constant, it should vary, I am right? So I am concerned about this.

Most of the time during datalogging the car was idling, but I also rev the engine to 2000 and 3000 rpms holding it there for a few seconds, and finally I drove the car for about 10 minutes.
The fuel rail pressure, the injectors pressure and fuel pump voltage values never changed.
Since I do not have experience data logging I wanted to know what you guys think. Are these values right?
if not, what can be causing this?

These are the rest of the parameters I data logged.
fuel pump fuel rate: constant at 2.8
fuel pump voltage from table: constant at 3.25
intake air temp: average 123 F
long term fuel trim bank 1: average 0.94
long term fuel trim bank 2: average 0.99
short term fuel trim bank 1 and 2: average 0.98
fuel pump duty cycle: constant at 0.30 during the first 8 minutes, then between 42-45 after 8 minutes.
battery voltage : min 13.19, max 14.06, average 13.58

My car has only a few bolt-ons:
windstar intake manifold
x-midpipe
flowmaster dual exhaust
bama tune

I have replaced the maf sensor, IAC valve, throttle position sensor, and the fuel rail pressure sensor and the problem persists.

Sorry for my bad English.
Any response will be appreciated.
 
Last edited:

Jesse01V6

Away from V6's for now........
I don't see where there is a problem.

You said it drives fine, I'm assuming there is no check engine light on, and its not getting bad gas mileage? Honestly think you are looking into a problem that isn't there.
 

davidcseifert

that V6 guy
I had high 60's rail pressure for a while, never could figure it out so I just had the tune modified to command 40psi constant. The 60+psi did screw with my idling, but it was low and searching for an idle constantly not hanging like yours. Doesn't have a problem now though.
 

AaronTG04

Member
Thank you for your replys. I'm sorry, I focused on the datalog data that I didn't give much details about the issue, I and also forgot to mention other symptoms.
For instance if I am driving the car on the highway at 60 mph on fifth gear the car is at, let say 1800 rpms, and I shift to neutral or just press the clutch the rpms hang there, at 1800 rpms. As long as the car is moving in neutral the rpms do not drop. They only drop when I stop the car, then the car idles fine at around 800 rpms.

This situation does not happen all the time. What happens most of the time, using the example of the highway, the rpms do drop but they stop at between 1300 and 1500 rpms and hang there until the car is not moving. Some times when the rpms drop to 1300 they go up a little bit to 1500 and hang there, again until the car stops moving, then it idles fine. This cannot be normal.

There is another symptom that occurs occasionally when I am driving in the city. For example, if I slow down because of a red light and I shift to neutral or press the clutch the rpms drop very fast but they drop below 500 rpms. The car recovers from this very fast and the rpms go up and the car idles normal.

The last thing I have noticed only happens in summer when the temperature is really high, above 100 F. The car hesitates between 1000 and 2000 rpms, unable to make power. If I keep driving like that eventually throws a code. I don't remember the code number but it is a lean condition on bank 2.

I "fixed" the hanging rpms problem with a IAC restrictor plate. Now the rpms drop to 1300 or lower. I believe this confirms that the IAC is adding air for some reason and the problem is not cause by a vacuum leak.

I have seen in other posts in this website and in others that the fuel pressure at the injectors should always be close to 40 psi, and I'm getting 65 psi. They also mentioned that high pressure can be caused by a faulty fuel pump driver module, which is located in the trunk.

I also believe that, since my car is a 2001 and has a returnless style fuel system, the voltage at the fuel pump should no be constant at 12.44 volts, am I wrong?
 

tec_41

Member
Aaron, my car does the exact same thing, with pretty much the exact same mods (restrictor plate and SCT X3 Tuner). Isn't there a parameter in the tuner for "moving idle" or something like that? I just got mine and haven't had a chance to mess with it.

As for the RPMs dropping below 500, I think that's a side effect of the restrictor plate. I did two 1/4" holes and mine will do this for a while after resetting the ECU. But I believe it learns after some time and the issue goes away.

With a tuner we should be able to get rid of the restrictor plate. I just haven't had a chance to tinker with it yet.
 

AaronTG04

Member
Aaron, my car does the exact same thing, with pretty much the exact same mods (restrictor plate and SCT X3 Tuner). Isn't there a parameter in the tuner for "moving idle" or something like that? I just got mine and haven't had a chance to mess with it.

As for the RPMs dropping below 500, I think that's a side effect of the restrictor plate. I did two 1/4" holes and mine will do this for a while after resetting the ECU. But I believe it learns after some time and the issue goes away.

With a tuner we should be able to get rid of the restrictor plate. I just haven't had a chance to tinker with it yet.
Aaron, my car does the exact same thing, with pretty much the exact same mods (restrictor plate and SCT X3 Tuner). Isn't there a parameter in the tuner for "moving idle" or something like that? I just got mine and haven't had a chance to mess with it.

As for the RPMs dropping below 500, I think that's a side effect of the restrictor plate. I did two 1/4" holes and mine will do this for a while after resetting the ECU. But I believe it learns after some time and the issue goes away.

With a tuner we should be able to get rid of the restrictor plate. I just haven't had a chance to tinker with it yet.

I think you are right about the restrictor plate causing the rpms to drop below 500. This does not happend very often so I'm not worried about it. What concerns me is the high fuel pressure.
There are two options in the x3 to change the idle speed. One is the idle speed at neutral and the other one is the idle speed while driving. I'm using a tune from bama and they set the idle speed while driving at 670 or 720 rpms, I don't remember. You can lower this idle speed, but in my case, it did not fix the hanging rpms.
 

AaronTG04

Member
I had high 60's rail pressure for a while, never could figure it out so I just had the tune modified to command 40psi constant. The 60+psi did screw with my idling, but it was low and searching for an idle constantly not hanging like yours. Doesn't have a problem now though.

How was your car tuned? Did you take it to them or they sent you a tune by email?
I have bama tunes for life, so do you think that I can just ask them to give me a tune with 40 psi constant?
 

6 Shooter

Well-Known Member
For starters, suggest you data log time, RPM, MAF counts, engine load, STFTs bank 1 and bank 2, LTFTs bank 1 and bank 2, engine coolant temp, inlet air temperature, idle air controller position, throttle position absolute (AD counts), throttle position relative, spark timing, battery voltage, and gear or speed. The order of the list does not matter per se.
 

AaronTG04

Member
For starters, suggest you data log time, RPM, MAF counts, engine load, STFTs bank 1 and bank 2, LTFTs bank 1 and bank 2, engine coolant temp, inlet air temperature, idle air controller position, throttle position absolute (AD counts), throttle position relative, spark timing, battery voltage, and gear or speed. The order of the list does not matter per se.

Thanks
 

Phil II

Cone Destroyer
You may want to inspect the Fuel Rail Pressure Sensor, which can sometimes partially fail while the car continues to work. One clue is if the vacuum line leading to it smells of gasoline.
 

AaronTG04

Member
You may want to inspect the Fuel Rail Pressure Sensor, which can sometimes partially fail while the car continues to work. One clue is if the vacuum line leading to it smells of gasoline.

Thanks I'll check that. The FRPS is new, so I guess I should put the old one back and datalog again to see if the pressure or something else changes.
 

JTsStang

Boosted V6
Fuel pump duty cycle shows it is commanding fuel so it's good. The pcm will relearn the correct voltage and correct itself.
 

TonyDee

Active Member
I just did the IAC mod and can report that it had an immediate affect at reducing the idle hang problem. It has also improved the drive-ability of the car. With my performance cam, the car tended to buck at low speeds but it has been reduced in severity. Wish i could have done this in the tune.
 
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