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Author Topic: 2004 Ford Taurus 3.0L VIN"U" Fuel Pressure problems.  (Read 7928 times)

Offline metaltech

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2004 Ford Taurus 3.0L VIN"U" Fuel Pressure problems.
« on: July 08, 2008, 11:41:20 AM »
I have a Ford Taurus 3. 0L OHV VIN "U" it has a sharp surge while driving, from idle through the power band.
While checking the fuel pressure Alldata listed the pressure as 30-55 psi key on engine off and 26-45 psi engine on.
I get 60 to 61 psi key on engine off and 55 to 57 psi at idle and the pressure bounces up and down "at idle" from 55 to 57 psi.
Alldata is kind of vague on troubleshooting the fuel pressure sensor.

Offline autodr

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Re: 2004 Ford Taurus 3.0L VIN"U" Fuel Pressure problems.
« Reply #1 on: July 08, 2008, 07:17:38 PM »
That's normal. Ignore the specs unless you have a scan tool that can read fuel pressure. The spec is as it is read through the fuel rail pressure sensor. It will NOT match a mechanical gauge. In fact, a mechanical gauge is of very little help on that electronic retunless system. The pump would have to be nearly dead for a mechanical gauge to work. The 2 do not match because the FRP sensor is referenced to manifold vacuum and the mechanical gauge is referenced to atmospheric air. To get the 2 to match, you will need to unplug the vacuum hose to the FRP to get the FRP referenced to atmospheric air like the gauge is.

When using a scan tool to determine a pump problem, you'd not only look at pressure but also percentage of pump "on" time (40psi at idle with 23% duty cylce from PCM is good, but 40psi at idle with 45% duty cycle from PCM is bad). Then you'd also have to use an oscilloscope to check the output of the fuel pump driver module to ensure it is ramping up the pump "on" time per the command from the PCM (just because the PCM is commanding it, doesn't mean the driver module is running the pump right).... the twist there is that whatever duty cycle is present on the PCM data PID, the FPDM will double that (25% command from the PCM is 50% from the FPDM to the pump, 50% command from the PCM is 100% on command from the FPDM to the pump).

What you are seeing when you see the pressure raise and low, is the pump turning on and off... there is no pressure regulator. The PCM watches the fuel rail pressure sensor (FRP) and commands the pump on enough to achieve target pressure. Target is 40psi on cold fuel, and up to 55 psi on on hot fuel. pressure is NOT targeted on engine load like old returnless systems that used a vacuum operated pressure reg and return line.

Here is how it works. http://www.babcox.com/editorial/us/us120532.htm

Any codes? a dying fuel pump will set a P0191 (FRP performance) and often a P0148 (Fuel delivery error)... along with P0171 and P0174 (bank 1 and 2 lean)

If you don't have those... move on and leave the pump alone.
« Last Edit: July 08, 2008, 07:38:11 PM by autodr »
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Offline metaltech

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Re: 2004 Ford Taurus 3.0L VIN"U" Fuel Pressure problems.
« Reply #2 on: July 09, 2008, 11:32:33 AM »
Thank so much for the information, and help.   I somewhat understood the return fuel systems but not the new ones, great information.
I connected a scan tool last night and there were no code set, the FRP was showing 60 - 67 PSI AVG was 62 PSI "hot motor".   I never suspected the fuel pump so much because the pressures seemed high rather than low.   The long term fuel trim on both  banks was around -3. 5 and short term varied usually negative.   

Offline autodr

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Re: 2004 Ford Taurus 3.0L VIN"U" Fuel Pressure problems.
« Reply #3 on: July 10, 2008, 05:51:24 PM »
Here are some good and bad.

The first one is a bad fuel pump on a Contour (got it today). You'll see the FRP reading 40psi which is target for this vehicle. I included the RPMs so you can see what the engine was doing.

The first one is at idle and the second one is at WOT. Even though both of these fuel pressures are "good", the pump is still bad because it is having to work too hard to achieve a good pressure.  This engine ran good while I had it because it was getting enough pressure... but still the problem could be seen.

You can see in the first one that at idle, I had a good 40psi (FRP), but.... the command from the PCM to the fuel pump driver module (FP#) was at 40.33%.  The fuel pump driver module doubles that at the pump. So 40.33% on the scanner here means that the pump was having to run at 80.66% of the time just to make enough pressure to keep up with the injectors at idle. That's not good. It is having to run at near full capacity at idle.

In the second one, I am driving the same bad pump now with my foot on the gas at wide open throttle. In the RPMS, you can see that it just hit 5800 rpms, and the trans shifted (that's why the RPMS dropped). You can see the commend is at 50% just to make enough pressure. Double that on the PID, and the pump is actually running 100% of the time just to barely keep up with the injectors. Not good at all! The car runs normal. AS the driver in the seat, I can't tell for feel... but I can see it on the scanner.

In regards to the pump command, the PCM is screaming "I'm giving her all she's got captain!"

There was no P0191 code on this because fuel pressure never dropped to low. It had enough pressure.... it just didn't have anything left over. This pump was about to leave this little old lady walking or feeling like she has to push the car.... it just hadn't actually done that yet.

I'll post the "good shots" in a separate reply to reduce confusion. 

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« Last Edit: July 10, 2008, 06:01:08 PM by autodr »
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Offline autodr

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Re: 2004 Ford Taurus 3.0L VIN"U" Fuel Pressure problems.
« Reply #4 on: July 10, 2008, 05:58:31 PM »
Now... for the good fuel pump.

Same vehicle. This was after it got a new pump and fuel filter.... and yes, the filter was restricted and I did test pressures on scan tool after replacing the filter and before the new pump... the filter alone did not fix.

Now... with the new pump.... you can see at idle that the pump doesn't have to work as hard. To make 40psi at idle now, it only needs a command from the PCM of 24.18%.  Which means that the actual pump is only having to run at 48.36% capacity. Less than half capacity at idle... that's good. That means the pump is no longer working so hard to meet demand.

In the second shot, I am at wide open throttle and the trans is up shifting. To hit 40psi, the PCM only had a pump command of 33%. So even when I now demanded as much fuel as the engine could ever need, the pump was able to meet that demand at only 66% actual capacity.... lots of surplus available... that's good! The new pump isn't breaking a sweat!

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Offline autodr

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Re: 2004 Ford Taurus 3.0L VIN"U" Fuel Pressure problems.
« Reply #5 on: July 10, 2008, 06:07:23 PM »
That is how you determine good from bad fuel pumps on a Ford electronic returnless fuel system.

Will your scan tool access mode 6 data?  That is where you will find cylinder misfire data on a Ford. You can look to see which cylinders are skipping. What kind of scanner do you have? 

Normal trims for a Ford will usually hang around -1 to -5.... that's common. As long as you don't see a variance of about 10% or more then no biggy.
« Last Edit: July 10, 2008, 06:09:31 PM by autodr »
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Offline metaltech

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Re: 2004 Ford Taurus 3.0L VIN"U" Fuel Pressure problems.
« Reply #6 on: July 14, 2008, 09:11:08 PM »
The scan tool I'm using is a  "OBDII Automotive Scan Tool and Virtual Dashboard" ( hxxp: www. obd-2. com/index. html#home )
TRICAN sold by Alex Peper.  It was recommended here I think!  It's borrowed and I'm not real familiar with it but it does "Ford mode 6  defined test results and optional negative notation selection"

Offline metaltech

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Re: 2004 Ford Taurus 3.0L VIN"U" Fuel Pressure problems.
« Reply #7 on: July 14, 2008, 09:21:30 PM »
Oh I forgot no misfires that I can see.   I have started getting a P0122 at random, although I have replaced the TPS already, and when I read the scanner showed it at about 14% to 17% throttle position that should be about . 7 Volt right or am I not looking at the right setting.   At idle the RPM go up and down 50 to 125 RPM setting still, and the scanner shows the load going up down also.

 

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