Tork Tech Low Fuel Pressure Questions

[2001bullitt03937]

hey guys...
Recently installed a Tork tech kit on my Bullitt and went to start it with a start up tune and it was running like crap if it ran at all. Either way, a bit of diag later I found that my fuel pressure that the frps is seeing is 19 psi key on and drops quickly to about 4 psi... Just wondering if this is a tune issue or if I'm looking at a bad pump. I installed a new walbro 255lph during the build. It has spark also. Thanks

 

[2001bullitt03937]

A pic of the fuel pressure. It's in kpa, but doing the conversion is where I got the psi. This is just key on, no cranking. I can hear the pump turn on for about half a second...

 

[wmburns]

First things first. What about the fuel rail pressure sensor intake vacuum reference line? Is it connected and leak free? Is it connected to a vacuum intake port that "sees" vacuum and boost? If the vacuum line is disconnected and plugged, what does the fuel pressure do? Is there any raw gas in the line?

What is the fuel pressure as reported by the PCM?

 

[2001bullitt03937]

Thanks for the response. The frps vacuum port is currently connected to the upper port on the bypass valve of the blower. It also has a t in it to the boost port on the lower back section of the blower. I will add pics of this when I get home. I did not notice any raw gas in this line, but will double check. Also, reported by the pcm with key on the fuel pressure is 145 kpa (I believe is 19-20 psi)

 

[2001bullitt03937]

Got a bit further today. removed the pump and found small rubber o-rings that sit on the bottom of the pump assembly were off. I removed these completely, they don't secure well tot he walbro pump and will probably just cause problems. Things got interesting after reinstallation. So, i started the car and it ran fine for about 2 seconds. Shut off. Then i had a CEL, found a high fuel rail pressure code. After that, back to the old 19 psi BS. This time, it was 19 PSI every time i checked it, no higher, no less. Has anyone experienced this? Some sort of ford default maybe if it sees high pressure at the FRPS?

 

[wmburns]

If you expect good answers to your questions always post the full DTC codes. There are 1000's and they each have a story to tell.

But in general, the PCM does have a crude method to protect from high fuel pressure. It's not perfect. Also note one of the reasons that the protection is needed is to lessen the chances of rupture of the fuel rail pressure sensor (FRPS) diaphragm. Once the FRPS is damaged, it will never give accurate readings. This is why it's VITAL to have the intake vacuum reference line connected to the correct location and be leak free. This goes double for any boosted application.

Confirm that you have used the correct fuel pump for the application. There is a difference between a FP for a return and a return-less system. Installing a return style FP in a return-less application will cause problems.

Has any changes been made to how the fuel pump driver module works?

If the motor is running at idle and the FRPS intake vacuum reference line is disconnected what does the PCM monitored fuel pressure do? The details are important.

Do you have an external fuel pressure gauge? This offers a way to cross check the PCM reported fuel pressure to atmospheric pressure. Hint. When the FRPS vacuum line is disconnected the external gauge and PCM reported values should be the same. Never run a boosted motor under load with the FRPS vacuum line disconnected!

Also note, the fuel pressure should stay up between starts. The FP is designed to run for a few seconds at initial key on and then shut off. So if monitoring the fuel pressure the FP should rise at initial key on and then REMAIN high until the motor is started. So if the FP quickly bleeds down, this indicates a problem in the fuel system. Either a leaking fuel injector or a bad FP check valve or a leak in the gas tank flex lines.

Me personally couldn't look at a picture of your set up and tell if it's plumbed correctly. Perhaps someone else with a Tork Tech kit can help. However one would think that one advantage of buying a kit is to take advantage of the set up information that comes with the kit.

Bottom line. it's important to confirm that the FRPS is working correctly and is actually changing the fuel pressure in response to changes in the intake referenced pressure (vacuum or boost). IMO this should be done before looking elsewhere for the problem. Start with the basics and work up.

 

[2001bullitt03937]

Thanks for the response. The code is p0193-high input into the frps. Today I replaced the frps. No difference. Still maximum pressure in the fuel system I'm getting is 19psi. Not sure where to go from here, is it possible it's a tune issue? I did return the vehicle to stock and there is no difference. The vehicle will not start no matter what. I know the fuel pump is correct because I actually have been in contact with the fuel pump manufacturer to confirm. I also have been trying to contact the tuner who sent me this "start up" tune to see if he has seen an issue like this.

 

[2001bullitt03937]

I also have put the factory known good pump in the tank and then only got 11 psi max. I've tried everything I can think of. Resetting injectors, disconnecting frps, resetting entire vehicle memory. I know I have 5v reference going into the frps. Is it possible my pcm is fried?

 

[wmburns]

You haven't answered the questions about what the fuel pressure does under the conditions requested. It seems to me that you have dropped into "parts changing" mode.

In answer to your question about the P0193. Yes it's possible that the PCM is bad. And a "part changer" would swap it out in order to rule it in/out. IMO this is likely to generate as many problems as it resolves.

What else have you done to rule out a wiring fault to/from the FRPS? This could be something as simple as a bent/pushed pin in the FRPS signal return line. Were any wiring changes needed to support the super charger install? Extender pigtail perhaps?

>>
P0193 - Fuel Rail Pressure Sensor Circuit High Input (FRP)

• FRP signal shorted to VREF or VPWR.
• FRP signal open (gasoline only)
• Damaged FRP sensor.
• Damaged PCM.