My car is an '09 GT manual transmission with 88k miles on it. Totally stock except for FRPP CAI and Brenspeed tune. Ever since I bought it (75k miles) its had a hesitation that often happens when I first let out the clutch from a stop. Its also a little jerky as I accelerate in first and into second gear (normal city driving). Throttle body is clean, TPS is new, and plugs have been replaced. Fuel filter is also new. O2 sensors are also new. Reading some of the threads here on fuel pressure and pumps, I decided to data log mine. Based on what I saw in this thread (http://www.s197forum.com/forum/showthread.php?t=106864&highlight=pressure&page=2), I'm thinking that my pump could be bad. My pressure (FRP) varies from 33 up to 51 lbs. I've attached a snip from the data log showing the FRP variation. RPM is also in the chart showing me from a start and into second and third gears. This was normal city driving (not WOT). Should the pressure vary as much as the chart is showing?
Thinking my fuel pump might be bad...
- Thread starter roegs
- Start date
My understanding of returnless systems is that FRP is reading delta p which is basically the difference between manifold vacuum and pressure in the rail. The system tries to maintain around 39 lbs of pressure across the injectors regardless of changes in manifold vacuum.
In the link attached to the first post, petersonb shows two data logs...one with a bad pump, and the other a known good pump. The good pump maintained a more constant FRP log.
Its a little hard to see in the chart I attached, but orange is the FRP log and green is RPM. The orange FRP varies quite a bit which is why I'm thinking that the pump may not be operating correctly.
What's your fuel pump duty cycle ?? (FPDC). Beware, what indicates off the OBD port is exactly one half of what it actually is. IE: '50' = 100% duty cycle. '40' = 80% etc. Fuel rail pressure should be a constant 39-40 psi at any rpm.
I had a problem with sky high FPDC. Installed the 10 ga wiring upgrade kit..and made no difference, then got worse, 98% at wot. Finally it started to gag if I tried to go into boost. New fuel filter installed, no change. Problem turned out to be the strainer filter on the bottom of the fuel pump. It was clogged with all sorts of debris and crap. Pump was removed from tank, and strainer filter removed,and cleaned with high pressure water (or loads of brake clean). Re-installed, and FPDC dropped like a rock. Now back to normal. When it gagged, the fuel rail pressure dropped as well, like way below 40 psi.
With the aeroforce gauges, I can see the FPDC and rail pressure simultaneously.
I had a problem with sky high FPDC. Installed the 10 ga wiring upgrade kit..and made no difference, then got worse, 98% at wot. Finally it started to gag if I tried to go into boost. New fuel filter installed, no change. Problem turned out to be the strainer filter on the bottom of the fuel pump. It was clogged with all sorts of debris and crap. Pump was removed from tank, and strainer filter removed,and cleaned with high pressure water (or loads of brake clean). Re-installed, and FPDC dropped like a rock. Now back to normal. When it gagged, the fuel rail pressure dropped as well, like way below 40 psi.
With the aeroforce gauges, I can see the FPDC and rail pressure simultaneously.
Never seen a failing pump give you more pressure. Sounds like its a tune issue.
I did contact Brenspeed and was disappointed. The guy told me that he's never even heard of data logging fuel pressure, and then went into this spiel of how these cars have to operate under various altitudes and temperatures and they each have their own quirks. At the end he says "I tell everyone that they cannot expect perfection". At that point I knew I was not going anywhere with this guy. Maybe I need to get back to them and ask for someone that can talk fuel pressures...
Fuel pressure at the rail should not budge, or extremely little. With key in "on" position, (eng OFF) my fuel rail pressure is 50 psi. Turn the key and start engine and it drops to 40 psi. It deviates from 39.6 to 40.3 psi....sorta wanders up /down between those two points...regardless of idle or WOT at 6 krpm. They all do that.
What is your fuel pump duty cycle ??? It should be lowest at idle..and highest at WOT. (6 krpm). No way in hell will the rail pressure wander from 33-51 psi in any normal, working setup. The only time the rail pressure will dip way below 40 psi..is if the strainer filter on the fuel pump is clogged up. That strainer filter is also known as a pre-filter. Even with a clogged pre-filter, the rail pressure will only decrease when u put ur foot into it. It will never increase.
Your 33-55 psi rail pressure deviation imo, is a tune related issue. The rail pressure is set in the tune, they can tweak it to anything they want. Normal deal is... its set at 40 psi.
As far as not data logging fuel rail pressure..he's an idiot. You can data log anything and everything. You can also data log the fuel temp if you want to, cat temps, you name it. If you have a fuel rail pressure issue, you data log the rail pressure..and also the fuel pump duty cycle and fuel temp.
If Brenspeed won't co-operate, get a real tune from Lito, VMP, LUND, or JDM.
What is your fuel pump duty cycle ??? It should be lowest at idle..and highest at WOT. (6 krpm). No way in hell will the rail pressure wander from 33-51 psi in any normal, working setup. The only time the rail pressure will dip way below 40 psi..is if the strainer filter on the fuel pump is clogged up. That strainer filter is also known as a pre-filter. Even with a clogged pre-filter, the rail pressure will only decrease when u put ur foot into it. It will never increase.
Your 33-55 psi rail pressure deviation imo, is a tune related issue. The rail pressure is set in the tune, they can tweak it to anything they want. Normal deal is... its set at 40 psi.
As far as not data logging fuel rail pressure..he's an idiot. You can data log anything and everything. You can also data log the fuel temp if you want to, cat temps, you name it. If you have a fuel rail pressure issue, you data log the rail pressure..and also the fuel pump duty cycle and fuel temp.
If Brenspeed won't co-operate, get a real tune from Lito, VMP, LUND, or JDM.
Thanks again for the replies. I did another log yesterday on a cold engine. The deviation is still there but the overall average pressure is lower which makes sense as I believe the the PCM increases pressure when fuel is hot to avoid vapor issues. The photo also shows pump duty cycle. Assuming that you double the duty cycle value, my original chart was 32/70/48 (min/max/average). This latest chart is 40/70/44.
I'll go back to Brenspeed and see what they say. Before calling them I wanted to ask if anything else could be causing the swings such as a bad fuel pressure / temperature sensor on the fuel rail? I have the Ford emissions manual and that has some checks I can do this afternoon on the sensor. I'd try swapping, but its a $$ part and I'd want to be pretty certain before swapping.
BTW...the Y axis in the attached chart is RPM and it shows me starting out and going 1 -3 gears. Again, normal daily driving.
I'll go back to Brenspeed and see what they say. Before calling them I wanted to ask if anything else could be causing the swings such as a bad fuel pressure / temperature sensor on the fuel rail? I have the Ford emissions manual and that has some checks I can do this afternoon on the sensor. I'd try swapping, but its a $$ part and I'd want to be pretty certain before swapping.
BTW...the Y axis in the attached chart is RPM and it shows me starting out and going 1 -3 gears. Again, normal daily driving.
Attachments
You are exactly correct the frps also senses temperature and will raise delta pressure based on temperature. Everything looks to be working. A bad frps will usually throw codes. I have a spare I used for troubleshooting for sale in the classifieds. My money is on the tune.
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