2007_Shelby_GT Posted September 6, 2010 Report Share Posted September 6, 2010 Received and then today installed the Ford Racing Dual Fuel Pump kit. I figured I'd get this over with before my S/C tune appointment with VMP next week. (Whew! If you do this yourself, buy a fan and wait for cooler weather!) Anyhow, the install went smoothly and I noted no issues - she started right up on the first try! The fuel quantity and fuel pressure gauges are reading/functioning properly, at least I think so, and therein lies the question: With the new dual pump, what sort of readings should I be getting from the fuel pressure gauge? With the single pump, I usually maxed out under WOT around 45 lbs or so, and the rest of the time it varied between 20-40 lbs in different driving conditions, (idle, light throttle, moderate throttle, etc.) Now, with the dual pump, i've seen WOT readings jump to 60+lbs! Cruising at moderate speeds it settles around 30 lbs, but fluctuates depending on throttle use, (the "jumping gauge" that everybody talks about) So, those with the dual pump set-up, chime in with your numbers! Sam Link to comment Share on other sites More sharing options...
SGT/SC2873 Posted September 6, 2010 Report Share Posted September 6, 2010 Received and then today installed the Ford Racing Dual Fuel Pump kit. I figured I'd get this over with before my S/C tune appointment with VMP next week. (Whew! If you do this yourself, buy a fan and wait for cooler weather!) Anyhow, the install went smoothly and I noted no issues - she started right up on the first try! The fuel quantity and fuel pressure gauges are reading/functioning properly, at least I think so, and therein lies the question: With the new dual pump, what sort of readings should I be getting from the fuel pressure gauge? With the single pump, I usually maxed out under WOT around 45 lbs or so, and the rest of the time it varied between 20-40 lbs in different driving conditions, (idle, light throttle, moderate throttle, etc.) Now, with the dual pump, i've seen WOT readings jump to 60+lbs! Cruising at moderate speeds it settles around 30 lbs, but fluctuates depending on throttle use, (the "jumping gauge" that everybody talks about) So, those with the dual pump set-up, chime in with your numbers! Sam it's working. Cruising I run around 40 but once the boost kicks in it jumps! Craig Link to comment Share on other sites More sharing options...
TheKurgan Posted September 6, 2010 Report Share Posted September 6, 2010 I see 40psi at WOT. It doesn't matter if I'm spraying nitrous or not. 35psi at idle. Basically the same as the stock pump. I did see a reduction in fpdc after I installed the GT500 pumps. Link to comment Share on other sites More sharing options...
2007_Shelby_GT Posted September 7, 2010 Author Report Share Posted September 7, 2010 I see 40psi at WOT. It doesn't matter if I'm spraying nitrous or not. 35psi at idle. Basically the same as the stock pump. I did see a reduction in fpdc after I installed the GT500 pumps. Hmmm, just a thought, but are you sure both pumps are functioning? Those numbers are what I was seeing with the single stock pump, (around 40 psi WOT), as opposed to the dual pump which is reading above 60 psi WOT! I don't know, but maybe it's just your set-up vesus mine? (I have 41 lb injectors with the E-force charger, everything else stock.) Thanks for the replies! (Oh, and I found some more numbers on the GT/SC forum!) Sam Link to comment Share on other sites More sharing options...
doogie65 Posted September 7, 2010 Report Share Posted September 7, 2010 How long did the install take? I have one sitting in the garage and I need to install it before my dyno tune on the 24th. But I purposely have waited for the cooler weather to arrive for that same issue you mentioned! Link to comment Share on other sites More sharing options...
2007_Shelby_GT Posted September 7, 2010 Author Report Share Posted September 7, 2010 How long did the install take? I have one sitting in the garage and I need to install it before my dyno tune on the 24th. But I purposely have waited for the cooler weather to arrive for that same issue you mentioned! I work a little slower than most - about 4 hours. Make sure your fuel level is low, the lower the better. It was easy getting to the access port and by appearances it looks like you can't get the old pump out and the new pump in because the access port doesn't align with the pump! It takes a little twisting and turning to remove the old one and replace with the new - take your time and watch out for the hoses. Hook ups and wiring were straight forward and I had no issues. Oh, and get a fan because the gas fumes are awful! Sam Link to comment Share on other sites More sharing options...
doogie65 Posted September 7, 2010 Report Share Posted September 7, 2010 Good point about the fan and fumes! I hope to tackle it this weekend since it supposed to rain on Sat. What pulley you planning to run? I am switching to the 3.5in along with swapping out my stock airbox for a CAI... so I should be in the 450RWHP range after the tune. Link to comment Share on other sites More sharing options...
2007_Shelby_GT Posted September 7, 2010 Author Report Share Posted September 7, 2010 Good point about the fan and fumes! I hope to tackle it this weekend since it supposed to rain on Sat. What pulley you planning to run? I am switching to the 3.5in along with swapping out my stock airbox for a CAI... so I should be in the 450RWHP range after the tune. Oh yea, along with the fan, make sure to stuff a large towel (at least as large as you can get in the access hole) in there to soak up excess fuel when you disconnect the fuel line! I depressurized the system per instructions and still had about a quart of fuel squirting out! I used a small towel and had to quickly snap the fuel line back in place to avoid a flood! For now, I plan to have the car tuned with the stock pulley with the original Ford Racing CAI. My numbers should be close to what you are getting (420+hp and 390+ torque) at the rear wheels. Horsepower is addictive, so that may change! Sam Link to comment Share on other sites More sharing options...
TheKurgan Posted September 7, 2010 Report Share Posted September 7, 2010 Hmmm, just a thought, but are you sure both pumps are functioning? Those numbers are what I was seeing with the single stock pump, (around 40 psi WOT), as opposed to the dual pump which is reading above 60 psi WOT! I don't know, but maybe it's just your set-up vesus mine? (I have 41 lb injectors with the E-force charger, everything else stock.) Thanks for the replies! (Oh, and I found some more numbers on the GT/SC forum!) Sam Those are the readings that are coming from the PCM so I hope they are right. I don't think they would work at all if they weren't hooked up right. Also verified the idle with my analog gauge on the fuel rail so the calibration seems right to me. If you are supercharged that might be the reason you see higher pressure since I also have a fuel line going to my zex wet kit. Also the fuel pump duty cycle went down so as long as that is not close to maxing out I'm fine....hopefully! Link to comment Share on other sites More sharing options...
TheKurgan Posted September 8, 2010 Report Share Posted September 8, 2010 Here's some good info on how our cars read and calculate fuel pressure. Pretty good read and explains why the PCM uses delta fuel pressure instead of actual fuel pressure... Fast forward to the present Mustangs, and things are QUITE a bit different. The fuel pump is now totally responsible for fuel pressure. There is no longer a fuel pressure regulator and a return line. There is only one line, and a fuel rail pressure sensor at the end of the rails. This sensor is also vacuum referenced so that it can calculate what is called the pressure drop across in injectors, or delta fuel pressure. NOTE: There are different ways to read fuel pressure. Most mechanics are used to measuring rail pressure, or gauge pressure. If you connect a fuel pressure gauge to any car, what you see is the actual pressure in the rails. This number is lower when the engine is in vacuum, and higher when the car is in boost. In the world of returnless, we monitor delta pressure, which is simply rail pressure + vacuum, or rail pressure - boost pressure. Take a look. If you have a base pressure of 40 psi, but then add 10 psi of boost, there is 50 psi of fuel rail pressure. If you subtract the boost you are at 40 psi of delta pressure. This is useful, because you can command a delta pressure that should not change, while rail pressure does change. The PCM uses delta pressure to determine if there is too much pressure, or not enough. In either condition, the PCM adjusts the voltage to the fuel pumps to achieve the desired pressure. How does the PCM determine how much voltage to send to the pumps to achieve the desired delta pressure? There is a parameter in the PCM called the Fuel Pump Voltage Table. This table has 5 rows and 9 colums for a total of 45 cells. The X axis is fuel flow in #/min of fuel, the Y axis is Infered Rail Absolute Pressure (RAP). The output of this table is the voltage required. SO you swap a GT500 duel fuel pump setup in a Mustang GT that came with a single pump. What are the chances that the GT500 pump requires the EXACT SAME voltage? Not likely. So now that you have a new fuel pump, and the voltages are all wrong. Now there is a fuel pressure error. This means that the actual fuel pressure and the desired are not the same. No problem, the PCM compensates for error. By default the PCM can adjust the Fuel Pump Voltage Table by +/- 25%. This adaptive strategy is there so that the PCM can start raising the voltage up if the fuel filter starts to clog, etc. It was not designed to compensate for different pumps. 25% might be enough of an adjust in some areas of the table, but I can assure you, it will not totally compensate for the pressure error. Besides learning new voltages, the PCM has a PID controller. If any of you are electrical engineers, I'm sure you are familiar with these. The PID has 3 steps it takes to control the out of control fuel pressure. These have to be adjusted for new pumps as well. If you ever notice a HUGE pressure spike, followed by a huge dip, causing a hesitation (during a shift for instance) then you are experiencing an out of control PID controller. If the gains are not setup properly, then they will over correct high and low pressure spikes. I've worked on a quite a few cars that had different pumps. Sometimes there are issues with the pump swap that causes non-tune releated issues, that no amount of tuning will fix. The GT500 fuel pump setup is a tight fit and I have seen kinked lines causing huge pressure spikes during a deceleration (followed by a huge dip, thanks Mr. PID controller) and bad grounds that cause intermittant problems. One would think that the fix would be to just copy the voltage table from the GT500 calibration. Not that easy. I can't say for certain if the GT500 has different fuel pump and FPDM wiring or different size fuel lines (I haven't checked, if you know please tell me), but in the past the Mustang Cobra did have different gauge wiring. This causes CObra pumps to not support the same level power when installed in a GT. Took us a few years to figure this one out. The bottom line is, if you have swapped fuel system components, then you need an adjustment made to your tune. A competent tuner should already know this, so just make sure you find out when deciding who to let tune your car. The large majority of tuners just know how to adjust timing and airfuel to make power, and skip all the other important things because they either don't know how to adjust them, or are too lazy to spend the time to do it right. Link: http://www.modularfords.com/forums/showthread.php/120136-Fuel-Pressure-Issues-Look-Here Link to comment Share on other sites More sharing options...
2007_Shelby_GT Posted September 8, 2010 Author Report Share Posted September 8, 2010 Good info Kurgan - something I will definitely have looked at when I get my tune next week! Sam Link to comment Share on other sites More sharing options...
kahmann Posted September 9, 2010 Report Share Posted September 9, 2010 Excellent info Kurgan - I have a rail mounted gauge that obviously fluctuates like crazy, depending on throttle position. My delta fuel psi is typically right around 40. Link to comment Share on other sites More sharing options...
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