Testing Fuel Pressure

03SCGT · Oct 26, 2009

Just picked up an 03 GT with a Vortech V2 supercharger setup. The car appears to be done correctly with all the right components other than larger injectors than what came with the setup. On the dyno it was running way too lean so we need to hook up a fuel pressure gauge and watch the gauge while driving to see if the pressure goes downhill.

How/where do I get the correct components to hook up a fuel pressure gauge to this car? The quick disconnect is easy enough to take apart but finding a suitable FP guage/t-fitting is proving to be tough. I was kind of surprised to not see a schrader valve to hook into.

Also, any other suggestions regarding my lean condition would be appreciated.

Thanks guys.

oxfordgt · Oct 26, 2009

UPR, mmr and a few other companys make an adapter that goes under the FRPS.

03SCGT · Oct 26, 2009

oxfordgt said:
UPR, mmr and a few other companys make an adapter that goes under the FRPS.

UPR didn't have anything, sent me to Lethal Performance who didn't have anything either. Excuse my ignorance but what does FRPS stand for?

I can't believe this is so hard to find. You would think this would be a commonly requested part. I just want to be able to run a fuel pressure guage up to my windshield(taped down) to drive around and watch fuel pressure.

twogts4us · Oct 27, 2009

Fuel Rail Pressure Switch.
What do you know about the tune? Other than the larger injectors, do you know anything about the fuel system? IE - larger pump(s), boost-a-pump, ???

wmburns · Oct 27, 2009

Low tech suggestion. Use an ODB2 scanner to monitor the Fuel pressure PID from the PCM. No cutting/hacking required.

If you have a PC interface, it would be possible to data log. Consider data logging Fuel pressure, TPS, MAF, and O2.

Is your MAF clean? A dirty MAF will over state air flow at low flow. At higher flow, it will under state. This causes the fuel trim to go from big negative values at big positive values at high flows.

If the MAF is dirty, the AF will initially lean. In response to O2 input, the PCM will attempt to add fuel (delay).

Use the ODB scanner to monitor the short and long term fuel trim. If you notice it going neg at idle and positive at load, then the MAF is dirty. Use a cleaner made for MAF cleaning. It is fragile and easy to damage.

O2 sensors will respond slower as they age. If > 100k consider changing.

03SCGT · Oct 27, 2009

wmburns said:
Low tech suggestion. Use an ODB2 scanner to monitor the Fuel pressure PID from the PCM. No cutting/hacking required.

Great idea on the scanner/data logger. We hooked up a diablo tuner for a 03 Cobra which worked great for watching the fuel pressure as we drove around. The fuel pressure was around 40psi at idle and while driving around normally. When I put my foot into the gas, the fuel pressure stayed around 38-41 and didn't go up at all, hence my lean problem.

Now here's where I don't understand how Mustangs work. The fuel pressure regulator is just that little chrome silver unit with NO vacuum line going to it. Without a vacuum line at the regulator, how/why does a normal Mustang get it's fuel pressure to go up to 60psi at WOT? We hooked the Diablo up to the 03 Cobra and the fuel pressure shot up to 60psi as soon as we got on the gas.

I'm trying to understand how the Mustang fuel system works and what makes the fuel pressure go up to 60psi at WOT ???

wmburns · Oct 27, 2009

Delta pressure vs atmospheric

On the return-less system, the round silver disk is a DAMPER. It is there to control pulses (hydraulic hammer) generated by the open/closing of the fuel injectors. Saves wear and tear on the pump and evens out the pressure. The vac line is there just in case the diaphragm breaks. Should that happen, the raw fuel would be sucked inside the engine instead of all over the outside.

A return-less system does not have a mechanical pressure regulator. It is completely electronic based upon the signal from the fuel pressure sensor. In response to signals from the PCM, the Fuel pump relay module (FPRM) controls the pump's duty cycle (% on/off) to achieve the desired fuel pressure.

The fuel pressure PID reported by the PCM is a DELTA pressure (corrected/indexed to intake pressure). Therefore, it is normal for it to stay in a narrow range. It would indicate a problem if it DROPPED at WOT.

For a delta pressure sensor to work correctly the vac line back to the intake manifold is vital.

When you are measuring fuel pressure relative to atmospheric, then 60 PSI is a reasonable number in a boosted application because the pressure has not been indexed to the manifold. So if the pressure inside the manifold was 20PSI, the PCM would command the fuel pressure to be 20+40 PSI.

The PCM uses delta pressure because when the pressure is constant, then the mass of fuel becomes a straight line function of pulse width (injector duty cycle).

03SCGT, what is the duty cycle on the fuel injectors? Your fuel pressure is not really low if the PCM is reporting 38-41 at WOT. How are you measuring the AF ratio? How lean is it? Why doesn't it have the larger fuel injectors as recommended? Seams like an obvious reason it is running lean.

Note, a custom turn can change the way the fuel pump works. Remember, the PCM completely controls the fuel pressure.

twogts4us · Oct 27, 2009

Great post WMBurns. As I asked previously, we need a little more input on the fuel system setup, along with some info on the engine (completely stock or ?) and on the amount of boost you are running. Also, you stated "On the dyno it was running way too lean...". What did the dyno operator say? Did he modify the tune? Does it have a chip or handheld tuner or is it running the stock tune? How lean was it? Do you have the dyno graph you could scan and post out here?

03SCGT · Oct 28, 2009

twogts4us said:
Great post WMBurns. As I asked previously, we need a little more input on the fuel system setup, along with some info on the engine (completely stock or ?) and on the amount of boost you are running. Also, you stated "On the dyno it was running way too lean...". What did the dyno operator say? Did he modify the tune? Does it have a chip or handheld tuner or is it running the stock tune? How lean was it? Do you have the dyno graph you could scan and post out here?

Great posts guys, appreciate the help. Here's some more info on the car:

Engine: All original

Fuel system: original w/ 42lb injectors (the Vortech V2 kit came w/ 38lb injectors), also has an upgraded fuel pump with the kit.

Tune: Stock computer with Vortech piggyback chip specific to this kit.

Boost: 10-11 lbs.

On the dyno is was OK until WOT and building RPM's. The air/fuel under WOT was in the 14 range up to 3700 rpm where it hit 15, at 4000 rpm it was at 15 1/2 and still climbing. At that point the dyno operator freaked out and let off the gas saying this was dangerously lean.

03SCGT · Oct 28, 2009

wmburns said:
03SCGT, what is the duty cycle on the fuel injectors? Your fuel pressure is not really low if the PCM is reporting 38-41 at WOT. How are you measuring the AF ratio? How lean is it? Why doesn't it have the larger fuel injectors as recommended? Seams like an obvious reason it is running lean.

Note, a custom turn can change the way the fuel pump works. Remember, the PCM completely controls the fuel pressure.

We didn't check the duty cycle on the injectors. Do you think the Diablo will read that? As for AF ratio, see above post.

It does have larger injectors, see above post, even larger than what came with the kit.

It really shouldn't need a custom tune as Vortech supplies all the necessary components and piggyback chip for the tune. I just think I have a problem with the cars fuel system somewhere.

wmburns · Oct 28, 2009

Other things that can cause a lean conditon.

Vac leak. Any unmetered air bypassing the MAF will cause the PCM to compute too little fuel.

Dirty MAF has already been mentioned.

Pegged MAF. If the MAF is maxed out voltage wise, the PCM will not know that more fuel is needed. Stock MAF is good until around 300RWHP.

Exhaust leak could cause a false lean reading.

The #40 injectors should be good to 525 HP(Flywheel) assuming BSFC=0.5, 80% duty cycle, pressure=43.5 PSI.

525 HP to the flywheel is a lot for a stock bottom end. Maybe too much.

03SCGT · Oct 30, 2009

wmburns said:
Other things that can cause a lean conditon.

Vac leak. Any unmetered air bypassing the MAF will cause the PCM to compute too little fuel.

Dirty MAF has already been mentioned.

Pegged MAF. If the MAF is maxed out voltage wise, the PCM will not know that more fuel is needed. Stock MAF is good until around 300RWHP.

Exhaust leak could cause a false lean reading.

The #40 injectors should be good to 525 HP(Flywheel) assuming BSFC=0.5, 80% duty cycle, pressure=43.5 PSI.

525 HP to the flywheel is a lot for a stock bottom end. Maybe too much.

The car did have a bad exhaust leak on the drivers side header gasket. The car has dual exhaust so I had the dyno operator put the A/F sensor on the passenger side(since the leak was on the drivers side). Could that still have been a problem?

I ordered one of the top of the line Actron scanners with data logging, graphing, etc. It should be here in a few days. What should I be looking for on the injector duty cycle both at normal crusing and WOT ?

wmburns · Oct 31, 2009

What are your plans/goals?

The Mustang does not have a true dual exhaust system. Remember there is an H pipe connecting the two sides together. I would have doubts that a true AF ratio can be obtained with an exhaust leak (from either side).

I wouldn't have much faith in the dyno operator either. In some respects aren't you relying on his expect advice? Your car's life is certainly in his/her hands while it is on the rollers.

There is no PID for duty cycle. There is a PID for pulse width. Not all ODB2 scanners can access. Suggest that you log TPS, load, MAF, pulse width, O2, fuel pressure, long term/short term fuel trim, and anything else that you think might be useful.

Unless your setup has an after market MAF, you are over the air flow limit of the stock MAF. In order to be able to understand the data acquired, some knowledge of the Vortech is going to be required. For example, how does Vortech handle the MAF calibration? Does the PCM show the actual mass of air or is the tune “indexed” to some arbitrary number?

Others have also suggested getting stand alone wide band O2 sensors.

This detailed understanding is going to be necessary to turn the logged data into information.

My expertise is with fixing stock cars. This may be the limit of the help I can offer. There are a lot of very smart people on this board that actually have direct experience with a similar set up to what is being run.

On another note, what are your expectations? How much power do you want to make? Are you concerned that your stock bottom end is going to hold up under the levels of boost/HP being made? Why are you so certain there is a fuel problem? Especially since the fuel injectors are already larger than what came with the kit. Has any steps been taken to re-tune/calibrate for the larger injectors?

This may be some unasked for advice. This set-up has got to be pushing the limits. Anytime the limits are pushed right to the edge, safety margins can get to be razor thin. Bad things could be in store for the unprepared.

03SCGT · Nov 3, 2009

We actually just got this car and are going into it blind. It looks like a clean install but we don't have any way of contacting the previous owner. Over the weekend we dug up into the fender and found that the car still had a stock MAF sensor with a big cone K&N filter. The MAF looked fine, no restrictions, no garbage up in there. As this point we are questioning whether or not the car has an upgraded fuel pump. I ordered a Focus SVO 255gph pump which should be here in a couple days. I'm going to change out the pump and fuel filter.

Yesterday I got my Actron CP9185 data logging/recording/graphing scanner in. I'm a bit of a noob with these things but ready to learn. If you'll walk me thru some tests I can report the readings.

wmburns · Nov 3, 2009

If it truly is a stock MAF, it will be long pegged at your power levels. IMO, you are wasting your $$ upgrading fuel pumps before the MAF has been confirmed.

Data log the air flow, TPS, pulse width, load, O2, Long term fuel trim, and fuel pressure for starters. If the MAF is pegged, the log will show the air flow increasing until some maximum is reached. From that point on, the AF will begin to lean out as the PCM does not know to add more fuel.

The lean condition will show up in the O2 sensors. The PCM will after a delay, add fuel which will show up in the fuel injector pulse width and the long term fuel trim.

Once graphed, it will be easier to see. The graph will show a flat top when air flow and load are graphed together.

IMO, it is vital that all exhaust leaks and vac leaks be fixed before pushing to high HP levels.

I may be going out on a limb here but I see a possibility of bad things in your future. Recommend that you get a professional dyno tune for your combination or take things very slow and read/study a lot. Your set up is more than capable of doing major engine damage in just a blink of an eye.

03SCGT · Nov 3, 2009

wmburns said:
If it truly is a stock MAF, it will be long pegged at your power levels. IMO, you are wasting your $$ upgrading fuel pumps before the MAF has been confirmed.

Data log the air flow, TPS, pulse width, load, O2, Long term fuel trim, and fuel pressure for starters. If the MAF is pegged, the log will show the air flow increasing until some maximum is reached. From that point on, the AF will begin to lean out as the PCM does not know to add more fuel.

The lean condition will show up in the O2 sensors. The PCM will after a delay, add fuel which will show up in the fuel injector pulse width and the long term fuel trim.

Once graphed, it will be easier to see. The graph will show a flat top when air flow and load are graphed together.

IMO, it is vital that all exhaust leaks and vac leaks be fixed before pushing to high HP levels.

I may be going out on a limb here but I see a possibility of bad things in your future. Recommend that you get a professional dyno tune for your combination or take things very slow and read/study a lot. Your set up is more than capable of doing major engine damage in just a blink of an eye.

I understand completely what you're saying about doing major engine damage. That's why I'm asking lots of questions and taking it slowly. The first thing we did was fix the exhaust leaks.

I just got off the phone with Vortech and found that the V2 system came with 38lb injectors(I now have 42's), a 255gph pump and a 80mm MAF housing that uses the stock MAF guts.

I'll try to pull the wheel and wheelwell out tomorrow and measure the housing to see if it's correct but I'll bet it is. The mounting bracket and filter were what came with the V2 package according to the Vortech tech guy.

My Focus SVT 255gph pump should be here tomorrow. I'll probably change out pumps and a new fuel filter over the weekend.

I'm trying to learn this Actron CP9185 scanner and what it can do on this car. A Mustang buddy of mine told me to look for a "Fuel Pump Usage Percentage" parameter but I'm just not finding it. I see the "Fuel Pressure" parameter, it works fine. My long term fuel trim bank 1 was 7%, bank 2 at 4.7%. There are 2 more parameters available called "FuelSys1" which is staying at "closed" as the car is at idle and being revved at a stand still. There is a "FuelSys2" parameter also but it says "N/A".

Is there supposed to be a Fuel Pump Usage Percentage parameter on this scanner somewhere?

My buddy said to watch the MAF voltage parameter and see if it gets pegged out early. He said 4.97-5.00 was max.

Given that this is a supercharged 4.6 with 10 lbs of boost, what kind of WOT numbers should I want to see via the O2 sensors. I'm used to doing this on GM cars which like to be around .76-.90.

wmburns · Nov 3, 2009

Do not believe you will find a fuel pump used %. This would require a two way communication between the PCM and FPRM (could easily be wrong here). Remember the PCM is expecting a constant 40 PSI delta pressure. So it really only matters if the pressure drops.

If you have a link to the manual, post it so that I can study.

Putting the stock MAF in a larger tube works becuase the voltage of the MAF is re-indexed to a different level. Therefore, 5v means something different in an 80mm tube vs 5v in a stock tube.

The tables in the tune convert a voltage signal into "mass of air". A pegged MAF will show up as a peak near 5 volts.

I am not familiar with how the Vortech tune interfaces to the PCM. For example, will the MAF air flow units display in corrected units or stock units.

Frankly, it really scared me when you said that the MAF was stock. It makes more perfect sense placing a stock meter in a larger tube.

Note, the processing is different at WOT. When not at WOT, the PCM operates in "closed loop". The sensors are used to adjust AF.

In WOT, the PCM operates in "open loop". Fuel and air is computed via tables. Usually a tuner will err to the rich side at WOT.

In answer to your ? about O2 sensors, it would help to have some information regarding what the voltage levels mean. I can look through my reference materials and see what I can find. May take me a few days.

Sooner or later I hope someone that REALLY knows Vortech takes over. I am starting to get over my head.

Consider opening a new thread. This is no longer about testing fuel pressure. The real issue is the lean condition and how to tune it.

03SCGT · Nov 11, 2009

A little advice guys. I got my badass Actron CP9185 recording/graphic scanner in to test a few things and went out today to watch the MAF readings to see if they were getting maxed out. Everybody told me that 5.0(volts ???) was the max reading. With this scanner, I get a MAF reading listed as LB/M. I have no idea what that means. Accelerating through 2nd gear would give me numbers in the 14-15 range. I don't see any other tests with this scanner for the MAF sensor?

Can anyone give me some advice where to go from here? This scanner doesn't appear to be that helpful.

wmburns · Nov 11, 2009

03SCGT said:
A little advice guys. I got my badass Actron CP9185 recording/graphic scanner in to test a few things and went out today to watch the MAF readings to see if they were getting maxed out. Everybody told me that 5.0(volts ???) was the max reading. With this scanner, I get a MAF reading listed as LB/M. I have no idea what that means. Accelerating through 2nd gear would give me numbers in the 14-15 range. I don't see any other tests with this scanner for the MAF sensor?

Can anyone give me some advice where to go from here? This scanner doesn't appear to be that helpful.

LB/M means pounds of air per minute. This is the most common units of measure that the MAF uses. What you are scanning is the what the PCM has converted the voltage output of the MAF to.

From here, if you know the pounds of fuel per minute, this will compute the Air to fuel ratio.

There has to be a way to access the raw data (PID). Then you can look to see if the MAF is maxing out.

I found a link to the user manual. Will look at it when I can. http://www.actron.com/publish/2007/04/30/pdf_english_16336.pdf

The scanner may be smart enough to offer a built in graph of AF ratio.

Pearl02 · Nov 13, 2009

Wmburns, don't sell yourself short. Your doing a great job of helping 03scgt out. Your very sharp on this stuff. I wish I could help out but this is beyond me. I'm starting to understand better about how the pcm works. I just purchased a Innova/Equus 3130 scan tool a couple of month's ago. Seems like it's very similar to the Actron 03scgt has. I'm learning more just by reading the comments between both of you. Keep up the great work and good luck to you 03scgt. Pearl02.

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