car is running lean...

Yep

Are you still running speed density?

I am sure someone will chime in and say that an AFPR wont do anything long term bla bla bla and they are correct IF THEY HAVE MASS AIR. The computer will compensate, if you are Speed Density though, the AFPR or a custom tune is the answer.

Setting the fuel pressure out of its normal specs to "fix" a problem, will not address the real root cause of the problem.... IOW, what is causing the EEC to not be able to compensate fuel trim with all the non-EEC parameters within specs?

Check fuel pressure, run the system self tests. LUK

for what it's worth

For what it's worth (your situation may be different) I had no computer codes in my situation, my fuel filter had been replaced, fuel pump was testing good, car was never difficult to start, and I had consistent fuel pressure at the rail.
A Ford Mechanic of 15 years was the one who suggested the AFPR and it worked like a charm for me.

He told me that the introduction of free flowing exhaust and intake mods necessitated the increased fuel pressure in order for the Speed Density system to operate properly.

But hey what do I know.

justagt said:

A Ford Mechanic of 15 years was the one who suggested the AFPR and it worked like a charm for me.

He told me that the introduction of free flowing exhaust and intake mods necessitated the increased fuel pressure in order for the Speed Density system to operate properly.

But hey what do I know.

Click to expand...

What effect does a free flowing exhaust and intake mods have on the vacuum readings at the MAP sensor? Does a better exhaust cause the O2 sensors to provide false information to the EEC and cause erroneous fuel trim adjustments?

The fuel pressure regulator in 5.0 Mustangs is a shunt regulator that works in parallel with the fuel injection system. The regulator bypasses fuel back to the tank to maintain a constant 39 PSI to the injector tips. A constant pressure insures that the computer will always have the same flow rate to base its calculations on.

The 39 PSI pressure is measured at 29.92 inches of atmospheric pressure to get the proper flow rate. But the pressure inside the intake manifold may be higher or lower than the atmospheric pressure outside the intake manifold. These differences would cause the flow rate to change and mess up the computer’s air/fuel calculations.

As the vacuum inside the intake manifold increases, the effective pressure at the injector tips increases. Conversely, as vacuum inside the manifold decreases, the effective pressure at the injector tip decreases.

Some math to illustrate the effect:
39 PSI at 20” of vacuum inside the manifold works out to be 49 PSI,
since the 20 “ vacuum/2 = 10 PSI that you add to the base fuel pressure.
That gives you 49 PSI at the injector tip.
39 PSI at 5” of vacuum inside the manifold works out to be 41.5 PSI,
Since 5” vacuum/2 = 2.5 PSI that you add to the base fuel pressure
That gives you 41.5 PSI at the injector tip
39 PSI with 10 lbs of boost inside the manifold works out to be 29 PSI.
That gives you 29 PSI at the injector tip
That reduces the flow rate and explains the need for higher pressures on engines with pressurized induction.

Since intake manifold vacuum and pressure plays havoc with the pressure at the injector tips, what has to be done to get it back in the magic 39 PSI range? That’s where vacuum applied to the back side of the fuel pressure regulator comes in. Remember this: unless you have some really poorly designed or trick plumbing, vacuum is the same throughout the engine’s vacuum system.
Apply 20” of vacuum to the back of the regulator and the 49 PSI at 20” of vacuum at the injector tips drops to 39 PSI.
Apply 5” of vacuum to the back of the regulator and the 41.5 PSI at 5” of vacuum at the injector tips drops to 39 PSI.
Here’s another side effect: apply 10 PSI boost pressure to he back of the regulator and the normal 39 PSI at the injector tips increases to 49 PSI. Pretty clever of these engineers to use intake manifold vacuum and pressure that way.

Simply stated, intake manifold vacuum adds to the effective fuel pressure at the injector tips. Apply the same vacuum to the back side of the fuel pressure regulator, and everything balances out. Add pressure to the intake manifold and the effective fuel pressure at the injector tip decreases. Apply the same pressure to the back side of the fuel pressure regulator, and everything balances out.

Now you know why to disconnect the vacuum when making fuel pressure measurements.

Keep in mind

fordguy87 said:

Ok got to check the fuel pressure today and its holding 34psi at idle with the vacuum line hooked up but when u take the vacuum line off it jumps up to like 44 psi. With the vacuum line on and u rev it and hold the rev to like 3000 rpms it stays at 34psi. And when I left the gauge hooked up and turned the car off it kept the 34psi of pressure in the line So it seems like the FPR is holding the pressure but the pump can't keep up?

Click to expand...

Keep in mind an AFTERMARKET ADJUSTABLE fuel pressure regulator was needed in my case, replacing your stock one with another stocker set to 39 probably won't change a thing.

joel5.0 said:

What effect does a free flowing exhaust and intake mods have on the vacuum readings at the MAP sensor? Does a better exhaust cause the O2 sensors to provide false information to the EEC and cause erroneous fuel trim adjustments?

Click to expand...

I won't try to tell you that I know the answer. Like I said, a Ford mechanic is the one who told me to do it and it completely fixed my lean condition. My plugs were white too.

I bumped up the fuel pressure with no other changes made and the problem is now completely gone.

did the FPR fix your problem? i am having similar problems with my car

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical





If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.



The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.



The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

Do not jumper anything to the single dark brown connector. It is the power for the under the hood light. It is in another bundle of wires near the windshield wiper.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see EQUUS DIGITAL FORD CODE READER (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

fordguy87 said:

never did change the fuel pressure regular because i put in a bbk 190lph fuel pump and that put my fuel pressure to the right 39 psi but I still have the problem. I took it to the shop cuz i got sick of working on it and they suggested to change the coolant temperature sensor so I did that today and still i'm backfiring and sputtering. Anybody else have any ideas?

Click to expand...

Why would a shop make such a View attachment 307973 suggestion if no ECT codes were showing in a self test?

justagt said:

I won't try to tell you that I know the answer. Like I said, a Ford mechanic is the one who told me to do it and it completely fixed my lean condition. My problem was either starting off from a dead stop or after shifting into a higher gear and letting the clutch out and starting to get on the gas again, the car would sputter and backfire through the intake for a second and then take off line normal. My plugs were white too.

I bumped up the fuel pressure with no other changes made and the problem is now completely gone.

Click to expand...

That is what is known as a mask of the root cause of a problem, similar to attaching an air compressor to a tire that's loosing air, instead of fixing the puncture. Your car, your dough.

hmm

joel5.0 said:

That is what is known as a mask of the root cause of a problem, similar to attaching an air compressor to a tire that's loosing air, instead of fixing the puncture. Your car, your dough.

Click to expand...

I'm all ears if you have a "better" solution... To be honest, it seemed a little strange to me also, but it's the only thing that seemed to work and after pulling my hair out for months I'm happy.

After hours and hours of my own time, checking engine codes, replacing vac lines, gaskets, swapping parts and taking it in to 2 different shops this was the best solution I could find.

fordguy87 said:

They spent 2 hours checking everything out on the car and they came up with coolant temp. sensor because the way the car was acting sounded like it could be the problem.

Click to expand...

Any shop can monitor any sensor under a more rigorous set of rules, if they have (and they should) a scope or a monitoring DMM with MIN, MAX and AVG functions. If a self test and a real time monitor of the sensor doesn't show any type of glitches...... why suggest to replace it?

justagt said:

I'm all ears if you have a "better" solution... To be honest, it seemed a little strange to me also, but it's the only thing that seemed to work and after pulling my hair out for months I'm happy.

After hours and hours of my own time, checking engine codes, replacing vac lines, gaskets, swapping parts and taking it in to 2 different shops this was the best solution I could find.

Click to expand...

Here's a suggestion...... run a KOEO + a KOER and cylinder balance self test trio and LUK what shows up.

Guessing is not nearly as good as knowing. The shop manuals and my code definitions both have the
ECT/ACT temp to voltage and resistance to temp charts.

Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.
Note that that if the outside air temp is below 50 degrees F that the test for the
ECT can be in error.

The ECT sensor has absolutely nothing to do with the temperature gauge. They are
different animals. The ECT sensor is normally located it the RH front of the engine in
the water feed tubes for the heater.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate
readings.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is
a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower
intake manifold, the voltage readings will be lower because of the heat transfer.

Voltages may be measured across the ECT/ACT by probing the connector from
the rear. A pair of safety pins may be helpful in doing this. Use care in doing it
so that you don't damage the wiring or connector.

Here's the table :

50 degrees F = 3.52 v
68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.

50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms

Diagram courtesy of Tmoss & Stang&2birds



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring Mustang FAQ - Engine Information

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

joel5.0 said:

What effect does a free flowing exhaust and intake mods have on the vacuum readings at the MAP sensor? Does a better exhaust cause the O2 sensors to provide false information to the EEC and cause erroneous fuel trim adjustments?

Click to expand...

Nothing, and it has nothing to do with the readings at the MAP sensor.

The Speed Density fuel injection system is based on an assumption of the volumetric efficiency of the engine. When you modify the engine from stock, you're changing it's volumetic efficiency, however the computer cannot compensate for this because it has no way to know.

So as you do mods like a free flowing exhaust, that ultimately allow the engine to breath more air, you're not getting any more fuel with it, and you go lean. Even with all the electronics working.

Fordguy,

Your sig says that your 87 is mostly stock. If that's true, you shouldn't have any mod-induced lean condition. The fuel pressure numbers you're getting are what they should be.

Take it from someone who worked in a shop, you don't want to take your car to one. Shops throw money and parts at cars, they catch hell trying to charge customers diagnostic labor hours to actually troubleshoot a problem so they don't even try. A bad temp sensor could be the cause, but I seriously doubt that was more than an educated guess. If you want to know what's really wrong and not pay out the nose for it, you're going to need to do the troubleshooting yourself.

Pull codes like JR suggested. Off the top of my head, test your coolant temp sensor (new doesn't mean good), your intake air temp sensor, your MAP sensor, and your EGR position sensor... a remote possibility is there's something up with the EGR position sensor, telling the computer the EGR valve is open when it's not. When the computer thinks the EGR valve is open it pulls out fuel.

Yep

joel5.0 said:

Here's a suggestion...... run a KOEO + a KOER and cylinder balance self test trio and LUK what shows up.

Click to expand...

Not to threadjack just real quick:

Believe me, been there done that on the codes... I have a notepad with codes and numbers and stuff on it in the garage somewhere (not home right now).

Short version, the only code is a smog pump error because the previous owner removed it. The back of the heads are properly blocked though and there are no vac leaks. EGR was cleaned and swapped with a known good one. The solenoid for it was also tested. ECT, IAC, MAP, and others ( cant remember) all tested good and swapped out with known good ones to be 100% sure they are ok. Injectors bench cleaned and flow tested.
I am not a rich man, I like to do my own auto work and usually I do alright. This car I just couldnt figure out though and so I eventually took it to a shop I trust. They had it for a day, and told me it was lean and to give it some more fuel pressure with an aftermarket regulator and report back. I did and problem solved.

Just sharing what worked for me in hopes that it would work for the OP.