Foxbody Please Help! Injector Size?

To make sure that there isn't some other problem dump the codes BEFORE changing anything....

Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way 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.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.





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.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

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. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some 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.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

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

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10




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) 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 $22-$36.






Once you have fixed any outstanding code problems, here's the injector size info you asked for...
Fuel injector sizing & injector photos

Revised 26-Dec-2014 to add statement about figures are for flywheel HP and not rear wheel HP

Injector HP ratings: this flywheel HP, not rear wheel HP.
Divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines at the flywheel.

Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP
36/.5 = 72, 72 x 8 = 576 HP
42/.5 = 84, 84 x 8 = 672 HP

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

19/.5 = 38, 38 x 8 = 304 HP x .85 = 258 HP
24/.5 = 48, 48 x 8 = 384 HP x .85 = 326 HP
30/.5 = 60, 60 x 8 = 480 HP x .85 = 408 HP
36/.5 = 72, 72 x 8 = 576 HP x .85 = 490 HP
42/.5 = 84, 84 x 8 = 672 HP x .85 = 571 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See Stan Weiss' - Automotive Performance Software / Interactive JavaScript to Calculate Change in Fuel Injector Flow from change in Fuel Pressure to get the calculators used in these examples.

Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.

If you did turn up the fuel pressure, you might be able to change the injector duty cycle to get the air/fuel mixture ratio you want since the injectors will have extra fuel delivery capability.

With larger than stock injectors or higher that stock fuel pressure, you will need an aftermarket MAF that matches the injector size. The MAF “lies” to the computer to get a fuel delivery schedule that meets the engine’s needs and isn’t too rich or too lean. The best strategy is an aftermarket MAF and a custom tune to insure the best air/fuel ratio over all the RPM range.

Don't forget to increase the fuel pump size when you increase injector size or significantly increase the fuel pressure



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 - Wiring & Engine Info Everyone should bookmark this site.

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

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

The injecters are big enough for that combo of parts. If it's running poorly there is something else going on. What are the symptoms? And make sure you run through the above posted checklists.

I agree with Jrichker as far as checking codes. I however disagree with @A5literMan , he must not have had enough coffee and missed the fact that you have stock 19# injectors and STOCK fuel pump feeding Edelbrock aluminum heads and performer intake w/ 1.7 RR's. You are starving for fuel in my opinion. Please get yourself a Walbro GSS340 (255lph) fuel pump and then you can either purchase an Aeromotive adjustable fuel pressure regulator and turn up your fuel pressure a little bit to feed your engine through the 19# injectors or you can upgrade to 24# injectors and a matching 75mm MAF for 24# injectors.

A couple other questions.
What is your timing set at?
What is your fuel pressure set at currently?
Are you running a stock size MAF?
Does your car idle and cruise OK but sucks at wide open throttle?

FoxMustangLvr said:

I agree with Jrichker as far as checking codes. I however disagree with @A5literMan , he must not have had enough coffee and missed the fact that you have stock 19# injectors and STOCK fuel pump feeding Edelbrock aluminum heads and performer intake w/ 1.7 RR's. You are starving for fuel in my opinion. Please get yourself a Walbro GSS340 (255lph) fuel pump and then you can either purchase an Aeromotive adjustable fuel pressure regulator and turn up your fuel pressure a little bit to feed your engine through the 19# injectors or you can upgrade to 24# injectors and a matching 75mm MAF for 24# injectors.

A couple other questions.
What is your timing set at?
What is your fuel pressure set at currently?
Are you running a stock size MAF?
Does your car idle and cruise OK but sucks at wide open throttle?

Click to expand...

Lol...but 19's are probably not the problem. Which was his question. But you're right I didn't clarify,got lazy and gave mediocre advise. His combo is probably around 250-265rwhp. Stock cam Might need a little extra pressure and a pump is always a good idea. He should run codes and all the usual diagnostics before jumping into a MAF and injecters. Not to say he may need them lol.

Tim Steel said:

To everyone -- Thanks for your help!! I didn't know the HP ceilings for difference injectors so thanks for the chart.
Also, I didn't just not have my coffee(!), but I was also out to lunch when I matched these injectors with the build. Pure rookie move for sure. I'll run those codes (thanks!) in case it's something else. I agree, I'm very confident it's only around 250hp - it's just doesn't feel that much stronger than my totally stock 5.0 - which is pretty disappointing and I should know, because I bought this car new in 91 and still drive it today (270,000 miles on a near-stock car running no problem with the original t-5 tranny).
Also - my timing is set at 14 with no knocking; unknown fuel pressure using the 24 year old regulator; I bought a calibrated PRO-M 75mm aftermarket MAF matched to the stock 19s because I was told if I had a larger throttle body (70mm) then I need a larger MAF (probably another rookie move); starts and idles great, runs awesome around town but is almost flat and noisy at WOT.
Question #1: If the codes comes back clean, then I'll upgrade to the 24s (thanks for that) and the upgraded 255 fuel pump, aeromotive regulator, what PSI should I run? Or does it do it automatically?
Question #2: After I put these on, do I need a dyno tune or will the stock computer adjust accordingly with these mods?
Question #3: I'm still running the stock fuel rails. I should probably get new ones also, right?
Question #4: The machinist who refreshed my small block said that after it was put back together with new rings (stock-type, not chrome-molly), he measured a leak down test at 8%. He seemed almost apologetic but I wasn't sure what it make of that and left it alone but it's always been on my mind. Could this be the problem?
Question #5: I feel I lost some torque after I put on those headers and 2.5" exhaust system. Would these bigger injectors help bring that back by simply giving me more fuel?

THANKS GUYS!

Click to expand...

Question #1: If the codes comes back clean, then I'll upgrade to the 24s (thanks for that) and the upgraded 255 fuel pump, aeromotive regulator, what PSI should I run? Or does it do it automatically?
If you're not planning any other modifications in regards to horse power then I'd stick with the 19# injectors and matching MAF that you already have. Get the upgraded Walbro fuel pump and adjustable FP regulator with gauge. Stock fuel pressure I think is 39 psi. Start there and work your way up.
Question #2: After I put these on, do I need a dyno tune or will the stock computer adjust accordingly with these mods?
No need for tune, stock computer should compensate for your changes.
Question #3: I'm still running the stock fuel rails. I should probably get new ones also, right?
The stock fuel rails are OK and support up to 500HP just fine.
Question #4: The machinist who refreshed my small block said that after it was put back together with new rings (stock-type, not chrome-molly), he measured a leak down test at 8%. He seemed almost apologetic but I wasn't sure what it make of that and left it alone but it's always been on my mind. Could this be the problem?
I honestly don't know what a good number for a leak down test should be. @jrichker
Question #5: I feel I lost some torque after I put on those headers and 2.5" exhaust system. Would these bigger injectors help bring that back by simply giving me more fuel?
Headers are not your problem. I think you're running out of fuel at WOT. Running codes will clue you into anything else that may be going on if there are any.

8% is a good figure. When you get to 20%, it is considered a failed test.

Tim Steel said:

Many thanks FoxMustangLvr for the excellent advice and I'll keep my 19's right now and upgrade to more fuel and pressure via the Walbro and aeromotive regulator and gauge. Not to mention saving some much needed money too.

QUESTION: If (and that's if all codes come back clean) I go with 24lb injectors along with the other recommended things, would that somehow make my engine's performance LESS effective with my current hardware (no thanks to my stock cam that I shouldn't have installed in the first place), or to put it another way, would installing 24s hurt my engine or make it run crappy somehow in its current configuration?

Click to expand...

Short answer is no(it won't effect in a negative way). You might see less fuel economy. More so if you stick your foot into it often. You definitely need to run codes before doing anything else. Buy the code reader and manual. You will need these now and in the future. The electronics in these cars are obviously old and tend to fail. If you don't get any codes then purchase your fuel pump, and then If you want, grab a new MAF and injectors. I expect there are a few codes though.

Did you change anything before it sort of went south?

Did you do the heads and top end and it ran good, then all of a sudden gave you problems?

Did you ever check your fuel pressure? Upgrading stock pump good idea, they are pretty lame I think like 80 something gph. When you drop tank for pump be sure none of the baffles in tank have come loose messing with fuel supply, happens often on old foxes. I have similar mods except put in some explorer 19 injectors better spray pattern, mine runs ok on them.
View: https://youtu.be/ldrDFD59NQU

As recommended...

Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way 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.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.





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.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

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. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some 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.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

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

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10




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) 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 $22-$36.

Must have fixed it. Hasn't posted back. Lol