Poor Top End Performace

Czman30 · Jul 30, 2015

Hello, i recently bought a 1990 Mustang GT 133k. Mods, BBK cold air intake, long tube headers, off road H pipe, & Flow masters. Had sat for 4-5 years (previous owner would take it every once and a while for a spin). My first issue is that I have to turn the key a few times to get it started, once it runs it idles fine, for the most part ( thought I fixed most of the idle problems today, may be wrong). I have to pump the gas pedal a couple of times to get it to start (it's not converted to carb). My next issue 2 issues are that I have poor performance when my drive first starts, there is bogging/ backfiring in second gear (the backfiring and bogging don't really start unless its at or above 3k), and then if I let it idle after taking it for lets say 10 minute drive, it really looses performance and limps home ( doesn't really want to go over 2.5k rpm, or atleast the bogging is way worse). I have replaced Distributor Cap and rotor, Plugs, wires, fuel filter, and fresh oil change. I checked fuel pressure when I first started at idle with a harbor freight gauge I bought today, showed at 25 PSI at idle. Checked timing with my timing light, its at 10 degrees (may be a hair under 10) haven't checked if timing advances properly, car is currently running on 87 octane, ran some startron through the tank to help stabilize fuel, I changed fuel filter this morning and it seemed to make a small difference just like the other things I have done as a tune up. Any help for these issues is greatly appreciated.

Czman30 · Jul 30, 2015

Also, just went to check timing advance with the light, saw arking in 2 spots one onto the exhaust header from the plug wire for first cylinder on right. and on the dipstick from the second or third plug wire on the right side ( couldn't fully tell), don't know if this can cause anything.

bigc2330 · Jul 31, 2015

First check your plug wires and make sure that they are fully on the plugs.
If that doesn't fix your ark, then check your plugs and make sure you didn't crack the porcelain.
After you have fixed your spark problem, search the forum on how to check trouble code.
"Jrichker" has a fully detailed way and pics on how to dump the codes. Also, you can have trouble codes without the check engine light on.

mikestang63 · Jul 31, 2015

1. run the codes
2. replace the faulty spark plug wires
3. 25 psi for fuel pressure with the vacuum line off and pluged is no bueno. it should be 39-41. You either have a bad FPR, clogged line or what I suspect the in tank pump is on its way out

rbohm · Jul 31, 2015

the low fuel pressure is the key here. as noted 25psi at idle is no good, it should be closer to 40psi.

so chances are that your motor is going lean in the upper rpms, which kills the power. the first thing you need to check, and probably replace, is the fuel pressure regulator. the next thing to check is the fuel pump itself, it might be worn out and ready for replacement.

after that check the fuel lines for proper flow.

Czman30 · Jul 31, 2015

mikestang63 said:
1. run the codes
2. replace the faulty spark plug wires
3. 25 psi for fuel pressure with the vacuum line off and pluged is no bueno. it should be 39-41. You either have a bad FPR, clogged line or what I suspect the in tank pump is on its way out

Just had the plugs, wires, distributer cap and rotor, fuel filter, and oil change done. Still have to run codes. 25 psi isn't good? Still new to the mustang scene, I had a focus originally, loved the car but wanted something with more power and better aftermarket parts support. I have been toying with the idea that fuel pump might be going out. But not entirely sure.

jrichker · Jul 31, 2015

Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 38-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.

Fuel pump pressure test
Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line coming from the regulator. Stick a bolt in the other end of the hose and make sure that all your connections are tight and leak proof as possible. When this powers up, you don't want fuel squirting everywhere. Hook up the fuel pressure test gauge. Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the ECC test connector and jump the connector in the Upper RH corner to ground.

Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump
If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad. If the fuel pressure does not hit 55 PSI or more in a few seconds, the pump is bad or you have electrical problems.

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.
[/b]

Czman30 · Jul 31, 2015

jrichker said:
Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 38-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.

Fuel pump pressure test
Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line coming from the regulator. Stick a bolt in the other end of the hose and make sure that all your connections are tight and leak proof as possible. When this powers up, you don't want fuel squirting everywhere. Hook up the fuel pressure test gauge. Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the ECC test connector and jump the connector in the Upper RH corner to ground.

Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump
If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad. If the fuel pressure does not hit 55 PSI or more in a few seconds, the pump is bad or you have electrical problems.

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.
[/b]

Just got done with the first test, I got around 27 PSI. In the process of starting the second test, Not sure which line is bigger of the 2. Anyways thanks for the help so far.

Czman30 · Jul 31, 2015

jrichker said:
Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 38-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.

Fuel pump pressure test
Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line coming from the regulator. Stick a bolt in the other end of the hose and make sure that all your connections are tight and leak proof as possible. When this powers up, you don't want fuel squirting everywhere. Hook up the fuel pressure test gauge. Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the ECC test connector and jump the connector in the Upper RH corner to ground.

Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump
If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad. If the fuel pressure does not hit 55 PSI or more in a few seconds, the pump is bad or you have electrical problems.

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.
[/b]

What if my supposed black and white wire is white and red? Is that okay?

jrichker · Jul 31, 2015

Go by the positions on the socket in the drawing. It shows the face view of the socket.

Czman30 said:
What if my supposed black and white wire is white and red? Is that okay?

Go by the positions on the socket in the drawing. It shows the face view of the socket.

Czman30 · Jul 31, 2015

So I've pretty much figured it out that its most likely my fuel pump. I drained most of the tank with the weak fuel pump. No codes came up on engine diagnostics. My return line would not come out of the clip, but i did test the fuel pump with just the car off and used that jumper, only got 20 psi.

mikestang63 · Aug 1, 2015

Why didn't I think of that? Get a wahlbro unit. you can use a 155lph but most guys just get the 255lph, It;s a little noiser. runs about $05... Whiile you are at it, change the filler neck seal that goes to the tank and probably the sock in the tank.

Czman30 · Aug 1, 2015

mikestang63 said:
Why didn't I think of that? Get a wahlbro unit. you can use a 155lph but most guys just get the 255lph, It;s a little noiser. runs about $05... Whiile you are at it, change the filler neck seal that goes to the tank and probably the sock in the tank.

Already changed it and takes 2 seconds to turn on instead of 20. Made the world of difference.

Czman30 · Aug 1, 2015

Changed the fuel pump and solved all my problems, car starts in 2 seconds, has loads of power, and loves first and second gear now all I have to do it teach myself to behave

jrichker · Aug 2, 2015

I am glad to hear that you got it running good. Have fun, but be careful.

Poor Top End Performace

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