Engine Dies At Full Throttle

[ace940]

I have a 1990 lx 5.0. It will not rev past 2500 rpm in neutral at full throttle or go past 4k in gear. It will however go past at part throttle. Its not a tps i tried the one on my dads car. I have changed fpr, fuel pump, fuel filter, tfi module, ignition coil, temp sending unit, iat sensor, cleaned the maf and tried a maf from a 94 gt, plugs all look new no fouling, wires and cap and rotor are all newish, have cleaned ground to ecu and all motor grounds, checked for vaccum leaks with aerosol, cleaned iac valve. Im stumped after i did the fuel pump it ran great for about a week now its again. Maybe the pump is faulty. Im waiting for a fuel pressure gauge to see if im pulling 38psi at idle. Any help would be greatly appreciated [emoji106]

 

[ace940]

Oh and i had oreileys read my computer. The only codes that came up were egr no flow... isnt hooked up and something about being rich i believe.

 

[jrichker]

Does this only occur on a warm engine or warm and cold?

 

[ace940]

No anytime

 

[jrichker]

I would encourage you dump the codes and post the results here on Stangnet. The numerical codes are needed to make any kind of diagnosis.

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 (3145It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.

 

[ace940]

I already said what codes i had. Egr no flow and rich condition

 

[jrichker]

I already said what codes i had. Egr no flow and rich condition

You gave a vague description. If you want a precise answer, cooperate and provide what is requested. It is in your best interest to do so, since a lack of willingness to cooperate suggests a lack of willingness to take good advice when you get it. No one here wants to waste time and effort trying to help someone who is difficult to work with.

 

[ace940]

Im sorry im frustrated. My last mustang did this too

 

[mikestang63]

Anyone adjust the valves recently?
is the exhaust and cats free flowing?

 

[ace940]

Stock valvetrain. Can they even come unadjusted? The exhaust is full length no cats only mufflers

 

[jrichker]

Codes, please.

At this point in time you are having either a fuel management problem or the PIP inside the distributor is dying. The codes may help pinpoint the source.

 

[ace940]

I know what the problem is. At full throttle my fuel pressure drops to between 5 and 10 psi. Its not the regulator and i just replaced the pump. Maybe the pump already went bad. I installed the pump and it ran awesome for a week and then started doing the same things again as it did before

 

[90sickfox]

The aftermarket fuel pumps have been having problems with the hose that runs from the top of the pump to the pump assembly outlet. Two people I know have had the same problem....the factory put the clamp on the hose too far up...causing it to back off and cause pressure problems. May not be your case but hopefully it helps.

 

[ace940]

What tells the pump that im going to full theottle. Im assuming that it gets a voltage bump when u pin it

 

[90sickfox]

The fuel pressure regulator senses vacuum changing fuel pressure...no ramping of fuel pump voltage in fox mustangs. At start up I have heard of what is called cylinder clear out. That function was designed to clear flooded cylinders by cutting fuel when cranking with the pedal to the floor to dry out plugs... That's done through cutting the injectors and not the fuel pressure.

 

[ace940]

What would cause that?

 

[jrichker]

What would cause that?

Here's how it works, maybe this will help you understand the process better.

How the fuel pressure regulator works

Revised 5-Jan-2014 to add how to set fuel pressure,

Step 1.) 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 us-mg6.mail.yahoo.com/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 37-41 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.

Step 2 .) How the fuel pressure regulator works
The fuel pressure regulator in 5.0 pushrod 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 pump pressure with 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 pump pressure with 5” of vacuum at the injector tips drops to 39 PSI.

Here’s another side effect: apply 10 PSI boost pressure to the back of the regulator and the normal 39 PSI at the injector tips increases to 49 PSI. That overcomes the 10 PSI in the intake manifold to give you 39 PSI at the injector tips. 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.

 

[Foxslider]

Yes, old thread bump..

I just got thru deciding it was electrical/ignition. Lol. But yesterday i decided, no its fuel pump. Mine doing the samething.


I chose that b/c i gave it full throttle and it doesnt die, but it basically does. Motor is still running, but (at full throttle still) then the rpm just creep down from 25-3k. Till i let off, then it picks up fine.. and its like its getting no ignition is what i thought.
(Edit: if it was getting no ignition then motor would actually die, not dying, yes so it is fuel)

I've seen 2 threads both similar and ended up being fuel pump.

Ya, i need a fuel pressure guage i can check while driving to see if this is happening.



2 day later EDIT: It was the fuel pump. Also did a new fuel filter while i was down there. Runs good now. Full power back, no miss crusing, better starts... Crazy how a pump can act so weird and not just go out completely.