Ready to blow the car up

Codes are:
15 Power Interruption to computer memory or EEC (PCM) Keep Alive Memory (KAM) test failed
31 EVP or PFE circuit below minimum voltage
33 EGR valve not opening properly
41 HEGO (HO2S) sensor signal out of range / always lean
91 HEGO (HO2S) sensor signal out of range /always lean

Where are you located ? What fuel pump is in the car ?

No you don't need fuel rails.
Are all the replacement parts you used for sensors from ford? The rest are garbage.

Just a thought, maybe a vacuum leak somewhere?

Work on fixing those codes before you start throw parts at the car blindly. Biggy on that list is the 02 codes, your ECM doesnt' know how to trim the car out without good 02 sensors.

Give forced open loop a try and see if it helps out. Since you can't change it in your tune, unplug the o2 sensors.

I might be wrong, but in "theory" I would think you could just unplug the IAC, and adjust the idle with the throttle blade screw like you would an idle stop screw on a carb. I have never done this though.

You are not the first guy with a surging idle problem. A search would have uncovered this jem...

See the "Surging Idle Checklist” for help with all your idle/stall problems. Everything you need to find and fix idle problems is in there.

The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

I've had a surging idle for years and lived with it.
Recently the car really started acting a donkey....would die with no warning, fuel pump stuck on when ignition was on, successfully cranked only intermittently. It would throw a different code every time I pulled codes.

New computer fixed all issues including the long term idle problem. Car runs like it did from the new car lot now.

Maybe you could swap a friend's computer??

Worked for me but my car is all stock.

Cajun93 said:

I've had a surging idle for years and lived with it.
Recently the car really started acting a donkey....would die with no warning, fuel pump stuck on when ignition was on, successfully cranked only intermittently. It would throw a different code every time I pulled codes.

New computer fixed all issues including the long term idle problem. Car runs like it did from the new car lot now.

Maybe you could swap a friend's computer??

Worked for me but my car is all stock.

Click to expand...

Why spend $120+ for a refurb computer? You must have money to burn. If you do, send some to me, its cold here in middle Georgia and I could use some kindling...

Seriously, the b]"Surging Idle Checklist” [/b] covers the surging idle problem throughly. Spending 2 or 3 hours to save a bunch of $$$ is much better investment of time and money than just throwing expensive parts at a problem and hope you fix it.

What brand are the injectors ? what brand and part number is the MAF ?

jrichker said:

Why spend $120+ for a refurb computer? You must have money to burn. If you do, send some to me, its cold here in middle Georgia and I could use some kindling...

Seriously, the b]"Surging Idle Checklist” [/b] covers the surging idle problem throughly. Spending 2 or 3 hours to save a bunch of $$$ is much better investment of time and money than just throwing expensive parts at a problem and hope you fix it.

Click to expand...

I purchased a computer because I needed a computer. Mine was not functioning. I then made the observation that it fixed my surging idle that plagued me for years. Something the "Surging Idle Checklist" could not do. Deduction.....
I think I remember why I haven't been on this forum in a few years.

Try flippin/mount the IAC upsidedown.

s0lidllama said:

Guys/gals I need help. Im at a point with my car that I want to just put a slug straight through the block.

Ive been having the surging idle issue that many people have. MAF,TPS,Temp sensors have been replaced. IAC is brand new. New sparkplugs and O2 sensors. I follow step by step Idle reset instructions to no avail.

On top of that I have a dead spot between 2500-3500 RPM Where the car sputters and has no power till it gets past those RPMs. Ive replaced MAF, Injectors, triple checked the timing. The only time the car doesnt sputter is when I put my FPR up to about 55psi (Vac. off) That just seems like its way too high?

Codes are:
15
31
33
41
91

Ive tried resetting the computer by unplugging the battery also. Nothing helps. Have I missed something? The only thing I havent replaced yet is the plug wires.

Mods are
306
E303
GT40 heads
Performer intakes
CAI
24lb injectors + Maf
70mm Throttle body
Full MSD Ignition
LT Headers

Click to expand...

As I read your post, I found no mention of the Surging Idle Checklist. It just isn’t in there. If you have another post on the same subject you made no mention of it. I have no clue of what you have and haven’t done before your current post. The best plan is to put any additional information in the original post so there is a continuous trail of what your problem is and what you have done. Trying to remember this post is more of that post plus the other post just makes it hard to keep up with. No wonder you are getting run around in circles. PM the moderators, supply them with the names of your posts on the same subject and ask them to merge them. You’ll get much better results that way.

Code 15 - No Keep Alive Memory power to computer pin 1 or bad computer (Memory Test
Failure). The voltage to the Keep Alive Memory (KAM) is missing (wiring problem)
or the KAM is bad. The KAM holds all of the settings that the computer "learns" as
it operates and all the stored error codes that are generated as a result of
something malfunctioning while the engine is running. Use a voltmeter to check
the voltage to the pin 1 on the computer - you should always have 12 volts. No
constant 12 volts = bad wiring. If you do always have the 12 volts, then the KAM is
bad and the computer is faulty.

If the computer has to "relearn" all the optimum settings every time it powers up,
the initial 5-30 minutes of operation may exhibit surges, poor low speed performance,
and rough idle.

Note that some aftermarket chips will cause code 15 to set. Remove the chip,
clear the codes and retest.

Before replacing the computer, remove the battery ground cable for about 20
minutes. This will clear all the codes. Retest after several days of running. If the 15
code is gone, then don't worry about it. If it is still there, then you get to do some
troubleshooting.

Wiring diagrams for the proper model years are next…

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

Diagram courtesy of Tmoss & Stang&2birds


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

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif


CODE: 31 (KOEO) - EVP circuit below minimum voltage. Sensor removed or disconnected, Vref (5 volt reference voltage supplied by the computer) missing or broken wire or bad connection in circuit. Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or MAP sensor located on the firewall near the center of the car. Use the black/white wire for the ground for the DVM.
With the sensor removed from the EGR and still connected, press the plunger and watch the voltage change on the brown/lt green wire. Pull the passenger side kick panel and measure the voltage at the computer. You will need to remove the plastic cover over the wires and probe them from the backside. A safety pin may prove very useful for this task. Use pin 27, EVR input (brown/lt green wire) and pin 46, signal ground (black/white wire) to measure the voltage. The orange/white wire is Vref and should always be 5 volts -/+ .25 volt. Be sure to measure Vref at the EGR sensor to rule out any broken wires or bad connections.
Measuring the voltage at the computer helps you spot broken wiring and intermittent connections.


Code 33 - Insufficient EGR flow detected.
Look for vacuum leaks, cracked vacuum lines, failed EGR vacuum regulator. Check to see if you have 10” of vacuum at the EGR vacuum connection coming from the intake manifold. Look for electrical signal at the vacuum regulator solenoid valves located on the rear of the passenger side wheel well. Using a test light across the electrical connector, it should flicker as the electrical signal flickers. Remember that the computer does not source any power, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.
Check for resistance between the brown/lt green wire on the EGR sensor and pin 27 on the computer: you should have less than 1.5 ohm.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif


EGR test procedure courtesy of cjones

to check the EGR valve:
bring the engine to normal temp.

connect a vacuum pump to the EGR Valve or see the EGR test jig drawing below. Connnect the test jig or to directly to manifold vacuum.

Do not connect the EGR test jig to the EVR (Electronic Vacuum Regulator).

apply 5in vacuum to the valve. Using the test jig, use your finger to vary the vacuum

if engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.

if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.

if engine stumbled, connect EGR test jig to the hose coming off of the EGR Valve.
Use your finger to cap the open port on the vacuum tee.
snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
did the vacuum gauge show about 2-5 in vacuum?
if not the EVR has failed

EGR test jig


The operation of the EGR vacuum regulator can be checked by using a test light applied across the wiring connector. Jumper the computer into self test mode and turn the key on but do not start the engine. You will hear all the actuators (including the EVR vacuum regulator) cycle. Watch for the light to flicker: that means the computer has signaled the EGR vacuum regulator successfully.


Code 41 or 91 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

Revised 24-Sep-2009 to correct computer pin description for 94-95 5.0 Mustangs

Code 41 is a RH side sensor,
Code 91 is the LH side sensor.

Code 172 is the RH side sensor
Code 176 is the LH side sensor

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Testing the O2 sensors 87-93 5.0 Mustangs. Note: an Analog voltmeter or Digitial voltmeter with a bar graph is needed for this test. A regular Digital voltmeter will give inaccurate results.
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Testing the O2 sensors 94-95 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 43 (LH O2 with a red/black wire) and 44 (RH O2 with a gray/lt blue wire). Use the metal next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

If you get only code 41or 91 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.
A secondary problem with only a code 41 or 91 is for cars with an intact smog pump and cats. If the tube on the back of the heads clogs up, all the air from the smog pump gets dumped into one side. This excess air upsets the O2 sensor calibration and can set a false code 41 or 91. The cure is to remove the crossover tube and thoroughly clean the insides so that there is no carbon blocking the free flow of air to both heads.

Cajun93 said:

I purchased a computer because I needed a computer. Mine was not functioning. I then made the observation that it fixed my surging idle that plagued me for years. Something the "Surging Idle Checklist" could not do. Deduction.....
I think I remember why I haven't been on this forum in a few years.

Click to expand...

Evidently you didn’t appreciate my attempt at humor. It was not my intent to make fun of you or intimidate you.

The Surging Idle Checklist is a guide to solving the most common causes of idle problems. The concept is to troubleshoot the problem as simply and inexpensively as possible. Most of the guys here don’t have the $120+ to go purchase a replacement computer on a wild card guess. That’s why it is troubleshoot and diagnose time. In the 1000’s of posts I have read and made, I have seen maybe 3 or 4 where a computer that would successfully dump codes was the cause of a problem. If the computer dumps codes and passes the internal self tests, it is not normally the source of problems.