Rich At Idle, Maybe Cruise Too

FYI: I will be without computer or Internet for the next 5-6 days, so if you don't get follow up help message from me for a while, don't fret.

If all the sensors and wiring are working correctly, you get a code 11 and nothing else without the engine running.

The engine running codes will be 11, and then 4. The engine will then test the EGR by opening the EGR valve , causing the engine to stumble if it is working correctly. At that point pushing the throttle above the 2500 RPM point will start the cylinder balance test.

If the computer has internal problems, there are only 2 codes it will set, code 15 and code 19. If the computer has serious problems, the codes won't dump and/or the engine won't run.

Code 15 - No Keep Alive Memory power to PCM pin 1 or bad PCM (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.

See the following website for some help from Tmoss (diagram designer) & Stang&2
Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

Diagram courtesy of Tmoss & Stang&2birds


Code 19 - Engine off - No Vehicle Power (pins 37 + 57) or bad PCM VPWR Diagnosis. This is a wiring problem that is from a bad ECC power relay, bad connection, bad fuse link, bad ignition switch or a bad computer. The ECC relay is located on top of the computer under the passenger side kick panel. Pull the connector off any fuel injector and measure the voltage on the red wire: if its 12 volts or better, the ECC relay is OK. If the ECC relay is OK, pull the kick panel off and measure the voltage at pins 37 & 57. If it is 12 volts or more, then the computer's diagnostic firmware has taken a dump and is defective.

Engine running - Erratic idle during test (reset throttle & retest) - Idle Set Procedures .
See http://www.stangnet.com/mustang-forums/698148-help-me-create-surging-idle-checklist.html#post6855020 for the best way to set the mechanical base idle and cleaning procedure for the IAC/IAB.

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

If the steps I outlined for the EGR do not work, the only thing left is an intermittent bad connection or broken wire in the EGR sensor ground circut.

The fuel pump relay is less than $15 at AutoZone:.On 87-91 cars, it is under the seat, on 92-93 cars it is under the MAF by the A/C WOT cutoff relay. it takes about 3 minutes to replace it. Your just push the seat all the way back and you can reach it. There may be a bolt with a 10MM or 11MM head that bolts the relay mount bracket to the floorpan seat mount. Code 96 can also be caused by an intermittent bad connection or broken wire.

7991LXnSHO said:

OK, Here is as brief as summary as I can get. I took it to the dealer to get the code for the secondary fuel pump circut checked out. I TOLD them to Please replace the relay for the fuel pump and check out the circut for thet code 96 that kept coming back.

I also said it was running rich and to please replace the O2 sensors while it was in the air. I did not know the miles on the sensors and it would be cheaper than a separate trip. So he started with the O2 sensors, determined there was no power to the bank 2 heated wire, and after more testing, that lead to a bad computer determination. ( I hope not just a bad wire.) it had no codes on the o2 sensor, just more random goofy ones that did not make the ticket. There was NO work done on the relay or fuel pump circut since the code did not appear with the new/used computer with very little driving.

That made me mad. I do not want to end up stranded if there is a code 96 intermittent problem.

So we are back to codes 94, 44 (air pump system and cats that I would like to replace with hight flow nes) and code 34. He assumed I had blocked off the EGR, which I had not. I had not put that on the note with the list of modifications and he did not call.

I will try the EGR flow test and then shortening up the EGR sensor pintle and see if that eliminates the code 34.
(Test procedure and and lots of pretty diagrams on the EGR system are at this link.) http://www.stangnet.com/mustang-forums/threads/how-to-test-if-egr-blocked.860939/#post-8656265)

Why do I care? I want the car working just right before I step up to a bigger motor or more power.

Guru jrichker, I regret not testing the O2 sensors first instead of going top down. Do you have any suggestions on any next step on the EGR if it flows and shortening does not do it? Also, would you replace the fuel pump relay at 153K or 253K miles anyway? ( Carfax has both mileages on it, so I do not know the real miles). I'll find someone to help move the seat if I need to.

Click to expand...

code 94 and 44 are all to familiar... post #52 on this thread. http://www.stangnet.com/mustang-forums/threads/high-idle-rough-start.860113/page-3 jrichker led me by the nose to the problem and a little junkyard scavange for a usable tad and tab and it was all set.

7991LXnSHO said:

Are the gauge temp sensor and the computer temp sensor on COMPLETELY different circuts????

Click to expand...

Yes

I've been away to Florida cleaning up my mother-in-law's house. She's 94 and can't see all the dirt and isn't mobile to bend and reach even if she could. Here's my best answer:

Testing the O2 sensors 87-93 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.

Disconnect the O2 sensor from the harness and use the body side O2 sensor harness as the starting point for testing. Do not measure the resistance of the O2 sensor , you may damage it. Resistance measurements for the O2 sensor harness are made with one meter lead on the O2 sensor harness and the other meter lead on the computer wire or pin for the O2 sensor.

Backside view of the computer wiring connector:


87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
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.

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black 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 29 (LH O2 with a red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) 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. Using the Low Ohms range (usually 200 Ohms) you should see less than 1.5 Ohms.

87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Dark blue/Lt green wire in the LH O2 sensor harness and the Dark blue/Lt green wire on the computer pin 43
From the Dark Green/Pink wire on the RH Os sensor harness and the Dark Green/Pink wire on the computer pin 43

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 43
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 29

94-95 5.0 Mustangs:
Computer pin 29 Red/Black – LH O2 sensor
Computer pin 27 Gray/Lt blue – RH O2 sensor
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 29
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 27

There is a connector between the body harness and the O2 sensor harness. Make sure the connectors are mated together, the contacts and wiring are not damaged and the contacts are clean and not coated with oil.

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.

Measure the end to end resistance of the same O2 sensor wire. Open circuits or poor connections can cause weird problems.

Measure the O2 sensor voltage at the computer to make sure that the computer sees the O2 sensor output. Since it switches from .2 to .9 volt, an analog meter or digital meter with a bar graph scale is the best tool to observe a fluctuating voltage.