Engine When All Tests Done, What Next?

globaltefl · Jul 28, 2012

My 1990 5.0 has all new ignition parts--MSD coil, Mallory distributor, Ford Motorsport wires, iridium plugs. Did a smoke test and found 2 vac leaks one in EGR (replaced it) and coming out the distributor (new gasket took care of this). Also a new IAC valve and O2 sensors. The TPS checks out. The computer throws an 11 code key on engine off.

The Problem
The car starts and runs, but wants to die and sometimes does until warm. The idle is rought and misses on acceleration, except at high RPMs. I do get a 41 and 91 code key on engine on. The only thing I can think of is a bad injector. I did run BG cleaner through the engine and filled the tank with 91 octane, so they should be clean.

What is left???

jcgafford · Jul 28, 2012

O2 sensor wiring? i believe those are lean codes. was it running rough before all the new parts? is all the smog stuff still there?

a91what · Jul 29, 2012

http://www.troublecodes.net/Ford/
Yes your system is lean. What is the tps voltage set to? What is your FUEL pressure?
put a gauge on the schreder valve it should have 39-40psi with vac removed.

jrichker · Jul 29, 2012

Post your 5.0 Mustang codes and I will try to post a 5.0 Mustang code definition and fix.

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 20-Nov-2011 to include computer pin numbers for O2 sensor wiring for resistance checks

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
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.

If you get only code 41 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 is for cars with an intact smog pump and cats. If the tube on the back of the heads clogs up the driver’s side, 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. 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.

globaltefl · Jul 29, 2012

I have had the 41 and 91 codes for a long time. As mentioned, I had a forced smoke test for vacuum leaks done and corrected those.
I did an ohms test on the harness wiring from the two eec pins [29 and 43] to the harness end that plugs in to the O2 sensor. I got a reading
of 2 ohms on both. They are new O2 sensors and I had tested those too. I did this by removing the sensors, heating them up and watching
the voltage swing from 9-2 volts when heat removed [I believe that was the voltage swing]. Fuel pressure is 39/40 steady. I do still have all smog stuff on.

Two years ago, the car died in my garage--that's the positive. At that point I checked all the sensors and TPS and IAC. I replaced all ignition parts and it would start, but die right away. The latest was the smoke test, new EGR and plugs. But I still have the two codes.

One moment it runs great and the next it's missing. On cold start it will stumble and maybe die. Bad gas could have been part of the problem, and may still be until I go through a whole new tank.

a91what · Jul 29, 2012

My car had similar issues until i cleared code 11 out. You may not have something wired correctly or the eec may have got whacked with 12v on the sig. return. my issue was wrong o2 harness.

globaltefl · Jul 29, 2012

Tell me more about the 12v signal return. What are the ramifacations?

jcgafford · Jul 29, 2012

a91what said:
My car had similar issues until i cleared code 11 out. You may not have something wired correctly or the eec may have got whacked with 12v on the sig. return. my issue was wrong o2 harness.

code 11 is a system checks out ok code....

HISSIN50 · Jul 29, 2012

I might have missed something - if so, apologies.
To further stress what JR and others have said, those 3 exact codes have been attributed to a bad O2 sensor harness before. Has the harness been changed or modified?

globaltefl · Jul 30, 2012

I do get a code 11 on koeo. Good question about the harness. When I bought the car (2001) it had had another engine with a Kenbell supercharcher and GT 40 heads. The engine was replaced when someone burned up the heads (not sure why they had to change the engine). So whether or not the harness was also changed, I don't know. However, I bought it in California and it passed smog, so what does this tell you? I did not modify the harness. I now live in Colorado, so no smog needed.

a91what · Jul 30, 2012

jcgafford said:
code 11 is a system checks out ok code....

I was not recieving the 11 code untill i fixed the o2 harness the jumper wire for the eec was incorrect i had to repin the harness. sorry for the confusion

jcgafford · Jul 31, 2012

a91what said:
I was not recieving the 11 code untill i fixed the o2 harness the jumper wire for the eec was incorrect i had to repin the harness. sorry for the confusion

so it throws the 11 now and the other two codes?

a91what · Jul 31, 2012

No the eec was not recieving the return signal from the loopwire. It was causing coldstart and cold idle issues, the car would barely run before reaching 160*, The cruise control would not function, and a slew of other sensors were not functioning. The car would not give me any codes KOEO. My case was a A9L eec if it would have been an A9p i would have not had so many of the issues. The A9l should not be used with a O2 harness from an auto car, the eec is grounded at the starter solenoid with a Auto harness and when you start the car WHACK your eec is dead. Soooo I pulled the eec apart found the signal return on the board soldered in a jumper wire and repinned the O2 harness and placed a jumper in the switch for the clutch so the signal return is grounded for the A9l. since my car is an auto with a hodgepodge of parts. No wonder the previous owner gave up!!
So yes similar issues but my problem seemed like a nightmare, thanks to this site i found all the info i needed. Jrichker is the man he helped me through most of it.

jcgafford · Aug 1, 2012

a91what said:
No the eec was not recieving the return signal from the loopwire. It was causing coldstart and cold idle issues, the car would barely run before reaching 160*, The cruise control would not function, and a slew of other sensors were not functioning. The car would not give me any codes KOEO. My case was a A9L eec if it would have been an A9p i would have not had so many of the issues. The A9l should not be used with a O2 harness from an auto car, the eec is grounded at the starter solenoid with a Auto harness and when you start the car WHACK your eec is dead. Soooo I pulled the eec apart found the signal return on the board soldered in a jumper wire and repinned the O2 harness and placed a jumper in the switch for the clutch so the signal return is grounded for the A9l. since my car is an auto with a hodgepodge of parts. No wonder the previous owner gave up!!
So yes similar issues but my problem seemed like a nightmare, thanks to this site i found all the info i needed. Jrichker is the man he helped me through most of it.

Jrichker solved most of my problems too!

jrichker · Aug 1, 2012

I am glad to be of service...

globaltefl · Aug 3, 2012

Yes, you have been a great help with many of my issues. So once again, I ask on cold start, what effect do the 91/41 codes have, if any--the only two codes I have? Vacuum test passed. My car starts right up, but then idles really bad and then may shut off unless I give it some gas. When increase the rpms to about 11-1200, it really runs rough. Above that it smoothens out. After it warms up it will keep running but still idles rough.
This all said, yesterday I took it out and it ran like a scared rabbit right up to 5500 rpms and the idle settle in. This morning on cold start, the same old thing. What should I test next? I switched out the IAC but made no difference. The TPS? It did check out at one time.
What is next?

HISSIN50 · Aug 3, 2012

globaltefl said:
So once again, I ask on cold start, what effect do the 91/41 codes have, if any--the only two codes I have?

The adaptive strategy (including fuel trims) is used to modify and applied to open loop (cold start) fuel trim. Have you noted if the cold-start performance is different after resetting the KAM? The performance (idle quality, etc) may well be worse than better.

a91what · Aug 3, 2012

Have you tested your MAF sensor?
Try this, start the car and unplug the sensor. Then report back

globaltefl · Aug 3, 2012

Thanks for the input. I don't notice a difference when I disconnect the battery for even 20 minutes. But here is some interesting information that may apply to my car, especially the last paragraph:

http://www.cleanmpg.com/forums/showthread.php?t=2463

Resetting Keep Alive Memory (KAM)

Resetting Keep Alive Memory (KAM)

It may be necessary to reset the KAM in the PCM to the default setting after a Diagnostic Trouble Code (DTC) causes a engine or vehicle warning light. Other conditions may not produce a warning light, such as ethanol and poor performance conditions related to fuel mixtures that may warrant a reset. KAM creates adaptive learning contents such as idle speed, refueling event, and fuel trim.

For instance, after refueling and driving a short distance, I noticed a big decrease in FE. This has occurred a few times and is from a gas mixture that used oxygenates (ethanol), sometimes referred to winter gas. I no longer fill up at Citgo stations as a result.

Due to the fact that % of alcohol or oxygenates are not as combustible as gasoline, the oxygen sensors send a message to the PCM that there is a lean fuel trim and it makes an adjustment for a richer air/fuel mixture. The PCM alters the air/fuel ratio maps at the different RPM’s and engine load points, and the KAM stores this data as the long term fuel trim. There is not much you can do at this point other than burn the entire tank of gas. Once you refill with straight gas, it may take a few tanks for the PCM to adjust all the long term fuel trim maps stored in the KAM for each RPM/Load point. This means you will be getting a richer air/fuel mix at closed loop modes and your MPG will be reduced accordingly. In the past, I didn’t understand why my FEH continued to get poor MPG after I replaced the fuel with straight gasoline. After refueling a few times, my MPG returned to normal because the PCM eventually readjusted the air/fuel mixtures at all RPM’s and engine load points in the KAM air/fuel maps.

Any time the FEH has had a condition that may have altered KAM, a reset to the default mode can be done by using one of two methods. Adaptive learning contents such as idle speed, refueling event, and fuel trim are included in the reset of KAM. To clear the continuous DTCs in the PCM and have it reset the emissions monitors information, is also part of a KAM reset. Both can be useful in post repair or a big change in driving conditions. KAM can be reset by a diagnostic tool or by disconnecting the 12V battery ground cable for a minimum of 5 minutes.

After the KAM has been reset, the vehicle may exhibit certain driveability concerns. It is necessary to drive the vehicle to allow the PCM to learn the values for optimum performance. My recommendation would be to reset the KAM after the vehicle is warm and drive the most fuel efficient way possible afterwards. Always remember that KAM is reset when the battery is disconnected for more than 5 minutes.

GaryG

globaltefl · Aug 3, 2012

Yes, I did unplug the MAF and the car just dies.

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