89 LX - Once warmed up throws all sorts of codes. Very Strange.

[mavmavv]

So I still have a few gremlins to track down apparently on this bucket.

I mainly use the ride for short around town trips to work and back. Nothing very long at all. But lately I have been driving further and really letting the engine warm up properly. Once the engine seems to be at a decent temperature the car starts to buck and run like crap. Usually I can limp it home and check it out.

I checked the codes in Memory and got these:

22 MAP (vacuum) or BARO signal out of range - MAP

34 (R) EVP - EGR did not respond properly during test - EVP
(O,R,M) EVR - EVP sensor is/was high - EVR
(O,R,M) PFE - PFE sensor is/was out of range - PFE

54- IAT
61-ECT

I think its safe to say something is up with this string of sensors. This problem doesnt occur until ive been driving the car for at least 15 minutes or so. Since these sensors are all on the same ground, maybe I have a short somewhere? Once the car cools off, it goes back to normal.

Since I figured something could be wrong with the cars cooling, I went ahead and replaced the cars Thermostat and Radiator cap. Even drilled the thermostat to make sure I didnt have air in the system.

Tonight I was trying to get the car warm to burp the system some more and the CEL came on, so I came home and opened the hood. I touched the radiator cap and it wasnt even hot, the last cap was like this too. It would hold no pressure so I dont think its the cap.

The two problems are most likely unrelated, but im pretty lost for my next steps for both.

 

[jrichker]

Code 22 MAP (vacuum) or BARO signal out of range. The MAP or BARO sensor is pretty
much the same sensor for both Mass Air & Speed Density cars. The main difference is where it is
connected. Mass Air cars vent it to the atmosphere, while Speed Density cars connect it to the
intake manifold vacuum. Its purpose is to help set a baseline for the air/fuel mixture by sensing
changes in barometric pressure. The MAP or BAP sensor puts out a 5 volt square wave that changes
frequency with variations in atmospheric pressure. The base is 154 HZ at 29.92" of mercury -
dry sunny day at sea level, about 68-72 degrees. You need an oscilloscope or frequency
meter to measure it. There is no way you can use a common cheap voltmeter or DVM to accurately
measure the output signal.

The MAP/BARO sensor is mounted on the firewall behind the upper manifold.

Baro or MAP test using frequency meter - run the test key on engine off. The noise from the
ignition system will likely upset the frequency meter. I used a 10 x oscilloscope probe connected
from the frequency meter to the MAP/BAP to reduce the jitter in the meter's readout.

If it is defective, your air/fuel ratio will be off and the car’s performance & emissions will suffer

Some basic checks you can make to be sure that the sensor is getting power & ground:
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.
Check the resistance between the black/white wire on the MAP/BARO sensor and
then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm.
Next check the resistance between the black/white wire and the negative battery cable.
It should be less than 1.5 ohm.

The following power on check requires you to turn the ignition switch to the Run position.
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 EGR sensors. Use the black/white wire for the ground for the DVM.

Code 34 Or 334 - EGR voltage above closed limit - Failed sensor, carbon between
EGR pintle valve and seat holding the valve off its seat. Remove the EGR valve and clean it with
carbon remover. Prior to re-installing see if you can blow air through the flange side of the EGR
by mouth. If it leaks, there is carbon stuck on the pintle valve seat, replace the EGR valve ($85-$95).

If the blow by test passes, and you have replaced the sensor, then you have electrical ground
problems. Check the resistance between the black/white wire on the MAP/BARO sensor and then
the black/white wire on the EGR and the same wire on the TPS. It should be less than 1.5 ohm.
Next check the resistance between the black/white wire and the negative battery post.
It should be less than 1.5 ohm.

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.

Let’s put on our Inspector Gadget propeller head beanies and think about how this works:
The EGR sensor is a variable resistor with ground on one leg and Vref (5 volts) on the other.
Its’ resistance ranges from 4000 to 5500 Ohms measured between Vref & ground, depending
on the sensor. The center connection of the variable resistor is the slider that moves in
response to the amount of vacuum applied. The slider has some minimum value of resistance
greater than 100 ohms so that the computer always sees a voltage present at its’ input. If the value
was 0 ohms, there would be no voltage output. Then the computer would not be able to distinguish
between a properly functioning sensor and one that had a broken wire or bad connection.
The EGR I have in hand reads 700 Ohms between the slider (EPV) and ground (SIG RTN) at
rest with no vacuum applied. The EGR valve or sensor may cause the voltage to be above
closed limits due to the manufacturing tolerances that cause the EGR sensor to rest at a higher
position than it should.

The following sensors are connected to the white 10 pin connector (salt & pepper engine harness connectors)

This will affect idle quality by diluting the intake air charge

Code 54 – ACT sensor out of range. Broken or damaged wiring, bad ACT sensor. Note that that
if the outside air temp is below 50 degrees F that the test for the ACT can be in error.

Check the resistance of the black/white wire to battery ground. If it is less than 1.5 ohm, it is good.
If it is more than 1.5 ohm, the black/white wire has bad connections or a broken wire. Always take r
esistance measurements with the circuit powered off.

Then check the resistance of the ACT sender located in the #5 intake runner on most 5.0 stangs.

ACT & ECT test data:

The ACT & ECT have the same thermistor, so the table values are the same

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number
if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage
readings will be lower because of the heat transfer. Here's the table :

68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms

Code 61 - Engine Coolant Temperature (ECT) sensor is or was too low. Failed sensor or bad wiring for the ECT.

Note that that if the outside air temp is below 50 degrees F that the test for the
ECT can be in error.

Check the resistance of the black/white wire to battery ground. If it is less than 2 ohms, it is good.
If it is more than 2 ohms, the black/white wire has bad connections or a broken wire. Always
take resistance measurements with the circuit powered off. Make sure that you do not touch
the metal probe tips when you you’re your measurements. If you do, your readings will be off.
Check the resistance of the Lt green/yellow wire at the sensor connector and Pin 7 on the computer.
It should be less than 1.5 ohm. If it is more than 1.5hm, the Lt green/yellow wire has bad connections or a broken wire.

If those tests pass, remove the passenger side kick panel. Disconnect the computer
connector and disconnect the sensor from the wiring connector. Measure the resistance
between the Lt green/yellow wire at the sensor connector and ground. You should see 1
meg ohm or an infinite open circuit. Less than 1 meg ohm means you have some bad wiring,
or the Lt green/yellow wire is shorted to ground.

The ECT sensor has absolutely nothing to do with the temperature gauge. They are
different animals. The ECT sensor is normally located it the RH front of the engine in
the water feed tubes for the heater.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate
readings.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Voltages may be measured across the ECT/ACT by probing the connector from
the rear. A pair of safety pins may be helpful in doing this. Use care in doing it
so that you don't damage the wiring or connector.

50 degrees F = 3.52 v
68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.

50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms

Diagram courtesy of Tmoss & Stang&2birds

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

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

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

 

[mavmavv]

Thanks JRicher, but im pretty sure it doesnt have anything to do with those individual components. But with them being all on the same ground.

As I said, the car runs pretty dang good for those 25 minutes or so before it goes haywire.

I can run the KOER test and get no codes. The KOEO codes in the memory are the ones I listed. If I clear the computer and run the KOEO I get 11 (ALL OK).

 

[jrichker]

I am often curious as to how throughly people read the test paths and then think about what information is presented.

I was waiting to see if you would read all the test paths and find that all of them had the black/white signal ground wire
in common.

Go back and re-read and you will find the proceedure to check the black/white signal ground wire.

 

[mavmavv]

I have read your post many times over, in my threads and in other. I know for a fact that the ground checks out AOK on all of those sensors. The resistance is well within range.



I also posted this in my reply and the original post, stating that they all share the same ground.

Thanks JRicher, but im pretty sure it doesnt have anything to do with those individual components. But with them being all on the same ground.

Since these sensors are all on the same ground, maybe I have a short somewhere? Once the car cools off, it goes back to normal.


Maybe you should read my posts more thoroughly before you start copying and pasting.

 

[jrichker]

I have read your post many times over, in my threads and in other.
I know for a fact that the ground checks out AOK on all of those sensors.
The resistance is well within range.

I also posted this in my reply and the original post, stating that they all share the same ground.

Thanks JRicher, but im pretty sure it doesnt have anything to do with those individual components.
But with them being all on the same ground.

Since these sensors are all on the same ground, maybe I have a short somewhere?
Once the car cools off, it goes back to normal.

Maybe you should read my posts more thoroughly before you start copying and pasting.

It has been some time since your post, so it is doubtful that anyone else wants to try
and diagnose a computer electrical problem over the Internet.
With that in mind, maybe you should reconsider your opinions and thoughs about the
technical information I posted.

I think you need to learn the meaning of some electrical terms.

A short circuit is when electricity finds a path back to either power or ground that was not in
the design of the circuit.

An open circuit is when there is a break or fault in the wiring or components so that the
electricity is unable to flow through the circuit as it was designed to do.

Short circuiting the signal ground to power would cause some smoke in the wiring or computer.
If this happened, the signal ground foil trace on the computer circuit board would burn up.
Your 1.5 to 2 ohm path from signal ground to power ground would become a high resistance circuit.
This would disable all the sensors that used the signal ground for ground reference.

Short circuiting the signal ground to power ground probably would have minimal effect since
there is very little difference in resistance between the two grounds.

Therefore, the conclusion is that you have an open circuit that is intermittent in nature.

Until you determine that the MAP sensor is working properly, the likely source of the open
circuit is the junction of the signal ground wiring in the main wiring harness. If you can measure
the frequency output of the MAP sensor and find that it falls within spec, you can eliminate the wiring
junction in the main wiring harness as being the source of the open circuit. At that point, look at the engine
fuel injection harness as being the source of the intermittent open circuit.



If you still think that my thoughts and suggestions about your problem are of no value to you,
I will be gald to cease trying to help you and let you find help from other sources.