So it looks like my ECM (computer) may be garbage now. Constant codes 66 and code 98

[MustangLX-5.0]

I know what those codes mean and I know the 98 is a result of the 66. I'm sorry to say I have not been able to get my hands on a spare ECM (A9L) anywhere. Nobody has one. Now, I am constantly getting codes 66 and 98 on KOER. The computer appears to be ignoring any output from the MAF sensor to the SIG pin. Everything check out correctly. I tore through all the wiring between the sensor an d the computer. I beat on it.. Moved it all around .. shook it. Tested it at the computer directly. Ran Voltage tests and resistance checks.

90% of the time the engine starts with the Check Engine light on now. It was never like this before. And it runs pretty good with just a bit of throttle lag. But, every 4 or 5 engine starts, it will start up with the CE light OFF and then suddenly the engine is running so bad it backfires and will stall out. Then I re start it and suddenly the CE light turns on and the engine runs fine. While the engine is running now, I can unplug the MAF sensor and it wont change the way it is running. No effect in anything, Plug it back in ... no effect. I can jump the REF and SIG pins on the MAF plug with a low ohm resistor..nothing happens. Jump it directly, nothing happens.

Resistance between SIG and GND, while the engine is off and key off, it is a FLAT 50.0K ohms ( this is with the sensor unplugged). As soon as I turn the key on, the resistance drops to 39.8K ohms. Same thing when the engine is started. If I plug the sensor in while the engine is running then leave it for a half minute , then unplug it and test, the resistance goes to from 59k to 61k, sort of fluctuating a bit but only while the engine is running. As soon as the key gets shut off, the resistance drops right down to a flat 50.0k ohms. REF is at 5.5V. red hot positive wire at battery voltage.

The computer seems to be ignoring the MAF signal now. All the connections check out as they SHOULD be. ANd I have tried other MAF sensors with no difference. It seems, that the computer WILL try to use the MAF sensor every few engine starts, BUT when it does it sputters backfires and stalls out.

Can ANYONE test their MAF and tell me what they get on their SIG to GND resistance at the MAF connector pins with it unplugged AND key OFF? The harness plug , NOT the MAF sensor itself. My only other guess with this is that the computer has crapped out and is only running in a pre-programmed mode. Maybe it is damaged.

How do you removed the computer ? I removed the bottom bolt and unplug the computer harness but I can't budge the computer. Do I have to remove the dashboard for this?

Thank you all in advance.. and for dealing with my frustrations...... lol

 

[larrym1961]

I have a book on codes and what to look for and repair, for code 66 MAF applications it says.
Disconnect the MAF connector and confirm that 12V is measured between terminals A and B. Disconnect the 60 pin terminal from the ECA. Inspect the connectors for damaged wires and pushed or corroded pins. Check the resistance from MAF terminal D and pin 50 of the ECA; it should be less than 5 ohms. Check the resistance of MAF terminal C to pin 9; it should be less than 5 ohms. If these resistances are okay, check the resistance of each wire to ground; it should be infinate. Repair any of these wires as indicated through the test.
If wires test good; reconnect the ECA and the MAF sensor. Start the engine and allow it to idle. Check the voltage on ECA pin 50. If the voltage is between 0.2 and 1.5 volts, replace the ECA. If the voltage is not within these specs, replace the MAF sensor.

If your computer has never been removed before, they are secured by a plastic strap. I cut mine to remove my computer, I don't know how you want to do yours or not, but that is how I did mine. Also I don't know if you have checked, but Late Model Resto has A9L ECU's for $250, I also bought a used A3M from www.bieberfever.com for $125

Hope that helps you out some!

 

[MustangLX-5.0]

Yeah, actually the last part was helpful tho. and about the voltage on Pin 50. I've been helped here on this topic before. It's just a royal headache. I drive the car now with the MAF unplugged because really it doesn't make a difference. I think the ECU is getting wet. I pulled the pass side splash shield off the fender and saw a nasty mess of rust on the pass side inner fender... A huge amount of it being just behind the door hinges and where the antenna wire goes in. Hmm, ..excuse me for saying this, but I think this car is F****D! IF it is getting wet, then I wouldn't know how to prevent the new one from this besides wrapping it with something. The metal damage is beyond normal repair, you should see this... I get a photo in here shortly .. lol .. tryin to get rid of this car for $1000 now.

 

[jrichker]

Some more help...

Code 98 - basic computer internal tests not passed before it started processing the request to dump codes. Do a Key On Engine Off test before starting the engine. Wait until you see the 11 flash before pressing any buttons if you have a hand operated scanner. The computer is operating in Limp mode, so fix any codes it dumps prior to doing anything else.

Code 66 MAF below minimum test voltage.
Insufficient or no voltage from MAF. Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF. This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables.

The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

Changes in RPM causes the airflow to increase or decease, changing the voltage output.. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow. Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

At idle = approximately .6 volt
20 MPH = approximately 1.10 volt
40 MPH = approximately 1.70 volt
60 MPH = approximately 2.10 volt

Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 10K ohms between either pin C or D on the MAF wiring connector and ground. Make your measurement with the MAF disconnected from the wiring harness.

Diagram courtsey of Stang&2Birds

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

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

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

Computer,. actuator & sensor wiring
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Fuse panel layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Vacuum routing
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

 

[MustangLX-5.0]

Thanks Jrichker. I have done all of those tests. I don't think there are any more tests to perform on this thing. Everything passes. I finally yanked the computer out of there. What a pita to remove lol. Couldn't see much in the way of corrosion except a little bit of white chalkyness at the very top, where the little slit opening is .. looks like it was getting wet. Chalkiness is the anodized finish corroding. So either it got wet, or a tiny piece of rust dropped into the slit shorting something out. I say that because some rust chunks were falling out of there..from some place above it. Probably from the inner fender portion.

So , while I have it out, I tested the SIG wire into the computer harness while the engine was running. 0.83V and responds well to throttle changes. I grounded the meter at the ground screw next to the computer. I have a pic if you want to see. So, this obviously means the computer is NOT seeing the MAF SiG V. as everything tests out like it should. Time to find an A9P .

 

[MustangLX-5.0]

Thanks Jrichker. I have done all of those tests. I don't think there are any more tests to perform on this thing. Everything passes. I finally yanked the computer out of there. What a pita to remove lol. Couldn't see much in the way of corrosion except a little bit of white chalkyness at the very top, where the little slit opening is .. looks like it was getting wet. Chalkiness is the anodized finish corroding. So either it got wet, or a tiny piece of rust dropped into the slit shorting something out. I say that because some rust chunks were falling out of there..from some place above it. Probably from the inner fender portion.

So , while I have it out, I tested the SIG wire into the computer harness while the engine was running. 0.83V and responds well to throttle changes. I grounded the meter at the ground screw next to the computer. I have a pic if you want to see. So, this obviously means the computer is NOT seeing the MAF SiG V. as everything tests out like it should. Time to find an A9P .