Electrical Car is undriveable. Pulled codes, replaced parts still no bueno!

evintho

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'93 Mustang convertible. 5.0/AOD bone stock.

THE PROBLEM:
Starts right up and runs fine at high idle. CEL is on. After 30 seconds it dies. Start it again and I have to feather the gas for about 30-45 seconds to keep it running. After that it idles, although kinda rough. CEL is off. Take it down the street and under load it misses, bucks and barely has any power. CEL comes on and goes off, several times.

CODES:
KOEO - I get 82 - Air diverter solenoid circuit fault.
66 - MAF sensor fault/below minimum voltage.
96 - Fuel Pump secondary circuit fault/Hi-speed F/P relay open.
KOER - I get 94 - Air diverter solenoid circuit fault.
44 - Thermactor air system fault.

82, 94 and 44 I don't really care about 'cause the whole system will be removed soon. 66 and 96 are my primary focus. When I disconnect the IAC there's no change. When I disconnect the MAF the idle drops from around 800 rpm to 600 rpm. When I disconnect the SPOUT the idle drops from around 800 rpm to 700-750 rpm.

I've replaced the IAC, MAF, fuel pump, fuel pump relay and ECU. I've also tested the MAF using this procedure....
Everything checked out.
Here's a question. I've seen in a couple of different schematics online a MAF/O2 relay. Is there such an animal and if so, where is it located?
I've replaced all the components so it seems to me the only thing left is the wiring harness. Really don't wanna dump $500 on a new one!
Anyone have any ideas?
 
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Foxslider

im not that much of a idiot
Oct 25, 2019
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Ignition coil, new oreillys distributor (knocks out, pickup in dist. And a new TFI at once.) Then if it doesnt fix it. Ask them and make sure you can reuturn it when you buy it. And a new P.I.P sensor.

My only ideas. Pretty cheap on the coil. Dist, basically a free test.. pip cheap. New plugs.

Check grounds. Engine groubd, ground strap from head to firewall, and grounds on the shock tower area.

Could check fuel pressure under load while driving and see what it does when the problem appears.
 

Foxslider

im not that much of a idiot
Oct 25, 2019
480
139
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Houston, TX
Also i just checked my old code pull. I have 66 and 96. Among many others lol. Runs great. Not excellebt and top notch, but great, but im burning oil like a lamp and ya.. lol. BUT my CEL light is jever on. Probably doesbt work. Ha.

That was before i did the fuel pump. Didnt check after. But it fixed it. My issues were similar, but 3k and full throttle, full cut out like it was going to die. Let off, comes back.
 

evintho

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Replaced the IAC 'cause it was dirty and 25 years old, replaced the MAF and F/P 'cause they were known bad, replaced the F/P relay (why not?) and replacing the ECU was a desperate grasp at that elusive straw!
 

Mustang5L5

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Erase the codes. Then rerun them. It possible the code 96 is an old code as it appears when the key cycles without a response from the fuel pressure relay.

code 66 is what you should focus on. Wipe codes, rerun them. I know you said you replaced the MAF but if it returns will need to investigate the wiring back to the ECU

64729879-0779-4279-BC82-F3E6801BB024.gif
 

Mustang5L5

i'm familiar with penetration
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No. That doesn't erase them. They still stay stored.

To erase the codes, start the procedure to run the codes. Whent he codes start displaying, or the CEL flashes (if that's the method you are using) pull the jumper wire out in the middle of it displaying the codes. That should erase them.

Unplugging the battery for 30 mins will also erase them, but that method is a bit annoying when you lose your presets and the engine needs to relearn idle
 

Blown88GT

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Nov 13, 1999
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1. Replaced the IAC 'cause it was dirty and 25 years old,
2. replaced the MAF and F/P 'cause they were known bad,
3. replaced the F/P relay (why not?) and
4. replacing the ECU was a desperate grasp at that elusive straw!
1. They are easily cleaned & almost never wear out.
2. MAF's can be cleaned & rarely go bad. Fuel pumps go bad all the time.
3. They either work or they don't, didn't need replacing.
4. Maybe the replacement is worse than the original.

BTW, the EEC-IV has no flash memory. Pin-1 is "keep alive" power.

There are no sensors on the fuel delivery system. As was suggested by another, check fuel pressure under load.
 

evintho

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No. That doesn't erase them. They still stay stored.

To erase the codes, start the procedure to run the codes. Whent he codes start displaying, or the CEL flashes (if that's the method you are using) pull the jumper wire out in the middle of it displaying the codes. That should erase them.

Unplugging the battery for 30 mins will also erase them, but that method is a bit annoying when you lose your presets and the engine needs to relearn idle

I use this to read codes.

ihSFsCcl.jpg


If I unplug the code reader when the codes start displaying, will that erase the codes?
 

Mustang5L5

i'm familiar with penetration
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I believe thar reader can do it by pressing the test button while codes are running. It’s in the manual. I can’t get to mine right now but I kkow it’s very simple to do
 

Mustang5L5

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Page 38 of the manual.

pull the codes normally and when it starts displaying the CM codes, press and hold the test/hold button
 

evintho

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Page 38 of the manual.

pull the codes normally and when it starts displaying the CM codes, press and hold the test/hold button

Thanks, I'll try that tomorrow. I did the electrical tests for the MAF that you posted. On the first one I got 11.9v so it passed. On the second, I had my meter on the 20K ohms scale and it didn't register. Clicked it up to the 200k ohms scale and it read 130K ohms so I think it passed. On the third one, I had done the testing procedure that I listed in my original post and the MAF passed.
 

jrichker

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Replaced because you knew they were bad or replaced grasping at straws to fix the problem?
Code 66 or 157 MAF below minimum test voltage.

Revised 2 Nov 2019 to add details on MAF testing

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.

Computer wiring harness connector, wire side.
71316.gif


Computer wiring harness connector, computer side.
88243.gif


Diagrams courtesy of Tmoss and Stang&2Birds

ECC Diagram for 88-90 5.0 Mustangs
88-91_5.0_EEC_Wiring_Diagram.gif


ECC Diagram for 91-93 5.0 Mustangs
www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

94-95 Diagram for 94-95 5.0 Mustangs[/b]
94-95_5.0_EEC_Wiring_Diagram.gif



How the MAF works

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. Changes in RPM causes the airflow to increase or decrease, 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.

Actually, MAF pins C & D float with reference to ground. The signal output of the MAF is a differential amplifier setup. Pins C & D both carry the output signal, but one pin's output is inverted from the other. The difference in signal between C & D is what the computer's input circuit is looking for. The difference in the two outputs helps cancel out electrical noise generated by the ignition system and other components. Since the noise will be of the same polarity, wave shape and magnitude, the differential input of the computer electronically subtracts it from the signal. Then it passes the signal on to an Analog to Digital converter section inside the computer's CPU chip.

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).
89-90 Model cars: 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.

91-95 Model cars: Measure the MAF output at pins C & D on the MAF connector light blue/red 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.

MAF output readings: Use the computer connector diagram to help choose the proper pin connection on the computer when measuring the MAF output voltage. The idling voltage check can the done with the voltmeter directly stuck in the backside of the MAF connector.

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

If the output of the C&D pins exceeds the specs above, there are two possible problems:

1.) The MAF sensor is defective and needs to be replaced.
2.) The MAF sensor is installed in a different housing than the one it was designed for. The sensor is designed to work with a specific MAF part number or model MAF housing.

Check the resistance of the MAF signal wiring
For the next 2 checks make your measurement with the MAF disconnected from the wiring harness.

Pin D on the MAF wiring harness and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF wiring harness 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 pins A or B.

Reconnect the MAF to the wiring harness and proceed to the next section.



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 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
 

evintho

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OK, I erased the cm codes. Reran KOEO codes and got 82-10-11. Took the car for a drive. At stop signs it wants to die and the CEL comes on. Once I take off and get over 20mph the CEL goes off and car runs well even at WOT. However, every time I come to a stop it wants to die and CEL comes on. After driving, I ran codes again and got that pesky 82 and 66cm. Well at least I got rid of the 96 code! Thanks Mustang5L5!
Now I'm back dealing with the 66 code.
Looking at my notes when I measured at the MAF connector, providing I did it right (I measured KOEO, except for pin D and used a wire piercing tool to probe the backside), I got
Pin A - 14.29v
Pin B - 14.35v
Pin C - 14.34v
Pin D - 1.08v and when I rev it voltage rises to 4.5v then returns to 1.08v. Is that a problem?
 
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jrichker

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OK, I erased the cm codes. Reran KOEO codes and got 82-10-11. Took the car for a drive. At stop signs it wants to die and the CEL comes on. Once I take off and get over 20mph the CEL goes off and car runs well even at WOT. However, every time I come to a stop it wants to die and CEL comes on. After driving, I ran codes again and got that pesky 82 and 66cm. Well at least I got rid of the 96 code! Thanks Mustang5L5!
Now I'm back dealing with the 66 code.
Looking at my notes when I measured at the MAF connector, providing I did it right (I measured KOEO, except for pin D and used a wire piercing tool to probe the backside), I got
Pin A - 14.29v
Pin B - 14.35v
Pin C - 14.34v
Pin D - 1.08v and when I rev it voltage rises to 4.5v then returns to 1.08v. Is that a problem?
It sounds like you may have not followed my instructions on how to measure the MAF voltage.. For clarity's sake, here are the instructions again..

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).
89-90 Model cars: 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.


 
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evintho

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It sounds like you may have not followed my instructions on how to measure the MAF voltage.

OK, not sure where I fouled up. I did the 'MAF Electrical Tests' that were posted under the 'Mass Air Flow Sensor Connectors' diagram and posted the results. BTW, my electrical troubleshooting skills are abysmal at best, so please elaborate and feel free to speak to me as if I was a 6 year old! I'll eventually get it. LOL!
 

hftrud

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Feb 22, 2020
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Bremerotn
'93 Mustang convertible. 5.0/AOD bone stock.

THE PROBLEM:
Starts right up and runs fine at high idle. CEL is on. After 30 seconds it dies. Start it again and I have to feather the gas for about 30-45 seconds to keep it running. After that it idles, although kinda rough. CEL is off. Take it down the street and under load it misses, bucks and barely has any power. CEL comes on and goes off, several times.

CODES:
KOEO - I get 82 - Air diverter solenoid circuit fault.
66 - MAF sensor fault/below minimum voltage.
96 - Fuel Pump secondary circuit fault/Hi-speed F/P relay open.
KOER - I get 94 - Air diverter solenoid circuit fault.
44 - Thermactor air system fault.

82, 94 and 44 I don't really care about 'cause the whole system will be removed soon. 66 and 96 are my primary focus. When I disconnect the IAC there's no change. When I disconnect the MAF the idle drops from around 800 rpm to 600 rpm. When I disconnect the SPOUT the idle drops from around 800 rpm to 700-750 rpm.

I've replaced the IAC, MAF, fuel pump, fuel pump relay and ECU. I've also tested the MAF using this procedure....
Everything checked out.
Here's a question. I've seen in a couple of different schematics online a MAF/O2 relay. Is there such an animal and if so, where is it located?
I've replaced all the components so it seems to me the only thing left is the wiring harness. Really don't wanna dump $500 on a new one!
Anyone have any ideas?
94-95 pin out chart for the 5.0 shows oxygen sensors going to pin 44 on EEC and MAF sensor going to pins 9 and 50. Check for 12v in on the red wire to MAF sensor from the PCM with key on. No relays.