Electrical 1993 LX 5 speed ECU problem?

senorpavo

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Jul 19, 2018
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Puerto Rico
Hey guys! New to the forum and wanted to post this up.

Turn key to on, hear fuel pump prime and stop. Start car, starts right up.

Anything more than just a little off throttle and it just falls flat on its face. Some pop and backfire. But if I am reallly gentle with it, it drives and goes thru the RPMs without a problem.

Challenge: When I unplug the MAF the falling flat on its face thing completely disappears. You can hit the throttle and it responds and revs great! I think this rules out a mechanical issue. The problem is that with the MAF unplugged it won't idle or have good manners except for full throttle.

I have just sent/received the ECU back from theefi guy with new capacitors and its doing the same thing. Replaced the MAF, same. New plugs, wires and coil, same issue. I can't help but think this is a bad ECU? Ideas, suggestions are welcome. I'd even throw another ECU at it if I knew where to get a plug and play! Are there any direct plug in replacements? I suppose they are all $600......
 
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Replaced it. Same behavior.

Also if it was bad, wouldn't that also mean when the MAF was diconnected it wouldn't rev and respond correctly?

No. Two things can happen instead:

Only a portion of the TPS is bad. You can check this with a multi-meter and observe a full, smooth sweep to rule this out.

WOT tables are separate from close loop tables. MAF air is only measured as an adjustment to CAM and not in the same way that it's used to calculate partial throttle settings.

If you have not run @jrichker 's Surging Idle Checklist, it can be found here: http://forums.stangnet.com/showthread.php?t=698148

This will help you nail it down to a single component and ensure proper adjustments. What it will [not] do is make up for an EEC tune that is insufficient for X modifications.
 
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Hey guys! New to the forum and wanted to post this up.

Turn key to on, hear fuel pump prime and stop. Start car, starts right up.

Anything more than just a little off throttle and it just falls flat on its face. Some pop and backfire. But if I am reallly gentle with it, it drives and goes thru the RPMs without a problem.

Challenge: When I unplug the MAF the falling flat on its face thing completely disappears. You can hit the throttle and it responds and revs great! I think this rules out a mechanical issue. The problem is that with the MAF unplugged it won't idle or have good manners except for full throttle.

I have just sent/received the ECU back from theefi guy with new capacitors and its doing the same thing. Replaced the MAF, same. New plugs, wires and coil, same issue. I can't help but think this is a bad ECU? Ideas, suggestions are welcome. I'd even throw another ECU at it if I knew where to get a plug and play! Are there any direct plug in replacements? I suppose they are all $600......
Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/
 
check codes? or possibly timing? im having the same prob

Going to pick up the $30 reader at Autozone (part 3145). I was going to use the jumper trick but I can't locate the grey self test input connector near the diagnostic port.... Although now that I look at the reader, the self test input connector is going to be needed even by the device. Suck. I guess I'll have to keep searching for it.

Thanks for the replies guys. I get it, do the basic stuff first and CHECK CODES! Hopefully the computer spits out exactly what the issue is.
 
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So spent some time today trying to jumper the diagnostic port to get the CEL to flash out some codes. FAIL

The diagnostic connector wires do not align with the diagrams, someone has messed with it. To add to that, the wires are hard to distinguish colors due to age. Maybe I'll take another shot at it on another day. Super frustrating.
 
eec-iv_testing2.gif



View: https://www.youtube.com/watch?v=xdCUHULa4HM
 
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Thanks, that info is everywhere and in my case is practically useless. I have to solve a puzzle.

The diagnostic connector is present, so that is a good start. It appears however someone has hardwired the fuel pump circuit to run. The "Grey STI" connector is not there. I think someone has put the wire into one of the empty slots of the diagnostic connector but the wires are old and dirty and white has turned into a yellowish-tan color. lol

So my instructions are basically to find a white/red wire (SELF TEST IN) and a black/white wire (SIG-RTN) and jumper those. I think the 'self test in' has been shoved into the diagnostic connector #3 position to keep it from dangling around. I don't see a black/white wire at all. Then there is the issue that the ECU may have a bad trace wire. I visually checked it and it seems ok.....

I might just pull the ECU out from under its position at the passenger side kick panel and jumper the wires on the harness at that location.
 
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Turn the ignition off, disconnect the battery ground cable from the battery. Set the multimeter on low Ohms ( Ω ).
Connect one meter lead to the battery cable and probe the diagnostic connector to see which lead give a less than 1 Ω reading. That's the one to push back the covering and clean up to check the color.

The following are diagrams courtesy of Tmoss & Stang&2birds

Notice that the pin 46 wire changes color from gray/red to black/white…
Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
91-93_5.0_EEC_Wiring_Diagram.gif


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/ Everyone should bookmark this site.


TFI module wiring for 94-95 Mustang GT
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-IgnitionControlModule.gif

Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

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

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

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

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

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

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

Starter circuit
http://forums.stangnet.com/attachment.php?attachmentid=21328&d=1080916057

Alternator diagram for 94-95 Mustangs.
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-Alt.gif
 
...
The diagnostic connector is present, so that is a good start. It appears however someone has hardwired the fuel pump circuit to run. The "Grey STI" connector is not there. I think someone has put the wire into one of the empty slots of the diagnostic connector but the wires are old and dirty and white has turned into a yellowish-tan color. lol

So my instructions are basically to find a white/red wire (SELF TEST IN) and a black/white wire (SIG-RTN) and jumper those. I think the 'self test in' has been shoved into the diagnostic connector #3 position to keep it from dangling around. I don't see a black/white wire at all. Then there is the issue that the ECU may have a bad trace wire. I visually checked it and it seems ok.....

I might just pull the ECU out from under its position at the passenger side kick panel and jumper the wires on the harness at that location.
Now that you explained in detail, I understand your problem.
I have the same code reader but don't need it any more, since now have a different ECU.
Didn't see what year you have. It makes a difference, they are not exactly the same.
For earlier years, the Tmoss drawings are more detailed.
Appears to be pin 48 for all.
88-91_5.0_EEC_Wiring_Diagram.gif
 
Thanks for the diagrams. It turns out that the MAF circuit had a short in the ECU somewhere. I cut the RTN wire and the car ran better, but super rich.

Finally found a re-manufactured ECU and it solved that issue. Thanks everyone!
 
It was not easy to find and had to get a friend who works at an Oriley's auto to contact Cardone to try and get one! If they are available for $100 at autozone, which one? I'll get a spare..lol.
AutoZone carries Cardone. You have in input the year & model of your car.
I got an A9L by looking up their part number & finding the same Cardone number at AutoZone which they ordered.
http://www.cardone.com/
Cardone now wants VIN to order, can't get a '89 A9L for an '88 SD, that way.
I don't know why you have to give them a VIN to get an ECU?
78-4352 looks like the Cardone P/N for a non-Calif. 5-spd.

Part Number: 78-4352
5.0 Liters and 5 Speed and Exc. Calif. Emissions and Exc. Convertible
Correct VIN and OE Number Required When Ordering.;Units are pre-programmed at the factory.


AZ also carries Blue Streak ECU's.
They want a VIN, too. Bad!

I have my spare A9L in front of me, no Cardone part number, just their 15 digit serial number with REMFG at the end.
Ford label is still intact & was originally an A9L. If they reflash it for another model, the A9L is covered over.
 
AutoZone carries Cardone. You have in input the year & model of your car.
I got an A9L by looking up their part number & finding the same Cardone number at AutoZone which they ordered.
http://www.cardone.com/
Cardone now wants VIN to order, can't get a '89 A9L for an '88 SD, that way.
I don't know why you have to give them a VIN to get an ECU?
78-4352 looks like the Cardone P/N for a non-Calif. 5-spd.

Part Number: 78-4352
5.0 Liters and 5 Speed and Exc. Calif. Emissions and Exc. Convertible
Correct VIN and OE Number Required When Ordering.;Units are pre-programmed at the factory.


AZ also carries Blue Streak ECU's.
They want a VIN, too. Bad!

I have my spare A9L in front of me, no Cardone part number, just their 15 digit serial number with REMFG at the end.
Ford label is still intact & was originally an A9L. If they reflash it for another model, the A9L is covered over.

Having opened up the case on a A9L, all the code is stored in a 2716 eprom (remember those?) If I remember correctly there was a pin compatible EEPROM what could be socketed and them you could program it for almost any Mass Air application. The Ford & Mercury Mass Air V8 sedans could become donors for the hard to find A9L with not a lot of work and easily reprogrammed for whatever changes needed to be made.
 
Having opened up the case on a A9L, all the code is stored in a 2716 eprom (remember those?) If I remember correctly there was a pin compatible EEPROM what could be socketed and them you could program it for almost any Mass Air application. The Ford & Mercury Mass Air V8 sedans could become donors for the hard to find A9L with not a lot of work and easily reprogrammed for whatever changes needed to be made.
No, do you remember AM27C010-120DC EPROM? Needed 2, one for MSB, the other for LSB. The Data I/O programmer sat on my desk, since no one else knew how to use it.