Electrical 89 fox 5.0 crank no start when cold

DruryFoxbody

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Aug 23, 2022
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Little info on the car, I have a 89 Foxbody 5.0 AT car originally a 5.0 car but motor has been swapped with another 5.0, unknown when. Car sat for 10 years under a family members barn. Rats chewed several spots in wiring harness so I replaced that with a good 'ol ebay special (probably not the best idea) Car has no ac, PS pump relocated, and it has been giving me trouble ever since I got it. Self test port under hood does not communicate with multiple scanners, and koeo self test where CEL blinks does not occur either. Car runs really rough at idle, idles at about 1800 rpm, sputters, smokes like crazy, only starts with starting fluid once cold but will fire right up once warmed up. Coolant temp sensor has been replaced, along with distributor, plugs and wires, map sensor, vacuum tree, ignition coil, starter solenoid, and other things I'm sure I'm forgetting.

To start, id like to get the self test situation figured out first as it may guide me to figure put why its running rough. Any help would be appreciated, Thanks in advance
 
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General karthief

wonder how much it would cost to ship you a pair
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I would first send the computer to EcuExchange to get checked out, you can find them on Ebay, not being able to produce codes is a symptom of a bad computer, what harness and year was used to replace the chewed up stuff?
 
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90sickfox

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First thing to verify is that you are using the right small wire next to the " dog house " connector. The proper fuel test connector and the hood light connector look almost exactly the same. The fuel pump is a ground and the hood light is constant 12v. If you ground the fuel pump test connector, with the key on, the fuel pump should come on.

Edit; and what the Thief said. ECU Exchange is a good idea. There's a jumper that could be wrong depending on what harness you got off ebay. It also could hurt the computer. I'd pull the computer out and open it up to check it for burnt traces or leaking caps 9/10 the caps are bad.
 
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DruryFoxbody

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Aug 23, 2022
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I would first send the computer to EcuExchange to get checked out, you can find them on Ebay, not being able to produce codes is a symptom of a bad computer, what harness and year was used to replace the chewed up stuff?
Well, the first one I bought was from ebay and it said it was for an 89 AT car, however there were 2 plugs that were different over in the self test plug area (driver side above brake booster) still couldn’t pull codes. So I bought another harness also from ebay all plugs matched but still
Couldnt pull codes. Was able to start car with all 3 harnesses with a little bit of starting fluid but no codes.
 

DruryFoxbody

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Aug 23, 2022
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First thing to verify is that you are using the right small wire next to the " dog house " connector. The proper fuel test connector and the hood light connector look almost exactly the same. The fuel pump is a ground and the hood light is constant 12v. If you ground the fuel pump test connector, with the key on, the fuel pump should come on.

Edit; and what the Thief said. ECU Exchange is a good idea. There's a jumper that could be wrong depending on what harness you got off ebay. It also could hurt the computer. I'd pull the computer out and open it up to check it for burnt traces or leaking caps 9/10 the caps are bad.
I will pull the computer out later today and post a few pictures, it looked almost greasy from the little slot in the bottom but I couldn’t see much. I had it out of the car to test resistance between pins 46, 40, and 60 but everything matched with another forum I read but I’m sure it could still be messed up.
And if you’re talking about the small wire next to the self text port, the harness I have in Now doesn’t have the single gray plug with one wire. It has something very similar but down the harness a little closer to the coil.
 

rednotch

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If it sat for 10 years do your self a favor and order a new tank, fuel pump, sending unit, filler neck gasket and fuel filter, any car that sat that long that I've worked had a badly rusted tank. You can get it all for about $250 with a decent 255 or 320lph pump if you shop around. Won't take much to kill a new pump if you just swap one in..... Blow the lines out from the fuel rail side .

if you can't pull codes its either wiring or the ecu, need to remove the board from the case and check both sides. Best bet is to show pictures of the harnes you installed, there pretty easy to identify by the body plugs connectors at the driver side firewall area. Have you checked the timing with it running? without the spout and with the spout plugged in?
 

DruryFoxbody

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Aug 23, 2022
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If it sat for 10 years do your self a favor and order a new tank, fuel pump, sending unit, filler neck gasket and fuel filter, any car that sat that long that I've worked had a badly rusted tank. You can get it all for about $250 with a decent 255 or 320lph pump if you shop around. Won't take much to kill a new pump if you just swap one in..... Blow the lines out from the fuel rail side .

if you can't pull codes its either wiring or the ecu, need to remove the board from the case and check both sides. Best bet is to show pictures of the harnes you installed, there pretty easy to identify by the body plugs connectors at the driver side firewall area. Have you checked the timing with it running? without the spout and with the spout plugged in?
I have replaced the fuel tank, fuel pump, fuel pump relay, and have gone through about one tank of gas with it. As far as the fuel filter, I’ll look at that if it’s not in the tank. Also I have tested fuel pressure with a mechanical gauge, fuel pressure is within spec however I do suspect the fuel injectors may be a cause of it running rough but that’s a whole different story
I have not checked timing with it running, I will try to do that today. And for the spout, are you referring to something on the distributor?
 

rednotch

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The spout is the little 2 prong plug right by the distributor module just follow the harness you will see it. you remove it to set base timing at 10*, when you plug it back in the computer now controls the timing and should raise it past 10. If you swapped the distributor and just tried to line it up and didn't use a timing light its a good chance the timings not correct. The fuel filter is in front of the tank/ spare tire well sheet metal under the car
 

DruryFoxbody

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Aug 23, 2022
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First thing to verify is that you are using the right small wire next to the " dog house " connector. The proper fuel test connector and the hood light connector look almost exactly the same. The fuel pump is a ground and the hood light is constant 12v. If you ground the fuel pump test connector, with the key on, the fuel pump should come on.

Edit; and what the Thief said. ECU Exchange is a good idea. There's a jumper that could be wrong depending on what harness you got off ebay. It also could hurt the computer. I'd pull the computer out and open it up to check it for burnt traces or leaking caps 9/10 the caps are bad.
82215F4B-79BB-4B69-A9AD-9F09FBEA1A59.jpeg FA05874D-D597-4EC9-9EB8-6B357B3A9519.jpeg
Not sure what I’m looking at but nothing sticks out to me at least
 

DruryFoxbody

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Aug 23, 2022
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I will pull the computer out later today and post a few pictures, it looked almost greasy from the little slot in the bottom but I couldn’t see much. I had it out of the car to test resistance between pins 46, 40, and 60 but everything matched with another forum I read but I’m sure it could still be messed up.
And if you’re talking about the small wire next to the self text port, the harness I have in Now doesn’t have the single gray plug with one wire. It has something very similar but down the harness a little closer to the coil.
26E2F029-E956-45CF-BDE4-A04BE17A9C19.jpeg 8942A7B9-D854-4EF9-841A-DB393F9B682A.jpeg 342A17BD-F841-46F2-97BC-AB3DD6DFC44B.jpeg 71E3B948-EDD2-47D4-8804-CC80843DBF73.jpeg
Not sure if this helps but here’s what I got
 

90sickfox

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There's another single wire little plug around the dog house connector area. Usually there are 2 single wire connectors...one is gray and the other is black ? Or brown ?

The a9p is the correct computer. I didn't see anything else but that capacitor on the computer board.
 

rednotch

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Aug 14, 2000
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The traces that most often short are on the other side of the board, need to remove it from the case to inspect them or can test with a dvm.

I'm guessing that's an 87-88 harness converted to mass air based on the test port only time I see the screwed up test port wiring is on pre 90 cars with harness swaps or mass air conversions... Your sti is the tan wire with the red strip, 4th spot on bottom of the connector, It should lead to pin 48, the white wire with the red strip should be sto but is usally black/ white. should lead to pin 46. i would probe those and verify the pin out with a dvm, check both for voltages then try to pull codes with the test lamp method and those jumped.... This why I hate dealing with mixed matched wiring, I've dealt with too many problem cars over the years with mixed and matched stuff lol.

And the two connectors in the last picture are for the wiper motor..
 
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@DruryFoxbody

Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

Foxbody Diagnostic connector

foxbody-mustang-diagnostic-connector-jpg.586766


Foxbody Diagnostic connector close up view


foxbody-diagnostic-connetor-closeup-view-jpg.586765


If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

583777


The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

583778


The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and drivability problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10
4




Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Reader/dp/B000EW0KHW Equus - Digital Ford Code Reader 3145.
Or for a nicer scanner see www.midwayautosupply.com/Equus-Digital-Ford-Code-It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.

Order it at Walmart for a better price and free shipping

41P3GQVDSHL._SS270_.jpg





Computer will not go into diagnostic mode on 86-90 models 5.0 Mustangs .

Revised 23 May 2020 to include warning about jumpering the dark brown connector with a black/orange wire.(12 volts) to the test connector.

Disconnect the battery positive terminal before making any resistance checks.
The voltage drop in the ground cable will cause incorrect resistance readings.


How it is supposed to work:
The black/white wire (pin 46) is signal ground for the computer. It provides a dedicated ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the computer into self test mode. If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. Since it is a dedicated ground, it passes through the computer on its way to the computer main power ground that terminates at the battery pigtail ground. It should read less than 1.5 ohms when measured from any signal ground on the engine mounted fuel injector harness with the battery pigtail ground as the other reference point for the ohmmeter probe.

Engine mounted fuel injector wiring harness sensors for a 5.0 mustang
63347


What sometimes happens is that the test connector black/white wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60.

WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

OR

If an O2 sensor harness from an automatic transmission Mustang is used with an A9L manual shift transmission computer. The 12 volts from the automatic transmission starter circuit will damage the A9L computer.

The STI (Self Test Input) is jumpered to ground to put the computer into test mode. Jumpering it to power can produce unknown results, including damage to the computer. The ohm test simply verifies that there are no breaks in the wiring between the test connector and the computer input.

How to test the wiring:
With the power off, measure the resistance between the computer test ground (black/white wire) on the self test connector and battery ground. You should see less than 1.5 ohms.

attachments\58312


If that check fails, remove the passenger side kick panel and disconnect the computer connector. There is a 10 MM bolt that holds it in place. Measure the resistance between the black/white wire and pin 46 on the computer wiring connector: it should be less than 1.5 ohms. More than 1.5 ohms is a wiring problem. If it reads 1.5 ohms or less, then the computer is suspect. On the computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than 1.5 ohms. More than that and the computer’s internal ground has failed, and the computer needs to be repaired or replaced.

While you have the computer connector disconnected from the computer, turn the ignition switch to the Start position and look for 12 volts on pin 46 of the computer wiring harness. If you see 12 volts then you have an automatic transmission O2 sensor harness. That will damage the A9L manual shift transmission computer.

See the pictures below for help finding and fixing the burnt computer trace.


hash-146a243133771eeba54f17b17d721b1f-jpg.646628


The fix is some careful soldering of a small jumper wire across the burnt section of copper trace.

20160325_234845-jpg.553347


If the first ground check was good, there are other wires to check. Measure the resistance between the STI computer self test connector (red/white wire) and pin 48 on the computer main connector: it should be less than 1.5 ohms. More than 1.5 ohms is a wiring problem

The following is a view from the computer side of the computer wiring connector: it is for an A9L, A9P computer.
eec-iv-computer-connector-for-5-0-mustang-gif.88243


a9x-series-computer-connector-wire-side-view-gif.71316


Diagram courtesy of Tmoss & Stang&2birds

Check out the diagram and notice all the places the black/white wire goes. Almost every sensor on the engine except the MAF is connected to it.

88-91_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

See the graphic for the 10 pin connector circuit layout.
salt-pepper-10-pin-connectors-65-jpg.68512
 
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