The car runs fine, it failed because the check engine light doesn't come on with the key on. Apparently there isn't one in the early speed density cars. I'm trying to figure out how to prove that.
"Plan A" You are correct; there is no CEL on 86-88 Mustangs Speed Density cars, The 88 California Mustangs had a MAF and a working CEL. Contact your local Ford dealer and they may be able to provide the Factory OEM data.
"Plan B" Here's some help ;
Copied from mustang88GT:
I have not finished it yet but I put the bulb in and it works. There are wires that you can tap into and run to the self test connector. The reason I have not run the wires yet is because I am tripping 2 codes because I did not run wires for the secondary fuel pump or speed senor yet for the MAF conversion... but it should be real easy to do here is
Adding a "Check Engine" light
Another difference between the speed density and MAF cars is that MAF cars have a "Check Engine" light in the dash to alert you to possible serious problems and it makes reading out self test codes much easier. The MAF cars have the "Check Engine" light located in the light panel on the lower right of the instrument cluster. Speed density cars don't have this window, but there is a "Check Engine" position for a light in the tachometer face, though there is no bulb installed. The wire from the EEC to the bulb (via the flex connector) is also missing.
In the '88 harness (not sure of other years), there is a tan and a black/blue wire connecting up to the 'Check Engine' circuit on the instrument cluster flex circuit. For MAF models, the tan wire hooks to the EEC STO/MIL line and the black/blue is for the lamp test out when you start the car. I don't know what these are connected to in an '88, but the test out feature does not work, and the STO/MIL line at the EEC-IV and self test connector is yellow/black. The wires connected to the check engine lamp probably end at some open connector somewhere, but I couldn't track it down, so I cut the tan and black/blue wires off the flex connector and ran a new wire to the STO/MIL wire on the self test connector under the hood (you could also tap in by the EEC-IV, but it was easier for me to go through the firewall. You can get a bulb socket from the HELP! rack at the local parts store, put in a N194 bulb, and voila, you now have a working check engine light.
"Plan C" Print this tech note off and show it to the test guy...
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 Diagnostic connector close up view
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.
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.
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.
What to expect:
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 driveablity 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
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
