Starting/Fuel/Computer issue?

[xtcvapor]

Ok guys, I got a problem w/ my 89 GT. Here's the details...

89 GT, was an AOD car, was swapped out to a Tremec 3550 before I got it. Still has the A9P computer in it. The A/C was removed and a Vortech S trim put in. MSD box/Distributor/Coil, AFR 185's, and a "supercharger" cam.

The car will start when I get home in the afternoon, but won't start in the morning. When I turn the key, the fuel pump continuously runs (morning) and the car starts and runs like CRAP. It won't idle, and I have to keep the gas pedal pressed some. The Check Engine Light is constantly on too, and I tried driving it, and it just won't get out of it's own way.

Yesterday afternoon, I got home and low and behold, the car acted perfect! Put the key in, and the fuel pump primed and stopped. The car started up, and idled perfect. No Check Engine Light. Thinking moisture was my culprit (nice morning dew) I took the computer out last night (right after running it) and brought it inside so it wouldn't get damp. Hooked it up this morning and same problems as yesterday morning, fuel pump running constantly and not stopping after the priming cycle. It won't idle, and I have to keep the gas pedal pressed some. The Check Engine Light is constantly on.

I've read it's probably the computer, because of the fuel pump prime cycle not stopping. If it were a bad computer, would it be erratic like this? I mean the car ran wonderful last night. Please help, as I have to bum rides to work because of this now....
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OK well I bit the bullet and ordered one from AutoZone's website, they said it was available, unlike the store. No core charge though, for $104 shipped. Not too shabby. Hopefully this fixes the problem, I'll post back when I get it.
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Alright guys, this is NOT a computer problem. Just got a 100% tested Remanufactured computer from autozone today. Put it in and the SAME PROBLEM EXISTS. OMG, I can't for the life of me figure this thing out. Please Please help!
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OK I replied yesterday about how I swapped back in my original computer. Well, I needed to drive the car to work, so I did last night (I'm on night shift right now), and it drove great, ran great. This morning, go to start it, put key to ON and fuel pump constantly runs, CEL is on. OMFG really? Well I had my other brand new computer with me, and swapped it out. No FUEL PUMP at all? And I hear clicking. I asked a friend to stay a couple minutes and eventually gave me a ride home. I'm gonna go back sometime this afternoon and try to get it started and back home. This is driving me friggin nuts! Anyone ever have issues like this? Please help! Thanks

 

[jrichker]

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 19-May-2009 to update drawing for dumping the codes on 86-88 Mustangs with no check engine light.

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

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.

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

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 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.

Here's the link 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.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical

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.

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.

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

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.

Or for a nicer scanner see http://www.midwayautosupply.com/pc-7208-90-equus-digital-ford-code-reader-3145.aspx – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

 

[xtcvapor]

Thanks jrichker, I've found that TS guide a couple days ago... problem is that I can't get the dang computer to spit the codes out.... anybody have a clue?

 

[xtcvapor]

Ok I found a new symptom, when this "phenomena" occurs, the fuel gage is pegged high, when I had filled it up the other day (when it was running normal) it only went up about 3/4 the way. Any insights? Please help as my car is stuck in my work's parking lot right now. Thanks

 

[jrichker]

Thhe fuel gauge is a separate problem from your other ones. The fuel gauge and computer circuits are complely separate circuit on 5.0 Fox Mustangs.

Fix your current problems and then make another post for the fuel gauge or do a search on my user name and fuel gauge. There is a tech note that will tell you how to troubleshoot and fix the fuel gauge.


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

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

Computer diagnostic connector:

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 anyplace on the engine harness with the battery
pigtail ground as the other reference point for the ohmmeter probe.

What sometimes happens is that the test connector black/white wire gets jumpered to power.
There is a dark brown connector with a black/orange wire near the diagnostic connector. It is
the 12 volt power to the under the hood light. If this happens, it 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. It is best if an experienced electronics technician opens the computer up & repairs the trace if
it burns up and creates an open circuit.

The STI (Self Test Input ) is jumpered to ground to put the computer into test mode. The STI
has a gray connector shell and a white/red wire 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.

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 that 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 that that and the computer’s internal
ground has failed, and the computer needs to be replaced.

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 that 1.5 ohms is a
wiring problem

The following is a view from the computer side of the computer wiring connector.

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.

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


See Computer issue? - Mustang Forums at StangNet for more help on fixing the computer innards.