Engine 1988 gt crank no start
- Thread starter Crexun
- Start date
out of my finger and screwdriver lol.
When you say you can't pull codes you mean the computer does not communicate? Thats the problem.
Yeah I just get a steady light instead of any flashing. It's now starting fine without fluid for the moment but it dies if given too much gas. Can throttle slightly into the whole range but only slightly. Open it up too much it bogs down and dies. Also dies if left alone for too long it seems though thats not been a consistently repeatable experience.
Computer will not go into diagnostic mode on 86-90 models 5.0 Mustangs .
Revised Dec 23 2107
- To clarify signal ground connections on the engine mounted fuel injector wiring harness and add diagram for the engine mounted fuel injector wiring harness
- To add warning about using an automatic transmission O2 sensor wiring harness with a A9L manual shift transmission computer.
]b]Disconnect the battery positive terminal before making any resistance checks.
The voltage drop in the ground cable will cause incorrect resistance readings.[/b]
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
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.
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.
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 http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix for the computer internal signal ground.
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.
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 http://www.veryuseful.com/mustang/tech/engine
See the graphic for the 10 pin connector circuit layout.
Have a test light and a battery/alternator tester. Test the fuel relay fuses and they're fine as well as the other fuses. When testing the solenoid I received a nasty shock but I didnt see a bolt jump from the plug wire to the distributor. Like I said it starts now and all that but any more than slight pressure on the throttle causes a shut down so I figured fuel related but from what I've been able to test I've got nothin.
If you have a constant cel, and you can't get the computer to go into test mode then you have a computer or wiring problem,
What kind of computer do you have, is your car speed density or mass air, is it stock or have you got aftermarket parts on it, have you looked at the checklist to see what you have to do to check the computer.
Blown88GT
Founding Member
Speed density as far as I can tell its stock. The people I purchased it from were either dishonest or unaware and any attempts to gain more information from them has been unsuccessful at best. I understand I'm not giving a fountain of information for you guys and I do apologize. I'm just hoping that in all this someone recognize a familiar symptom and can point me in a somewhat correct direction.
You have been given the direction to go in. You can't get an accurate diagnosis over the internet. Several problems have the same symptoms. Go through the diagnostic steps or you can just start replacing things and maybe fix it.
just by what I've read here so far I would guess computer problem but that is a guess and in no way based on my experience with this vehicle.
just by what I've read here so far I would guess computer problem but that is a guess and in no way based on my experience with this vehicle.
Blown88GT
Founding Member
They have more than their share of problems, too.
1. Takata air bags which can kill you.
2. HVAC control modules that die from heat & humidity.
Blown88GT
Founding Member
'88 Speed Density EEC-IV is DA-1, still have my original. Opened it up again today to compare to A9L. Very different, only 1 capacitor instead of 3, better quality also (Nichion).
I'll be buying more diagnostic tools this weekend but from the information I've been able to gather I'm starting to believe it's either a computer or wiring issue. I tried to adjust the timing the other day and it will not go below 2k without dying. That and the whole little throttle good big throttle bad thing.
Blown88GT
Founding Member
All I know about your vehicle is you have an '88GT.
You may not know much more about it or how many previous owners it had & what they screwed up.
I've had my '88 for 30 years, been doing mods for 25.
Any relevant info you can provide is helpful.
Typical of Ford, '88 is somewhat of a transition year, only California had MAF, other 49 had SD.
SD EEC-IV is fine for unmodified engines. Not that SD is bad, just that the computer is a dinosaur & cannot compensate for large changes in idle vacuum or air flow greater than it was designed for. MAF computers can be "chipped" via the service port, but an after market ECU is the best if you have the time & patience to work on the "tune". Some go the dyno route, but that's expensive.
You will need the EVTM & my scanned copy is here:
View: https://drive.google.com/open?id=1on5czXKmpETzxUggWTGtoUuVkJT2UUxN
You may not know much more about it or how many previous owners it had & what they screwed up.
I've had my '88 for 30 years, been doing mods for 25.
Any relevant info you can provide is helpful.
Typical of Ford, '88 is somewhat of a transition year, only California had MAF, other 49 had SD.
SD EEC-IV is fine for unmodified engines. Not that SD is bad, just that the computer is a dinosaur & cannot compensate for large changes in idle vacuum or air flow greater than it was designed for. MAF computers can be "chipped" via the service port, but an after market ECU is the best if you have the time & patience to work on the "tune". Some go the dyno route, but that's expensive.
You will need the EVTM & my scanned copy is here:
View: https://drive.google.com/open?id=1on5czXKmpETzxUggWTGtoUuVkJT2UUxN
It's a speed density. I have replaced the fuel pump, filter, transmission, clutch, valve cover gaskets, spark plugs and wires, cap and rotor, some minor electrical work was done as well to fix issues with the fuel delivery and the warning lights. New radiator as well. Important to note the old radiator is still there the new one is just right behind it with new mounting hardware and such. Outside of the mechanical breaks which have all been taken care of thus far it has stalled on me twice now because the battery is mysteriously but only slightly drained. First time was after I picked it up from my original mechanic and drove it home. Would not start again less than 5 minutes later. Most recent it died while I was driving. Would not accept throttle input and slowly stalled out as I came to a stop. Once again I charged the battery and it starts fine. Right now it sometimes needs starter fluid and sometimes doesnt. I attempted to adjust the timing to being the idle down and it will only increase from 2k any attempt to lower it only causes stalling.
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