HELP: '87 runs super rich and dies if it idles lower then 1,900 rpms

87fromMI

New Member
Mar 23, 2011
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I just got the car. It runs so rich that it will burn your eyes and will thin the oil. It has had a scan tool hooked up to it and wouldn't show any codes. the car could possibly have a cam. I does have M.A.C. equal length headers with duels and a H pipe, it has not cats, but O2 sensors. other than that its stock. The car hasn't moved a mile in almost 2 years. I just plugged the computer back in yesterday and ran it at a 2,000 rpm for a couple minutes. if it got below 1,800 rpms it would die. this car runs extremely rich.

Anyone have some idea of where i should start. this car has already stumped 2 other owners. I really don't want to put a carb on it, but if I can find out whats wrong with the fuel injection, I will so I can drive it this spring and summer.
 
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thanks. i was inside the car while it was running so i could keep it from stalling, my dad said he heard a vacuum leak. the exhaust leaks because where the header and exhaust pipe come together isnt tight. when i tighten it tomorrow I'll have him listen again.

thanks
 
Pull the vacuum line off of the fuel pressure regulator and check to see if the line has gasoline in it. If so you need a new fuel pressure regulator.

There are some vacuum lines hidden under the upper intake, you might have to pull the upper intake to see them (not hard to do). If you remove the upper you might as well replace the lines while you are at it.
 
Pull the vacuum line off of the fuel pressure regulator and check to see if the line has gasoline in it. If so you need a new fuel pressure regulator.

There are some vacuum lines hidden under the upper intake, you might have to pull the upper intake to see them (not hard to do). If you remove the upper you might as well replace the lines while you are at it.

Very good advice, do it first.


You got no codes or an 11? The 11 indicates that the computer passed it's internal diadnostics and can dump codes. No code 11 and you have computer or wiring problems.
 
its had other computers in it to see if thats the problem. Also It was just switched to mass air and it ran even worse, so it when back to speed density.

You have not answered my question. In order for me to narrow down the list of possible problems, I need good answers. Without them there is very little I can do to try and help you. Please answer: did you get a code 11 or not?
 
I was not the one who did the scan the guy that i got it from on a trade did. he works at fords and he had their tech at ford hook up the scan tool to it. he told me that the scan came up with not 1 code. the scan did not show any codes at all.

I just tried to see if I could get some codes by using a paper clip and a test light and it didnt do anything.
 
I just talked to the guy who had the car before me, and he said that they were thinking that it was a electrical problem too.

He said they tried to run a self test where the tool elevates the rms and what not. It would not run a self check, it was unresponsive.

Also he replaced the fuel pressure regulator, map sensor, and he wen through the whole thing and fixed all the vacuum leaks, he took the upper intake off to put all the lines back together. he use a vacuum gauge to test it and it was good. The ford tech and the guy I got it from both thought it was electical because of the unresponsiveness of the car.

Anyone got Ideas of how to prove if the electrical system is damaged.
 
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 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 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
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. Only an experienced electronics technician can open
the computer up & repair 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. 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.

attachment.php


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.

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 that 1.5 ohms is a
wiring problem

The following is a view from the computer side of the computer wiring connector.
eec04.gif


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 Mustang FAQ - Wiring & Engine Info

harness02.gif
 
while i was looking at the wiring diagram, I looked at the black/white 46. The first thing it passes through is the neutral gear switch. mine is broken. they just took a piece of speaker wire and jumped the starter solenoid and connected it to a push button to start it, its kinda rigged up but works. if that switch doesn't work, will it inhibit the flow of electricity through the system. the car doesn't start by turning the key. you have to turn the key to give everything power then hit the button to turn the motor over, if the car isn't in neutral or the clutch isn't pushed in and you hit the button the car will role forward because of the starter.
 
I agree with jrichker completely, bad grounds can wreak havoc with these cars. I would take them all apart and clean them down to shiny metal ! Also look for any grounds that might be missing.

Next I would check for any stuck injectors. It's not common on these cars but it happens and could be pouring gas down the intake. Check out this thread in order to do that. http://www.stangnet.com/mustang-forums/786225-86-5-0-injectors-not-opening.html

Check to make sure you have the proper injectors. http://www.stangnet.com/mustang-forums/799352-injector-identification.html

If the computer and other parts have been swapped around I would attempt to varify that you have the proper computer for your application. This link might help with that. Your Mustang's Computer Code (1987-2011+) - The Basics at AmericanMuscle.com

In your case I would be tempted to start over with mass air parts and make sure you have the proper computer to match. If you have speed density and you already have a cam in the car, that could be part of your problem. From what I've heard not all cams are speed density friendly.
 
thank everyone for your help so far. I've learned a lot. the computers that were tried in the car were both out of '87s with 5 speeds. both computers made the car run the same.
 
jrichker I tested the resistance and I got .3-.5 consistently. There has been 2 or 3 different computers in this car and they all made the car run the same. Except the mass air computer when it was swapped, it ran worst and is now back to speed density. So I find it hard to think theres something wrong with the computer.
 
The mass air computer swap reqires the installation of a Mass air harness pigtail and moving of several pins in the computer harness. Did you add in the mass air harness pigtail or swap the entire harness out for an 89 or later 5.0 Mustang?

See MASS air conversion instructions from Mustang Mass Air Conversion « for more details.

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.
 
Are you sure the computer is not bad? My car could never pull codes, couldnt even get the check engine light to come on. I took my computer out and there were broken capacitors inside. You may want to at least open it and inspect it. Dont try to clean it or anything. You say you just plugged the computer back in, did you have it stored somewhere it may have been damaged?
 
The car does sound like a hack job, and the prior owner (PO) sounded dumb.

I am an ASE master tech, and from the sounds of this I would not touch it. For you to take someone's word (PO) who probably did half of the hack job, when they say a Ford technician looked at it...is probably half true. The tech probably tried to run a scan only, but once they realized all the wiring snafus, they ran away saying they couldn't help.

Your posts really sound like you can turn a wrench, but not own a meter or gauge of any type.

How about this: Next time post some pictures of your areas of concerns, tell the whole story...no matter how long it takes. As for this post, I would not assist with the intentional butchering of a car.

I usually try to buy cars where people have mildly butchered them, because I can get them for a couple hundred bucks, fix for $10 bucks, then sell for a couple thousand.

Good luck.