Please help my PCM is flooding my engine

A9L is a MAF ECU, if that's what you have now.

4eye86 said:

My 86 hatch has been having a fuel problem. The PCM has been keeping the injector in Cyl. 8 open, effectively giving me poor gas mileage and a whole lot of fuel flooding the engine and saturating the oil. There's been a few modifications done, a slightly bigger cam, MAF conversion, cobra intake, EGR and smog delete, and an off-road h-pipe has been installed. and my future plans are to install different heads and intake. Possibly bump up the injectors to 24lbs. What options do I have for a new computer? Is the aftermarket better than an A9L?

Click to expand...

Dump the codes before you do anything else...


Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/

Can't help you without knowing more details.
'86's were speed density.
Someone may have done the MAF conversion incorrectly.
What MAF sensor & MAF housing do you have?
What ECU's do you have? It's printed on the label.
What injectors do you have? Original 19 lb/hr?

Someone correct me if I'm wrong here....

The ecu doesn't typically fail in a way that would leave one injector constantly open. Most likely, as the General mentioned above, a wire/ground was damaged somewhere... The S&P shakers makes sense...
What does a noid light show on the questioned injector? For the other injectors on that bank?

The driver for the injector could have failed, but other than a hardware failure like that, I can't see HOW the ecu could command one injector open all the time. The entire bank would be treated the same way...

a pinched wire makes the most sense here as the injectors are supplied with 12v and the ECU simply grounds them.

another option is you have a bad injector. a noid light to check the harness is my first suggestion, if the circuit functions as it should then the injector is bad.

vristang said:

Someone correct me if I'm wrong here....

The ecu doesn't typically fail in a way that would leave one injector constantly open. Most likely, as the General mentioned above, a wire/ground was damaged somewhere... The S&P shakers makes sense...
What does a noid light show on the questioned injector? For the other injectors on that bank?

The driver for the injector could have failed, but other than a hardware failure like that, I can't see HOW the ecu could command one injector open all the time. The entire bank would be treated the same way...

Click to expand...

With sequential SEI, one injector is switched to ground at a time. If you pinch one injector wire and ground it out, that injector will always be on.

I'm fixing to dump a lot of very technical stuff on your plate, so you may want to print it out and highlight the sections that relate to your current problem.

Fuel injectors inoperative, one or more injectors either on all the time or will not squirt.

Revised 11 Aug 2018 to clarify injector wiring continuity testing

Tools needed: Noid light, Multimeter (volts & ohms), 10 MM socket &
extension, & ratchet.

Note: Do all of the steps and do them in order. The results of the subsequent tests are based on the prior tests being successfully passed.

1.) Each injector has a red power wire to provide power to the injector. Turn the ignition switch to Run and remove each injector electrical connector and use the multimeter to check for 12 volts on the red wire. Each injector should have 12 volts +/- .5 volt. More voltage is always better than less voltage. No 12 volts on a singe injector and the wiring for that injector is broken inside the engine fuel injector harness.

No 12 volts on all injectors:
A.) Check for a bad connection at the 10 pin connector. Check for 12 volts at red wire on the MAF or TAD/TAB solenoids mounted on the aft side of the passenger strut tower. Good 12 volts there and you have a wiring problem with the 10 pin connectors or associated wiring.

See the graphic for the location of the 10 pin connectors:


See the graphic for the 10 pin connector circuit layout.


The injector power pin is the VPWR pin in the black 10 pin connector. [/b]

B.) Bad ECC power relay. The relay is on top of the computer, it provides power to the fuel injector system. This is relevant ONLY if you do not have power to all injectors.
It is somewhat difficult to get to, since it requires you to remove the computer from its 2 bolt mounting. If the relay or socket is bad, you will not have 12 volts on any of the red wires in the engine compartment or to pins 37/57 on the computer. The pins 37/57 are the main power feed to the computer.



C.) Blown fuse link – The blue fuse link for the computer is up near the starter solenoid. Check for no 12 volts on the ECC relay socket or computer black/orange wires. No 12 volts and the fuse link is blown open. If the fuse link blows, there is no power for any of the computer functions.
Fuse links at starter solenoid


D.) Bad wiring. Broken or damaged red wire to the chassis side of the 10 pin connectors.

Some basics about the computer:
Remember that the computer does not supply power for any actuator or relay. It provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

2.) Get a noid light from AutoZone or other auto parts store, or even better a set of them.

This one is from http://www.summitracing.com/parts/oes-25142?seid=srese1&gclid=CMXk7M6dmM0CFdgOgQodGUMHWQ and costs about $6.

3.) Use the noid light to determine that the injector pulses and isn’t stuck in the on position.
If you have a set of them install all of them and compare the pulse intensity. Install the noid lights, turn the ignition switch to Run and crank the engine. A light that doesn’t pulse and stays on has a short to ground in the computer side of the circuit. That can be either a wiring fault or a failed computer.

Disconnect all 8 fuel injector connectors from the injectors and leave them disconnected for steps 4-6.

If this is the case, remove the passenger side lick panel and disconnect the computer connector.
There is one 10 MM bolt holding it in place. Pull the connector all the way out of the computer so that you can see the computer side pins.

Use the list from the graphic below to find the fuel injector pins for the injectors that didn’t turn the noid light off.







4.) Set the multimeter to low scale Ohms and measure between the computer ground located below the computer and the suspect fuel injector pins. You should see greater than 100 K Ohms resistance. If you see less than 100K Ohms, the wiring between the injector and the computer has an internal short to ground and needs service.
Check the harness and look for damage, kinks or frayed spots. A Short to ground would result in an injector that never turned off.

5.) A single noid light that never turns on is either a wiring fault, or a failed computer. Either the injector has no DC power or the computer or wiring has failed and cannot switch the injector circuit to ground. Determine if the injector has power by using the multimeter to check for 12 volts on the red wire on the suspect injector connector. No 12 volts and you have a wiring fault.


If none of the noid lights flash and you have 12 volts at each injector, check to see that you have good spark. Before you even think about replacing the computer, see step 6.

Check the injector wiring for open circuit or broken wiring or bad connections.
Check the harness and look for damage, kinks or frayed spots. Check the 10 pin salt & pepper shaker connectors for bent pins, corrosion and damage.

Next check the fuel injector wiring for open circuits. Set the multimeter to low scale Ohms. Each fuel injector has a red wire (power) and a non-red wire (computer controlled ground).

Inside the car, take a short piece of 14 gauge bare wire and jumper it to the ground below the computer. Use the computer wiring diagram and select one of the injectors. The recommended procedure is to start with cylinder #1 and test each injector in numerical sequence 1,2,3, etc. Then stick the ground wire into the computer wiring harness socket for the injector you want to test. Don’t forget to move the ground inside the car each time you test a different injector.

Under the hood, set the multimeter to low ohms and ground one of the test leads to the engine block. Then measure the resistance between the non-red fuel injector wire in the fuel injector connector and the meter ground on the engine block. You should see less than 1 Ohm. More than that means a bad connection or bad wiring.

The 10 pin connectors are the first place to look for problems when it fails the above test.

Engine side testing Unplug the black 10 pin connector from its’ mating half. Use the 10 pin connector diagram in this tech note to locate the injector you are currently testing. Measure the resistance between the non-red injector wire and the injector pin on the engine mounted side of the fuel injector harness; you should see 1 Ohm or less. More than that indicates a broken wire or bad connection.

Body side testing Use the 10 pin connector diagram in this tech note to locate the injector you are currently testing. Again, the black connector that is connected to the car body side of the wiring harness is the one to use for this test. Make sure that you test the injector pin for the wire side of the computer wiring harness pin that you grounded. Ground one lead of the multimeter on the engine block and check the resistance; you should see 1 Ohm or less. Test all 8 injectors in numerical sequence, and move the grounding wire at the computer wiring harness each time you test a different injector.

6.) Use an ohmmeter set on the low resistance scale and measure the resistance of each injector across the two contacts inside the injector electrical connector. You should see between 11-16 ohms. More or less than that is a bad injector. Next, measure between either one of the contacts and the metal on the injector body. You should see greater than 100,000 ohms. Don’t hold the metal probe tips with your bare hands when you make this measurement; It will give incorrect results if you do.

Once you have determined that the suspect injectors have good power and good wiring, the computer is the likely suspect, since a ground is required to complete a circuit and make it function. The computer provides the ground: if doesn’t, then the noid light will not flash. If the noid light stays on, the computer has an internal failure.

7) If you have gotten this far, then the problem is likely ignition related. Remember the noid test using all of the noid lights? All of them were supposed to be equally bright. Since you have already tested all the electrical side of the fuel injector circuit, the one remaining common item is the pip sensor inside the distributor. A failing pip sensor, damaged shutter wheel or bent distributor shaft could all cause the pulse delivered to the injectors to be faulty. A bad pip sensor will cause all the injectors not to fire and you will have no spark. Dumping the codes will usually show a code 14.


8) Spark plugs indicate one or more cylinders not firing: use the multimeter to measure the resistance of the spark plug wires. The wires should measure 2000 ohms per foot of length. A 2 foot wire would be 4000 ohms and a 3 foot wire would be 6000 ohms. Some Taylor and Accel wires have metal cores and will measure much less: that’s OK.
Next examine the spark plug wires very carefully for burn spots, cracks and damaged insulation. One good thing to try is to start the engine while the car is a very dark area, open the hood and look for sparks or blue glow. They indicate the electricity is leaking out of the spark plug wires.

Thanks to Tmoss & Stang&2birds at www.veryuseful.com/mustang/tech/engine/ for some of the graphics

Thanks also to www.oldfuelinjection.com for some of the graphics.