Drivetrain Help with Check Engine Light after Transmission Swap - 1990 Mustang LX 5.0

jglass3

Member
Oct 12, 2020
56
7
18
69
Virginia
Hi guys, Got an email today that my A9L ECU is on it's way back from ECU Exchange in Green Acres, FL. Their price is just under $100 to go completely through the ECU plus shipping with 48 hour turnaround. They found a burnt internal ground, that with your help, I had already found. They also discovered that the power supply was faulty. So, they repaired the ground circuit, replaced the power supply, replaced all the capacitors with upgraded capacitors, replaced voltage regulators and beefed-up areas where Ford ECU's are known to fail. They also provide a lifetime warranty and will repair at no charge, even if the failure is due to my own incompetence. :oops: I never would have gotten to this point without all of your help. Thanks so much and I'll let you know what happens after the reinstall. Any suggestions on anything I should do before I reinstall the ECU to make sure that I don't blow it again? As you know, you already walked me through the rejumpering of the O2 harness.
 
  • Sponsors(?)


Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
34,657
10,824
224
Massachusetts
Test for voltage on pin 46. Before you install the ECU connect one probe to ground and the other to pin 46. Turn key to on, crank and back to on and you should have zero voltage through any of those conditions
 

jglass3

Member
Oct 12, 2020
56
7
18
69
Virginia
That's a great idea Mustang5L5 and I will be sure to do that tomorrow. I'm assuming that if I get no voltage on Pin 46 during off, on and start, I should not have too much of a fear of burning the ECU internal ground?
 

Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
34,657
10,824
224
Massachusetts
Correct. That is what causes the pin 46 trace to burn. For a 5-spd wired car, should be zero voltage. You can double check your o2 sensor harness jumper as well to be sure.
 

jglass3

Member
Oct 12, 2020
56
7
18
69
Virginia
Don't know if I have good news or bad news. I checked voltage from pin 46 to ground and there is no voltage on off, run or start....that's good! Not sure if this is bad news or not: I checked continuity from pin 46 to ground and got nothing. If this is the internal ground for the ECU, should there have been continuity between pin 46 and ground? If there should have been continuity, and ideas?
 

jglass3

Member
Oct 12, 2020
56
7
18
69
Virginia
Well, here's what I got using two meters...a cheapie analog and a cheapie digital:
Ignition off, battery disconnected: 46-60 No Continuity, 46-40 No Continuity-digital, 3,000 ohms-analog
Ignition off, battery connected: Same Readings
Ignition on run, battery connected: 46-40 (.74 volts), 46-40 (.80 volts)
Ignition on start, battery connected: 46-40 (.70 volts), 46-60 (.40 volts)

Is this anything near what I should be seeing or do I have deep problems?
 

Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
34,657
10,824
224
Massachusetts
The no continuity worries me. You should have continuity. You might want to open up and see if they repaired the trace
 

jglass3

Member
Oct 12, 2020
56
7
18
69
Virginia
I apologize! This is not on the ECU, but the connector in the car. The ECU is on the way to VA from FL. Should have it within the next several days.
 

jglass3

Member
Oct 12, 2020
56
7
18
69
Virginia
I assume that once I receive my ECU, the tests from pin 46 to pin 60 and pin 46 to pin 40 are simply continuity checks, correct?
 

jglass3

Member
Oct 12, 2020
56
7
18
69
Virginia
Got my ECU back today and checked continuity between pin 46 and pin 40/60 and got continuity. Reinstalled the ECU and did a OBD-1 KOEO test just for grins. I did not have to ground the single lead from the car's harness (success #1). I got the following codes: 67-O, 85-O and 15-C. Next, I decided to fire it up. Uh-Oh...engine does not crank and the tach needle is going crazy so I disconnected the battery, turned on the headlights, turned off the headlights and reconnected the battery. Hit the ignition and the car started like nothing had ever happened...and most of all: NO CEL!!! Tried a number of restarts and the car did not miss a beat. I think my dilemma is solved. You guys are fantastic! Thanks for hanging in there with me and encouraging me to fix it the right way!!! I hope that some day I might be able to return the favor.
 

Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
34,657
10,824
224
Massachusetts
Nice!

you should do a code dunp anyway just to see what the “real” codes are. Not all stored codes trip the CEL, although the ones that don’t tend to be minor, like code 85 -eVap purge
 

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
27,339
2,678
234
74
Dublin GA
lowendmac.com
Got my ECU back today and checked continuity between pin 46 and pin 40/60 and got continuity. Reinstalled the ECU and did a OBD-1 KOEO test just for grins. I did not have to ground the single lead from the car's harness (success #1). I got the following codes: 67-O, 85-O and 15-C. Next, I decided to fire it up. Uh-Oh...engine does not crank and the tach needle is going crazy so I disconnected the battery, turned on the headlights, turned off the headlights and reconnected the battery. Hit the ignition and the car started like nothing had ever happened...and most of all: NO CEL!!! Tried a number of restarts and the car did not miss a beat. I think my dilemma is solved. You guys are fantastic! Thanks for hanging in there with me and encouraging me to fix it the right way!!! I hope that some day I might be able to return the favor.

Code 15 or 511 - No Keep Alive Memory power to PCM pin 1 or bad PCM (Memory Test Failure).

Revised 4-Jan-2019 to add removing any custom tuning chip for minimum configuration testing.

The voltage to the Keep Alive Memory (KAM) is missing (wiring problem) or the KAM is bad. The KAM holds all of the settings that the computer "learns" as it operates and all the stored error codes that are generated as a result of something malfunctioning while the engine is running. Use a voltmeter to check the voltage to the pin 1 on the computer - you should always have 12 volts. No constant 12 volts = bad wiring. If you do always have the 12 volts, then the KAM may be bad and the computer is faulty. Read on further to make this determination, since there are some exceptions.

Clearing the codes by pressing a button on the scan tool or disconnecting the test jumper used to start the code dump does not erase the “learned settings”. Disconnecting the computer from the wiring harness or disconnecting the battery (either power or ground cable) will erase the “learned settings” If the computer has to "relearn" all the optimum settings every time it powers up, the initial 15-30 minutes of operation may exhibit surges, poor low speed performance, and rough idle.

Note that some aftermarket chips will cause code 15 to set. Disconnect the battery and remove the chip, reconnect the battery and retest. If you have a custom burned chip using the data gathered from a dyno session, this may not be advisable since it may drastically alter the fuel/air and timing tables.

Disconnect the battery negative terminal for the next step.
Remove the passenger side kick panel and examine the computer. It is held in place by a diagonal plastic strap and 2 screws in the strap. The end of the computer opposite the wiring harness may have an accessory PC board with a big chip in a socket. That chip is a custom tune to accommodate the mods that affect fuel /air mixture, ignition timing and emissions equipment. If it is present, remove it and see if the engine runs any better. Remember that the car will need to be driven at highway speeds for at least 15-20 minutes in order for the computer to relearn the adaptive settings.

For stock engines or engines with minor modifications (OEM cylinder heads, stock 19 LB injectors, no NO2 or pressurized induction).
Before replacing the computer, remove the battery ground cable for about 20 minutes. This will clear all the codes and “learned settings”. Retest after several days of running. If the 15 code is gone, then don't worry about it. If it is still there, then you get to do some troubleshooting.

See the following website for some help from Tmoss (diagram designer) & Stang&2
Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

Diagram courtesy of Tmoss & Stang&2birds
88-91_5.0_EEC_Wiring_Diagram.gif


http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif



Code 67
Revised 18-Mar-2017 to include warning about the necessity of having a 5 speed O2 Sensor wiring harness when bypassing the wiring for test purposes

Cause of problem:
Clutch not depressed (5 speed) or car not in neutral (5 speed and auto) or not in park (auto) or A/C in On position when codes where dumped. Possible neutral safety switch or wiring problem. This code will prevent you from running the Key On Engine Running tests.

External evidence from other sources claims that a code 67 can cause an idle surge condition. Do try to find and fix any issues with the switch and wiring if you get a code 67.

What the NSS (Neutral Safety Switch) does:
5 speed transmission: It has no connection with the starter, and the engine can be cranked without it being connected.
Auto transmission: It is the safety interlock that prevents the starter from cranking the engine with the transmission in gear.
What it does for both 5 speed and auto transmission cars:
The computer wants to make sure the A/C is off due to the added load on the engine for the engine running computer diagnostic tests. It also checks to see that the transmission is in Neutral (5 speed and auto transmission) and the clutch depressed (T5, T56, Tremec 3550 & TKO)). This prevents the diagnostics from being run when the car is driven. Key On Engine Running test mode takes the throttle control away from the driver for several tests. This could prove hazardous if the computer was jumpered into test mode and then driven.

The following is for 5 speed cars only. Do not do this unless you are sure that you have a 5 speed O2 Sensor harness!!!! Smoke, sparks and expensive pain in the wallet may ensue if you don’t.
The NSS code 67 can be bypassed for testing. You will need to temporarily ground computer pin 30 to the chassis. Computer pin 30 uses a Lt blue/yellow wire. Remove the passenger side kick panel and then remove the plastic cover from the computer wiring connector. Use a safety pin to probe the connector from the rear. Jumper the safety pin to the ground near the computer.
Be sure to remove the jumper BEFORE attempting to drive the car!!!

Computer wiring harness connector, wire side
71316.gif



Code 85 CANP solenoid - The Carbon Canister solenoid is inoperative or missing.

Revised 11 –Jan_2015 to add warning about vacuum leaks due to deteriorated hose or missing caps on vacuum lines when the solenoid is removed.

Check vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.

If you disconnected the carbon canister and failed to properly cap the vacuum line coming from under the upper intake manifold, you will have problems. You will also have problems if the remaining hose coming from under the upper intake manifold or caps for the vacuum line are sucking air.

Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.

Connecting the gas tank vent line directly to the intake manifold will result in fuel vapor being constantly sucked into the intake manifold. There is unmetered fuel that the computer cannot adjust for. The result is poor idle and poor fuel economy.



It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook it up & use it?


The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.

The purge valve solenoid should be available at your local auto parts store.

Purge valve solenoid:



The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
Carbon Canister:
903_AIRTEX%20_pct_2F%20WELLS_7310014_1.jpg
 

jglass3

Member
Oct 12, 2020
56
7
18
69
Virginia
Well, just got back from taking the car for a fairly long drive. I can tell it's running a little leaner since it's no longer in "Limp" mode. No CEL...and that was my goal! Got home and did a code dump: KOEO, I got 67-O, 85-O and 33-C. That's it. I'm pretty sure my NSS is defective because before I installed it into the T-5 I checked continuity with the little pin depressed and released....no continuity either way, but I didn't want to hold up the T-5 installation so I let it go. Replacing it while the transmission is in the car looks absolutely impossible. As for the purge solenoid and the EGR, who cares.......unless you tell me I should care. Thoughts, Recommendations? You guys saved me from pulling a redneck (remove the CEL bulb) move and I am eternally grateful for your help!
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
18,554
6,093
193
polk county florida
The purge solenoid regulates the gas tank fumes, it also has an effect on part throttle cruise. Is the purge canister still installed and hooked uo?
 

jglass3

Member
Oct 12, 2020
56
7
18
69
Virginia
Yes, I never touched the evaporative emissions because I knew there was probably nothing (or very little) to be gained. Have you ever tried to replace a NSS on a T-5 with the tranny in the car? I don't have a hanging idle, so I don't see much of a problem there. Also, on code 33-C, I did remove the EGR and used LMR's resistor plug...