Pip or ECU failure? Help diagnosing

chuckdavis16

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I'm working on swapping an engine from a 93 GT into an 85 4 cylinder car that was carbureted. The wiring harness and ECU is an A9L from a 91. The fuel pump is a generic CarQuest inline pump. We had it running, but after hooking up the electric fan it won't start. I unhooked the fan and it still will not start. I may have made a mistake by using the coil + wire to power the electric fan relay? Here are the results from what we have been troubleshooting so far:

1) Spark at coil, distributor and cylinders
2) Fuel pump stays on whenever key is on (it was doing this before the fan wiring and would start)
3) Power at TFI
4) Also tried swapping TFI from 4 cylinder motor that was running
5) Fuel injectors have 12V at red wire
6) test light used as NOID light on injector harenss - no flash
7) EEC codes - 24, 24, 67, 85, 87, 15

I'm thinking it is either the EEC or Pip sensor preventing the injectors from firing now. Are there any other checks to verify what can be wrong?
 
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jrichker

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See the graphic for the 10 pin connector circuit layout.
68512.jpg


Computer wiring harness connector, wire side
71316.gif


Computer wiring harness connector, computer side
88243.gif


Fuel injector wiring harness sensors for a 5.0 mustang
63347.gif


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 24 - Intake Air Temperature (ACT) sensor out of range.
Bad sensor, bad wiring. The ACT for Mustangs built before 95 is in the
#5 intake runner. It measures the air temperature in the intake to help
computer the proper air/fuel ratio.

Note that that if the outside air temp is below 50 degrees F that the test for the ACT can be in error. Warm the engine up to operating temperature and retest.

ACT & ECT test data:

The ACT & ECT have the same thermistor, so the table values are the same

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts.
It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in
the lower intake manifold, the voltage readings will be lower because of the heat transfer.
Here's the table :

50 degrees F = 3.52 v
68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v

Ohms measures at the computer with the computer disconnected,
or at the sensor with the sensor disconnected.

50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms


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!!!




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:



Code 87 – fuel pump primary circuit failure. The fuel pump lost power while the engine was running. Check fuel pump relay, check inertia switch, wiring to/from inertia switch, red wire going to inertia switch for +12volts. Check the other side of inertia switch for +12 volts.

Diagram of the fuel pump wiring for 86-90 cars



Diagram of the fuel pump wiring for 91-93 cars.
 

chuckdavis16

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Thanks for the information. We will go through the items listed and see if that helps. I did also check the PIP sensor last night with a LED test light and it flashes when the motor turns over, so I believe it is OK.
 

chuckdavis16

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Wiring harness appears to be ok. We went ahead and opened up the computer last night and found this. Can anyone help identify this blown component on the board? Is it repairable like the capacitors?
 

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Blown88GT

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It's a resistor, they don't blow without taking out taking out a board trace.
I got these pics off the internet from TMoss.
caps.jpg

notrubskwah.jpg

tmoss_A9L repair.jpg

trace2.jpg


Google found this...
 
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chuckdavis16

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Thanks for the pictures, I was thinking it was a diode. I was able to scrape enough crust off to find 1r5j and 1w which looks like a 1 watt 1.5 ohm resistor. Judging by the heated outer layer and solder leak around it I don’t think it will hurt to swap it out
 

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Blown88GT

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See the last pic. Look at the trace on the back of the PWB, it's probably burned out. You'll have to solder a piece of wire across it to complete the circuit.

I think this is what happens when the under hood lamp connector is mistaken for the Self Test Input connector.
 

John Dirks Jr

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Had the same symptoms with mine. It was the ECU. I tried repairing by replacing the capacitors but it didn't fix it. I wound up sending it in as a core for a refurbished unit. Perfect now. It was about $100 for the swap out service.

I used this vendor. I wound up getting refurbished ECU's for both cars. Quick turn around.

 
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chuckdavis16

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Update, Replaced the 1.5ohm resistor, and the two 47uF capacitors. The electronic store I was at did not have the 10uF. I put the ECU back in the car and I still have the fuel pump running all the time. It does not start initially, and not firing injectors. After double checking a few things and unhooking the battery power again, now it starts and runs. Is there a "reset" that the ECU needed so it would start again, or do I have an intermittent power or ground that I need to find? Does anyone know what circuit on the board controls the fuel pump relay? It is wired so that when pin 22 goes to ground it fires the relay, I have confirmed that the relay is not stuck.
 

John Dirks Jr

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I can't answer your specific question but I have one for you. Is the fuel pump priming event correct now? When the key is turned to the run position, the pump should run for a second or two then shut off.

BTY, both replacement ECU's I got the vendor replaced the 10uf resistor with a 47uf. I questioned them on it and they insisted it was an intentional upgrade. All three in each unit were replaced with 47uf 35v.
 

chuckdavis16

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The fuel pump comes on when the key is turned to "run" and does not turn off. Is this controlled by the 10uF capacitor? If everything else works will this cause a problem? We do have an inertia switch wired into the fuel pump circuit for safety.
 

John Dirks Jr

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If the fuel pump prime event is not correct, I wouldn't trust it. It could still be faulty and function only intermittently. When mine started failing, it would cut out randomly. It would usually start right back up. Then it would start cold and and seem to run ok. Then if you tried a hot restart, no go. Eventually, no start at all

Another thing you can try is dump the codes. If it wont do that correctly the ECU is not working properly.
 
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Blown88GT

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The fuel pump comes on when the key is turned to "run" and does not turn off. Is this controlled by the 10uF capacitor? If everything else works will this cause a problem? We do have an inertia switch wired into the fuel pump circuit for safety.
electrical engineering 101

Capacitors don't control anything, they are passive devices.
The multi-pin DIP (Dual Inline Package) does all the control; not directly but through a power transistor.
The big DIP is digital, everything else is analog.
The ECU works by grounding a circuit to activate a function.
The ECU does not source power, it sinks power.
Google "sourcing & sinking power".
 
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chuckdavis16

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I believe I understand. When I check the wire going to pin 22 with a test light connected to the + battery terminal it lights up whenever the key is on and stays lit. Am I correct to say that the ecu is commanding the fuel pump to stay on?
 

Blown88GT

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I believe I understand. When I check the wire going to pin 22 with a test light connected to the + battery terminal it lights up whenever the key is on and stays lit. Am I correct to say that the ecu is commanding the fuel pump to stay on?
Correct. It's supposed to time out if the engine does not start. The cause is almost never the DIP. Could be the power transistor is shorted to ground.
You can't use a test light for most of this because it actually completes the circuit if none exists. If you're going to attempt to fix this yourself, you will need a multimeter. There are places that test & repair these ECU's. There's another thread here with a link.