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1989 SMEC ASD signal dead after 2 SMECS

6K views 67 replies 5 participants last post by  NAJ 
#1 ·
Got a 89 turbo harness/smec in a 87 non turbo new Yorker ( I didn't do it)

Ran good for 6 months, randomly died a couple times then restarted. Then, a final time, didn't restart

Found no ground signal ( blue/yellow stripe wire) from computer to asd/fuel pump relay. I wired in a relay to ground it, and drove another 20 miles, then it died again. Took smec apart, SEEMS burnt on one component.

Checked powers/ground to smec, all ok. Installed used SMEC from 89 turbo lebaron. Ran about 15 miles, then lost that ground signal again. Will start if I ground that blue/yellow wire. I've been told to inspect molex pins, how do I do this?

What am I missing? Can anyone tell me through a pic what the component that is possibly damaged, runs?

TIA
 

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#2 ·
That component is custom hybrid array, they are also used extensively on the SBEC as well. I have not reversed engineered them yet as I would need to destroy a few ECUs. It appears to be a combination of resistors and capacitors for signal conditioning, at least for the SBEC2 I disassembled. It is unlikely you can find a reference to the part as usually they are labeled only with a Mopar part number which is not very helpful.

Could you check the error codes on this ECU as it might help us.
 
#4 ·
Do you have a Factory Service Manual (FSM)? you are getting at a point that you really need one.
The ASD relay coil activation is a medium current requirement as these are handled by the SST 15 or 16 pin driver chip which is the long black device beside the Orange Electrolytic cap.
My gut tells me something other than the SMEC is causing issues here.
 
#5 ·
I put a noid light on, and grounding the ASD relay and cranking, I found the light very dim

All injectors ohmed out ok, but #3 sounded different when i powered it up. I replaced it, still dim light when plugged in. If unplugged, the light of Is normal.

I also found the red/black wire was cut to the air charge sensor, I ran a new one to sme

I also noticed the 2 wires into the coolant temp sensor are frayed going in. I separated them with tape

My noid light is bright now, but no ASD unless I ground it

The chip next to the caplooks ok, it's the ones below that that might be cooked in the old smec

I do not have a fsm, but have downloaded diagrams, and ran through ASD testing, to the point of "replace smec" and I believe also something else is telling the SMEC to turn off
 
#8 ·
Am I missing anything that causes the ASD ground signal for 1 second on key up? Still don't have that
1. Powers and grounds good to.logic board, one 8 v source reads 8.6v
2. Clean/inspected computer connection
3. Cleaned, inspected grounds under computer, behind engine, and next to fuel rail

As far as I know, there's no reason I should have lost the ASD ground signal, beyond a another bad computer, but I want to make sure

Thanks again for any help, this is my work vehicle
 
#9 ·
If your ground circuit is not complete the current will look for an alternate path to ground which could be back where it came from.
Be 100% sure your Main Controller Ground is properly connected to a Clean Metal Surface and Secure.
Text Diagram Passive circuit component Line Design

Using an Ohmmeter verify all controller ground circuits have continuity to ground (less than 5 ohms)
SMEC 14 Pin Connector Cavities 6 and 7
SMEC 60 Pin Connector Cavities 5, 15, 16

If all of that checks OK then you can proceed to diagnose the ASD Relay circuit.
The ASD circuit is very simple.
Two power feeds, ground side control and an output to the Injectors, + Coil, Fuel Pump.
RD - Constant Battery Power through a Fusible Link
DB - Switched Ignition Power from the SMEC 14 Pin Connector, Cavity 3
Power in is from the Ignition Switch to SMEC 14 Pin Connector Cavity 4
DB/YL - Ground Side Control
Using your ohmmeter verify continuity to ground on the ASD ground control circuit, Smec 60 Pin Connector, Cavity 58 (less than 5 ohms)
DG/BK - Power Output To Components and SMEC.
Power will only be present for 1 second with initial key on and not again until the controller
sees a crank/fuel sync signal from the HEP with the engine cranking.
If both power feeds are present and you have ground side control and there is no output on the DG/BK wire, replace the ASD Relay.

You can manually actuate the ASD Relay by grounding the DB/YL wire in the Underhood Diagnostic Connector with the Key On to verify output.
Wire Technology Auto part Electronic device Cable


Text Font Line Parallel
Text Font Parallel
Text Font Line Parallel
 
#14 ·
Excellent. So my first thought is why is the 5V at #13 at 8V. Since the PM board supplies 8V(9V in your case) this means that the voltage regulator circuit is toast. The external demand for 5V is very low as it only powers the MAP and TPS. Remove the 60 way and measure the resistance from pin #13 to ground. I get 530 ohms on my 87 CSX which calculates out to 10mA. If yours is significantly more you likely have a short somewhere. As a side note, do you have a variable power supply to generate 8V if we need it
 
#16 ·
Just so you are aware, if the controller is fried and this is not the first one you need to find out why.

GM had a problem back in the 80's with faulty ECU's under warranty.
GM used "quad drivers", one driver controlled 4 components.
They would replace the ECU and it would die a few months later.
they asked their techs to start checking resistance in the circuits affected to check for faulty components that may be killing the ECU's.
That did not solve the problem.
They then asked their techs to activate the circuits and check amperage flow to the failed Quad Driver, that uncovered the faulty component.

Learn from GM, be sure you determine exactly what killed your controller or you will be right back here again.
 
#18 ·
To clarify my request, measure the resistance from #13 on the 60 way connector to ground. This will check for short circuits on the 5V supply line from the 60 way to the MAP and TPS.
Using resistance is fine to trace shorts on simple circuits.
In Electrical Engineering the rule is "Thou shall always be measuring voltage"
When troubleshooting and measuring voltages it is very important to do so under load. Of course, voltage under load is used to measure current V=IR. As NAJ story above explains, resistance measurements in a complex circuit is nearly useless. I found that out the hard way in the early 70's when I started my training in electronics.
 
#19 ·
Found my modis hookup, and hooked on up

Got a waste gate/baro code, but I assume that's from having them disconnected. I did that last night. Code 42 showed up too

2 weird things. Modis shows 11.5 volts at test connection, battery is at 12 ( see pic) also, I can turn in the fuel pump from the modis ( through ASD) but when I go to actuate the ASD, nothing happens
 

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#22 ·
2 weird things. Modis shows 11.5 volts at test connection, battery is at 12 ( see pic) also, I can turn in the fuel pump from the modis ( through ASD) but when I go to actuate the ASD, nothing happens
I am OK with the 0.5V drop, this is likely due to the load of the scanner on the SCI connector. I do find the fuel pump experiment odd. I assume the blue/yellow stripe wire is now connected to the SMEC.
Did the ASD function of this scanner work in the past on a SMEC.
 
#25 ·
Right now you are attempting to repair what is assumed to be a faulty controller.

When diagnosing a circuit all components and wiring are tested, if they check OK it is then assumed the controller is at fault.

You can test the ASD circuit as outlined in post #9 to determine if this is actually the case.
I am going to send you the 88/89 Code 42 diagnostics through PM, this will tell you what the issue is in the circuit.
 
#26 ·
As far as I know, I have run all test for code 42, but I'm willing to run what ever you send
I have solid power, solid ground to the SMEC, and all power/grounds to ASD relay. This is my second used SMEC, so I am stumped at this point. I took both SMECS apart looking for obviously damaged components, and none found. I don't want to junk the car. Thanks for your help
 
#29 ·
I sent you the diagnostics.
Code 42 sets when the controller actuates the ASD and does not see voltage at Cavity #10 of the 60 pin connector.

Do you know what body style the 89 harness came out of?
 
#30 ·
I do not know exactly what it came out of, the guy who did it was 2 owners ago. Assuming a turbo 1989 lebaron. It ran for about 6 months when I got it going. It died twice originally, but would start right back up.

When it originally died for certain with the original smec, it had lost ASD actuation also at the blue/yellow wire also.
 
#31 ·
Update: I grounded the ASD to make it run

It ran for 30 min, than I turned it off. It wouldn't restart

ASD was providing power to everything
I used a noid light, light seems dim again, but during use it restarted

The 5v reference is at 4.9 at map and throttle position. I'm running it again. It defently starts harder than normal
 
#33 ·
Does your scan tool use the ASD line on the SCI connector? If so that may explain the differences it your two different test.
I do find it strange that the #13 is 5V at some times and 8V at others.
Perhaps you have a bad connection of your 60 way female pins. It could explain your issue.
here is a way to check.
How to test quality of 60 way female pins

Deoxit5 is a great product to clean up automotive electrical connections.
 
#34 ·
It's pi
Does your scan tool use the ASD line on the SCI connector? If so that may explain the differences it your two different test.
I do find it strange that the #13 is 5V at some times and 8V at others.
Perhaps you have a bad connection of your 60 way female pins. It could explain your issue.
here is a way to check.
How to test quality of 60 way female pins

Deoxit5 is a great product to clean up automotive electrical connections.
It's pin 52 that's at 9v, supposed to be 8. Map reference voltage has always been ok.

As far as how the snap on modis test the ASD, I have no idea unfortunately

I will check female pins again. I did clean them with the little deoxit I had left
 
#39 ·
Apparently there is an issue in the ASD circuit that is killing the SMEC.

Have you checked the DB/Yl wire for a short to voltage?
Have you checked all controller ground circuits for shorts to voltage?

You are concentrating on the end symptom and not the cause of the issue.

I just went through this myself this weekend.
Two years ago the L/F caliper locked up.
It was frozen pins/slides.
Replaced all of the hardware, lubed it up and it was difficult getting the new metal bushings in, not remembering I assumed it was just a PITA to do and did not give it a second thought.
Friday driving to my Son's house the L/F caliper locked up again, I drove another 6 miles that way.
The issue was again frozen slides/hardware.
Bought new parts and attempting to install the new bushings into the rubber boots they would not go in no matter what I did.
Then it dawned on me that the issue was with the caliper itself.
I used my die grinder to remove all rust and scale from the caliper holes where the boots go in and now the pins go right into the boots and I can move the caliper back and forth with a finger.

The point of all of this is to find the initial cause of the issue, not the final result of the issue.
 
#41 ·
Just another analogy...
GM direct ignition systems (waste spark Ignition) 2.8/3.8L used to be towed in with a no start.
The reason for the no start was a faulty ignition module.
The cause of the ignition module failure was caused by an open ignition wire or high wire resistance.
If only the module was replaced it would die again in short time.

You have to find the cause of your SMEC failures, I am trying my best to help with that to uncover the mystery.
 
#44 ·
At this point you need to verify that...
1)No controller ground circuits are shorted to voltage and all have less than 5 ohms continuity to ground.
2) All power feeds into the controller are showing 12 volts and have no continuity to ground.
3) Controller 5 volt and 8 volt outputs read the same at the component as they do at the controller.
4) There is no corrosion on the SMEC connector.
5) Does this harness have a connector for a 4 wire O2 sensor?
a) Is that connector compromised in any way?
6)All body grounds are connected, right side engine mount/pigtails from - battery cable.
 
#45 ·
1. All grounds test under 5 ohms at smec connector, no shorts to ground
2. All 12v feeds have full voltage
3. I will have to check reference voltage to components. Map/tps good
4. I cleaned connection with deoxit, but didn't have much. No corrosion evident. Will re check
5. The O2 CONNECTION was cut when I got it. I put new crimp connectors on. I will double check my work
6. All body grounds cleaned. I do not have one on the engine mount, but there is one on the back of the engine to body that I made.
 
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