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Discussion Starter #1
I'm re-posting this cause I haven't heard from anyone who knows anything about code 53 ignition problems.

To read the diagnostic codes on a 91 R/T, simply connect wire from ground through a 470 ohm resistor to the cathode (-) of an LED and the anode (+) of the LED to pin 1 ( upper left pin on diagnostic connector ). LED will continually flash error code anytime the key is on. Mount this on your dash, and error codes are imeadiatly obious!
My code 53 was 5 long flashes, pause, and 3 short flashes, really easy to read. This code repeated continually as long as the ignition is on until reset by removing battery cable for a few seconds erasing memory. With no error, light flashes porportionally on/off like the curser on your computer.

As soon as you get a check engine light, the light it immeadiatly flashes the error code and repeats. Cool !!!

Iknow, "Nobody cares" But, lets say that once warm, the STEALTH faulters and "LIMPS IN" on 4 cylinders. With a check engine light and a diagnostic code 53 one would find that the book says the EFFECT is "Limp-in, Cuts fuel of an Ignition signal abnormal cylinder." and the PROBABLE CAUSE is "Ignition Coil failed, Disconnection or short circuit of the primary ignition circuit or imperfect contact of the connector, Ignition Power Transistor Unit failed or Engine Control Module failed." Wow, must have a tech writer write this stuff!

Anyway, Including the origional parts, I have tried 3 sets of Ignition Coils, 2 Ignition Power Transistor Units and 3 Electronic Control Modules.

In any and all combinations, the simptom of cutting spark to cylinders 3-6, when warm continues.

Are there any diagnostic genuses out there?
If so, what say you?

I hooked an O-scope to the inputs and outputs on the Power Transistor Unit, and see that both the input and the output signals to the transistor to coil 3-6 is distorted in comparison to the other two once the temperature is reached were it exhibits this problem.

Now, is it the ECM driver, the power transistor the coil?

Lets say that "if I were to have a problem with ignition coil 2-5, would get an error code of 52." That being true, then if I were to swap drive signals to the Power Transistor Unit driving the 2nd and 3rd coils, and swap plug wires between the 2nd and 3rd coils that I would be firing in the right order, but through a different path.

I say that If the 3rd Power Transistor or the 3rd coil is causing the problem that sense I'm driving these with the 2nd ECM driver, I should get an error code 52. On the other hand if the problem is the 3rd ECM driver, I will still get a fail code of 53 and sense I swapped the signal paths, I will still missfire on cylinders 3-6 but from a dead 2nd coil.

Easy huh? Will the swapping is done. I must have done that correctly cause she's running so good right now.

Now I'm going to take it out and run her up to operating temperature until it fails and see what code I get !!! Later !

By the way, I would like to express thanks to Andrew Caple for the diagnostic connector specifics, Fastboy and Joe-Patterson for support and glad that at least one individual, Hans91GT, made use of the LED code reader technique !



[This message has been edited by EP (edited December 25, 1999).]
 
C

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Had the same problem with my 93, guess what it was. Bad wire, give it a check.
 

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Discussion Starter #3
As I explained in the initial post, I swapped ignition paths looking for a change to error code 52 that would indicate a Power Transistor Unit or the 2nd coil. No change, still 53.

I put an O-scope in it and discovered that the ECM output to cylinders 3-6 is not happening. Sense I tried two other ECMs, I still suspect that the ECM is good, but sees something that it doesn't like and is shutting down one coil to make you Limp-in to a dealer for service.

Next, I am going to replace the $ 97.00 oxygen sensor to eliminate any question of it.

Has anyone experienced O2 sensor problems?

It could be a wireing problem, but it comes on slowly, first at heavy throttle, and then continually until I let things cool. Then, it runs good for a time porportional to how long I let it cool.

The O2 sensor is a shot in the dark, but I know that the ECM depends heavily on its input.

Are there any other opinions of what constitutes "Limp-in" as mentioned in the manual?
 

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Discussion Starter #4
Well, they didn't have an O2 sensor in stock so I go to a salvage yard and find a $ 10.00 one. Installed it with no change of symptom. I also questioned the chance of a faulty engine temp sensor making the ECU think that the engine was overheated. I removed the connector from the sensor and inserted a 1K resistor into the connector. 1K should equal about 120 deg F. Still drops down to run on 4 cylinders when warm.

Arn't there any technicians on this board or anyone that has seen this problem?

Anyone heard of Limp-in?
 

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Discussion Starter #5
OK, Thought that I may be missing some pulses from the Camshaft Position Sensor (Crankshaft Angle and Top Dead Center Sensor) but, no such luck. Still missing on 3-6, but both pulses from the sensor are steady and not intermittent.

If your following along, take a look in Volume 2 - Electrical, page 8-56. Thats the most information that I can find on the Crank Angle Sensor. Appears to be that pins 3 and 4 light two LEDs that couple to 2 photo transistors thru an optical interrupter disk. Outputs may be observed on wires to pins 1 and 2.

Anyone ever go here before?
 

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Discussion Starter #6
LOVE THAT THROTTLE !!! Today is the first day in weeks that I’ve been able to run to work and put my throttle anywhere I wanted to! Last night I see on the O-scope that my # 3 drive pulse to the Power Transistor Unit was deteriorating as I watched at the edge of cylinders 3-6 failing.

These 3 pulses to the Power Transistors all look good when cold, but at operating temperature the height of # 3 reduces from approximately 1 V and shrinks slowly to almost nothin. On the way down 3-6 start missing and then cut out completely.

Ah, but low and behold, if I pull this wire through a resistor to a positive voltage, the pulse gets larger. Add another 1 K res in parallel with the other and the pulse gets large enough to turn on the Power Transistor to that coil. Cool, runnin on all 6 again!

Thanks In part to Curtis, I started looking for a corroded wire or resistive contact.

I expect to find a problem between the ECU # 3 Ignition Driver and the # 3 Power Transistor input.

The pull-up resistor to turn on the base of the Power Transistor is at the ECU end, all the way down that wire. Hence adding the 500 ohm res pull-up to the Power Transistor input balances that pulse on either side of the Power Transistor’s turn on current.

Getting sweeter all the time !!!
 
J

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Good to see someone with some technical ability having success and more importantly sharing it in a concise manner. Keep up the good work.
 
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