Help! Check engine light on and a black smoke ball

[tave]

It was a beautiful and sunny Saturday morning, I was about to stop my 93 Corvette coupe in a red light when the check engine light turned on, a black smoke ball came out from the muffler and finally the car stalled. I tried to start it again but only worked 30 minutes later. Any ideas?

 

[ecss]

Take a piece or wire or paper clip and short pin A to pin G on the diagnostic connector
located under the dash above the drivers right knee area.

Turn the ignition On (don't start the engine).
Look at the dash cluster LCD. You should see some numbers scroll on the display.
It will stop with 1.0 displayed.

Note what numbers or number are displayed for module 4 which are trouble codes for the ECM.

Module 1 is the CCM
Module 4 is the ECM
Module 9 is the ABS

 

[tave]

Found the connector!

Hi ecss,
Thank you very much for your response
I've finally found the connector loose under the dash and as you said, shorted pins A to G .
For module 4 (the smaller number under the big ones) the code H15 is displayed.
Just FYI, for module 1, codes H51, H72 and H74 are displayed.
Cheers!

 

[ecss]

Hi ecss,
module 4 the code H15 is displayed.
odule 1, codes H51, H72 and H74 are displayed.

Module 4 DTC 15 is an engine coolant temperature sensor low temperature indicated. The sensor
is screwed into the water pump. The two pin connector has a Yellow wire and a Black wire.
Remove the plug and verify the sensor isn't leaking inside the plug. Also verify the connector
is secure.

The 15 code indicates the computer thinks the engine temperature is less than -52F :ugh

You can look at that sensor by doing the following. On the dash cluster DIC buttons press the Gauges
button which displays the Oil temp. the Coolant temperature or the Battery voltage on the
dash cluster LCD. Keep pressing the gauges button until the coolant temperature is displayed.
When it displays the coolant temperature it should be what the engine temperature is.
Compare the temperature to the temperature on the analog temperature gauge.

If the sensor is not accurate, replace it. It just screws out. You will need to drain some of the coolant out or
if you're quick, unscrew it and screw another one it and you won't loose much coolant. :L

If you do this, cover the optispark with a towel so no coolant gets on the Optispark.

The 51 is an invalid pass key. The key pellet resistance did not match what the CCM was programmed for.
The Security light on the dash cluster should be on and the starter won't crank the engine. You have to wait
5 minutes before retrying. Could be a dirty or worn key pellet, bad contacts in the ignition key cylinder or the two
wires of the ignition key cylinder are going bad. Every time you turn the ignition key the two stranded wires
twist and eventually break.

72 and 74 are due to an aftermarket radio being installed. When you remove the factory radio some pull up
resistors are also removed so when the CCM does a power up self test it sets the two codes indicating something is wrong with the LCD and LED dimming circuits. SYS will usually flash in the LCD.

Below is a picture of the ECT sensor in the water pump.

Also the Technical Service Bulletin to fix the 72 and 74 which is to solder (2) 1K ohm resistors to the proper
wires.

Click the link below for the radio fix.
http://www.corvetteforum.net/c4/dave8476/index4.shtml

 

[tave]

Hi ecss,

As you suggested, I had the temperature sensor connector unplugged and it looks dry.
After plugging it again I noticed that the check engine light now turns off right when I start the engine even though it is always on when I turn the ignition on.
I have checked the codes again and the H15 is still there.
With the check engine light now off, I've driven the car for 40 minutes and it didn't stall.
I also compared the 2 temperatures (analog and LCD) and they fairly match.

 

[ecss]

When you turn the key to On the service engine soon/check engine light should be on solid.
It's controlled by the computer and is an indication the computer is working and the bulb works.
It should go off when the engine starts.

There are two types of codes C current codes
and H history codes.

History codes are codes that don't currently exist.

Some codes are always tagged H :eyerole

To clear the ECM codes you short A to G.
Let the display cycle and stop with 1.0

Press Trip Reset until you see 4.0
Press Trip/'ODO until you see 4.7

Press and hold ENG?MET until you see ---- in the LCD
Turn ignition OFF

With A and G still shorted turn ignition On

All codes should be deleted C12 is not an error code.

To clear the CCM codes (72 and 74)
After the display cycles and 1.0 appears
Press Trip/ODO until 1.7 appears
Press and hold ENG/MET until ---- appears.

72 and 74 will eventually come back because of the aftermarket radio.
Indicated by (SYS) flashing in the LCD.

Or you can delete all codes by disconnecting the negative battery terminal for a couple of seconds.
You will lose the radio presets and when you turn the ignition on the HVAC will do a recalibration
of the blend door which takes about 20 seconds. (Only for auto climate control HVAC C68).

If the black smoke and 15 sets again compare the digital display with the analog
display and see if they are close. If it happens again it could be a wiring problem or the sensor
is flakey or the reseating of the connector plug may have solved the problem.

 

[tave]

OK! Thank you very much! I've REALLY appreciated your help!
Best regards,