could anyone help me with an intermittent check engine light,ive only been able to catch it once long enough to get my code reader on it and it gives me code 43,which is electronic spark timing,electric spark control,had it in the shop awhile back and computer showed bad oxygen sensor,replaced that,got it again and the mechanic told me to try the ignition module,replaced that,,still the same,when the light comes on most of the time its when the engine is cold,it runs like crap,very mushy throttle,as soon as the light goes off she runs great again, a friend told me its probably the knock sensor,,this is driving me crazy,,,any ideas would be greatly appreciated!,,this is a 91 trans am ,305 tpi,5 speed,stage one chip,flowmaster,throttle body bypass,

 

Code 43 -- ESC electronic spark control module.
Electronic spark control is accomplished with a module that sends a voltage signal to the ECM. When the knock sensor detects engine knock, the voltage from the ESC module to the ECM drops and this signals the ESC to retard timing. The ECM will retard the timing when the knock is detected and rpm is above about 900 rpm.

Code 43 means the ECM has been low voltage at CKT 485 terminal "B7" for longer than 5 seconds, with the engine running or the system has failed the functional check.

This system performs a functional check once per start up to check the ESC system. To perform this test the ECM will advance the spark when when coolant is above 95 degrees C(194 Degrees F) and at a high load condition ( near WOT). The ECM then checks the signal at "B7" to see if a knock is detected. The functional check is performed once per start up and if a knock is detected when the coolant is below 95 C then the test has passed and the functional check will not be run. If the function check fails, the SES light will remain ON until the ignition is turned OFF, or until a knock signal is detected.

Ok to test the stuff out to find what is wrong do this.
1.

Clear Codes

idle engine for 1 minute or until a SES light comes ON

read new codes

No code 43
This test will dtermine if the system is functioning at this time. Usually a knock signal can be generated by tapping on the right exhaust manifold. If no knocksignal is generated, try tapping on the block next to the area of the sensor. Follow the following steps.


run engine at about 1500 RPM

trans in park/nuetral and at normal operating temp

tap engine block in area of knock sensor and check for rpm drop


If the RPM drops the problem is intermittent, if there is no rpm drop then there is no problem
But if you do get a code 43
3.with the engine idling check terminal B7 with a VOLTMETER to a ground and note the voltage

If over 6 volts it is a faulty connection at ECM terminal B7 or ECM
If under 6 volts do the following

4. Ignition on, but engine stopped
recheck the voltage at ECM terminal B7
If over 6 volts change the ESC module
If under 6 volts do the following

5. Ignition off
disconnect ECM "A-B" connector
turn ignition on and recheck voltage
If over 6 volts Replace the ECM
If under 6 volts do the following

6. Disconnect ESC module. check voltage from ESC connector terminal B to ground.
It should read battery voltage
If not OK repair open in CKT 439
If OK do the following

Check for open or short to ground in CKT 485. If not open or shorted to ground, it is a faulty esc connection

 

Well, that would certainly be the manual's way to check it. Even easier...bypass the knock sensor w/ a 3.9k ohm resistor to ground (you can cut in the engine compartment or the dash.) Now drive around. Have you stopped getting that intermittent code? OK, you've established your sensor was bad (or a remote possibility is the wire between where you bypassed and the sensor is bad). If you still get the intermittent code even with it bypassed, i'd look towards a bad ECM/ESC circuit in the memcal.
...ed

 

I pulled out nearly every hair I had left in my head trying to figure out why I was getting a code 42. I checked every possibility.

Guess what it was

A loose female in the connector to the ECM.

Try a wiggle test on them and make sure they are all making connection.


------------------
Mike L.

The Weapon of Choice:
1987 IROC Z 5.7 TPI A4 3.27 Borg-Warner four wheel disc
Mods: 2300-2500 Stall Converter, Shift Kit(GM parts), TPI Specialties Stage 3 PROM, Modified Airbox w/ K&N's, homemade cold air, Relocated MAT sensor, Gutted MAF, 160* thermostat, MSD 6A, Accel 8mm Wires, bypassed TB coolant, Flowmaster 3 chamber single 3" in/out muffler, 3" MAC mandrel intermediate, custom dual !cat Y-pipe. airfoil, ported plenum. !smog, few others I forgot...???

**BOYCOTT LAPEER DRAGWAY**