I have a 1996 GMC Sierra 4X4 5.7 litre engine. It keeps throwing a code that indicates the ignition control module is bad...I replaced it and it ran great. But the check engine light keeps coming on. It will intermintally come on and go off when I restart the engine. Now the engine is dying when it gets hot again, just like it did before i replaced the module. Why woud it keep making the module go bad?

Do you know how to test fuel pressure ? With a gauge ? How to test for spark ? Pull a spark plug wire an hold it near ground (metal on the engine ) Have a helper crank the engine . ( turn the key to start position ) Before replacing parts randomly you need to find what system isn't working correctly . Fuel , ignition , engine mechnical (compression ) P0700 is a transmision code
https://www.autocodes.com/p0700_gmc.html Or a bad transmission control module is shorting out the system . Your best bet mite be to take your vehicle to a qualified repair shop .

If coil near plug, the computer controls spark.
How long since a tune-up? Any applicable trouble codes? Are you missing anything besides spark? Engine cranking, you used a gage and you have good fuel pressure? Also, you have fuel injector pulse?
What is litre size of engine?

This can be caused by anything limiting fuel pressure or ignition spark. Tune up items, bad coil/module, bad fuel pump, filter, relay, bad converter, muffler, dirty air filter, vacuum leak, EGR, or others.

Depending on the actual trouble code, the problem may be the ignition module inside the distributor or the coil.

Testing of the fuel and ignition systems is in order. Intermittent problems need testing when the problem is present, otherwise it won't help find the problem.
I would start by checking for spark on a spark plug wire (or two or three plug wires, in case it may be a bad coil), during those times when it won't start. You need to see a blue, snapping spark to verify ignition system is working.
To check the fuel system, have the fuel pressure checked, and the injector circuit checked. Good that you hear the pump, but you don't know if fuel pressure is correct, or if fuel is getting into the cylinders. One short test is to spray starting fluid or carb cleaner into the intake while engine is cranking. If engine fires up for a few seconds, you know it is a gas related problem.
If ignition system is the intermittent problem, could be failing coil or coils, ignition module, crank position sensor, even the computer, or a wiring problem like a bad connection. Testing of each component will be required, or you could start throwing new parts at it, like many people do, until you find the bad part. Find a reputable mechanic-there still are a few, lol.

replace the ignition module or pickup coil located under the distributor cap ignition modules work when cold and will stop firing when they are warm when they r going bad

Stop throwing parts at it.
Is it a 5.7 eight cylinder ? I'm not aware of a 1990 model with a 4.7 engine.
If the check engine light is on you should check the computer for trouble codes next.
It could be a faulty injector, or fuel pressure regulator, or any number of things.

There are two ECM fuses - marked ecm 1 and ecm B.
ECM B powers the fuel pump and the Veh control module which handles most of the sensors.
ECM 1 powers the ignition module, coil, injectors and the rest of the engine sensors.
You may need a repair book with diagrams to check all of the circuits for shorts.

CODE 42 Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.
During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.
An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.
The conditions for setting this code are:

• System in BYPASS mode but the ignition module is still controlling timing
  - or -
• Engine speed > 600 RPM with no EST pulses (ECM controlled timing) going to the ignition module for 200 msec.

Typical causes for this code include:
1) BYPASS line is open or grounded
2) EST line is open or grounded
3) PROM or CALPACK not seated properly in the ECM
4) Poor connections between ignition module and ECM
5) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise)
6) Faulty or incorrect ignition module
7) Faulty ECM


Thank you for using fixya and keep us posted

From http://www.obd-codes.com/trouble_codes/
The P0300 is a misfire and P0506 indicates low RPM at idle.

A misfire can be caused by poor ignition (spark plug, plug wire, coil, ignition module/engine control module).
OR
Poor air/fuel (air filter, fuel injector, fuel pressure, fuel filter, fuel pump, bad gas, or engine control module).

Check your maintenance requirements and see if any of these items are due for replacement first.