Pontiac Repair: Bad Quad Drivers Showing on Scan Tool, throttle position sensor, advanced auto parts

Question
QUESTION: Hello Sir,

I have a 1993 Pontiac Grand Am 2.3 ltr engine code 3. I replaced the head gasket about a year ago because it was blown. Before replacing the gasket, I had the head checked for cracks because of a recall on some of the heads for that year and engine module. There were no problems found. After replacing the head and gasket,the car performed well for about a year. It never ran hot. While driving on day I heard a loud 'clank" like something came loose in the motor and the car lost power. It would barely get up any speed. I did a compression check on it and checked for proper vacuum. Compression readings were within 80% from lowest to highest cylinder pressure. The entire exhaust system was replaced with OEM parts.I scand the ECM for codes with a scan tool. No codes found. All the components, IAC, Throttle Position Sensor etc. are within specs. But I did notice that there were three BAD quad drivers indicated on the scan tool. Therefore, I replaced the ECM with a new one from Advanced Auto Parts but the scan tool still said that there were 3 bad quad drivers. Note: I am aware of the difference between quad drivers and output drivers. I've tried to find a diagram of the ECM through ALL DATA that would tell me what the quad drivers operate. No luck. The only thing I can now think of is that either I purchased a bad ECM, the Prom/Cal Pak is bad or my ignition module or coils are weak and are not putting out enough voltage supply. Oh, yes I also replaced and properly reset the timing chain, slides, tensioner, and cam and crank gears. Any ideas?

Thanks
Jonathan

ANSWER: Hi
is it setting QDM codes 26, 27 or 28?
QDM code 26 is the MIL (service engine soon) control output.
QDM1 code 27 is the TCC solonoid and the EVAP Purge solonoid valve outputs.
QDM2 code 28 is Coolant fan relay, A/C Clutch and "TEMP/CHECK GAGES" light output.
You can use your Spark tester (graduated scale type)and check voltage output. Remove the coil housing cover. then, in place of the short plug boots, get some short (6-12 inch) plug wires and test that way. It should jump AT LEAST 70kv. Check your coils and coil housing, like said you are.
PLease I hope this helps, if not follow post back.
Good Luck
Pawl

---------- FOLLOW-UP ----------

QUESTION: Hello Pawl,
Thanks for your reply it was very helpful. In answer to your question concerning QDM codes, no it has never set any codes of any kind. The only codes available for this particular year that is related to a QDM is code 28 according to AllData. I also for got to mention that I also replaced the IAC sensor due to rough idle. Yes, I did set the new IAC as required by grounding the ALDL for 5 seconds, but I am still getting a rough idle. The motor shakes slightly and all the motor and transmission mounts are good. I replaced the IAC because the was no change of RPMs when the car is put into gear. It now has only a slight change in RPMs. I have promised this car to my son so that he can get back and forth to school starting this 2007-2008 school year. Do you have any more suggestions?

Thanks
Jonathan

Answer
Hi
Getting back to original post, have we attempted to determine what the "clank" was you heard while driving?
Have you yet checked the coil housing/coils?
Cyls 2/3 should have 5-8ohms from coul housing tower to tower.
1/4 same. any resistance between like 2/4 or 1/3 the housing is faulty.
any coil with hight\er or lower resistacnce should be checked closer.
Look at the coild for burned spots in the corners fartherest away from the outputs.
I will be waiting reply.
Pawl