ok, this is kind of strange. Anyone experience this? I know how to properly set my timing on my 91' tpi car. Ok, i disconnect my est,Started the car, loosened the dist. hold down bolt ,Start the car, and advance or retard the dist. Ok.next , I have always then turned the car off , disconnected battery cable, connected EST and then re-connected neg. battery cable after a minute or so and then driven the car. Now i noticed something strange the other day. If i disconnect EST, start car, set timing, turn off car,then plug EST back in and drive it without disconnecting the battery for a minute or so, then for some reason i am able to raise timing to a point where it should be pinging and knocking. In other words ,if timing was already at 6* BTDC(no knocks) and normally it would knock at 8*. Then if i go and advance my timing and leave out the last step of not disconnecting and then re-connecting battery,then i am able to have no knocks at 8* and enjoy higher timing. WHY IS THIS??? Some one out there knows.

 

In other words , imagine setting timing without disconnecting and re-connecting negative battery cable afterwards. I do not get a check engine light after i plug the EST back in. Yet the car can run this way at a level of timing in which it would otherwise knock and ping at. I wonder why?

 

I believe to only real reason to disconnect the battery is to reset the 42 error code caused by unhooking the bypass wire. The ECM/program will try to adjust the advance/retard for whatever the engine needs based on sensor input.

 

Nope , you are incorrect. If you dont disconnect battery,the ecm will not recognize the timing change. I have experimented with this before.I found this out on my owm ,I guess.LOL. Question answered

 

Well, all I can say is that my ECM does recognize the changes and GM and every resource that I can find, says that disconnecting the battery is to clear the code. Now yours may be different, but as you know, running at 2 degrees before TDC is not normal and you may have other things going on. It certainly doesn't hurt to unhook the battery if you want. Just saying, I don't need to.

 

You give the ECM far too much credit.

The ECM has absolutely no clue that the base timing has been changed.

I've never heard of disconnecting the battery after setting timing.

 

Well on mine this is what i noticed about that: Say the timing is at 2 * BTDC and it runs great, right at the edge of detonation. Ok, so if i normally raise it to 4*BTDC the car knocks. So, i then go outside and disconnect the EST and raise the timing to 4* BTDC. Then just simply plug the EST back in and go. Now, if i do not un-hook the battery at all , i can run the car at this timing with no pinging. Car will accelerate a little better at part throttle too like it should with the timing slighlty advanced. Now if i was to have unhooked the battery after i raised that timing, waited a minute or two and plugged the est back in and THEN re-connected the battery. Then the ecm would only then recognize the change in timing. I just noticed that pattern . It would be this: Remove coil, remove egr solenoid, Disconnect est, loosen dist. hold down bolt, re-connect egr solenoid, remount coil, start car, adjust distributer, turn off car , remove coil again, tighten hold down bolt, re-mount coil again. start vehicle to double check timing. Now, VERY important, disconnect battery, THEN re-connect EST, wait about 30 seconds for ecm to re-set, then re-connect battery. Then drive. I usually put it in D2 and listen for pinging

 

You're doing all that for what is a two minute job? First of all, 2 degrees is wrong. 6 degrees is correct and matches the initial programming in the PROM. You CANNOT set timing with the Bypass wire connected. You will be fighting the ECM for control of the timing. Set it at 6 degrees and forget it. Set at 2 degrees, you are essentially removing 4 degrees across all of the spark tables. You should not hear any pings or knocks at any setting between TDC and say 10 degrees. If your engine does not run well at 6 degrees you have other problems. probably mechanical. If it pings at idle in drive you definitely have problems. The ECM could care less where you set the timing initially. It assumes that you are correctly setting it to 6 degrees and that is where it starts from. I still say the ONLY reason to disconnect battery ever is to reset the codes. True, the ECM will start in learn mode again but that is normal after every start sequence. I also don't understand your references to removing the EGR and coil. Why? I think I'll stick with the tried and true method shown in all of the books. That's what works for me.

 

I would never set timing with the Est connected. The coil and egr solenoid have to come off on an F-body so you can gain acess to the distributor hold down bolt. Then the coil should be re-connected, when the vehicle is started to ground it.