Suggest to start with a basic battery/alternator check. My diy’er version, battery should measure about 12.6 volts before first start of the day (car sitting unused overnight), then immediately after starting the engine, 13.5-15.5 volts. Measure w/lab DVM, don’t relay on car gauge. Does your car pass that test? If not, what voltages do you measure? Note that it is possible to fail this test with a new battery and alternator.
When you say “engine doesn’t turn over” I presume you mean you don’t hear the normal rrrr rrrr rrrr cranking sound when the key is in “start”. That’s called a no-crank of fails-to-crank in mechanics parlance. Do you hear anything at all with key in “start”? Just a click?
Common reasons for fails to crank
Battery is faulty or discharged
Battery connections are corroded, coming loose, etc.
Battery’s ground connection corroded. Locate the wire from the battery negative to where it connects to the chassis. Any corrosion there?
Transmission safety switch faulty.
Security system faulty, thinks you are trying to steal the car.
Since this occurred after replacing serpentine belt, double check you’ve reconnected all the wires that you had to disconnect for access. Especially wires going between alternator and battery, both power and ground. Did you change the alternator mounting? If so, double check it remains properly grounded to engine.
Given that you didn’t make any changes in the area of the ignition switch, I’m guessing the security system warning is a red herring, problem is some fault with car’s electrical system, and that dashboard warning is just a symptom. Weird electrical system symptoms can occur in cars if battery isn’t making a solid connection, b/c the battery is necessary to smooth out the alternator’s voltage spikes. Could also explain the poor engine performance when it does start.
You may have to pay a shop to use their lab o-scope to check for that.
Double check you are using the correct diameter alternator pulley.
OK, Thanks to all, again, for so many helpful replies and suggestions, early and more recent. I’ve been OOC for the day.
As of this evening and after running the LeSabre to town and back (in a failed search for auto trans sealant) I now know more about car’s apparent issues but I’m still “scratching my head”!
Two main issues: (1 Unpredictable cranking. 2) Running rough
Crank/not Crank: Continues to be problematic. Car fired right up this morning and at several other times today, but after town trip it went back to being unpredictable. However, I THINK this issue may well be centered in the key ignition. It APPEARS that if I just keep switching the key back and forth, a connection eventually gets made. Car fires right up. I’m gonna try some graphite tomorrow.
This issue is very debilitating. Can’t trust the car for out and about until I figure this out.
Car battery puts almost 13 volts at start up (when it cranks!) And it soon levels about just above 14, so it SEEMS like the voltage and amps are there but the connection is no guarrantee.
Running rough…At present judging by the way the car behaves and given that the “check engine” light is flashing when car is running…I think car is not running on all cylinders.
Helpful guy at A. Auto could not use his diagnostic tester because I was afraid to cut the car off in town.
He said it sounded like a "ground issue: to him.
I don’t really know what next to nail this issue down.
I tried stop leak once and it clogged the entire cooling system. Had to pull the head and clean passages. Not a good idea - radiators are cheap. Unless bought at a stealer. Good part about gm (and suchlike) is that cheap aftermarket stuff is actually better than whatever junk gm slams together.
I opted against the stop leak. Wanted to see if the JBWeld Steel Stick would work. It did!
Appears now that maybe…just maybe…the ignition/crank issue might have been resolved by my just unhooking both leads (+/-) from battery and leaving it long enough for the car brain to reset to correct connections. I say this advisedly. I tried this on advice from a friend who said it would work “for a while.”
I seriously doubt jbweld will last - it’s not flexible in terms of heat expansion/contraction at least compared to aluminum so it’ll likely crack and separate from the fins but nevertheless good luck!
I do understand you being reluctant to pump money into a buick…
I will be of little help but I too would wonder about jb weld. If you have reasonable access, you can use an aluminum welding rod. Only problem is it is more like solder than a weld so will drip some, but will hold up. A guy once welded a leak in my transmission line with silver solder, but that was steel.
Disconnecting the battery will clear codes and will return the various settings back to factory original. Then when you drive, it will start using the readings from the sensors. If it clears up the rough running, it is related to a bad sensor reading/performance. By clearing the codes though, you just don’t know which one. If/when it returns, you need to get the fault code.
JB “Steel Stik”: I had my doubts about it but it came well recommended as a ready fix. I kneaded the compound well, pressed it into the radiator aluminum fin section. I let it cure well more than the minimum hour. So far it’s fine. It’s day by day with this car for now, anyway, until I see how well I can address the rough running and transmission issues.
Getting the faulty code is next step tomorrow. I already took it to a local auto parts store Friday or so to have guy get a read on the code. But I could not follow through on that because at that point, I was afraid to cut car off.
So with the cranking/ignition problem remedied, temporarily or otherwise, I’ll go get the car hooked up for faulty code tomorrow. Fingers crossed.
So far no luck finding any trans sealant. Get that at Oreilly’s tomorrow I hope. At least give it a try.
It’s all an ongoing pain in the backside but I have to take it bit by bit. If I can get a faulty code read out tomorrow, I can then get after that issue.