Looking for answers or a highly highly highly educated guess. Fi rst, I have a 2002 bonneville sle. I bought it with 70k, at 98k I had an issue with it stalling while driving. Not stalling at idle or a stop light, but stalling going 70 mph or 55 or 35. Sometimes it would fire back up, other times it would take a while before it would start back up. Dealer told me the cam sensor and crank sensor shorted out the pcm. So i had new sensors, new wiring harness, and a used pcm put in. Never had a problem with it stalling again and still havent to this day. What i believed happened, was during one of those stalling sessions, i developed a rod knock, so at 104k i dropped a new motor in it which is a series 3 and came from a 2006 buick lucerne with very low miles. I could tell that it was very new and clean because when you drop $1400 on a motor you have every right to see it before it goes in your car. The oil pan even looked like it had never seen oil. My first oil change after 3500 miles had oil that wasnt even black. The new engine came with a 3 year warranty/unlimited miles. So i am pumped right? Thinking i got this awesome engine and i should be able to easily put 200k on it, right? WRONG! Car has 112k on it, so just over 8k on the new series 3 engine, and it has developed a rod knock. Its all getting taken care of with no charge to me except the inconvenience. Now, there is one thing i need to add, my oil psi gauge will constantly fluctuate between 20 and 40 after my car is warmed up and it is at an idle. I would assume that pressure should be at a constant bc the rpms are at a constant. It has done this since i bought it.

So one 3800 had a rod knock at 98k, another which had no more than 10k developed one as well. I truely believe i am the only one that has had problems with two of these great engines in the same car. I think the problem is outside of the engine. Any ideas?

By the way, The first engine actually blew when i was driving so it was definitely a rod knock.

I can't speak for the Series III, but my Series II has oil pressure around 35 psi when idle, 40-60 psi when running.

My best guess is that your oil wasn't circulating properly. If you're draining clean oil after 3,500 miles, there'* definitely something wrong with the oil circulation. I'd hate to see your cylinders.

I've seen quite a bit of these engines. Lots of different things. I personally had the stalling at highway speeds as well. Ended up being only a crank sensor.

On to the real puzzle though, why two engines.. I've seen things happen and from time to time these engines are picky about being transplanted. When they transplanted it..they had to swap the oil pan, UIM, Alt bracket and rear exhaust manifold. Nothing there should make the L26 get rod knock. Unless they didn't clean the oil pick up tube well and or if they didn't get a good seal on it where it meets the block.
On the fluctuation.. I'd check the pressure sender. They do leak and give odd readings at times.

BTW I'm the master of the 10 mile motor. Literally... and it would have blown sky high had I needed another mile.

It'* simply a good clean motor. My oil is clean after 3500 miles and I beat the snot out of it. You'd thnk it should come out very dirty. A clean motor that is taken care of..can drain clean oil.