While on our trip through the Rocky Mountains in our newly purchased XLR our engine began Knocking on start up. Very noticeable the first time and variable since. I have some experience with engines and this sounds bad. Unless there is some issue with oil pumps priming on these engines this is excessive bearing clearance/rebuild. Engine only has 29k, previous oil changes have been at 7k intervals and the present oil is new and at proper level. We are under GMPP and I am going to take it in to the dealer for diagnostics. Any similar experiences? More to come...

Dave

Dave:

Sorry to hear of your problems. To my knowledge I haven't heard or read of this issue before.

FWIW: I agree with your decision to take it into a dealer and let them decide what is going on. That way if they don't locate the source, you are still on record in the event something more serious occurs.

Please let us know how this is resolved.

Best wishes

Jerry

What kind of Gasoline are you using in the car? I noticed if you use a no name gasoline brand that you find at a redneck gas station it can cause a ping/knock sound.

We were on the road but using various name brand gas, 91 octane or higher. It has lasted through a few tank fulls. It happened first after a long mountain run and a 1 hour lunch break. The engine temperature while up there peaked at about 230 near as I could tell from the gauge. It normally runs much cooler, about 190. The oil pressure got down to 20 PSI idling at that 230 temp. Normal cruising was at around 60 PSI.

Dave

Hmm well depending on what the Temp. was outside it could affect the car. I remember when I drove down to California last year and was going up long winding roads at only about 30 mph my XLR completely shut down. It was about 100 F outside and I had to pull over underneath a tree and open the hood and let her cool down for about 1 hour. The whole dash lit up like a Xmas tree lol. Sure enough after the hour it was okay functioned as normal.

Hmm well depending on what the Temp. was outside it could affect the car. I remember when I drove down to California last year and was going up long winding roads at only about 30 mph my XLR completely shut down. It was about 100 F outside and I had to pull over underneath a tree and open the hood and let her cool down for about 1 hour. The whole dash lit up like a Xmas tree lol. Sure enough after the hour it was okay functioned as normal.

Had this happen on a few other vehicles, too, but it was for no apparent reason and never came back. Stuff like this always scares me pretty bad because you never really know what it is. I guess if you can, pull codes and see what's up. I wish they made on-board diagnostics on most cars a little more sophisticated, however. Stuff like dates, engine loads, and gauge readings at the time of a problem would be SOOO helpful.

It was getting progressively milder since the first and loudest occurrence. Now it is gone completely, for now...no knocking on start up. It never did knock while driving that I could notice, even on heavy accel or reving. I'm gonna keep driving it like I stole it! More to come and thanks for the responses.

Dave

Had this happen on a few other vehicles, too, but it was for no apparent reason and never came back. Stuff like this always scares me pretty bad because you never really know what it is. I guess if you can, pull codes and see what's up. I wish they made on-board diagnostics on most cars a little more sophisticated, however. Stuff like dates, engine loads, and gauge readings at the time of a problem would be SOOO helpful.

I totally agree that if we were to see whats happening on the car and where the problem is being called from then we wouldn't be so lost all the time and be able to sometimes fix the issue ourselves without resorting to the dealer.

I don't know if you ever read a post I made with unlocking a secret menu in the GPS section. Since I made the post no one ever reported on finding anything else but I still play around with it and still have no luck unlocking any of the menus.

I totally agree that if we were to see whats happening on the car and where the problem is being called from then we wouldn't be so lost all the time and be able to sometimes fix the issue ourselves without resorting to the dealer.

I don't know if you ever read a post I made with unlocking a secret menu in the GPS section. Since I made the post no one ever reported on finding anything else but I still play around with it and still have no luck unlocking any of the menus.
That's why a very few owners invested in Tech II tools. Unfortunately, the rest of us will need to rely on our own instincts and experience, the forum, the tech II owners or the dealer.

That's why a very few owners invested in Tech II tools. Unfortunately, the rest of us will need to rely on our own instincts and experience, the forum, the tech II owners or the dealer.

Yea I was looking into getting a Tech 2 also but to spend $2000 on one I can't justify it yet. I however found something interesting with some 3rd party software that works under my laptop allowing the same diagnostics as the Tech 2 tool.

If we keep this car past the warranty expiration I may be one of those who buys the tool.

After doing some reading about the Northstar engine I am beginning to think that I might have dislodged some carbon on that mountain run do to high heat and high vacuum from overhauling in low gears. Then got it lodged in the squish area of the cylinder/head. Has anybody heard or experienced what they call "cold carbon rap" on these engines? The previous gal who owned this car may have dogged it around. The more I WOT it the better it seems to run.

Dave

Sounds logical.

I wonder if the dealer has an additive that would help to dissolve the deposit.

Please keep us informed.

Jerry

Yea I was looking into getting a Tech 2 also but to spend $2000 on one I can't justify it yet. I however found something interesting with some 3rd party software that works under my laptop allowing the same diagnostics as the Tech 2 tool.

Which software might that be?

If we keep this car past the warranty expiration I may be one of those who buys the tool.

After doing some reading about the Northstar engine I am beginning to think that I might have dislodged some carbon on that mountain run do to high heat and high vacuum from overhauling in low gears. Then got it lodged in the squish area of the cylinder/head. Has anybody heard or experienced what they call "cold carbon rap" on these engines? The previous gal who owned this car may have dogged it around. The more I WOT it the better it seems to run.

Dave

My understanding of the N* design is that it loves to be thrashed. Indeed, it will benefit from it, keeping the rings moving properly and oil flowing correctly. Coasting it around town will not improve the N*'s life I gather.

I would think you have freed something up perhaps. Maybe a valve adjuster was sticking a bit. An early oil change might be a good thing if it is picking up deposits.