Non p-car, well... Pontiac, strange engine issue. any ideas??
 

Hey all, I have been scratching my head over this all day, I figured I would see if anyone here has an idea as to the issue. A friend of a friend was going to scrap a 2000 Pontiac Grand am because it had "problems". A local shop wanted close to 3k to repair the problem. So, I ponied up $300 for it since the body is PERFECT figuring I could make back the $300, even at a salvage yard. Anyway to the issue at hand.

The car has the 2.4 "quad 4" engine that runs awesome at startup, and idle (oil pressure is good, no timing issues of any sort and really a quiet motor). However as the rpms approach 2800, it starts to make a "knocking" sound. At first I suspected timing chain slap, so I removed the t-cover: removed the chain, tensioner, and guides. The chain hasn't stretched a bit, and the guides are barely worn. Plus there are no "scuffs" on the timing housing indicating any sort of chain slap, damn! (Yes, I double checked the timing before removal, and it was fine, I could slide bolts on both the intake and exhaust cam alignment holes with crank at TDC)

Normally, I wouldn't expect this to be a rod bearing issue since it is silent at idle, but I have only worked on a handfull of these quad 4 engines... Any ideas?

TIA,
-Nick

so if the shop wanted 3K to fix the problem...
what problem did they intend to fix?

Any error messages ??

Balance shaft out of phase?

Something broken in the valve train?

My mother in law has the same car, the issue it has is piston slap, she couldnt afford the repair (also about 3K) so she is just going to keep driving it until it croaks

I've had rods that you couldn't hear knock at lower RPMs. Especially if the bearing has spun in the big end. I'd start by removing one plug (remove not just unplug) at a time to locate which rod it might be.

I seem to remember that the quad 4's had a lot of issues with piston pins, skirts, cyl wall ovalling, etc. Most would last the life of the engine but the noise is annoying

Thanks guys!
Let's see if I can answer everyones questions:
The shop that gave the quote was just going to drop in a used engine, and didn't do any sort of trouble shooting. Their statement was "it just needs a new motor"!

There are no trouble codes what so ever, not even a knock sensor code (though the OBD is working correctly as I can still force codes by unplugging sensors and plugs: knock, misfire, etc.)

I drained the pan first thing, and there wasn't any metal on the magnet or in the pan, so I still don't think it is a bearing. Tomorrow will be killing each cyl one at a time, but with this engine, it is a real PITA with the coil pack in the top cover, and direct spring connections to each spark plug... It wont be fun.

I think loonybin may end up being right on this one. If all else fails, I'll probably end up pulling the head, and sliding the pistons out to measure the cyls. Of course that will prove to be fun with this engine as the chain driven balance shaft assemb. resides directly beneath the crankshaft :( So, just to get to the rod bearings I have to pull the pan, baffle, oil pump, balance shaft chain, balance shaft assemb, then each rod cap...

Me thinks this may turn into a parts car real soon!

-Nick

It's piston slap. It's a known issue with Quad Fours.

Those motors, btw.....junk.

Still, buy it for 300 and drop a low mileage Quad four in it, and you can make yourself a couple grand in resale.

Sniper wins!!
Sure enough it was piston slap on cyl #1.
Next time I'm in Philly, I'll get the first round of drinks!! After that we'll have to drop challange coins to see who buys from there on out :) Good call!

Thanks,
-Nick

For anyone else in the future with a search:
pontiac, gmc, quad 4, 2.4, grand am, knock, at high rpm.

Glad to help. Sorry it wasn't better news.

Still, if you can pick up a used motor at the yard for say 500 or 600, even if you pay another 600 to have it installed, you're only into the car for 1500. In these times, a sporty little 4 cyl pontiac in really nice shape is worth a good $2500-3000 around here, person to person(way more for a used car dealer). Nice, easy way to double your money.