Need help: internal engine damage? skipped timing?

[redbonneville]

Hi Club,

2005 GXP, 75k miles. Does not use coolant, but car leaks oil from valve covers, and always has after I bought it used with 45k on it. I never got around to it. Usually change full synthetic at 5k mile intervals. When getting close to 5k, sometimes I would need to add a quart. Never really a big deal. I was out of town and the low oil light came on for my wife. Typical as it was 5,200 mi from last oil change. She drove it home. Drove beautifully. Pressure stayed fine, just a quart low. She parked it and added about a quart of Delvac in the morning. Ran it for three more days, totally normal. When she tried to start it in the morning last Wednesday, it ran extremely rough. Like the engine was running on 3 cylinders. When parked it was fine.

I tried starting it yesterday to finally diagnose it, and the engine was extremely unbalanced, and a loud noises seemed to be coming from under the intake. I’m thinking it is missing badly or the timing is off. Maybe even backfiring into the intake. Code P0300 was the only code. I checked for misfires with the tech2, and 4 and 8 were misfiring. Historically the tech2 says 2, 4, and 8 were misfiring. Checked wiring because how did two or more coil packs die at once on the same side? It looked good. I cleaned the connectors and applied dielectric grease. I replaced 4 and 8 coils with old ones I had. Pulled plugs while I was at it on 4 and 8 they were fouled and it looked like oil—no fuel smell—cleaned and reinstalled.

Restart. Same issue, but Tech2 stopped witnessing constant misfires on 4 and 8. Only said 2 misfires each in about 2 minutes of running. New code for map sensor. Had to quit for the day.

I did the oil change today. I observed some slack in the timing chain, maybe 1/4 inch of deflection in the chain with your finger on it in the oil fill. It is definitely not tight. I’m not sure what is normal there. The old oil had silver dust in it, but no shavings or flakes. Hard to see any sparkles. It was really black, and seemed to have layers of density. I am going to cut open the old filter. I pulled all 4 front side spark plugs, all were fouled, no mechanical damage. Seems like no spark or pig rich, but no fuel smell. Haven’t looked at the rears because of the PITA factor.

I’m going to put in a map sensor, but I don’t think that’s going to do it. It might be confused by the possibly dead cylinders. I’m going to get a fuel gauge to do an injector test with the tech2. Maybe it’s pig rich because of the map or a bad regulator? Why no fuel smell on the plugs?

Once the engine goes into loop and starts to read the o2 sensors it can stay running and trims the fuel to help a bit, but it is extremely rough—not drivable at all. It stalled one time in all the testing.

Any help would be appreciated. I’m worried a bearing or two are toast based on how bad it is running, lor 4 cylinders are dead from a bad crank sensor or cam sensor. Seems like it is running on 3 cylinders.

Thank you.

[harofreak00]

I see the Northstar with ignition coil issues all the time. I know you replaced some coils and cleaned the plugs, but I would start with all new plugs and new coils. Even the cheap ones seem to work well: https://a.co/d/bFzTqnV

[redbonneville]

Update: So I did the map sensor, new plugs and new coils for the left/front bank, 2,4,6,8. tested for power on plugs checked okay, power to injectors, tests ok. No change. I could feel the misfiring into the intake on those cylinders as it produced heat.

Today I pulled all plugs and did a compression test. Rear plugs looked great. Compression on 1,3,5,7 was 190, 180, 190, 200. Compression on 2,4,6,8 was 0,0,0,0. With the plugs pulled you can sometimes hear the valves hitting the pistons. This all says timing skipped somehow. The chain is still there and still rotating the cams on the front/left bank, but they are open when they should be closed.

Anyone ever swap a head and timing chain with the engine in place? Is that foolish because there will be damage to the bottom end from the interference or from bits of metal?

Maybe I have to pull the head to know how bad it is. Any thoughts appreciated.

[harofreak00]

You wouldn't be able to work on it in the car because the front bank chain goes behind the rear bank chain , meaning the rear chain would need to come off as well. The Northstar simply isn't designed to be worked on while in the car. You'd be better off just getting a used replacement motor.