tech2

the used engine is out of what model year? can the wrecking yard confirm it ran fine for them?
my guess, and that's all it is without being able to do a visual, the timing belt has jumped a tooth or maybe a throttle body problem.


maybe pull the front cover and inspect the timing marks....its needs a belt anyway by the mileage.
what is the fuel trim at idle and at 2500 rpm. if its at +25 at 2500 rpm, its not a vacuum leak. vacuum leaks disappear at high rpm do to drop in manifold vacuum.

Pellucid

Thanks, Tech2.

On the timing belt change, I thought that the 2009+ Aveo with Ecotech had a 100,000mi belt? This is a penny pinching job (I'm doing it for free + materials as a favor to a broke friend) so I was going to tell her to change it in 30k miles which would be 90k on this belt assuming it's the original.
I know the earlier cars had a 60k belt and issues with them breaking. You still think it need a belt at 60k?

The car the engine is now in is a 2010 and it came out of a 2011. This car is a 5spd, the donor was an automatic so I had to swap over the engine harness from the old engine. Everything plugged right up to this engine. I notice the pinout at the firewall is quite different between the two but the donor had A/C and was an auto so I'm not surprised by that. But the only new things in the car are physically on or in the engine, all the wiring is what it drove in here with.

I'm not sure how this board is about external links but here's the ebay listing I got it from. The pics are still up 10 11 Aveo Engine 1 6L Motor Vin E 8th Digit Opt LXV 353243 | eBay

I'm a total skeptic but from the looks of it and calling them I felt like it was a pretty good deal. Having been all over the engine it looks like it was well cared for, not a drip of oil and very clean internally looking through the filler. I'd say it always had synthetic oil. From the damage to the car I'd guess it was probably a runner when it got hit on the side.

The throttle body may be an issue but I'm going on the fact that it gives the same (engine off) readings as the one from the old engine to say it's probably okay. I attached the old TB to the harness but haven't actually swapped them. I guess that's going to be on the short list of things to try.

Does that 3,000rpm cutoff point for problems say anything to you? I'll see if I can get a reading at 2,500 but I don't know if I'll be able to. As soon as it's under 3k it falls off a cliff and the fuel trims spike and so far the only places it will old a speed is anything over 3,000 or sometimes it'll "idle" around 750-850 with the fuel trims up in the 20's, with short term dropping down to normal ranges for a second now and then.
That sharp, specific point where things go to hell really makes me think it's not just a vac leak, that and not being able to find one. There just aren't that many hoses on this car. MAP readings where in the 3.5-5 range at speeds above 3k, I'll double check on low speed if I can get it idling again.

Do you think a better (GM) scanner might capture something a HF scanner won't? I'm totally perplexed that it can run like this for multiple heat cycles and not throw any codes. In fact it had some permanent codes from the old engine for the cam position sensors and those went away.

I'll pull the upper cover and check the cam marks. Can I rely on #1 TDC on compression for the crank timing? I'd rather not pull the crank pulley off if I don't have to but if I do I do.

tech2

i don't think a factory scan tool will show anything helpful.

I would pull the lower cover and crank pulley and check all the marks.

I wonder if the 09 has a conventional 02 sensor and if the later models went to an air fuel ratio sensor? I assume the connector plugged in ok. what if you disconnect the front 02? Sorry, I really don't have any solid answers, just guesses.

cleveland63b

if theres no vacuum leaks I agree looking at 02 sensor data would be the next move, if its showing 25% at idle the ecm is trying to add fuel some reason, just need to figure out whats making it think it needs to add that much

Pellucid

Thanks for the input, guys.

Well nuts. I was hoping a factory tool would look more in depth or flag blips in the data.

All the Ecotec Aveo's (09+) use the same o2 sensor, according to Rock Auto and NAPA at least. I disconnected the front sensor and it stated and ran a little better, maybe. It hunted around a lot more, from maybe 750-2000 but it didn't seem to die out. I only let it run about a minute but it would have died from a cold start in under 15 seconds before.
So, I swapped in the sensor from the other engine. The one that came out looked sooted up but no more than I'd expect from running super rich for a minute. With the other o2 sensor from the old engine installed it ran the same overall, maybe slightly better but still showing 25+ fuel trim low speed. The sensor in the old engine only had about 10k on it.

One thing I noticed that might be new or I might have missed it that when it's revving along at 3500 or so the LT trim will be about 0 and the ST will be fluctuating in the negatives but every now and then it will flash to +25 then back to fluctuating negative. I don't hear any difference in the engine sound when that happens and it's so quick it would be easy to miss.

I checked the timing and it's lined up. I cheated, but I think it was okay. On the old engine I noticed a mark on the lower cover and a mark on the pulley. I checked that against the #1 piston and they line up at TDC, the cam marks also lined up then, spot on.
I did the same on the installed engine. I felt the piston rise with a dowel and then with a ruler against the dowel for the last 1/4in or so and when it topped out the two marks were line up, so were the cam marks. The belt and teeth look to be in great shape, I'd pulled the upper cover before I installed the engine. I also pulled it through tonight and looked at all the teeth, just to be sure. All look good.


I'm starting to think I need to go at it with the "fine adjustment hammer."

O2 sensor readings are about .7 to .75 volts on the downstream and .5 to .8 or so and fluctuating on the upstream, seems normal I think.

I guess tomorrow I'll get it running and start wiggling wires.

tech2

the downstream 02 are not used for fuel metering so pay not attention to them.


I have no clue...for giggles maybe try a idle relearn procedure.


hard to say with no service information. a fantastic pay site is identifix. You may be able to buy a day subscription for a small fee. I have used it in the past for unsolvable problems. type in your concern and it will list causes, what fixed it for others and straight forward testing procedures. It also has oem factory service information.
https://www.identifix.com/direct-hit/

Pellucid

Thanks for that link, I'll check it out.

Here's question though, have I just overlooked something very basic? I've read that if you change the engine/Crank Position Sensor you need to do a relearn on the CKP.

I didn't actually know that until the engine was in and I was finishing up the plumbing but I figured I'd start it and see how it ran. Maybe I got sidetracked by it running well over 3,000 and this has been the problem the whole time but I also thought it would throw a code if the CKP wasn't set.

I mean, it says this:
Note: The crankshaft position (CKP) system variation learn procedure is required when the following service procedures have been performed, regardless of whether DTC P0315 is set:
• Engine replacement
• Engine control module (ECM) replacement
• Crankshaft damper replacement
• Crankshaft replacement
• CKP sensor replacement
• Any engine repairs which disturb the crankshaft to CKP sensor relationship

But I was going on the assumption it would throw a code of some sort. I mean it seems like these cars will throw a code if the air freshener is the wrong scent...

It also seems like the car would have a hard time with the last two steps of the Learn procedure unless the scan tool sets the ECM into some sort of basic mode. I also don't know why the fuel trim would be so crazy.

3.8. Start and idle the engine.
3.9. Accelerate to wide open throttle (WOT). The engine should not accelerate beyond the calibrated fuel cut-off RPM value noted in step 3.1. Release the throttle immediately if the value is exceeded.

Right now it really won't idle without a lot of starts and screwing around and it won't accelerate from idle to WOT, period. I can screw around with the throttle and catch it on an upswing, get it above 3k and THEN it will accelerate to redline.

tech2

false misfire dtc will set at high engine rpm if the crank relearn is not done...not related to what you have going. It will not cause a idle problem. It should be address after this problem is resolved. the way the vehicle is running now...you probably couldn't complete this procedure anyway.

Pellucid

Not what I wanted to hear, man... not what I wanted to hear. I've never been so stumped by a mechanical problem.

Pellucid

So what all does the ECM/ECU look at to determine the fuel trim? It's looking at the front O2 sensor, MAF sensor, IAT? ECT? What else? At this point I'm ready to just swap over anything and everything from the old ending.

I finally found a wiring diagram so I'm going to pinout the harness tomorrow and see if I find anything. The harness looked okay but maybe some bad insulation cracked when I was swapping it over and it's shorted somewhere.

Thanks for the help so far.