Hi guys! Well me and my dad had an 04 Aveo in the shop for an engine replacement. The last mechanic to work on it said there was a hole in the block, turned out there was a hole in a piston. The valves broke off. 80K miles... Anyhow, we got an engine, changed around all the stuff on it, and put it in. It started right up and runs beautifully... or so it seemed. When we drove it the check engine light started flashing. The codes were cylinders 2, 3, and 4 misfires. You can't tell it's misfiring when you are driving it, it must be very minor. We've checked all over this engine and nothing is amiss. We changed the coil pack, put new wires and new plugs in it to no avail. No vacuum leaks, all the ground wires are plugged in. I even checked the resistance on all the injectors, and all 4 are 12.2 ohms. I would change the injectors, but the ones that came with the new engine have different plugs and read a different resistance. I deleted the codes and drove it around for a long time, and the check engine light stayed off. I stopped at a gas station and turned the engine off to fill up, as soon as I started it the light came on. One funny thing though, on our scanner, the datastream shows a reading for only 1 oxygen sensor, even though it has 2. I don't know why but the 2nd one is not showing up in the datastream.

As of now my dad put a bunch of fuel inejctor cleaner in the tank and he's been driving it to see if that changes anything. Anyone have any input for us? We're just :banghead: right now...

Hi madman. Since you've put in a new coil pack, plugs and wires I sispect the miss is not an ignition problem.

There is a TSB about leaky valves for the 04 Aveo. Also, this will make the Check Engine Light come on.

Here's the Fix. At 16 oz. of Marvel Mystery Oil to the crankcase and add 4 oz to the gas tank. The valves aren't seating completely I think this is from varnish on the stems. Marvel Mystery Oil is a light weight oil with a solvent property. Aircraft mechanics have used this stuff for years to solve stuck valves. Get an oil change after about 100 miles. In 2-3 hours your engine light should be off and the miss from the engine should be gone. If it's not gone after 2-3 hours reset the CEL with your scanner. This is a shade tree repair, but beats going to the dealer. Dave

There is a TSB about leaky valves for the 04 Aveo. Also, this will make the Check Engine Light come on.

But will the leaky valves make the CELight come on for misfires? BTW the CEL flashes = "hard code." If so, I'll have to try that! And yes, shade tree repair, but sometimes those are the best. I think I've solved more minor problems with rtv silicone than with new parts :P However my dad already gave the car to the customer and told her to drive it for a couple hundred miles and bring it back, since the misfires didn't hinder the performance. So do you think driving it for say 200 miles would solve the problem? If not, I'll try your mystery oil tip. :grinyes:

BTW Thanks a lot for the tip ;)

If it is a hard code (ongoing process) the CEL has to be reset after a few hundred miles on the MM oil. Just use your scanner or take the + terminal off the bat for 10 minutes or so. I read somewhere that a hard code has to be reset where a soft code (happening only once not showing up now) will change the light after 20 or so cycles of starting the engine up. This just speeds up the process. Sure is nice posting to someone who knows what they are doing. Dave

Sure is nice posting to someone who knows what they are doing.

Ditto my friend :)

Hey Dave, need backup!

Well we got the car back and tried your marvel mystery oil trick. Didn't work. Not your fault though, I suspect we did not diagnose the problem very well. My dad got some diagnosis procedure papaers for this particular problem. One of the first things it told us to do was to use the scanner to look at the misfire counter (why we didnt do this before is beyond me). So with the car parked and running, looking at the counter, 0 misfires, even when you rev. Take it out on the road, and the total misfires jump to 500-600, but misfires for each of the cylinders is still 0. So these papers tell me that a transmission code will make the misfire code come up. Apparently it did/does continuously. Because when we looked in the transmission codes, there was one (forgot the number) for loss of signal from the crank sensor. We changed the crank sensor. Nope. We ran the car in park and bounced it up and down, while wiggling the crank sensor wires at the same time! And separately... No misfires either way. Only on the road, around the shift to 2nd gear but it'll happen even in 1st. Now those papers say that trans code could come from "certain" uneven road surfaces, unbalanced tires or brakes, or some other suspension problem. So basically if you drive over potholes you're screwed? And I'm talking tiny potholes, not even potholes, more like cracks int he asphault, like we'd have to find a freshly paved road to test it on if this was the case. The diagnosis papers tell us to test the continuity of the wires between certain engine computer and trans computer plugs, and my dad doesn't know which computer is which. He's been working on it since I've been laden down by other jobs around the shop :/

On a side note, the electrical system is a little screwy. The clock will randomly lose power and memory at the same time, when it decides to turn back on again it's 1:00. The daytime running lights are messed up as well. Sometimes, they decide to start flashing on and off, as if they were wired to the hazard flasher, very steady on/off. But if you turn on the headlights while this is happening, I noticed, the DRL light on the dash will still flash, but, with the headlights on, it is very irregular flashing, goes faster and slower, sometimes just flickering. I *HATE* DRL... funniest thing I ever read on a public bathroom stall door was "Daytime running lights SAVE lives!" lol but I digress...

So any ideas? And where are the computers? :) Thanks!

Ah nevermind. Those diagnosis papers helped. My dad found a wire between the computers with too much resistance, replaced it and no more problem!

Glad you got her fixed. Too much resistance on a wire between the computers. Your dad must be really talented because most of us don't even know where the computers are. Oh, I just wanted to thank you for posting back and letting us know what the outcome was. It'll help someone else. Dave

*sadface*

Well it *WAS* fixed... now it has more codes than before. I'll post them later :/

Ah yes we fixed it again. My dad decided to change the intake manifold. When I was prepping the engine to put in the car, my dad told me not to change it. They were a tad different. I could have changed it in 20 minutes since the engine was out. He spent a day and a half changing it in the car. It appeared to have been leaking. And it worked. It worked all day long until we stopped to fill up gas, as soo as we pull out of the gas station that cursed engine light started blinking. That happened before, after fixing the problem, filling up gas makes it come back. Funny thing is: all day whilst it was fine, we kept stopping and opening the gas cap. For some reason you need to put gas in the tank to make it happen. Ugh my dad wants to change the engine but I have a bad feeling that it's a computer or transmission problem, which it is, clearly. There's always a trans code. *Sigh*