Please Help! Stalling, violent idle, no acceleration

[avguy]

Yes, the timing marks look fine, but those compression readings you posted are still a question mark. It's hard to imagine anything other than bad timing which could produce consistently low compression across all cylinders, so I can't tell you what's up with that. But OTOH, if some of the cylinders vary quite a bit, then that brings a blown head gasket into play. I don't have first hand experience with an Aveo engine running at 150 PSI, but it certainly seems possible it could be the reason that it's running so poorly.

Can you find the time to do another compression test? And if all 4 are still around 150, then would it be possible for you to get a loaner tester from Autozone, and confirm that it's not your tester reading too low?

Do you happen to remember what that cam sensor code was?

[Chrisj4269]

Ill definitely go ahead and get a loaner to do another comp test. I do recall that all four cylinders were very close together. I don't remember exactly what the code was just that it came on and was saying "camshaft position sensor.." so I replaced it.

[Chrisj4269]

Just remembered that I did take pics of the codes when I scanned them. It was P0340.

[avguy]

In order to fairly compare my compression numbers to yours, I'll just mention that I first removed the fuel pump relay and ran it out of gas before running the test. And I cranked 4-5 times while holding the gas pedal to the floor, and did the test 'dry' (no oil added to the cylinders). I don't know how much different the test results would be if you weren't doing the same things, but in order to be certain of a good comparison, I suggest doing it as described above.

[Chrisj4269]

I haven't had a chance to do compression test yet but one thing I did want to share is that with the ignition on, engine not running, OBD2 shows throttle position at 18% when I'm not touching it to 28% when I floor it. The video below is me slowing going from no throttle to full throttle. It only reads three places: 18%, 24%, 28%.

[OG-Lou]

I had trouble with low engine power and miss-firing and no codes for well over a year. I finally found a carbon track on the inside of a spark plug boot that created a path to ground for the spark to jump on acceleration but the engine ran well at idle and at hwy sspeeds. You can read my 2 threads listing the things I tested and replaced.

OK, back to your problems.

When i did my first compression test using a borrowed compression tester, I got 150 PSI on all 4 cylinders. A year later and a different borrowed but new compression tester, my readings were 175# after 4 compression strokes. Both tests were dry.

About your throttle positions, the gas pedal position sensor and the computer determine the throttle position which is moved by a small electric motor that opens or closes the throttle plate. So pushing the gas pedal to the floor just informs the computer what the driver wants to do but the computer determines how far open the throttle will be based on several other inputs. If the RPM's are low, the throttle will not open all the way.

About the coil pack. The design of the ignition system is it fires the spark at the end of the compression stroke and fires the plug at the end of the exhaust stroke. There are 2 coils and 4 cylinders. The engine only needs 2 coils and each coil has 2 terminals.

I have or had 3 Aveo's and once one car had a miss so I put a can of fuel injector cleaner (Chevron Techron) in my gas tank that had about 4 gallons of gas. No more miss.

Question? Did you ever remove the crank shaft sensor? I have read if the crank shaft sensor is even disturbed in any way, you have to do a crank shaft relearn procedure.

When my spark was going to ground I replaced my crankshaft sensor with a new one and the engine ran about the same. I also replaced my ECM with a used one from a car the same as mine and the engine ran about the same. At this time I didn't know the spark was going to ground only on acceleration and it ran fime at idle and over 35 MPH.

Personally after working for a car dealership (a long time ago) the 150 PSI doesn't bother me. I have seen lots of older used cars run smooth on 110# PSI compression, as long as the compression readings are within 10 to 20 PSI of each other. One very old car I remember had 75#PSI and ran well when it was sort of even warmish outside but it was difficult to start when the temperature dropped below freezing.

I wish USA Aveo's had a factory installed fuel filter like the Mexico versions. If the fuel injectors were easy to get to, I might suggest taking them out to look at them and maybe run some carb cleaner through them.

I can't see 4 injectors having trouble at the same time but strange things do happen.

Confession: I replaced a bunch of parts on my Aveo before I found the spark going to ground on the inside of the one spark plug boot, so "parts hanging" (replacing parts that are OK) is fairly common, especially with the high cost of dealership diagnostic fees. Now I have a small supply of perfectly good replacement parts on hand. I will most likely never need them but I have less money invested in parts I really didn't need, compared to just the dealership diagnostic fee, and who is to say the dealer would have found my root problem on their first diagnosis?

[Chrisj4269]

So you don't think the throttle reading is indicative of the issue I'm dealing with

[avguy]

So you don't think the throttle reading is indicative of the issue I'm dealing with

Nothing can be ruled out until testing proves it out. Unfortunately, having no wiring diagram for your vehicle, I can't help you with that. Yes, you could just replace the throttle body (and the APS assembly as well), but I always prefer to test instead of part hanging whenever possible.

How did the second compression test turn out? Personally I believe 150 could cause a significant performance issue on these tiny engines, but it's a forum and everyone is entitled to their opinion.

[Chrisj4269]

Sorry I've been offline for a while. I did borrow a compression Gage from O'Reilly's and you were right, about 180psi and within about 4 psi max cylinder to cylinder. Unfortunately the car still won't stay running and I was forced to replace it. It just didn't make sense to keep renting a car for a couple hundred bucks a week. I really didn't want to get to this point at only 70k miles and brand new tires I just put on but it is what it is. Definitely leaves a bad taste in my mouth towards Chevy products. If you know anyone interested in figuring it out, it is currently for sale as is. Willing to let a potential buyer do whatever testing they want so they know the engine isn't shot.

[avguy]

... Unfortunately the car still won't stay running and I was forced to replace it. ....

Sorry to read you had to bail on it, but I certainly understand where you're coming from and why you had to make the move. With the proven good compression, here's one final suggestion for you. If you have a pick-a-part boneyard in your area, IMO it's worth a try to hang on a used throttle body from another drive-by-wire Aveo. A $40 (or so) roll of the dice might turn into a 2K sale for a decently running used car (versus not much the way it runs now). But in any case, hats off to you for giving it a really good effort, and best of luck with your new ride!