Please Help! Stalling, violent idle, no acceleration

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?

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.

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

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.

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%.
https://youtu.be/h9LHLSLUTyQ

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?

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

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Originally Posted by Chrisj4269

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

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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.

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.

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Originally Posted by Chrisj4269

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

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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!

So I can't give myself to give up on this car with so few miles... It's just sitting in my garage now that I have a replacement but I'd like it out and running. I recently retried the fuel pressure test at the recommendation of a local mechanic who said the pump may be priming but not maintaining pressure after. It primed to 50psi ran it's normal 10 seconds and died with the Gage still at 50psi. Does that mean the fuel pump is good?

My 2007 acted a lot like this and it turned out to be the throttle body needing replaced. The computer threw so many freaking codes it ran like crap would idle surged all over the place trying to idle.

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Originally Posted by EyeintheSky

My 2007 acted a lot like this and it turned out to be the throttle body needing replaced. The computer threw so many freaking codes it ran like crap would idle surged all over the place trying to idle.

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Is there a way to test the throttle body? My car is not throwing any codes to reference

I have a 2004 Aveo LS sedan with 41,000 miles on it. It was purchased new. One of the first in CT I think. Ordered in Jan. of 2004 and didnÂ’t arrive here until May! Has every factory option. Great little car with really no major problems.

A few questions, I have never really had great gas mileage with this car? My 2010 Ford Escape 4 cyl. AWD gets better mileage! I have read here that others have talked about all different spark plugs for good mileage, but everyone seems to have a different opinion. Is there one that I should definitely try? I think the car is very peppy.

A long time ago, the key in ignition and headlights on buzzer stopped working. ANY clue where would be a good place to start. I have been told several times that there must be a short somewhere but nobody seems to want to take the time to find it.

Lastly, for now, I THINK the “head gasket” is leaking oil because it looks wet there. I have not seen any oil spots on the ground but I can smell it when I drive it.

Thank you for any advice you can give me. 👍👍🤷*♂️🤷*♂️🤷*♂️

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Originally Posted by fastdriver

I have a 2004 Aveo LS sedan with 41,000 miles on it. It was purchased new. One of the first in CT I think. Ordered in Jan. of 2004 and didnÂ’t arrive here until May! Has every factory option. Great little car with really no major problems.

A few questions, I have never really had great gas mileage with this car? My 2010 Ford Escape 4 cyl. AWD gets better mileage! I have read here that others have talked about all different spark plugs for good mileage, but everyone seems to have a different opinion. Is there one that I should definitely try? I think the car is very peppy.

A long time ago, the key in ignition and headlights on buzzer stopped working. ANY clue where would be a good place to start. I have been told several times that there must be a short somewhere but nobody seems to want to take the time to find it.

Lastly, for now, I THINK the “head gasket” is leaking oil because it looks wet there. I have not seen any oil spots on the ground but I can smell it when I drive it.

Thank you for any advice you can give me. 路*♂️路*♂️路*♂️

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Why not create your own thread rather than posting on my troubleshooting thread?

One other thing, I disconnected the crankshaft position sensor and tested the wires leading to the car. with key on engine off, 2 of the wires read exactly 2.5 volts and the 3rd wire was ground (verified through continuity). Are those normal readings? I was expecting a 12v feed, signal, and ground but am not super familiar with this cars wiring.

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Originally Posted by Chrisj4269

Why not create your own thread rather than posting on my troubleshooting thread?

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Sorry, I have not posted here in ages and didn’t realize that I was posting in your site or your area. I’ll have to see how I start a separate thread.

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Originally Posted by fastdriver

Sorry, I have not posted here in ages and didn’t realize that I was posting in your site or your area. I’ll have to see how I start a separate thread.

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No worries, it happens!

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Originally Posted by Chrisj4269

One other thing, I disconnected the crankshaft position sensor and tested the wires leading to the car. with key on engine off, 2 of the wires read exactly 2.5 volts and the 3rd wire was ground (verified through continuity). Are those normal readings? I was expecting a 12v feed, signal, and ground but am not super familiar with this cars wiring.

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Seems like you’ve been through the wringer with this issue, reading through the thread it appears things went downhill after the camshaft sensor replacement.

I’m not familiar with the 2007 wiring but check this link , it may have relevance to your issue.
https://electronics.stackexchange.co...ab-environment

Cheers

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Originally Posted by JB_Fraser

Seems like you’ve been through the wringer with this issue, reading through the thread it appears things went downhill after the camshaft sensor replacement.

I’m not familiar with the 2007 wiring but check this link , it may have relevance to your issue.
https://electronics.stackexchange.co...ab-environment

Cheers

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Yes you are correct. After the cam sensor the car ran fine for about 48 hours then the real issues began. I should not that since they happened, I have replaced the cam sensor once again with another new GM sensor. I have also replaced the whole PCM since then. Do you know where I should begin looking for a bad wire or anything?

If the diagram from the link is correct (I’m not saying it is!) then you should have a definite ground and power +12v, with your signal running to the ecm.
There is a fuse that supplies power to this sensor (check that first, although I would think there would be other things missing if the fuse was bad, but just to know ,check it anyways).

With the fuse removed, you should likely still see your 2.5v on both signal and power pins because I believe it is coming from the pull up resistor embedded in the ecm circuitry.

If you believe the circuit diagram is correct, you could run a wire from the fused side of the circuit to the connector , back probing would be easiest (likely) to get power to the sensor cable. You Need To Verify That Connection Should Be 12v!

If your willing to trace the wiring then use your ohm-meter to check for continuity, this will be difficult without a schematic. As well verify the pins on the connector are in good shape and no corrosion is present.

Cheers

Similar problems have been posted on here regarding these cars doing this, and from what I have read, the problem tends to be the valve cover gasket leaking oil, and pooling in the spark plug wells in the top of the motor, causing the spark plug wires to short to ground on the top of the engine. Remove the top cover off of the engine, and check the boots for carbon tracking, and look for oil, or traces of oil around the spark plugs.

Hope this helps. Good luck, and let me know what you find.

possibly some bad fuel.... drain and replace....pull coil rail and test with all plugs connected... there you tube video on how to test coil rail.... check for good blue spark...fuel pressure??possibly weak pump

PCV possibly... only fix is to replace valve cover... good luck

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Originally Posted by Hoosiertrucker

Similar problems have been posted on here regarding these cars doing this, and from what I have read, the problem tends to be the valve cover gasket leaking oil, and pooling in the spark plug wells in the top of the motor, causing the spark plug wires to short to ground on the top of the engine. Remove the top cover off of the engine, and check the boots for carbon tracking, and look for oil, or traces of oil around the spark plugs.

Hope this helps. Good luck, and let me know what you find.

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My valve cover gasket and plugs/wires were just recently replaced. I did verify they are still bone dry though. Thanks for the suggestion

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Originally Posted by viciousvîc

PCV possibly... only fix is to replace valve cover... good luck

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I tried running without pcv valve which should have let any excess pressure bleed off and it made no difference. I was also thinking bad fuel initially as well but I was about halfway through the tank of gas I got a few days before it stopped running. That and the fact that it still fires right up and runs normal for 5-10 seconds led me to believe it wasn't fuel.

I'd still remove fuel line from injector and fill quart glass jar....it wud only take small drops water to plug up injector....water does not compress.... when pressure is removed water will give way to good fuel to injector.... as soon as you turn key on pressure builds... giving you only seconds of fuel.... is car automatic or manual trans.... if manual try pull starting.... see if you can get it to run few blocks.... this might also set a new DTC .... somewhere else or new to look for ideas... good luck... drain all fuel.... this can give you a lean run for few seconds... now you can control the fuel source.... start looking for chafing on wiring...eg. coil...injector... crank sensor.... cam sensor... all the time you have put into this... makes me think simplest solution.... stick with it... curiosity got me edge of my seat...

pcv is part of valve cover... not sure If you can bypass... you tube has pcv diagnostics ...

I had similar symptoms, various symptoms led to the fuel hitting the cat converter being too hot for it too handle over time. Had it replaced under the little known federal warranty. The service guys showed me a mangled mess. Basically, it was just clogging everything up. New cat, ran fine, no codes.

I didn't address the underlying issues fully, and I'm fiddling with an exhaust that has sprung various holes/gaps that don't seal long with exhaust cement, but it runs, just a little loud.