Losing power but no codes

I have an '04 manual and several months ago I was having some issues where the car was idling too high. I checked hoses, cleaned out the throttle body, and even replaced the IAC. The issue was intermittent and more annoying that anything.
Well, for the last few weeks I've noticed that I am severely lacking power. The CEL has not lit up once and I have no stored or pending codes. Again, I've checked hoses for vacuum leaks, checked to make sure there was nothing blocking the intake, etc. I still can't find any obvious cause. The way the car is driving reminds me a lot of how my van was acting recently before I replaced the cat, but that was accompanied by codes from the O2 sensors.

The way it's driving now, if I give it gas like I would under normal situations, the car just doesn't respond like it should. It accelerates much more slowly. It feels kind of like it feels like I'm in too high of a gear for the speed. If I give it more gas, the RPMs will go high and while the car speeds up, it's still obvious that the power just isn't there.

Any ideas what would cause this without throwing any codes? I have a scanner that I can log data with, so are there some recommended PIDs to monitor?

Did you buy this Aveo new? What I'm really asking is do you know the history of it? The '04 was prone to early timing belt breaks. Another big problem is the POS plastic thermostat housing which has caused numerous overheats for Aveo owners. If you don't know the history of your Aveo (or had one of those 2 problems), you might consider a doing a compression or leak-down test (which hopefully will show nothing wrong).

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Originally Posted by avguy

Did you buy this Aveo new? What I'm really asking is do you know the history of it? The '04 was prone to early timing belt breaks. Another big problem is the POS plastic thermostat housing which has caused numerous overheats for Aveo owners. If you don't know the history of your Aveo (or had one of those 2 problems), you might consider a doing a compression or leak-down test (which hopefully will show nothing wrong).

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I've had it for about 8 years, and it belonged to my brother-in-law prior to that.
I replaced the head about a year ago due to the infamous timing belt, and the thermostat housing was replaced not too long after following a wonderful coolant geyser.

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Originally Posted by SpiffWilkie

I've had it for about 8 years, and it belonged to my brother-in-law prior to that.
I replaced the head about a year ago due to the infamous timing belt, and the thermostat housing was replaced not too long after following a wonderful coolant geyser.

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I think you definitely should do a compression and/or leak-down test.

It could also be a throttle positioning sensor. The ECU wouldn't be able to calculate engine load and throttle angle if the sensor is faulty. It might not show a fault even if it's bad because it's drive by cable.

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Originally Posted by avguy

I think you definitely should do a compression and/or leak-down test.

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Just checked the compression. I'm not sure of the accuracy of the gauge (it's been through a lot), but the cylinders were all consistent at just over 120psi.

Edit:
My testing methods (in case I did something wrong).
- Ran the engine for a few minutes to warm it up.
- Pulled the fuel relay
- Removed all plugs

Did you open the throttle all the way when you were cranking the engine?

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Originally Posted by Daox

Did you open the throttle all the way when you were cranking the engine?

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Sorry, yes. I had it floored.

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Originally Posted by ontarian_frog

It could also be a throttle positioning sensor. The ECU wouldn't be able to calculate engine load and throttle angle if the sensor is faulty. It might not show a fault even if it's bad because it's drive by cable.

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I checked the voltage on the TPS. It read from .58 to 4.4. I didn't notice any issues as I changed the throttle position. The voltage changed smoothly, and I banged on it a bit and wiggled the harness to see if there were any drops in voltage.

Would I be getting this noticeable of a power loss due to a bad cat without a code? I'll log the o2 sensors when I go home tonight and see what the graph looks like.

Well it sounds like the engine is ok (which is good news!). I didn't read your OP carefully enough, and see now that you said it had been running this way before a cat replacement. Whenever I have a problem, I always review recent repairs, because that would always be my first and prime suspect. Do you think that anything could have gone wrong with that job? Maybe a bad O2 sensor (or wire) that's not throwing a code?

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Originally Posted by avguy

Well it sounds like the engine is ok (which is good news!). I didn't read your OP carefully enough, and see now that you said it had been running this way before a cat replacement. Whenever I have a problem, I always review recent repairs, because that would always be my first and prime suspect. Do you think that anything could have gone wrong with that job? Maybe a bad O2 sensor (or wire) that's not throwing a code?

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Sorry, I was comparing how it's running now with how my other vehicle was prior to a cat replacement. This is still running with the factory cat.

you would most likely get a secondary o2 code for a clogged cat, but partially clogged would slow air.

I think you have either a fuel restriction, or air restriction. being 10 years? old, i would check the fuel pressure in the rail. do more than just initial pressure, check pressure under load. then replace the fuel filter in the tank. cheap, labor intensive but not difficult.

Air restriction is on the exhaust side (most likely cat) or air filter. easy ways to determine those is (if you are wreckless ;) ) is to pull the air box. I would also check the intake plumbing the aveo will not account for unmetered air going into the intake if it does not go past the sensor. So a torn intake pipe will allow more air, but stop acceleration.

if you think the cat is clogged pull the primary o2, and run the car. if the car runs better, then the possibility of a clogged cat it true.

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Originally Posted by petrified.rabbit

you would most likely get a secondary o2 code for a clogged cat, but partially clogged would slow air.

I think you have either a fuel restriction, or air restriction. being 10 years? old, i would check the fuel pressure in the rail. do more than just initial pressure, check pressure under load. then replace the fuel filter in the tank. cheap, labor intensive but not difficult.

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Question about fuel pressure. The manufacturer specification is 55-62psi. Should it pressurize to that the first time I turn the ignition on? With just turning the ignition to on once, I got around 30 psi. Turning it on and off, it got to 53 psi.

What's the best way to check it under load? Do I need to purge the gauge while someone has their foot on the gas and see if it climbs back to the 55-62psi range?

Edit: Another question about the filter. I know that the filter is technically not user-serviceable. Is it still possible to replace it? I've searched and searched on this site and can't find a thread where someone has done it or explained where to get one.

Resurrecting this thread...I got around to checking the fuel pressure with a good gauge and it is good.
My issue with lack of power took a big turn for the worse over the last couple of days. It was tolerable for the last month and I poked around and tested things as time permitted (between work/school/family). Well, yesterday it seemed to get appreciably worse and then today it's basically not driveable...and the clutch smells awful. So...that sucks.

still no codes? how does the air intake look? if the rubber intake is torn or letting in air you are probably just leaning out and since the monitoring reflects less air, then you lose power.

is it top end/all around? if your clutch is smelling bad, why? maybe your clutch was just slipping this whole time?

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Originally Posted by petrified.rabbit

still no codes? how does the air intake look? if the rubber intake is torn or letting in air you are probably just leaning out and since the monitoring reflects less air, then you lose power.

is it top end/all around? if your clutch is smelling bad, why? maybe your clutch was just slipping this whole time?

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The intake tube was replaced about a year ago. I've checked it recently to verify that there are no cracks/leaks.
I'm still not getting any CEL or pending codes on the scanner.
The lack of power is pretty much from low to high now. Getting the car going in first takes considerable more throttle than normal, and even in reverse where I could normally let the car use it's own power (no throttle on my part) to back up, I have to give it more gas than normal.
Yesterday I was trying to pay more attention to the engine speed while I was driving down a level road. Acceleration under normal circumstances (i.e. not mashing it) from 50-55 in 5th had the engine about 3700RPMs.

I read through a lot of posts about the clutch, and it's definitely a possibility. What else can I do to diagnose that prior to taking the thing apart? If it is the clutch, I'm also concerned about whether there was a primary issue (something leaking internally?) that caused the clutch to have issues. I don't want to replace it but neglect to fix any other problems that might be lurking and cause a premature failure again.

Thanks

What is the RPM when it's parked in neutral, and your foot is not on the gas? And still parked in neutral, if you rev it up to 5.5 - 6K, does it miss or drop out at all? And is there any difference (miss or drop out) if you rev it up slowly, or punch down WOT?

avguy is on the ball, if the power loss is associated with the clutch you would be able to rev up with no problems sitting in neutral. diagnose that first.

once you see if it is running correctly, then test on some accelerations to see if the rpm stays consistent with vehicle speed.
try starting in 2nd and 3rd to increase the clutch drag to see if it slips (it will slip trying to start from a stop in 3rd gear normally) but you would be able to feel it worse.

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Originally Posted by petrified.rabbit

avguy is on the ball, if the power loss is associated with the clutch you would be able to rev up with no problems sitting in neutral. diagnose that first.

once you see if it is running correctly, then test on some accelerations to see if the rpm stays consistent with vehicle speed.
try starting in 2nd and 3rd to increase the clutch drag to see if it slips (it will slip trying to start from a stop in 3rd gear normally) but you would be able to feel it worse.

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Bringing this from the dead again. I haven't worked on the car due to weather and life in general. Today, I went back out and poked around a bit. I still need to do some more testing with the RPMs and whatnot. Someone had suggested before that I try and start the vehicle in gear without pushing in the clutch pedal. Well, this morning I gave it a shot and was able to start the car in 3rd and leave it idling with pushing the clutch pedal.

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Originally Posted by avguy

What is the RPM when it's parked in neutral, and your foot is not on the gas? And still parked in neutral, if you rev it up to 5.5 - 6K, does it miss or drop out at all? And is there any difference (miss or drop out) if you rev it up slowly, or punch down WOT?

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Finally got around to working on this. THIS LINK has graphs of RPM and throttle position with me revving the engine in neutral and then graphs of RPM, throttle position, and speed with me starting from a stop in 1st, 2nd, and 3rd.

The data the graphs are based on is HERE.