Question : 2001 Alero 3400 lacking power

[el_roy1985]

Someone asked me to check out there 2001 Alero because it is lacking power.

At first start up, the throttle response was slow and the RPMs would drop slightly before going up. Checked for codes, but nothing. Checked fuel pressure and it was a steady 50 and would jump slightly at rev up then settle back at 50 while holding an rpm. There are no apparent misfires and my spark tester showed healthy spark. The most engine load I could get the computer to register was about 50%, is that normal?

I was able to obtain a scanner that gave me a live reading, here are some parameters of the last reading. This reading is right as I was reaching the top of a hill. I was hoping to get it mid hill, but it read the data a little too late and I was unable to give it another try.

Load Value - 30.4%
Coolant - 190
STFT - Bank 1 - 0%
LTFT - Bank 1 - 21.8%
Manifold Pressure - 26.7 in.hg
Engine RPM - 3625
Vehicle speed - 27 mph
Ignition advance - 21.5 deg
Intake air temp - 82
Maf flow rate - 0.9lb/min
Bank1 - sensor1- 02S Output 0.920v
Bank 1 - sensor1 - STFT 0.0%
Bank 1 - sensor2 - 02S Output 0.830
Bank 1 - Sensor2 - STFT 99.0%

I'm not sure what the STFT and LTFT readings are, so if anyone else could let me know that would be great.


The car noticeably lacks a lot of power while accelerating onto the interstate and up a short hill.

[robertisaar]

i don't know much about obd2, but i know LTFT(long term fuel trim) and STFT(short term fuel trim) are essentially the equivalent of BLM and INT.

i don't know if the 21.8% is adding or subtracting fuel, but thats not very close to ideal...

from the way it sounds, there might be a major restriction in either the intake or exhaust, meaning air filter or cat..... take your pick. let the exhaust cool down and rap your hand up against the bottom of the cat. if you hear any kind of rattling, there's part of your problem...

is there any funny smell while idling(after its warm of course)?

[geldartb]

Other possible causes are:

- vacuum leak
- faulty O2 sensor(s)
- faulty mass air meter
- bad coils and/or plugs (causing misfires and leading to false lean AFR readings)

negative number pcm is removing fuel, positive number, pcm is adding fuel.

[heavymtl]

i dont know if you have checked the plugs for gap and wear but it couldn't hurt any....i work in a shop and we had a minivan come in one day and ran like crap....would rev slowly...had hardley any power to it...found the plugs to be overly gapped (95k or more gap on em) from wear....the wires were originals also and needed replacements...just those 2 things made a HUGE difference....maybe this will help you

[heavymtl]

grrrrr almost forgot...you MIGHT have a plugged or blocked catalytic converter

[Azrael]

Is 26.7 in-hg of vacuum normal? Under part throttle acceleration I would think it should be somewhere between 10 and 20.

[torq455]

looks like it's running rich. 02's are reading rich. post converter 02 should be close to .450 mV. the PCM is adding 26% fuel, which means the PCM thinks it needs to add more fuel. iirc, in-hg is reverse thinking. idle is about 8 in-hg, and wot is about 28 in-hg. i remember thinking that's weird since idle should be 20 in-hg.

[el_roy1985]

Alright, if I take another look I'll make sure to have time to check more in depth. Last time I just stopped over at her place to check out some of the easy stuff. Plugs and wires was one thing I mentioned to her, and she hadn't know if they had been replaced before. The looked somewhat old just by looking at the plugs.

Apparently the 02 sensors were recently replaced by her uncle that works at a GM dealership back in texas. (just moved up here) So they should be quality sensors. That was also before this problem popped up, so it wasn't in attempt to fix this issue.

Thanks for everyone's input. This is the first time I've used a scanner that lists sensor readings, so you guys have helped me a lot in understanding what all this is.

[SofaKingWeToddDid]

i was gonna say the cat too... but i know nothing.

[robertisaar]

iirc, in-hg is reverse thinking. idle is about 8 in-hg, and wot is about 28 in-hg. i remember thinking that's weird since idle should be 20 in-hg.

correct.

[sprucegagt]

Someone asked me to check out there 2001 Alero because it is lacking power.

At first start up, the throttle response was slow and the RPMs would drop slightly before going up. Checked for codes, but nothing. Checked fuel pressure and it was a steady 50 and would jump slightly at rev up then settle back at 50 while holding an rpm. There are no apparent misfires and my spark tester showed healthy spark. The most engine load I could get the computer to register was about 50%, is that normal?

I was able to obtain a scanner that gave me a live reading, here are some parameters of the last reading. This reading is right as I was reaching the top of a hill. I was hoping to get it mid hill, but it read the data a little too late and I was unable to give it another try.

Load Value - 30.4%
Coolant - 190
STFT - Bank 1 - 0%
LTFT - Bank 1 - 21.8%
Manifold Pressure - 26.7 in.hg
Engine RPM - 3625
Vehicle speed - 27 mph
Ignition advance - 21.5 deg
Intake air temp - 82
Maf flow rate - 0.9lb/min
Bank1 - sensor1- 02S Output 0.920v
Bank 1 - sensor1 - STFT 0.0%
Bank 1 - sensor2 - 02S Output 0.830
Bank 1 - Sensor2 - STFT 99.0%

I'm not sure what the STFT and LTFT readings are, so if anyone else could let me know that would be great.


The car noticeably lacks a lot of power while accelerating onto the interstate and up a short hill.

Hmmm. Low vacuum, low ignition advance, LTFT adjusted very rich and a rich B1S1 O2 reading. I bet if you were monitoring KR, it was doing quite a bit. First thing I would look for is a plugged converter, if not then look for a healthy exhaust leak somewhere upstream of the O2 sensor located in the rear manifold.

[no_doz]

sounds like a restriction in the exhaust to me, have someone rev the car with your hand and inch or so from the exhaust outlet & see if you can feel much, if its very weak you have a plugged exhaust.

sometimes people go around cramming stuff in other peoples exhausts & sometimes exhaust components will rust & break/bend/snap their way in the way of the exhaust & it will make whatever car it is run like $%^ if at all.

also if there isnt much flowing out the back exhaust make sure its not coming out somewhere else underneath the vehicle as that may be the cause as well/rather than a blocked exhaust.