Low power at low rpm's
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Time for some data- If your scan tool does data, get fuel trims (again), O2 readings, MAP readings and so on.
See if trims are indicating lean conditions and see if the O2'S are verifying that. Do the O2's respond to lean or rich inputs?
What does the MAP reap at idle? KOEO?
Can you check the back pressure in the cat?
Does your scanner have the ability to read misfires on each cylinder? Maybe you have an inject that is getting plugged and not fully functioning?
See if trims are indicating lean conditions and see if the O2'S are verifying that. Do the O2's respond to lean or rich inputs?
What does the MAP reap at idle? KOEO?
Can you check the back pressure in the cat?
Does your scanner have the ability to read misfires on each cylinder? Maybe you have an inject that is getting plugged and not fully functioning?
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Originally Posted By: gregoron
Try disconnecting the battery for a minute or two to reset the ECU if that helps. You may want to look at vacuum leaks around the throttle body or throttle control valve if it has one. Some of those hoses leak over time.
That's a good idea, but the battery has been disconnected a few times since this all began and I haven't noticed a difference.
Originally Posted By: The_Eric
Time for some data- If your scan tool does data, get fuel trims (again), O2 readings, MAP readings and so on.
See if trims are indicating lean conditions and see if the O2'S are verifying that. Do the O2's respond to lean or rich inputs?
I stare at trims all the time. LTFT usually sits at about 0% at idle and is either 2.34% or 3.12% on the highway steady state. If you floor it the trim will sometimes go up to 6-7% but have not seen anything more than that.
Originally Posted By: The Eric
What does the MAP reap at idle? KOEO?
The MAP data usually matches what I would expect. I forget how the numbers work but I think it usually sits at 14.7 with KOEO so I don't really suspect anything there. I haven't seen anything erratic in the readings.
Originally Posted By: The Eric
Can you check the back pressure in the cat?
I don't have a way to check backpressure at the cat, although the thought is sometimes in the back of my mind.
Originally Posted By: The Eric
Does your scanner have the ability to read misfires on each cylinder? Maybe you have an inject that is getting plugged and not fully functioning?
No way to count individual misfires. It's just an OBD2 scanner. I suppose I could look into getting a more fully featured scanner to look into that.
Originally Posted By: Vikas
Assuming your gauge is accurate, 18 sound on the low end of the vacuum at sea level.
Spec says 17-22" of vacuum is normal. I did look around at all the vacuum hoses, pushed, pulled, pinched everything to check and didn't notice anything. There aren't too many vacuum hoses on the engine so there are only a few places to check.
There are a few things that could result in individual symptoms, but the strangest symptom is the way at a certain RPM the engine suddenly surges forward with power under acceleration. It's not a gradual increase in power, it's like a light switch is flipped. And there's no corresponding data change that I've seen when it happens such as a timing change or something. A clogged converter shouldn't allow things sudden surges of power, although I could be wrong.
I did order a new O2 sensor because at $43 and with the current one being original at ~140k miles, I might as well. We'll see if that changes anything. I do have a scope but haven't put it on the O2 sensor. The extent to which I have looked at O2 data is noting that the number bounces around to between 0.1 and 0.8 volts as I drive, but I realize that's worth little, especially for transient conditions.
My logic to replacing the O2 sensor was that fuel trims might not look out of whack if the O2 sensor wasn't reading properly, in other words if it was reporting a good A/F mix the trim would look okay even if it was not.
Try disconnecting the battery for a minute or two to reset the ECU if that helps. You may want to look at vacuum leaks around the throttle body or throttle control valve if it has one. Some of those hoses leak over time.
That's a good idea, but the battery has been disconnected a few times since this all began and I haven't noticed a difference.
Originally Posted By: The_Eric
Time for some data- If your scan tool does data, get fuel trims (again), O2 readings, MAP readings and so on.
See if trims are indicating lean conditions and see if the O2'S are verifying that. Do the O2's respond to lean or rich inputs?
I stare at trims all the time. LTFT usually sits at about 0% at idle and is either 2.34% or 3.12% on the highway steady state. If you floor it the trim will sometimes go up to 6-7% but have not seen anything more than that.
Originally Posted By: The Eric
What does the MAP reap at idle? KOEO?
The MAP data usually matches what I would expect. I forget how the numbers work but I think it usually sits at 14.7 with KOEO so I don't really suspect anything there. I haven't seen anything erratic in the readings.
Originally Posted By: The Eric
Can you check the back pressure in the cat?
I don't have a way to check backpressure at the cat, although the thought is sometimes in the back of my mind.
Originally Posted By: The Eric
Does your scanner have the ability to read misfires on each cylinder? Maybe you have an inject that is getting plugged and not fully functioning?
No way to count individual misfires. It's just an OBD2 scanner. I suppose I could look into getting a more fully featured scanner to look into that.
Originally Posted By: Vikas
Assuming your gauge is accurate, 18 sound on the low end of the vacuum at sea level.
Spec says 17-22" of vacuum is normal. I did look around at all the vacuum hoses, pushed, pulled, pinched everything to check and didn't notice anything. There aren't too many vacuum hoses on the engine so there are only a few places to check.
There are a few things that could result in individual symptoms, but the strangest symptom is the way at a certain RPM the engine suddenly surges forward with power under acceleration. It's not a gradual increase in power, it's like a light switch is flipped. And there's no corresponding data change that I've seen when it happens such as a timing change or something. A clogged converter shouldn't allow things sudden surges of power, although I could be wrong.
I did order a new O2 sensor because at $43 and with the current one being original at ~140k miles, I might as well. We'll see if that changes anything. I do have a scope but haven't put it on the O2 sensor. The extent to which I have looked at O2 data is noting that the number bounces around to between 0.1 and 0.8 volts as I drive, but I realize that's worth little, especially for transient conditions.
My logic to replacing the O2 sensor was that fuel trims might not look out of whack if the O2 sensor wasn't reading properly, in other words if it was reporting a good A/F mix the trim would look okay even if it was not.
Okay, replaced O2 sensor yesterday.
No change.
This morning, did a more thorough vacuum test to see if there was any exhaust restriction. If I give it a steady 2000 rpm's the vacuum climbs a bit and then stays slightly elevated.
So I've ruled out something like a clogged converter, and the O2 sensor.
I hooked the fuel pressure gauge up again and this time drove around with it connected. Fuel pressure did not drop or behave erratically, even when the "lumpiness" was in full effect.
I'm starting to run out of ideas completely here, unless it is some kind of electrical issue.
No change.
This morning, did a more thorough vacuum test to see if there was any exhaust restriction. If I give it a steady 2000 rpm's the vacuum climbs a bit and then stays slightly elevated.
So I've ruled out something like a clogged converter, and the O2 sensor.
I hooked the fuel pressure gauge up again and this time drove around with it connected. Fuel pressure did not drop or behave erratically, even when the "lumpiness" was in full effect.
I'm starting to run out of ideas completely here, unless it is some kind of electrical issue.
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It sounds almost like the valve timing has jumped and is now retarded, which shifts the power band up
I would say it is unlikely on this engine though.
I would say it is unlikely on this engine though.
Interesting thinking, either way. I also think its unlikely, I'm also not sure that would cause the lumpiness in power delivery, either.
I just came in from checking the 24X crankshaft position sensor. The thought to check it popped into my head, but it's operating correctly.
At this point, barring any suggestions of things to check, I'm left thinking it is either ignition/spark related, or fuel injector related. The engine appears to be mechanically sound, the intake side is clear, the exhaust side is clear, I've checked many of the sensors, I'm running out of ideas.
I just came in from checking the 24X crankshaft position sensor. The thought to check it popped into my head, but it's operating correctly.
At this point, barring any suggestions of things to check, I'm left thinking it is either ignition/spark related, or fuel injector related. The engine appears to be mechanically sound, the intake side is clear, the exhaust side is clear, I've checked many of the sensors, I'm running out of ideas.
Since you're grasping at straws now, try unplugging the MAF sensor and take it for a drive. That will obviously trip the check engine light, but if it drives normally, you know the MAF sensor went bad.
It's easy and worth a try.
It's easy and worth a try.
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Originally Posted By: Drew99GT
Since you're grasping at straws now, try unplugging the MAF sensor and take it for a drive. That will obviously trip the check engine light, but if it drives normally, you know the MAF sensor went bad.
It's easy and worth a try.
See above, he already did that
Since you're grasping at straws now, try unplugging the MAF sensor and take it for a drive. That will obviously trip the check engine light, but if it drives normally, you know the MAF sensor went bad.
It's easy and worth a try.
See above, he already did that
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Originally Posted By: cchase
Interesting thinking, either way. I also think its unlikely, I'm also not sure that would cause the lumpiness in power delivery, either.
It can (depending on the engine I am sure). My buddy had the guide let go on his 4.6L (Modular) which caused the timing to jump a tooth. Only symptom at idle was a lumpier idle and it kind of felt like a misfire. He had no mode 6 data to match an actual misfire though.
Condition "cleared up" as soon as you got into the rev's, and it pulled hard once it got up there.
He didn't know what the heck was going wrong and took it to the dealer. They diagnosed the broken guide (there was no noise BTW) and that the timing had jumped. New chains/guides and it was good to go.
Interesting thinking, either way. I also think its unlikely, I'm also not sure that would cause the lumpiness in power delivery, either.
It can (depending on the engine I am sure). My buddy had the guide let go on his 4.6L (Modular) which caused the timing to jump a tooth. Only symptom at idle was a lumpier idle and it kind of felt like a misfire. He had no mode 6 data to match an actual misfire though.
Condition "cleared up" as soon as you got into the rev's, and it pulled hard once it got up there.
He didn't know what the heck was going wrong and took it to the dealer. They diagnosed the broken guide (there was no noise BTW) and that the timing had jumped. New chains/guides and it was good to go.
Originally Posted By: cchase
Originally Posted By: The Eric
What does the MAP reap at idle? KOEO?
The MAP data usually matches what I would expect. I forget how the numbers work but I think it usually sits at 14.7 with KOEO so I don't really suspect anything there. I haven't seen anything erratic in the readings.
I missed this the first time around, but I think GM engines should read actual barometric pressure with the key on, but engine off- the voltage should be around 4.5 volts at sea level. Engine running it should be in the vicinity of 1v.
Would you be willing to re-check this?
Originally Posted By: The Eric
What does the MAP reap at idle? KOEO?
The MAP data usually matches what I would expect. I forget how the numbers work but I think it usually sits at 14.7 with KOEO so I don't really suspect anything there. I haven't seen anything erratic in the readings.
I missed this the first time around, but I think GM engines should read actual barometric pressure with the key on, but engine off- the voltage should be around 4.5 volts at sea level. Engine running it should be in the vicinity of 1v.
Would you be willing to re-check this?
Originally Posted By: The_Eric
Originally Posted By: cchase
Originally Posted By: The Eric
What does the MAP reap at idle? KOEO?
The MAP data usually matches what I would expect. I forget how the numbers work but I think it usually sits at 14.7 with KOEO so I don't really suspect anything there. I haven't seen anything erratic in the readings.
I missed this the first time around, but I think GM engines should read actual barometric pressure with the key on, but engine off- the voltage should be around 4.5 volts at sea level. Engine running it should be in the vicinity of 1v.
Would you be willing to re-check this?
I will definitely double check with a multi-meter, but the units I was giving were psi, not volts. I'm more than willing to use a multimeter though, since I trust that more than OBD2 data anyway.
On a somewhat related note, today marks the first time I've put a scope on a crankshaft position sensor, so it was really neat to see a nice little square wave.
Originally Posted By: cchase
Originally Posted By: The Eric
What does the MAP reap at idle? KOEO?
The MAP data usually matches what I would expect. I forget how the numbers work but I think it usually sits at 14.7 with KOEO so I don't really suspect anything there. I haven't seen anything erratic in the readings.
I missed this the first time around, but I think GM engines should read actual barometric pressure with the key on, but engine off- the voltage should be around 4.5 volts at sea level. Engine running it should be in the vicinity of 1v.
Would you be willing to re-check this?
I will definitely double check with a multi-meter, but the units I was giving were psi, not volts. I'm more than willing to use a multimeter though, since I trust that more than OBD2 data anyway.
On a somewhat related note, today marks the first time I've put a scope on a crankshaft position sensor, so it was really neat to see a nice little square wave.
Okay, a meter would do the trick- I was thinking your scan tool would read voltage as well, as I know many do.
If it was giving you units in PSI, then I suppose 14.7 is in the ball park.
Basically what you're looking for is the high voltage, KOEO (around 4.5v) and low voltage at idle (highest vacuum/lowest pressure) at around .7v to 1.5 or so volts.
Also, forgive me if you've stated, but are you seeing any timing retard below the magic number or 3k RPM?
As a test, you could remove the knock sensor from the block, then reconnect the harness to it and ground the threaded portion, then take another test drive. No worries about coolant- they aren't tapped into the water jackets.
Another thing you can do is to drop it into gear, then while holding your foot firmly on the brake, apply WOT throttle. Should see over 1500RPM on the tach.
If it was giving you units in PSI, then I suppose 14.7 is in the ball park.
Basically what you're looking for is the high voltage, KOEO (around 4.5v) and low voltage at idle (highest vacuum/lowest pressure) at around .7v to 1.5 or so volts.
Also, forgive me if you've stated, but are you seeing any timing retard below the magic number or 3k RPM?
As a test, you could remove the knock sensor from the block, then reconnect the harness to it and ground the threaded portion, then take another test drive. No worries about coolant- they aren't tapped into the water jackets.
Another thing you can do is to drop it into gear, then while holding your foot firmly on the brake, apply WOT throttle. Should see over 1500RPM on the tach.
I'm not seeing any knock retard at any time during the lumpiness or the power surge.
I will check the MAP in the morning with a multimeter though.
I will check the MAP in the morning with a multimeter though.
I still have not checked the MAP sensor manually.
But, I did check the operation of the EGR tonight with a multimeter. The pintle is moving correctly, or at least the sensor is reporting that it is moving correctly.
It is fairly clear though, that the car is way down on power in general. And, I would have to say it is getting worse as time goes on, too.
But, I did check the operation of the EGR tonight with a multimeter. The pintle is moving correctly, or at least the sensor is reporting that it is moving correctly.
It is fairly clear though, that the car is way down on power in general. And, I would have to say it is getting worse as time goes on, too.
I agree with an above post.
It sounds like your ignition timing is being "pulled" for some reason. When this happens, uneven acceleration is often the result, coupled with lack of power.
1) It's possible your knock sensor is bad
2) It's possible your knock sensor is picking up some other noise
3) It's possible your octane is too low for summer conditions
4) It's possible that the air/fuel ratio is promoting knock
The first thing I'd try is to disconnect the knock sensor, as I'm fairly sure you've tried premium fuel from a name brand, high quality (and different) gas station.
It sounds like your ignition timing is being "pulled" for some reason. When this happens, uneven acceleration is often the result, coupled with lack of power.
1) It's possible your knock sensor is bad
2) It's possible your knock sensor is picking up some other noise
3) It's possible your octane is too low for summer conditions
4) It's possible that the air/fuel ratio is promoting knock
The first thing I'd try is to disconnect the knock sensor, as I'm fairly sure you've tried premium fuel from a name brand, high quality (and different) gas station.
I went to 93 octane w/ ethanol in my focus (10:1 compression with port injection) after getting great results with 91 ethanol free gas because it's cheaper from Sams Club.
The car has noticeable increase in torque below 2500RPM. As in, I can now shift at 2000RPM when starting out at the bottom of my hill. Before, I'd have to wind it out to 3000 otherwise it would just fall on it's nose.
Looking at the scanner, there's significantly less timing retard happening in the lower RPMs now.
The car has noticeable increase in torque below 2500RPM. As in, I can now shift at 2000RPM when starting out at the bottom of my hill. Before, I'd have to wind it out to 3000 otherwise it would just fall on it's nose.
Looking at the scanner, there's significantly less timing retard happening in the lower RPMs now.
Does the car downshift like it's supposed to when passing a car on the freeway?
That's lack of fuel supply. Try 1st stage fuel pump or 1st stage injectors could be weak. Only cure is to replace some of these parts
Originally Posted By: Cujet
I agree with an above post.
It sounds like your ignition timing is being "pulled" for some reason. When this happens, uneven acceleration is often the result, coupled with lack of power.
1) It's possible your knock sensor is bad
2) It's possible your knock sensor is picking up some other noise
3) It's possible your octane is too low for summer conditions
4) It's possible that the air/fuel ratio is promoting knock
The first thing I'd try is to disconnect the knock sensor, as I'm fairly sure you've tried premium fuel from a name brand, high quality (and different) gas station.
The only thing is that timing is not being pulled. I sit there and stare at the timing while driving along, accelerating, decelerating, and don't notice any anomalies. The same goes for all the other data I can poll, be it O2 sensor, fuel trims, MAF sensor, MAP sensor, engine load... Otherwise, I agree. I will try disconnecting the knock sensor. I have tried higher octane fuel to experiment but did not notice any change.
Originally Posted By: Merkava_4
Does the car downshift like it's supposed to when passing a car on the freeway?
The car downshifts normally.
Originally Posted By: Rosetta
That's lack of fuel supply. Try 1st stage fuel pump or 1st stage injectors could be weak. Only cure is to replace some of these parts
When I tested fuel pressure at the rail, it sits right where it should be at idle and WOT.
The latest "test" I tried, since the car is about to go on a 1000 mile trip, was to pull the (new) O2 sensor completely out of the manifold and try driving briefly. I would swear the problems went away, though I am not sure (it's hard to tell since the car is so loud which makes it seem faster regardless, and I did not want to do more than 2 accelerations with exhaust aimed right at the firewall). That, to me, points to an exhaust restriction, although it didn't show as such with a vacuum gauge...
I agree with an above post.
It sounds like your ignition timing is being "pulled" for some reason. When this happens, uneven acceleration is often the result, coupled with lack of power.
1) It's possible your knock sensor is bad
2) It's possible your knock sensor is picking up some other noise
3) It's possible your octane is too low for summer conditions
4) It's possible that the air/fuel ratio is promoting knock
The first thing I'd try is to disconnect the knock sensor, as I'm fairly sure you've tried premium fuel from a name brand, high quality (and different) gas station.
The only thing is that timing is not being pulled. I sit there and stare at the timing while driving along, accelerating, decelerating, and don't notice any anomalies. The same goes for all the other data I can poll, be it O2 sensor, fuel trims, MAF sensor, MAP sensor, engine load... Otherwise, I agree. I will try disconnecting the knock sensor. I have tried higher octane fuel to experiment but did not notice any change.
Originally Posted By: Merkava_4
Does the car downshift like it's supposed to when passing a car on the freeway?
The car downshifts normally.
Originally Posted By: Rosetta
That's lack of fuel supply. Try 1st stage fuel pump or 1st stage injectors could be weak. Only cure is to replace some of these parts
When I tested fuel pressure at the rail, it sits right where it should be at idle and WOT.
The latest "test" I tried, since the car is about to go on a 1000 mile trip, was to pull the (new) O2 sensor completely out of the manifold and try driving briefly. I would swear the problems went away, though I am not sure (it's hard to tell since the car is so loud which makes it seem faster regardless, and I did not want to do more than 2 accelerations with exhaust aimed right at the firewall). That, to me, points to an exhaust restriction, although it didn't show as such with a vacuum gauge...
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