Why does the renesis "lope" at idle?
05-17-2004, 12:52 AM
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Why does the renesis "lope" at idle?
You all know what I mean... kind of a lope or lump or just generally not a smooth idle.
Can someone explain this to me? I would think it would be perfectly smooth, kinda like an electric motor whirring away, but it's not. Is it fuel delivery problems, or some function of how the rotary engine runs?
Rotarygod? MazdaManiac? (etc) Any of you experts listening?
Can someone explain this to me? I would think it would be perfectly smooth, kinda like an electric motor whirring away, but it's not. Is it fuel delivery problems, or some function of how the rotary engine runs?
Rotarygod? MazdaManiac? (etc) Any of you experts listening?
05-17-2004, 03:12 AM
#2
I was long wondering about the same thing.
Those little hiccups during idle sound like the car is kinda misfiring... why is it not as smooth like at high revs? Strange.
My ten years old Ford Probe GT with 128K miles seems to have a smoother idle.
Those little hiccups during idle sound like the car is kinda misfiring... why is it not as smooth like at high revs? Strange.
My ten years old Ford Probe GT with 128K miles seems to have a smoother idle.
05-17-2004, 07:09 AM
#4
Momentum Keeps Me Going
Yea, every time I sit in the car waiting for a light w/hand on the shifter, I ask myself the same question.
Then again, I think the whole car feels a little 'rough' in character when going slow too. It definitely smooths out wonderfully after getting up to speed.
Perhaps it has the 'exotic-car' trait of being much more at home at high speeds/high RPMs where it can stretch it's legs?
Then again, I think the whole car feels a little 'rough' in character when going slow too. It definitely smooths out wonderfully after getting up to speed.
Perhaps it has the 'exotic-car' trait of being much more at home at high speeds/high RPMs where it can stretch it's legs?
05-17-2004, 07:25 AM
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doea anyone here have the K and N, becuase that has a history of a rough idle. Mine runs just as smooth as any other car that i have ever owned, maybe even smoother.
05-17-2004, 08:02 AM
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Originally posted by RAM
mine purrs. No loping here.
mine purrs. No loping here.
What we need is for someone whose car "lopes" to check out in person someone else's car that supposedly doesn't "lope."
05-17-2004, 08:59 AM
#8
FOr those that believe your engine does not "lope" or "surge" at idle:
Look at your shifter ****. If it moves at all while the car is idling, your engine lopes.
I wonder about the auto people since so much is different in their vehicles.
The loping is mostly due to the inability to reach a satisfactory mixture at idle.
Idle is the most inefficient RPM range for any engine and it is even more so on the Renesis.
In order to keep the emissions as low as possible, the PCM runs the motor very lean at idle and reverses the ignition sequence to effectively advance the ignition to make up for the -5° or so retard that takes place.
It is suprising that the motor idles at all!:p
Look at your shifter ****. If it moves at all while the car is idling, your engine lopes.
I wonder about the auto people since so much is different in their vehicles.
The loping is mostly due to the inability to reach a satisfactory mixture at idle.
Idle is the most inefficient RPM range for any engine and it is even more so on the Renesis.
In order to keep the emissions as low as possible, the PCM runs the motor very lean at idle and reverses the ignition sequence to effectively advance the ignition to make up for the -5° or so retard that takes place.
It is suprising that the motor idles at all!:p
05-17-2004, 09:04 AM
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Originally posted by PhineasFellOff
You know what people are thinking- that your car "lopes" but you're just not cognizant of it.
What we need is for someone whose car "lopes" to check out in person someone else's car that supposedly doesn't "lope."
You know what people are thinking- that your car "lopes" but you're just not cognizant of it.
What we need is for someone whose car "lopes" to check out in person someone else's car that supposedly doesn't "lope."
How could anyone miss it if their car lopes? I know smooth . . . I know purr . . . I know steady . . . a tach with a steady rpm at idle isn't loping.
05-17-2004, 09:08 AM
#10
Originally posted by RAM
How could anyone miss it if their car lopes? I know smooth . . . I know purr . . . I know steady . . . a tach with a steady rpm at idle isn't loping.
How could anyone miss it if their car lopes? I know smooth . . . I know purr . . . I know steady . . . a tach with a steady rpm at idle isn't loping.
Loping is not a change in RPM and the RX-8 tach is to slow to report any fast variations in RPM if they existed, anyway.
05-17-2004, 09:58 AM
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ok. So if one can not know if one is loping or not . . . since a smooth steady idle and a steady rpm are not evidence of a lack of loping (no little hiccups or the other descriptions used on the thread) . . . then how can anyone possibly say they aren't loping . . . and if that is true why would anyone ask the question to start with since the only acceptable anwers seem to be 1) yes or 2) no way for me to tell so I don't know. (unless of course I have equipment to test for "loping" but I thought the question was based on sense rather than mechanical measurement.)
05-17-2004, 10:21 AM
#13
Originally posted by RAM
ok. So if one can not know if one is loping or not . . . since a smooth steady idle and a steady rpm are not evidence of a lack of loping (no little hiccups or the other descriptions used on the thread) . . . then how can anyone possibly say they aren't loping . . . and if that is true why would anyone ask the question to start with since the only acceptable anwers seem to be 1) yes or 2) no way for me to tell so I don't know. (unless of course I have equipment to test for "loping" but I thought the question was based on sense rather than mechanical measurement.)
ok. So if one can not know if one is loping or not . . . since a smooth steady idle and a steady rpm are not evidence of a lack of loping (no little hiccups or the other descriptions used on the thread) . . . then how can anyone possibly say they aren't loping . . . and if that is true why would anyone ask the question to start with since the only acceptable anwers seem to be 1) yes or 2) no way for me to tell so I don't know. (unless of course I have equipment to test for "loping" but I thought the question was based on sense rather than mechanical measurement.)
05-17-2004, 11:37 AM
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In my old 1st Gen 7, (carburetted - no EFI) the popping sound was backfiring. Soft and subtle, but backfiring none the less. It did it for the life of my car, and was due to the ham handed emissions systems on the early models.
Perhaps the 8's rich mixture is igniting in the cat?
Perhaps the 8's rich mixture is igniting in the cat?
05-17-2004, 12:03 PM
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On my previous car ('93 FD) I noticed a bit of this...when I think of a "loping idle" I was thinking of something more rhythmic...occasionally the FD would sound a bit like a miss, but it would generally stay steady. It has done that for as long as I can remember. I haven't really noticed it so much with the 8, but the shifter vibrates a lot more. Now, is that a lope? Its constant, and way too quick to be considered irregular, so I don't think so. Now, I'll have to go listen for anything else. The exhaust on my FD was MUCH louder, so that undoubtedly made it more obvious than on the 8.
jds
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05-17-2004, 12:08 PM
#19
Well, I think we are using the term "lope" incorrectly, which is why I put it in quotes in my original post.
There is a wide array of what is considered "smooth" since it is an aesthetic judgment.
It is also important to note that this "lope" is not a problem of some sort, just a characteristic of a running motor, regardless of design.
There is a wide array of what is considered "smooth" since it is an aesthetic judgment.
It is also important to note that this "lope" is not a problem of some sort, just a characteristic of a running motor, regardless of design.
05-17-2004, 12:31 PM
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I think the problem is that "loping" hasn't been sufficiently described. What I thought Omicron was referring to was a intermittent yet very noticeable fluctuation of engine idle vibration levels in the cabin, i.e. pitch or roll of the body, shift lever vibration, seat vibration, etc. Idle may seem smooth for a few seconds, but then seems to transition to a rougher idle, then back to smooth, and so on.
Since I consider myself to be relatively knowledgeable about this subject, let me point out a few things:
First of all, there is no such thing as a perfectly smooth engine, as you probably all know. Even a rotary engine with no reciprocating parts will not have a perfectly smooth idle. If you look at a time trace of engine speed or flywheel torque versus time, there is oscillation, or a so-called dynamic component, due to explosions of the air-fuel mixture, exhaust, intake, etc. I'm not sure how the magnitude of this dynamic component for rotary engines compares with gasoline engines, however. For instance, diesel engines have a much larger dynamic component than gasoline engines, and hence are much harder to isolate from an NVH (noise, vibration, and harshness) standpoint. I would imagine, in fact, that the dynamic torque from a rotary engine is similar to or higher than that of a piston engine since it generates a similar amount of torque with a much smaller combustion volume. Someone please correct me if I'm wrong--I'm a rotary newbie.
However, dynamic torque generated by the engine is only half of the equation when it comes to a perceived "rough" or "lopy" idle. The other half depends largely on how the powertrain is isolated, or mounted. A good isolation scheme can make even the roughest of engines appear smooth to the driver, while a poor isolation scheme can make a smooth engine seem extremely rough. This is a complicated issue since tradeoffs must be made among cost, NVH, packaging, and durability when the powertrain mounts are being designed. It's a compromise that doesn't always yield an optimally tuned mount.
Also, manufacturers employ a number of measures to quantify the interior NVH quality. The most important ones are usually seat track vibration, steering wheel vibration, shift lever vibration (manual trans), and sound pressure level and spectral contents at the driver's ear. I think Mazda did a great job with respect to most of these measures, with the exception of the shift lever vibration. (MazdaManiac--the shift lever in any vehicle would vibrate if not properly isolated, so it's not really an indication of "lopy" idle). I had a '90 Integra that had an insane amount of steering wheel vibration, shift lever vibration, and wind noise. (In general, Honda lags behind the rest of the industry when it comes to NVH, but they are improving quickly.)
As for my opinion on the lopy idle: if my interpretation of what Omicron is describing is correct, I have the same issue. The idle seems really smooth for a period of time, but encounters some rough periods that can definitely be felt in the cabin. It's difficult to say what exactly is happening since the PCM employs a rather complex control scheme. It might be related to changing air-fuel mixtures, or it might just be interaction with the various engine accessories (water pump, compressor, power steering pump, etc.) that create a constantly varying load on the engine. Any number of factors would change the vibration characteristics of the engine, and it's not always possible to design an isolation scheme that will sufficiently attenuate interior vibration levels for all of these cases. Overall, I'm happy with the NVH characteristics of my particular RX-8. If some of you believe you are experiencing more extreme symptoms, it's possible you might have a problem, however.
Since I consider myself to be relatively knowledgeable about this subject, let me point out a few things:
First of all, there is no such thing as a perfectly smooth engine, as you probably all know. Even a rotary engine with no reciprocating parts will not have a perfectly smooth idle. If you look at a time trace of engine speed or flywheel torque versus time, there is oscillation, or a so-called dynamic component, due to explosions of the air-fuel mixture, exhaust, intake, etc. I'm not sure how the magnitude of this dynamic component for rotary engines compares with gasoline engines, however. For instance, diesel engines have a much larger dynamic component than gasoline engines, and hence are much harder to isolate from an NVH (noise, vibration, and harshness) standpoint. I would imagine, in fact, that the dynamic torque from a rotary engine is similar to or higher than that of a piston engine since it generates a similar amount of torque with a much smaller combustion volume. Someone please correct me if I'm wrong--I'm a rotary newbie.
However, dynamic torque generated by the engine is only half of the equation when it comes to a perceived "rough" or "lopy" idle. The other half depends largely on how the powertrain is isolated, or mounted. A good isolation scheme can make even the roughest of engines appear smooth to the driver, while a poor isolation scheme can make a smooth engine seem extremely rough. This is a complicated issue since tradeoffs must be made among cost, NVH, packaging, and durability when the powertrain mounts are being designed. It's a compromise that doesn't always yield an optimally tuned mount.
Also, manufacturers employ a number of measures to quantify the interior NVH quality. The most important ones are usually seat track vibration, steering wheel vibration, shift lever vibration (manual trans), and sound pressure level and spectral contents at the driver's ear. I think Mazda did a great job with respect to most of these measures, with the exception of the shift lever vibration. (MazdaManiac--the shift lever in any vehicle would vibrate if not properly isolated, so it's not really an indication of "lopy" idle). I had a '90 Integra that had an insane amount of steering wheel vibration, shift lever vibration, and wind noise. (In general, Honda lags behind the rest of the industry when it comes to NVH, but they are improving quickly.)
As for my opinion on the lopy idle: if my interpretation of what Omicron is describing is correct, I have the same issue. The idle seems really smooth for a period of time, but encounters some rough periods that can definitely be felt in the cabin. It's difficult to say what exactly is happening since the PCM employs a rather complex control scheme. It might be related to changing air-fuel mixtures, or it might just be interaction with the various engine accessories (water pump, compressor, power steering pump, etc.) that create a constantly varying load on the engine. Any number of factors would change the vibration characteristics of the engine, and it's not always possible to design an isolation scheme that will sufficiently attenuate interior vibration levels for all of these cases. Overall, I'm happy with the NVH characteristics of my particular RX-8. If some of you believe you are experiencing more extreme symptoms, it's possible you might have a problem, however.
05-17-2004, 03:52 PM
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If you want an extreme example of loping idle, listen to a V8 with a 3/4 or full race cam. Radical swings in RPM due to the cam being designed to be optimal at higher rpms only.
Since the rotary has no cam, the loping is most likely tied to the PCM and the intake system. The PCM theoretically can be designed to be optimal at all speeds. The intake system is designed for three distinct rpm ranges but is suboptimal at idle.
Oh yeah, mine lopes significantly. Hard to tell the exact rpms, but I would say it varies between 900 and 600 rpms.
Since the rotary has no cam, the loping is most likely tied to the PCM and the intake system. The PCM theoretically can be designed to be optimal at all speeds. The intake system is designed for three distinct rpm ranges but is suboptimal at idle.
Oh yeah, mine lopes significantly. Hard to tell the exact rpms, but I would say it varies between 900 and 600 rpms.
05-17-2004, 04:00 PM
#25
Have you ever heard a bridge ported rotary at idle? That's the most beautiful music to my ears! BRAP, BRAP, BRAP...
Is this what you mean by loping? I don't own an RX-8 but when I test drove it several times now I thought it had the smoothest idle ever!
My protege5 shift **** also vibrates at idle (or any other rpm), does this mean I have rough idle?
What I don't like about the piston engine sound is the rickety-rack of the valve train, awful!
Is this what you mean by loping? I don't own an RX-8 but when I test drove it several times now I thought it had the smoothest idle ever!
My protege5 shift **** also vibrates at idle (or any other rpm), does this mean I have rough idle?
What I don't like about the piston engine sound is the rickety-rack of the valve train, awful!