I am new to this forum, but it seems that there is tons of useful information about Q's. I own Q45 1994 with 105K on it. The car runs fine until I push it to 100mph, which then starts vibrate only when I press the gas pedal. If I release the pedal, the car slows down smoothly but when I try to accelerate I fill rythmic vibration again. The vibration dissappears when I slow down to 40mph and then the car drives normal again. In the past two years I replaced all fuel injectors, fuel pump, egr valve, and valve cover gaskets. I was thinking about replacing the O2 sensors but don't know how to check if they are ok or not.
Any reply will be greatly appreciated.
Vibration only when reach 100mph!!
-
cweberj30t
- Posts: 457
- Joined: Sun Oct 05, 2003 7:24 pm
- Car: 1993 J30t
2003 G35
2007 G35X
2011 G37X
-
Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Measure the frequency of vibration at speed and rpm.
The engine has vibrations at 1800 and 3600 rpms [roughly 108 mph]........when were motor mounts last changed [they only last 100-120k].
2nd harmonic of tires can occur around 110 mph.
Without frequency data it's a guess! Tires, wheels, rotors, driveshaft, transmission- TC, or engine.
The engine has vibrations at 1800 and 3600 rpms [roughly 108 mph]........when were motor mounts last changed [they only last 100-120k].
2nd harmonic of tires can occur around 110 mph.
Without frequency data it's a guess! Tires, wheels, rotors, driveshaft, transmission- TC, or engine.
Here is more info about my situation. I have four new michellin XGT4 V-rated tires (all well balanced). Dealer checked my motor mounts about three months ago and said that they are ok. Also, the power balance doesn't show any inconsistency in engine performance. The vibrartion seems to be too strong to come from the road (vibration feels like if am playing with the gas pedal, pressing and releasing maybe every 1/3 of a second).
Thanks.
Thanks.
-
Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
"Dealer checked my motor mounts about three months ago and said that they are ok."
How would they know good from bad without removing them? Not something you can see!
"maybe every 1/3 of a second)."".....................human time perception is not reliable!
Don't assume tires [even new Michelins] and oem wheels [rotors] are ok unless you test them on Hunter 9700.
98% of time high speed [above 50 mph] vibrations come from tires wheels/rotors.
Simple test: change gears same speed in 4th and 3rd [good to 130 mph at minimum]...........if the vib is the same then its aft of the transmission
How would they know good from bad without removing them? Not something you can see!
"maybe every 1/3 of a second)."".....................human time perception is not reliable!
Don't assume tires [even new Michelins] and oem wheels [rotors] are ok unless you test them on Hunter 9700.
98% of time high speed [above 50 mph] vibrations come from tires wheels/rotors.
Simple test: change gears same speed in 4th and 3rd [good to 130 mph at minimum]...........if the vib is the same then its aft of the transmission
March tempo = 120 beats per minute. Half note triplets at that tempo would simulate the shudder frequency. 180 beats/minute. Seems a little slow for tires at 100 mph.Q45tech wrote:"maybe every 1/3 of a second)."".....................human time perception is not reliable!
This is a very reliable method for determining tempo. Some people use time and rhythm take make a living. Dennis, perhaps you might have been refering to a couple of drummers I've worked with. Then again, those guys aren't really all that human either.
-
Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Tires vibrate at 13 Hz at 60 mph...........6.544 feet divides into 88 feet/sec= 13 +- 0.5 Hz.........2nd, 3rd harmonics or 100 mph =36 Hz and 72 Hz.
What you are feeling is the difference beat between front rear tires as the diameters are different based on inflation and load between front and rear........if it really is 1-2 Hz.
If tires are not perfectly straight ahead there will be a difference in rotation distance/speed.
What you are feeling is the difference beat between front rear tires as the diameters are different based on inflation and load between front and rear........if it really is 1-2 Hz.
If tires are not perfectly straight ahead there will be a difference in rotation distance/speed.
Pythagorous discovered the harmonic series 2500 years ago. Fascintaing relationships. All things are resonant bodies and all things have precisely the same resonant frequencies based upon their fundamental pitch. This never varies.
The fundandental pitch resonates at a ratio of 1:1, the second harmonic at 1:2; third, 1:3; fourth, 1:4; fifth, 1:5; etc.
Tonally (frequency) this can be demonstrated as a fundamental of the given note C; its first overtone (or second harmonic) C1; second overtone, G1; third, C2; fourth E2; fifth, G2 [we have a nice sounding major chord so far]; 6th, Bb2 [now we have something called a dominant 7th chord which is disonant by definition], 7th overtone, C3 [or the eighth harmonic at a ratio of 1:4]; 8th overtone, D3 [we now have what is called a ninth chord which is quite disonant (notice how the intervals are becoming closer and closer in frequency)] and so on. Go high enough and you get to fractions of tones and then fractions of semitones.
If you have a piano you can roughly recreate this series of tones but the piano is a system of ultimate compromise. The intervals you arive at on a piano key board are tempered since the piano keyboard is tuned in a series of equidistant 1/2 tones. Why? because when you start dividing the ratios of the of the harmonics into the frequency of the fundament you arrive at non interger numbers.
I could go on about other things called resultant tones which are pitches that are created by the reinforcing of overtones by other overtones to create a more prominent pitch than would normally be there.
Dennis you are absolutley correct that tire inflations, different wear rates, loads will create interfere patterns. However, given the aproxiamate tires circumference the resultant pitch variation would sound more like a wavering humm.
People wonder what the heck a harmonic balancer is on their exhaust. Well, its there for a reason and that reason is wieght saving among other things.
Somebody please stop me...............
Now the interesting part that determines quality of the resonance is the prevalent overtones of the fundamental pitch which are comprised of its harmonics. A violin sounds different than a clarinet because of the prevalence of favoured harmonics reinforced by the characteristics of the resonant material..........
I'm stopping myself now.
The fundandental pitch resonates at a ratio of 1:1, the second harmonic at 1:2; third, 1:3; fourth, 1:4; fifth, 1:5; etc.
Tonally (frequency) this can be demonstrated as a fundamental of the given note C; its first overtone (or second harmonic) C1; second overtone, G1; third, C2; fourth E2; fifth, G2 [we have a nice sounding major chord so far]; 6th, Bb2 [now we have something called a dominant 7th chord which is disonant by definition], 7th overtone, C3 [or the eighth harmonic at a ratio of 1:4]; 8th overtone, D3 [we now have what is called a ninth chord which is quite disonant (notice how the intervals are becoming closer and closer in frequency)] and so on. Go high enough and you get to fractions of tones and then fractions of semitones.
If you have a piano you can roughly recreate this series of tones but the piano is a system of ultimate compromise. The intervals you arive at on a piano key board are tempered since the piano keyboard is tuned in a series of equidistant 1/2 tones. Why? because when you start dividing the ratios of the of the harmonics into the frequency of the fundament you arrive at non interger numbers.
I could go on about other things called resultant tones which are pitches that are created by the reinforcing of overtones by other overtones to create a more prominent pitch than would normally be there.
Dennis you are absolutley correct that tire inflations, different wear rates, loads will create interfere patterns. However, given the aproxiamate tires circumference the resultant pitch variation would sound more like a wavering humm.
People wonder what the heck a harmonic balancer is on their exhaust. Well, its there for a reason and that reason is wieght saving among other things.
Somebody please stop me...............
Now the interesting part that determines quality of the resonance is the prevalent overtones of the fundamental pitch which are comprised of its harmonics. A violin sounds different than a clarinet because of the prevalence of favoured harmonics reinforced by the characteristics of the resonant material..........
I'm stopping myself now.
-
Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
That'd why they make frequency counters and Fast Fourier Transform software to display the tiny increments between cycles [Hertz].
http://www.ecn.purdue.edu/Herr...n.pdf
http://www.vibratesoftware.com...l.htm
http://www.vibratesoftware.com...s.htm
http://www.vibratesoftware.com...e.htm
http://www.ecn.purdue.edu/Herr...n.pdf
http://www.vibratesoftware.com...l.htm
http://www.vibratesoftware.com...s.htm
http://www.vibratesoftware.com...e.htm
Tires will respond to the reduction of torque when you release the gas pedal. There is a considerable amount of power being applied to those drive wheels at 100mph. I had a set of tires that would vibrate when I released the gas. This made me think all kinds of things were wrong with my car from axles to the drive shaft. A new set of tires and every symptom went away. A miracle cure. Have you tried rotating your tires to see if it changes the vibration characteristic?
-
Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
The only way to know for sure is the Hunter 9700 radial force balance test at $25-$30 per tire ............. any tire wheel combo that shows over 5 pounds of radial force imbalance.
Even Michelin XGTV4 are not all 100% perfect after being used even 500 miles.
You didn't say what type of wheels you were using, even the oem get weird after the warranty........tiny microbends slowly getting out of spec expecially on inside lips.
Even Michelin XGTV4 are not all 100% perfect after being used even 500 miles.
You didn't say what type of wheels you were using, even the oem get weird after the warranty........tiny microbends slowly getting out of spec expecially on inside lips.
-
texasoil
- Posts: 875
- Joined: Mon Sep 02, 2002 3:18 pm
- Car: '92 Infiniti Q45A
'94 Infiniti Q45A
'94 Mercedes-Benz SL600
high speed vibration
First try raising the tire pressure to the max and see it it changes the vibration. If it does--look to tires.
Things get weird at higher speeds. I had a 560 SEL MBZ (89 was the BEST car every made IMHO) note not best value maybe.
At about 110 a strong shudder would develop in the front end--a low frequency one very far removed from tire speed. The suspension was new condition, nothing loose or work, properly aligned, etc. Wheel bearings were properly adjusted and smooth.
On a hunch, duct taped a stiffner behind the ends of the front bumper/spoiler---shudder disappeared. It was vortex shedding exciting the flexible bumper cover assembly.
Yours sounds more like high speed ignition miss or fuel starvation.
Things get weird at higher speeds. I had a 560 SEL MBZ (89 was the BEST car every made IMHO) note not best value maybe.
At about 110 a strong shudder would develop in the front end--a low frequency one very far removed from tire speed. The suspension was new condition, nothing loose or work, properly aligned, etc. Wheel bearings were properly adjusted and smooth.
On a hunch, duct taped a stiffner behind the ends of the front bumper/spoiler---shudder disappeared. It was vortex shedding exciting the flexible bumper cover assembly.
Yours sounds more like high speed ignition miss or fuel starvation.
-
AlabamaDan
- Posts: 1750
- Joined: Fri Aug 02, 2002 12:37 pm
- Car: 2015 Infiniti Q70
1998 Infiniti QX4
-
psychic_mechanic
- Posts: 296
- Joined: Wed Jan 07, 2004 6:45 am
- Car: the world's ugliest civic