Engine vibration, should I be concerned?

[qsiguy]

My car is a 94 Q45. Has just over 150K miles. Recently noticed more vibration than usual. Most noticable in the 2K RPM range under acceleration but it will do it sitting in park as well so I've ruled out the transmission. I did just have the oil changed a few weeks ago and it's gotten worse since then I believe. I've was thinking of selling (prior to this issue), then decided to keep and fix up and possibly even install a rear mounted turbo. Should I be concerned about this vibration? I'm wondering if I boost it via turbo is this motor going to self destruct? Or even without upgrades, is it on it's last leg or in major need of service? I've had the car for about 5-6 years and it's been reliable so far. Semi recent repairs include fuel pump, alternator, and water pump.

I used the search but nothing that came up matched my problem.

[chinaonnitrous]

Theres a bunch of crap in the technical help section

I just looked throuh 37 pages of it.

Seems like the culprits are either transmission/motor mounts, exhaust hangers, or a worn driveshaft......

[maxnix]

Need to follow the search tutorial. Do text body and archives.

Did the filter get changed from the top? Look at MAF connector and don't do it that way again.

Any vibration in a VH45DE is a matter of concern. Instant indicator something is wrong.

[goody90q45]

I agree with both posts so far. Both items are very easy to check. I haven't had MAF problems but there are plenty of posts on easy checks of MAF function. I did just change out my transmission mount and hangers and it got rid of vibrations I didn't even know I had. Before doing this I thought my vibration was limited to the 2000 rpm range. Check recent message thread titled "vibration at 2250 rpm" for detailed discussions.

Since you described the problem as "vibration" rather than "engine missing" my guess is the transmission mount and exhaust hangers. Easy to check. The two exhaust hangers are attached to the rear end of the transmission mount which is at the aft end of the transmission. Get the car off the ground and jack up the transmission at the pan about 1/2" to 1". Make sure to put a thick piece of wood between the jack and the pan. The wood needs to be longer (or wider) than the pan so you don't point load the pan when jacking. As you jack it up you will see the rubber pads of the exhaust hangers separate from their brackets. Mine were about 75% separated and my transmission mount was just about fully compressed. If you have vibration at all rpm's and even at idle, and it's not engine misfire or MAF related, then I would guess your exhaust mounts have completely separated. Bad engine mounts would also cause vibration but I haven't gotten to these yet on my Q.

Remember that all this is only a guess but as Wes suggested to me "check the easy stuff first". Good advice.

Good luck

[Q451990]

I'm leaning toward a bad injector causing an engine miss. Does your vibration feel more like a "bounce" at idle? If so I would ohm test your injectors - that won't tell you if it's physically clogged, but it's a start.

Heath

[Q_SHIP]

I would say bad injector as well. Mine had the exact same symptoms as yours and it turned out to be a bad injector. I replaced it and it ran like butter. Ohm test at your harness to check resistance. Very easy thing to do. Use this link for instruction.

http://q45.org/ohminjectors.html

Don't boost it untill that is fixed. Running cylinders lean on boost is a big no no oh

[elwesso]

I think members must go through an intense screening process in order to be allowed to modify their cars............ stereo, "boost", whatever.... doing modifications to an incapable car will only mean bad things........!

if its the booming noise, id check the thread about the exhaust..... There was a TSB (that i do not have on my laptop as im out of town).... it would happen at 50mph in 3rd gear and like 80 in 4th....

I have a vibration after 80mph, and im going to replace my transmission mount, possibly with a 300ZX poly mount so it limits engine movement and also wont go flat like the OEM ones.... exhaust isnt it i dont think because i have an aftermarket, but im gonna cut my rear cans out....

[qsiguy]

Thanks guys, there really isn't any vibration at idle, just around 2K rpm. There was a problem with the MAF harness but that was causing rough idle and stalling and is ok now. I suppose there still could be issues with it but it doesn't really feel like it. I'll check out the mounts and the injectors and I'll post my findings.

One question, the injector checking guide says "...check the injector resistance when the plenum is off." What does that mean? Ignition off? Guess i'm not sure what the "plenum" is.

[chinaonnitrous]

The big spider intake thingy.

[qsiguy]

Oh, I got ya. I thought that was the intake manifold! hehe. Guess "plenum" sounds more complicated and high tech.

[qsiguy]

OK, did the injector test procedure. Unplugged the socket, tested ohms, all around 48 ohms. Turned the ignition key on then off then they were all at 15-15.5 ohms. I don't believe they would all be bad?! The car runs strong, has plenty of power. Just has the slight vibration at the 2K rpm range driving or not. Going to check the mounts next.

[gniknave]

I'd re-ohm the injectors again. Between 10-14 ohms is where you want to be. I can't imagine all 8 would be at 15... That would be costly and you'd notice it a little more than just at 2000rpm... If the vibration you feel doesn't happen at idle, then I'd probably look past the injectors. Do you feel a loss in power? Have you done the "wiggle test"?

[qsiguy]

I think I've ruled out the MAF, yes did the wiggle test when it was idling rough and stalling and that's ok now. I'm a little confused about the injectors. Let me explain my findings and you guys let me know what's up. I have owned an auto electronics business for years so I know my way around a multimeter but I am getting some wierd readings.

Ok, first I unplugged the injector harness (as per the injector test procedure) and my first reading was about 48 ohms on each injector pin. Next I turned the ignition on and checked and they were all around 500K ohms +/- (I didn't pay much attention as I didn't think the key ON reading was pertinant). Then I turned the key off and that's when I got the 15-15.5 ohm reading on each injector. Since I posted my readings I've checked them two more times and got strange readings and cannot duplicate my 15 ohm test. One test showed again up near the first test and got about 52 ohms and later got around 60 ohms. I tried turning the ignition ON and OFF again but there was no change. Can anyone explain why I am getting strange readings? I plan to check it again tomorrow with a different meter (first was a Fluke meter, next one is also a Fluke but an upgraded one).

Like I said before, the car seems to have no power loss and the problem isn't noticable at idle. I did notice on the way home from work today that the vibration has an obvious low frequency resonation associated with it.

Sorry for the long post...

[Q45tech]

150k and 12 year old 94Q = motor and transmission mounts...........what is the frequency of the vibration at 2,000 rpm?

http://www.vibrationdata.com/software.htm

http://www.vibratesoftware.com/vibsoft/ ... om...e.htm

[Q45tech]

Dozens of things need testing without the frequency measurement of vibration.

[Q45tech]

"An extremely useful device can be added to all vehicles which is capable of monitoring many aspects of a vehicles operation. A warning can be provided whether a wheel becomes imbalanced, or a tire loses air pressure, or a universal joint is failing, or the engine is misfiring. Many other aspects of a vehicle are also capable of being monitored.The device is actually quite simple. The sensor is merely a broadband vibration sensor, such as many standard devices that are based on piezoelectric crystals, solidly mounted to the frame of the vehicle. This sensor is connected to a circuit that does Fourier analysis of the complex incoming waveform patterns. Again, this is really just a standard device, often used in music software, to create sheet music. In that use, any complex input musical composition is Fourier-analyzed, which determines exactly what dominant frequencies exist in the complex input signal, and the program then has the capability of writing the sheet music for the composition. That standard software is capable of recognizing a large assortment of separate frequency components in the complex source signal.

This application does the same thing, but uses the complex vibration signals from the vibration sensor as the source. If any dominant frequencies exist in that signal, the Fourier analyzer would identify them. Fairly simple software could then give output warnings (lights or messages) for the various conditions that could cause specific vibration frequencies.

A vehicle speed sensor is also necessary for the fullest analysis of such vibrations.

Let's say the vehicle is traveling at highway speed. The computer would know from the speed (and the pre-set wheel diameters) that the wheels were rotating at about thirteen times per second. If a significant vibration of 13 hertz appears, it would be an indication of a wheel that had become imbalanced. If a vibration of 26 hertz appeared, it could be an indication of a failing CV joint. If around 40 or 80, a universal joint could be failing. Certain higher specific frequencies could identify differential or transmission problems beginning.

If a vibration of around 30 hertz arose, it could be an indication of the beginnings of an engine cylinder that is not firing as well as the others. Certain very specific, very high frequencies are related to disk brake operation. Some of those frequencies are normally produced but some are indications that the brake system would soon need maintenance.

There are more sophisticated uses of this vibration information. There is ALWAYS a background of miscellaneous vibrations of many frequencies present. If the signal processing system (or computer) would record and store a normal vibration signature, then several more subtle applications could be included. Much of that background vibration is created in the suspension system and is primarily due to the conditions involved in the tires contacting the road. If the background vibration would suddenly get much less, this would likely be an indication that the vehicle is 'hydroplaning' on a wet road or sliding on a icy road. There are no other indicators of such situations that exist that cost less than a whole vehicle costs!

If, instead, the low and middle frequencies of the background vibrations remain, but the high frequency background vibrations become significantly less, this is likely to indicate that one or more tires have lost some air. A tire with low pressure actually 'rides' softer, which effectively means that the high frequency component of road imperfections would be substantially reduced.

A related application would probably involve such (inexpensive) sensors at each of the vehicle's wheels. A vehicle's loading affects the natural frequency at which the springs on each wheel oscillate (called the spring rate). A vehicle with just a driver would have specific, very precise spring rates for each wheel. If a passenger gets in, the additional loading for the suspension on the passenger side wheels would slightly alter the spring rates for those wheels. If each wheel is separately monitored, a vehicle could actually 'know' IF a passenger was present, and even the approximate weight of the passenger. It could identify if the trunk was loaded with weight, which could affect vehicle handling, and offer a warning for the driver. The sensing of a passenger should be accurate enough that a passenger seat belt warning could be presented, and even a dual power safety air-bag could know the weight of the passenger, so it would automatically use a low impact air-bag velocity for a child but a full air-bag deployment for an adult.

There are an assortment of other diagnostic applications, but I suspect you should probably get the point by now. Most of these maintenance matters are not monitored in any other way, so, generally an actual failure must occur in some assembly. This method of sensing is so sensitive that it would give indication of the various maintenance considerations far before an actual breakdown could occur. This includes such things as fan belts, which have their own natural resonances, and these frequencies gradually change well prior to a belt failing. This device could indicate a fan belt that would fail weeks in the future, and no other device could give such warning.

Best of all, the vibration sensor is on the scale of a dollar and a device with a Fourier-analysis processor could certainly be mass produced for under $20, so the whole system is remarkably inexpensive! No new or exotic technology is involved, and both vibration sensors and Fourier-analyzers are now very common devices."

[RobertsnewQ]

Transmission mount.

Just did mine. Makes a BIG difference around 2000 RPM.

[qsiguy]

Finally climbed under the Q to look at the transmission mount. Looks like it's due for replacement. I found a photo of a new transmission mount on here about 3 weeks ago searching for vibration problems but now I can't find it. Anyone have the link to the new transmission mount photo? I want to compare what I saw on mine.

[elwesso]

zer...age=2

[qsiguy]

Thanks, definitely needs to be replaced!

[maxnix]

I think members must go through an intense screening process in order to be allowed to modify their cars............ stereo, "boost", whatever.... doing modifications to an incapable car will only mean bad things............

Restore to OEM first, then change only after extensive reading of the posts on this board. Q45tech has tried virtually everything and has a litany of modifications that either don't work or are marginal considering the compromises they make.

Rear engine (transmission mount) is indicated when vibration is at 47-52 mph in 3 and 69-74 mph in D (depends on radius of tires).

Shouldn't this be in Infiniti Mechanic where this has been discussed in about 8 different threads?

[Jesda]

Hell, does the Online Mechanic section even need to exist anymore now that the models have been segmented? Its all pretty redundant to me.

[Rex]

Hell, does the Online Mechanic section even need to exist anymore now that the models have been segmented? Its all pretty redundant to me.

This point has been made and we (the mod team) will work more dilgently in tying thread like this to existing relevant threads or moving them.