Vibration @ 2250rpm

[GRADEST]

I Have a 94 q45t with a vibration @ 2250rpm. The tires are new and have been checked for balance. All the injectors are working properly and test @ the correct ohms. The driveshaft is original . The u- joints are good. The carrier bearing is good. The motor mounts are new. The transmission mount is 60%. The engine is timed properly. The plugs are not and have never been fouled. The transmission filter and fluid is new with 1 bottle of lubegard red. The vibration occurs in any gear at any speed provided the rpm's are 2250+/- 50. The vibration also occurs in nuetral and in park @ 2250+/-50 rpm's .

Can anyone help?

[RobertsnewQ]

Mine does exactly the same thing.

I suspect trans mount, but if yours is new that kinda rules it out.

What do you mean by "60%"?

[squeefoo]

Whoa lotsa good work !! My bet is on the trans-mount since you asked, esp. since it's 60%. How many miles ?

[goody90q45]

I have the same issue with my Q with vibration between about 1850 and 2250 rpm. I talked to a mechanic at Infiniti and he mentioned all of the things you've replaced but also suggested that it could be the torque converter. Apparently he'd dealt with this before and thought that it was more of an annoyance that was not worth the expense of replacing and would not cause a breakdown any time soon. I'll be intersted in seeing what the NICO moderators think about this.

[3Q Jay]

check to see if your cats have 'y2' stamped on them.there was a service bulletin back in '96.

mine does this too, trans mount new, but motor mounts original. have 2 new exhaust hangers that go by the trans mount waiting to install....

[maxnix]

The transmission mount is 60%.

What does this mean?

If it is rpm specific regardless of gear, it is not driveline sourced.

Could it be his harmonic damper or TC failure? How are your pulleys and belts?

[RobertsnewQ]

Could it be his harmonic damper or TC failure? How are your pulleys and belts?

OK - I'll bite. Please tell me how (in 500 words or less) a harmonic balancer failure would be felt in the cabin at 2200 rpm?

I'll give you a hint: IT WON'T!

[elwesso]

LOL!

I would bet that if your transmission mount is good, then the driveshaft is bad.

[96Qowner]

But is the driveshaft rpm-dependent?

This is one of the first issues I asked NICO about. Mine was really bad, centered right at 2250 in any gear. Replacing the transmission mount fixed roughly 80% of it, and replacing the motor mounts took away almost everything else. I still have a sort of a rumble going through 2250, which will subside a bit if I stay at that speed. It's annoying enough that I'd like to find the source. Maybe I need to replace the exhaust hangers, too?

I've asked before and never really got a definitive answer - is there an inherent engine resonance at 2250? This vibration would seem to involve only the moving parts before the tailshaft, or anything having to do with isolating the motor assembly from the body, no?

[elwesso]

It could be the exhaust like said... All 95 and 96 Q are covered under the said TSB.

[maxnix]

OK - I'll bite. Please tell me how (in 500 words or less) a harmonic balancer failure would be felt in the cabin at 2200 rpm?

I'll give you a hint: IT WON'T!

So, do you have any better ideas? Guess not.

[maxnix]

It could be the exhaust like said... All 95 and 96 Q are covered under the said TSB.

This is a possiblity since exhaust volume is related to rpm.

Time to check the hangers.

[elwesso]

Its not in the hangers... The cats cause a goofy backpressure thing.. Factory installed this goofy baffle thing.... under TSB...

I know Rob had this on his Q before he went to aftermarket exhaust...

attached is said TSB..

[RobertsnewQ]

I've asked before and never really got a definitive answer - is there an inherent engine resonance at 2250? This vibration would seem to involve only the moving parts before the tailshaft, or anything having to do with isolating the motor assembly from the body, no?

Yes on the second part, hard to say on the first. Resonances aren't easily calculated - at 1 pulse per 90 degrees of crank revolution, the freq. of engine vibration 's something like 150Hz at 2250 rpm... maybe that excites something in the body or engine to vibrate.

I have the exact same problem and I'm 100% sure it's NOT in the driveshaft. Doesn't matter if I'm sitting at a stop light or going 80.

[3Q Jay]

for the record, I'm not linking the forward exhaust hangers to the tsb. i don't have the 'y2' cat. but thinking the new hangers may help the vibe.

ditto on vibe in park, or on the road.

[impulscarbon]

rpm dependent vibe? = engine, check injectors, I had one, number 7 stuck closed and caused vibration at 2K

[96Qowner]

Its not in the hangers... The cats cause a goofy backpressure thing.. Factory installed this goofy baffle thing.... under TSB...

I know Rob had this on his Q before he went to aftermarket exhaust...

attached is said TSB..

"If a 1994-96 Q45 vehicle exhibits a booming/drone noise in the cabin or a vibration in the steering wheel and seats, the cause may be engine vibration transfer to the vehicle body through the exhaust tube and support mountings. You may observe these symptoms at engine speeds of approximately 2250 rpm (50 mph in 3rd gear and 70 mph in 4th gear)."

Heheh, ya, that sure sounds like it. I suppose the Nissan guys can't do it, huh? Gotta have an Infiniti dealer?

[stickw12]

I have a 95Q that had the exact same symptoms. My motor mounts and transmission mount were toast. Had them replaced and the vibration went down considerably, but was still there, and like you it bugged me. My car fits into the series with the tsb on the pre-muffler assembly being replaced. Just recently I decided to go ahead and have the Pre-mufflers cut out and replaced with a straight pipe. My vibration at 2250 is gone. The car is hardly any louder if at all and drives much smoother at 70mph-2250rpms. They were rusted out pretty good, and my car only has 65k on it. Hope this helps.

Nick

I Have a 94 q45t with a vibration @ 2250rpm. The tires are new and have been checked for balance. All the injectors are working properly and test @ the correct ohms. The driveshaft is original . The u- joints are good. The carrier bearing is good. The motor mounts are new. The transmission mount is 60%. The engine is timed properly. The plugs are not and have never been fouled. The transmission filter and fluid is new with 1 bottle of lubegard red. The vibration occurs in any gear at any speed provided the rpm's are 2250+/- 50. The vibration also occurs in nuetral and in park @ 2250+/-50 rpm's .

Can anyone help?

[elwesso]

I have a 95Q that had the exact same symptoms. My motor mounts and transmission mount were toast. Had them replaced and the vibration went down considerably, but was still there, and like you it bugged me. My car fits into the series with the tsb on the pre-muffler assembly being replaced. Just recently I decided to go ahead and have the Pre-mufflers cut out and replaced with a straight pipe. My vibration at 2250 is gone. The car is hardly any louder if at all and drives much smoother at 70mph-2250rpms. They were rusted out pretty good, and my car only has 65k on it. Hope this helps.

Nick

I was just getting ready to write a reply and then I read this... this is EXACTLY what I was going to say..

The problem is the pre-mufflers. So dont fix the symptom, fix the cause. The car will be PLENTY muffled by that rear can..... Just cut out those pre mufflers!!!!!!

[GreenQ45a]

Its not in the hangers... The cats cause a goofy backpressure thing.. Factory installed this goofy baffle thing.... under TSB...

I know Rob had this on his Q before he went to aftermarket exhaust...

attached is said TSB..

If your Q45 has the Y2 on it how much does Infiniti charge to fix them?Are TSB covered like recalls?

[elwesso]

If your Q45 has the Y2 on it how much does Infiniti charge to fix them?Are TSB covered like recalls?

NO.... youd have to pay for it....

again, its not the cats, its the premufflers... get rid of them...!!!

[3Q Jay]

..... its not the cats, its the premufflers... get rid of them...!!!

Wes, aren't the premufflers part of the exhaust mani? how does one 'get rid of them'?

[elwesso]

Jay your thinking of the pre-CATS not PREMUFFLERS which are just downstream of the secondary (primary) cats.

please look at the TSB that I attached above...... And it circles the area that needs to, in this case and IMO, be eliminated.

If you want to cut the precats, just go in there with a hammer and chisel... Thats what I did.... it was great fun!!! However it is an irreversible move and you will probably not pass emissions.....

[RobertsnewQ]

Actually you will probably pass emissions just fine - once warmed up, the precats don't do much.

[elwesso]

Probably so...

another trick to pass emissions is just bump the timing all the way back.....

[3Q Jay]

Jay your thinking of the pre-CATS not PREMUFFLERS which are just downstream of the secondary (primary) cats.

....

right.....

[GRADEST]

I was just getting ready to write a reply and then I read this... this is EXACTLY what I was going to say..

The problem is the pre-mufflers. So dont fix the symptom, fix the cause. The car will be PLENTY muffled by that rear can..... Just cut out those pre mufflers!!!!!!

Thanks for all the help! I know my car was built in 11-93, but looking at the cat. heat shield i dont see a stamp, just a sticker on the outside. I will remove the heat shield to inspect further. I also KNOW that the injectors can cause this type of vibration. I've benn thru the injectors on this car , and had a 94 j-30 that had a severe vibration when the injectors went out one by one, by one by one by one by one..........uuuuggghhh, infiniti injectors . Doesnt the tc stall around this rpm? What mechanically would cause a tc to produce a vibration besides ballooning or out of round? The weird part is that the frequecy and severity of the vibration change with temperature. Seems that in the morn. it is worse until it warms up. then levels out and seems to decrease, then worsens a bit if the drive lasts over an hour. The changes are extremely subtle so i may be mistaken. I am going to replace my transmission mount and when i changed my engine noticed the two insulator/hangers at the transmission mount were sagging and hard. I guess if that doesnt help i'll hack out the pre-mufflas and throw some straight pipes in. I refuse to pay to replace the cats, those might come up missing too. I'll keep all abreast of my developments. Sounds like a lot of people could use a definitive cure for this problem.

[texasoil]

The Q45 BODY has an inherent resonance and vibration node in it (all car bodies do BTW) that unfortunately can be 'excited' by engine and exhaust system vibrations at +/- 2500RPM --while standing or driving. The 'node' is just aft of the front seat rear track fastener--and where the rear cross member attaches. You CAN weld a reinforcing plate where the rear cross-member mounts (+/- 12" wide, across the body to at least 6" outboard of the crossmember mounts)--which will 'stiffen' this area of the frame/body enough so the engine/exhaust will not excite the body resonance node any more. Or you can renew the transmission mount and engine mounts and exhause hanger rubber components. There is also a 'passive dampener' --a weight on a rod basically-on 94's -95's that is very effective on this resonance. The main source seems to be exhaust system has a resonance at just about the same frequency as this body node---and the exhaust system transmitts its vibration through the stiff hangers on the transmission to the body through sagged transmission mount allowing the transmission to just touch the crossmember when vibrating--exciting the body.

Try drilling a few 1/4 inch holes length-wise in the exhaust hangers on the transmission- this lowers the stiffness so these hangers no longer transmitt the particular frequency of movement that causes the resonance in the car body.

Vibrations like these are not easy to track down, or easy tosolve simply. Usually lots of little changes are needed to resolve it cleanly. --Soften up the exhaust hangers, raise the transmission mount a tad, re-design the exhaust system to remove/change the root resonance source (a BIG deal BTW), stiffen the body (another BIG deal), or don't run the engine at that speed!

[texasoil]

Aircraft engine/propeller/mounts/airframes are a similar type system---lots of 'energy' in the rotating propeller with many different 'modes' of vibration in the blades, a very high torque pulse from each cylinder, a very high premium on any excess weight,etc. Many aircraft engines have sliding counterweights on the crankshaft that move around at different RPMS to counteract the torsional vibrations (some 6 cyl engines have over 300 parts on the crackshaft!!) and some even have 'DO NOT OPERATE' RPM ranges where vibrations cannot be managed by design and would cause early failure of critical parts. You can see exhaust pipes failing from vibrations, crankshafts breaking, engine mounts failing, excessive vibration throughout the plane, even propeller blades breaking!. They usually find these problems well before the plane/engine/propeller gets into service, but not always. One of the most popular 6 cylinder 300 HP aircraft engine models started breaking crankshafts at an alarming rate--and soon the entire fleet was grounded. Turned out the crankshaft manufacturer had made a 'minor' change in the manufacturing process (fully reviewed and approved, tested,etc) but it failed rapidly in real world service.

The 90-95 Q45 exhaust system/body interaction vibration is fortunately easy to resolve and deal with and low cost to boot.

[96Qowner]

Keith - you omitted the 96 and I definately have this resonance. I'm reluctant to remove the premufflers, as Wes suggested, because I like a very quiet cabin - one of the things I appreciate most about the Q, and I use it mostly for long trips on freeways. So I can pop for the expensive TSB fix, or I can fiddle with the existing hangers.

Do you have a recommendation?