# VIBRATION AT 28-29 HUNDRED RPM



## jmcguire (Sep 16, 2004)

I own a 1984 300ZX Turbo.It runs great.The only problem is the vibration at 28-29 hundred RPM.It doesn't matter if the car is moving or not.I can close my eyes and rev the motor and know when I hit 28-29.A vibration comes up though the gas petal/floor.Going over or under that RPM the vibration is gone.Any Ideas?Thanks, Jamie


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## JAMESZ (Mar 12, 2004)

Check your engine mounts. Is the engine stumbling while this is going on or does it sound fine?


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## PetrolKill (Apr 12, 2005)

dont know but i had the same prob once and it turned out to be a warped tire it was old any ways but check out the how tite your wheels are by jacking her up and turn em a lil see if they're off beat any . could be your rear end to


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## Zen31ZR (Mar 24, 2004)

PetrolKill said:


> dont know but i had the same prob once and it turned out to be a warped tire it was old any ways but check out the how tite your wheels are by jacking her up and turn em a lil see if they're off beat any . could be your rear end to


He just said he could feel it even if the car wasn't moving........
3000 rpm is right exactly where the ECU switches the injectors to batch fire. If you are hovering right near there, it's probably waffling a bit. Heck, mine used to make a noticeable "tick" when it switched over at 3000 rpm.


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## jmcguire (Sep 16, 2004)

Engine sounds fine.I have a digital dash so 28-29 is the exact RPM that the vibration occurs.Like I said, before and after this range the engine is Nissan smooth. Reving up the engine at standstill rules out transmission, tires and drive train.What do I look for when inspecting motor mounts.Could bad injectors be a problem.Thanks for the feed back.Jamie


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## Zen31ZR (Mar 24, 2004)

jmcguire said:


> Engine sounds fine.I have a digital dash so 28-29 is the exact RPM that the vibration occurs.Like I said, before and after this range the engine is Nissan smooth. Reving up the engine at standstill rules out transmission, tires and drive train.What do I look for when inspecting motor mounts.Could bad injectors be a problem.Thanks for the feed back.Jamie


What I've seen about the digital dashs, the rpm indicated is typically 100 short of actual. That's how it was on my car. My fuel cutoff was at an indicated 6400 rpm, but it's actually at 6500 rpm..... 
Bad injectors, the car wouldn't run as well as it does before and after that rpm. 
You might want to try a different ECU, or resetting the one you have now.


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## Spongerider (Nov 18, 2002)

This is just a guess but injector or vacume leak.


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## Zen31ZR (Mar 24, 2004)

Spongerider said:


> This is just a guess but injector or vacume leak.


He says the car runs fine at every other rpm.


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## Domdogg123 (Nov 12, 2004)

jmcguire said:


> I own a 1984 300ZX Turbo.It runs great.The only problem is the vibration at 28-29 hundred RPM.It doesn't matter if the car is moving or not.I can close my eyes and rev the motor and know when I hit 28-29.A vibration comes up though the gas petal/floor.Going over or under that RPM the vibration is gone.Any Ideas?Thanks, Jamie


Driveshaft?


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## Zen31ZR (Mar 24, 2004)

Domdogg123 said:


> Driveshaft?


It'd be a different rpm in each gear as driveshaft speed changes.


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## jmcguire (Sep 16, 2004)

It's going into the shop.I will keep you posted on what they find ( or don't find). Thanks everyone. Jamie


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## plane4fun (Jan 23, 2006)

I have the same problem on my 1984 Turbo Z. Did you find the reason for the 
ENGINE vibration? Again my problem is the same even when the car is sitting still and just racing the engine. About 3000rpm the vibration seems to come up from the floor. Even had the engine/trans mounts replaced in the last couple of months. I am the original owner and the car has 140k miles. I know this is not normal. Just wondering if anyone else had any suggestions.....


Thanks
Ryan


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## jmcguire (Sep 16, 2004)

Not driving the car ( put away for winter) but I never solved the problem.I could ( not recommended) drive with my eyes closed and KNOW exactly when I get to 2800-2900RPM.Jamie


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## Zen31ZR (Mar 24, 2004)

You guys don't read much, do you. For the last time, the ECU changes injection patterns at 3000 rpm (from double batch fire to single batch). You can physically feel the transition at part throttle, I could in my car. In fact, my car had the faintest hiccup passing through that exact rpm. Nothing you can do about it and I wouldn't worry about it.


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## EdwoodCA (Feb 1, 2006)

I tried to find the old magazine with the article, but from a late '80s auto mag that had the ten highest top speed production cars in America at time, the author/test drivers/totally-not-influenced-by-history-or-advertising-dollars-guys mentioned the Z's engine resonance at about that RPM range. 

It's always been there from the start. My Dad's '88 Turbo always had it from the day he drove it off the lot, brand new. Still has it to this day.

Zen31ZR's answer seems to be rather definitive.


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## asleepz (Feb 24, 2004)

Well the bad thing is, you've got to remember 28-2900RPM is right over 70MPH If your doing interstate cruising, that could be a pain


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## EdwoodCA (Feb 1, 2006)

asleepz said:


> Well the bad thing is, you've got to remember 28-2900RPM is right over 70MPH If your doing interstate cruising, that could be a pain


Yep. That's why I go 75-80mph to blend in with the L.A. traffic. [When it's not a giant parking lot, that is.]


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## jmcguire (Sep 16, 2004)

Well guys, it might be ''normal'', but on my 84,83T,86T and 81 300ZX's I never noticed it.On my current Datsun, a Anniversity 1984 300ZX Turbo I do.I really don't believe it is normal.Maybe if it was a American built anything It would be..................


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## Zen31ZR (Mar 24, 2004)

Any of those cars automatics? And there was no 81 and 83 300ZX....... You must mean 280ZX, and no that was not apparent on those cars. I drove one right after I bought my 300, was considering a possible stable mate, and didn't notice it at all. Noticed it instantly when I drove my 300 T. At first I thought it was a problem, but after a thorough checkup at the local garage it was given a clean bill of health. You also don't notice it at or anywhere near WOT at full boost.


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## jmcguire (Sep 16, 2004)

Yes Zen31ZR, you are right the 81 and 83 were 280's.The 83 was a Black Turbo with factory gold stripes. I put that one in the paper for a ridiculously high ammount of cash and got it.It was in awesome shape, with the ZX embossed seats and door panels.The guy flatbedded out of the yard.I loved all of my Z's.From the early to late 80's that was the best years for the Z's.Jamie


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