1990 RT 4WD- ZC Motor- Vibrating Badly

I have a 1990 RT that burned and leaked14 quarts of oil all the way from Alabama where I bought it to where I live just outside of Austin Texas.

Based on the bad condition of the engine I ordered a JDM ZC from H-Motors Online. It came with the matching transmission as well.

I helped 2 professional mechanics install it in my garage on my lift. We put in an upgraded Exedy clutch as I had planned on putting a Jackson supercharger or maybe a small low boost turbo on it later.

I’ve replaced all the suspension and bushings as the old stuff was shot.

I have had 3 mechanic friends and 3 Honda dealership mechanics look at it (two are shop foreman at their dealerships) and they couldn’t figure out why it’s vibrating so much.

It still vibrates when moving and when not moving. I’d say it’s at the worst sitting still at a stoplight.

Steve the owner of H-Motors said he hasn’t seen this issue before and made a guess that if I swapped in a D16A6 I take manifold it might fix the problem. His guess to do this is partly based on the vacuum lines are different on the ZC and the D16.

I would take the manifold and throttle body off the engine I pulled out, but that one turns out to be a ZC as well!

Can anyone confirm if Steve is onto something or have any other solid guesses?

I don’t want to spend a bunch of money and time swapping in a D16 intake manifold unless I’m somewhat confident it will fix the vibration.

I’d love to save the car and restore it back to good condition, but as it is the car is horrible to drive and might get dropped off at a junk yard or parted out locally soon.

Thanks for any well informed ideas!


  • arries289arries289 Wagonist
    So, it's vibrating at idle and during cruise, but the engine is not miss firing? I don't know what all troubleshooting has been done, but I would start with the basics. Check compression and make sure it is even across all cylinders. Make sure your motor mounts are solid and tight. You are going to have to give us some of the troubleshooting that has been done for more ideas.
  • Where abouts outside of Austin? I'm up in round Rock.

    Can you get a video posted so we can see.

    I'm assuming your mounts are good since you had help from your mechanic buddies. Only asking cause my motor was wobbling fore to back something fierce and I found out the rear mount was loose to the point that it stripped out the bolt holes.
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