89 240sx: Advice on Motor Mount replacement

[BlackHat]

I believe I'm having some trouble with dead motor mounts. When I got the car I could tell they were on their way out (the motor vibrates quite a bit). Lately the entire drivetrain has been shaking bad when in low rpm 1st and 2nd gear. I'm pretty sure this is the motor mounts, but just in case this sounds familiar to someone else I'll add a couple other details.

I just replaced the clutch with a mild performance clutch which I thought could be causing more stress on the motor mounts (old clutch was slipping). I also inadvertantly snapped the decaying plastic connection on the AIV, which I just recently found out shouldn't be that big of a deal anyway. But I had heard it can mess with idling, so I thought I'd mention it. Other than that I don't know of any other malfunctions with the car that could cause this.

Now, my question is, I have a kae that I'm rebuilding for Turbo applications but I'm probably about 4-5 months out before I'll finish it. The 240 is becoming very annoying to drive with the shuddering going on (not to mention I don't want to break anything because the engine is flailing around the engine compartment). Are there any reasons I wouldn't want to replace the motor mounts now and use them with the new engine when I get it done? Or is it something that I can't reuse when I get ready to swap engines?

[navysnail]

you can definatly reuse motor mounts when you change engines.

for the AIV, remove it and plug both the hole on the intake box and the line going to the exhaust manifold.

[BlackHat]

Thought i'd add here instead of posting new topic. As it does relate.

I had researched this problem more and found that it could be the EGR valve. Come to find out, the vacuum line going from the BPT-EGR valve going to the EGR valve was indeed torn completely in two.

I went in and removed the entire EGR assembly as well as the AIV assembly. I even got the Nissan plugs for the exhaust (Which are very clean looking). Sealed up the vacuum lines and did the nickel thing in the intake side. Other than a 5 minute seal problem with the nickel everything ran great.

However, I still get mild shuddering when starting from a stop. Although it's not as severe now, and doesn't seem to be quite as linked to warming up (before it would only do it after warming up, now it does it whenever). I'm kinda stumped, could it really be loose motor mounts? I can tell they are going (if not completely gone), just didn't think it would be this dramatic.

thanks

[180fan]

I'd think it were something with your injectors rather than everything else.

[BlackHat]

I ran a compression test when I first got the car about 4 or 5 months ago and cylinder 4 is low, other than that I wasn't aware of anything wrong with the engine. How would I check if the injectors are bad?

[180fan]

with the engine running pull one plug at a time. if the engine stumbles that one's fine. if it does nothing, you're in trouble.

[Arrow]

Yeah, pulling the plugs one at a time would work well. I had probably the same problem as you back a few years ago... My problem was that after having it in a shop I had a spark plug wire that was not connected or loose... so basically I was running on 3 cylinders. It caused the car to shake / vibrate on idle and once the car revved up a little generally speaking the shaking stopped. So a bad injector or loose spark plug wire could cause what you're describing.

And about the motor mounts, mine are shot... and they don't really cause much vibration while driving... at least not what you're describing.

[BlackHat]

Pulled the plugs one at a time. Car went rough on all 4. Idle doesn't really seem to be a problem. I'm kinda stumped on this one now. If anyone has any idea's I'll try them, otherwise I'm going to just make sure all of my vacuum/intake lines are connected in some form or another.

[NISTECH]

What kind of shaking are you getting?

A) I can see the whole engine moving an inch side to side in the engine bay.

B) I can feel a vibration in the steering wheel and the shifter at idle or when accelerating but the car seems to perform fine otherwise.

[BlackHat]

A, kinda. The steering wheel doesn't shake. It seems to just be the drivetrain. I would say it's more than an inch though. Seems pretty violent. As soon as the clutch is completely engaged it stops. This is only from a stop and at lower RPMs.

Come to think about it, this did start a short time after replacing the clutch. The last clutch wasn't really that bad off but the throw out bearing was screwed and made horrible sounds when engaging. After the replacement everything seems to be ok. Just recently I've been hearing a little noise from the transmission (sounded kinda like the throw out bearing again), but this just started. The shaking has been going on considerably longer.

I guess I didn't link them for some alien reason...

[NISTECH]

This sounds more like you ignition is breaking down. Like it misfires under heavy load. The violent engine shake under heavy load [1st and 2nd gear take off] Take a good look at your plugs and your dist cap.

[BlackHat]

Just got around to putting a timing light on the car. It was running 10* advance at idle.

Adjusted the dizzy and now it's not shuddering at 1st.

It does however have a little bit of stumbling at idle. Nothing bad, actually it's still better than the idle when the timing was off, but I noticed that advancing the timing to 16-17* stopped it. I was thinking it had to do with the poor compression on cylinder 4, but I was afraid to leave it at 16-17*. The last thing I want is to kill the engine before my other one is finished.

Is this something I should ignore until I get the new engine built? Or is it safe to run 16-17* advance on stock setup with 87octane?