diagnosing engine mounts

[JHZR2]

Hi,

How can I tell if an engine mount is bad? Ive posted about this engine before, but now Im looking at it a different way. My 98 ZR2 with 4.3L v6 has a shake at idle.

I have read that bad engine mounts are most noticable at idle. I have read that in bad situations, the fan can even hit the shroud or hoses.

My issue with the engine mount issue is, I can see if it is a vibration that is constant, however, my shake is more or less one shake side to side, then a 2 second pause, then another shake side to side, etc., etc. Of course, this could just be the period, and it could still, I suppose be a vibration.

Can an engine shake be the first indication of a bad engine mount? I have used injector cleaners, use FP regularly, am running GC, so I have a heavier oil in there, etc. No help.

Is there anything else that I can do to tell if they are bad? I have heard to hit gas with the brake pressed hard (like youre testing the stall of a torque converter), and see if the engine moves a lot. I cant see the mounts, and dont think this is the best thing to do for the rest of the driveline.

Any suggestions?

Thanks,

JMH

 

[jhnrckr]

you should have enough clearance to crawl underneith with a flashlight, you should be able to see at least one or two mounts. Look for dry rot on the ones you can see. The car is new enough that it probably isn't the mounts but rather the state of tune. If you want to make it shake flip the a/c on at idle, there are 50 ways to make it shake.

 

[JHZR2]

state of tune includes new plugs last summer (the originals looked brand new at 45k when I changed them), new wires and coil at same time (just in case), rotor points cleaned and lightly filed with spark plug file.

Fuel filter 2 years ~12k old.

Air filter less than a year (a few thousand miles old).

Trans fluid replaced this past summer.

I dont think the state of tune is the problem. Shake was same before and after tune-up.

Thanks,

JMH

 

[JohnBrowning]

If they are completly gone then the torque from the motor will lift the engine away from the two halfs of the mount and you can see this easily. You will also hear a metalic "clack" when the two halfs touch again. Every time you give it throttle you can hear it and feel it. You should have two motor mounts one on each side of the block near the lower portion of the block! It is also a good idea to check the transmission mount at the same time as they two wear out!

If it is vibrateing at idle with no throttle and no load then I would doubt that it would be a motor mount! Usualy poor idle is cause by things like IAC,tuneing valve, Map,Mass,CR/PS,CM/PS,injectors,ignition module etc.......

 

[JHZR2]

Ive never had a CEL for anything like that before, and ive had the truck since new. Apparently it isnt out of spec yet. Is there a way to verify things that are nearly out of spec, and could be causing such a phenomenon?

The only CEL Ive ever had was for a small valve, which cost all of $20 to replace, and the shake was the same before and after...

Thanks,

JMH