aaronk

I just did a compression test on my recently purchased 94 Pickup. The results are as follows:

#1 - 190
#2 - 190
#3 - 180
#4 - 160 (180 with a few squirts of oil)

The truck has 177K so I was expecting I wasn't surprised by the compression test. The #4 cylinder isn't horrible, but a rebuild is on the horizon.

With that said, the engine vibrates a lot at idle. The idle isn't rough, it stays consistantly around 900RPM. However, with the hood up you can see the engine shaking, sometimes it's vibrating pretty good. When inside the car you can see the gearshift lever shaking as well. When you give it a little gas, and get it above 1000RPM everything smooths out.

Any ideas on what's causing it and could it be related to the low compression in the #4 cylinder? The engine runs and sounds fine when not at idle. It's underpowered, but then again I have larger than stock tires and a canopy on. The engine doesn't burn any oil or use any coolant.

The timing chain was replaced about a year (and 10K miles) ago, according to the previous owner. I haven't checked the timing yet, would that be a good place to start or should I be looking somewhere else?

Thanks!

dcg9381

The odd compression isn't going to cause that.. If it was a rebuild, I'd suspect engine balance, but as an OEM motor, i'd simply consider replacing what are probable worn engine mounts.

84sr5yoty

The compression is too high in cylinders 1-3, meaning you have excess carbon buildup on the tops of those pistons. These motors only put out 175 PSI brand new off the showroom floor. You need to seafoam the engine and throw some BG 44K in the gas tank.

dcg9381

You'd need a ton of carbon to really raise the compression by 10% or more.. I suppose it's possible.
What's more likely is that your compresson gauge reads a little higher than most.. :-)

longhungsilver

agreed..

And i second the fact that the bad compression wont cause this type of symptom... your vibrations are caused by bad motor mounts.. the 22re motor mounts are relatively easy to do so dont sweat it.