Ran my first compression test today. It's an '03 VIII. It was a hot comp, and the results were this.

Cylinders 1,2,4 all ran around 120
Cylinder 3 was 90-95.

The car is nearly entirely stock.
130k on the motor.

Thoughts?

Is this the precursor to a larger problem?

 

So what prompted the comp test? If you just happened to do it, the results are a little low but for 130k expected, #3 should be higher--shouldn't be more then a 10% difference in cylinders--but then again, its got 130k--if its running fine, let it go. If your looking to refresh the motor you now have a reason. But all in all I would say its fine for the mileage. Going to need some help in the future though.

 

definitely low. prob just wearing/worn out. If it runs ok and you're not trying to make more power, run it. If you want to start building the car for more power, I would start with an engine rebuild.

 

It was the first time I've had the compression tested. I'm just trying to get it in line before my scheduled tune next Thursday. It is running totally fine. No problems whatsoever.

 

For the scheduled tune next Thursday, I was planning on getting a downpipe, O2 housing, and test pipe installed, to complete my full exhaust. Other than that, the car only has an intake and a boost controller. Should I already be thinking rebuild?

 

well, you're not trying to push anything crazy. See how it reacts to the tune. I wouldn't try to run E85 with lot of boost, that's for sure.

 

Follow these steps
1. Do it again, and in the low cylinder dump a cap full of oil in it.
2. If compression rises most likely you have some worn rings, if it doesn't change a valve is leaking most likely.
3. If the compression doesn't rise do a leak down to make sure it's leaking from the head and rebuild the head.

 

That's all I have planned for a while. Next winter I'm planning on parking it and getting the real build started. I'm hoping that this tune will be okay on the motor until then. And where I live, E85 is impossible to find. So I'll be sticking to 93.

 

Thank you, I'll have to try that when it's not 15° outside.