Can I do a compression test on a cold engine?

[Krischick33]

2001 2.5l, 5sp, 108k miles..
I've been chasing a rough idle for awhile. I've changed all TB sensors, plugs , wires, CPS, 02 sensors, etc.
Last week I decided to try a bottle of Cataclean. Added to tank with less than 1/4 tank. Ran for about 20 miles then filled up. The reason I tried the Cataclean... I was thinking I may have a valve issue. I did the dollar bill test at the tailpipe and it fluttered in and out. It was noticeable that the bill was getting sucked to the tailpipe.
Any, the next day the jeep was hard to start and it idled real rough. Got it home and parked it. Next day it wouldn't start. I had to roll it down a hill and jump it. Its seems to run well while driving and keeping the rpms up. Today it won't start again. While cranking it seems like its struggling to turn over. I removed the air intake and its sounds like a back fire through the TB.
Its time to take a step back and get some baseline info. I want to do a compression and leak down test.
Question- can I do a compression test on a cold engine?
Thanks

 

[JEEPCJTJ]

I've never really thought about that but the couple of different times I've done a compression test the engine was far from warmed up. Maybe not even run for a couple hours, maybe years, IDK. I would think that the warmer the engine the higher the reading would be but I was just looking to compare the cylinders to each other and hoping none were near zero.

I also think that with your results of "the dollar bill test" and "a back fire through the TB," a leak down test probably isn't needed because there won't be too much to leak down to begin with. I could be wrong on that, hopefully we'll get some other replies to let us both know.

 

[Lou]

If you suspect a valve issue a leak down test is the best test for pinpointing that.

 

[Krischick33]

Jeep CJTJ and Lou thanks. I'm planning on renting a compression and leak down kit this coming weekend. I'll update with the results. I'm struggling with the main cause of my issue...mechanical, fuel/air or electrical. If there are any other diagnostic that you recommend please let me know. Thanks