CRD compression test

olddesertrat · **Joined:** Sat Jul 28, 2018 10:54 am **Posts:** 34

Hello: Just did a compression test on my CRD had broken timing belt and possible broken rockers.

Noticed something strange.

Pistons 1 + 2 reacted normal. Pressure increased in steps and stopped at 110 psi.
Pistons 3 + 4 acted different. Pressure would bump up to 75 psi with 1st pass...then bump back down to around 20 psi. Repeated cranking both cylinders eventually made it up to around 110 psi.
Been around 15 years since did last compression test on a gas truck, isn't pressure ALWAYS suppose to go up and level off?

Thinking this could be evidence that intake and exhaust rockers for cylinders 3 + 4 are broken. If rockers are broken, then valves are always closed. As piston moves up, compression is created. However as piston moves down, a vacuum is created, which would cause pressure gauge to bump down in pressure.

Just my thoughts, would like some of you experts on CRDs out there to comment.

Also...what should compression be for CRD? This 2005 has 225,000 miles on it.

Thanks

WWDiesel · **Posted:** Sat Mar 18, 2023 3:13 pm

If your timing belt broke and engine spun over, this would allow some of the valves to come in contact with the top of the pistons which by design will break or crack hydraulic dampened rocker arms. This is an "Interference Engine"!
You more than likely got some valves that are not operating on cylinders 3 & 4? :dead:

Time to pull the intake/valve cover and see what damage has occured. :banghead:

Quote:

FYI:
The engine pictured below is one that had several rockers cracked, some bent, and a few completely broken in half. This was after a timing belt stripped a bunch of teeth and allowed the valves to contact the pistons while driving down the road.

olddesertrat · **Joined:** Sat Jul 28, 2018 10:54 am **Posts:** 34

Have search forum here and general internet search. did not find compression psi for 2.8L engine. Anybody know what is should be?

WWDiesel · **Posted:** Wed Mar 22, 2023 4:59 pm

olddesertrat wrote:

Have search forum here and general internet search. did not find compression psi for 2.8L engine. Anybody know what is should be?

Have you checked the FSM (Factory Service Manual)?

Index of /manuals/Jeep/KJ

2005JeepKJServiceManual.pdf

DieselJeepLuvr · **Posted:** Sat Mar 25, 2023 2:21 am

olddesertrat wrote:

Have search forum here and general internet search. did not find compression psi for 2.8L engine. Anybody know what is should be?

At this point I would not bother. Clearly something is wrong so just start disassembly.

DieselsRock · **Posted:** Tue Apr 18, 2023 3:27 pm

I just did a compression test on one of my CRD's, with 165k miles, and all four cylinders were right at 400psi, plus/minus a few psi.

CRD compression test

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