5.9 low compression all cylinders

2077 2
Hi all,

I recently bought a 1997 3500 dump box with the 5.9 engine code '5'. It has 83,000 miles and transmission was rebuilt at 76,000 miles.

It starts and runs fine but had a miss coming from the passenger side. So I decided to start by changing spark plugs and wires. In doing so the cylinder 1 plug broke off @ the threads so I'm kind of stuck at this point (extractor grabs but can't turn using 1/2" 16" breaker bar - and don't want to break the extractor off).

So... I decided to do a compression test on the other cylinders to see how the engine was doing in general and I found the following...

DR. Side PASS Side
cylinder 1 3 5 7 -- 2 4 6 8
static psi xxx 65 55 65 -- 66 60 57 70
static with 3 tsp oil xxx 85 80 83 -- 90 83 75 86

these are devastating low, but yet the engine (prior to breaking the plug) seemed to run OK - started great and ran but with a miss @ passenger side. With these low #'s, other threads on the forum seem to state the engine shouldn't even be running - is there something I'm missing?

wondering if it pays to bring the engine in to get the plug taken out or with the low compression readings if a replacement engine is a better use of the $.
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241 Posts
I'd run another test with a different tester, just to play it safe before making any expensive decisions. Either way it sounds like at least one head is coming off...
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