Either the valves are not seating (my guess), or you have a piston and/or compression ring issue. I would start by pulling the head; if it passes a visual inspection, do a leak test. If you have to resleave the #4 cylinder, that is a lot more involved. If you can't do the work yourself, it will cost you some $$$$. What is the status on your glow plugs, did you have the #4 tip break off?

Thank you for the response! Initially, I had a P304 code which is a misfire, but after doing my due diligence on the injector it was obvious it wasn't an injector issue so I took it in the shop. This morning is when they told me of the low to no compression on the #4.
I have no idea on what caused this, but I will certainly ask. Your response has given me some good questions to ask. Thanks!

Ken

If you aren't running an ECO tune or similar from GDE then your EGR valve is causing some serious buildup inside your intake as well as the head itself. Even if you're running it, if you didn't remove the intake and clean it this is still a possibility.

This MIGHT (it's not entirely impossible or unlikely) just be an issue of the head and intake being clogged.

If you don't have any issues with your engine overheating, coolant loss, lost glow plug tip at #4, I'd say it's as likely a candidate as any for the loss of compression.

I don't recall many issues that weren't catastrophic failures where there was a wet sleeve issue on these engines, but take that with a grain of salt I guess.

These engines get misfire codes all the time for air in the fuel, make of that what you will, our fuel system is known to be a sieve for air and it's part of the design, without a lift pump, that we all grudgingly live with.

You could also have a rocker/lifter issue at the #4 cylinder, how's it been running?

You won't know until you take the intake off, which is an endeavor but by no means insurmountable, I've done it a handful of times now with no formal training, just willingness to get it done and hands-on experience.

If you haven't done your timing belt service, go ahead and plan it, because you're going past that point to check the intake.

Where are you located? We might have some people who can help.

I have had a problem with my #4 cylinder that has had me stumped so I finally took it in to a local shop where they have diagnosed the problem as no compression in the #4 cylinder and they recommend a new engine!!!!!
Obviously, this is a HUGE shock and I don't have the funds for a new engine. Knowing the above, what are my options? As of now, I don't know why there is no compression and have little experience with such problems so any insight would be great! thanks

Ken

My best guess from here is a bad rocker, or a broken glow plug tip that has jammed a valve slightly open, or possibly a chunk of carbon which has done the same. Keep us posted on the findings. It'd be a shame if they went to the trouble to pull the engine only to one of these things though...

Update-The engine is out and I should find out today what the major problem is. The question that I have is what should I have done while the engine is out beyond the obvious repair? I thought I would update the radiator fan and will take care of the timing belt, but anything else that would be good to have done while the engine is out? Keep in mind that money IS an object so I have to keep it within reason, like no new turbos and such

Here is what my contact had to say
"Ken, The technician has the cylinder head and cams off the short block. There are extensive cam shaft/ rocker, lifter issues. The sum of the parts look like they may equal or exceed the cost of a long block. I am still working on numbers. Let's get together by phone or stop by Monday (or sometime next week) and we can discuss it further."

Any comments?

Sounds like it was overkill to pull the engine? The head can be easily pulled with out all this additional work.

I would be betting on a problem in the valves or rockers.

My thoughts exactly. I hope the shop "is familiar with CRD's," but we know how that tends to usually work out, unfortunately.

Broken rockers and metal running around the engine for who knows how long. Cylinder 3 and 4 seem to have a bit of blow by. After fully going thru the head, replacing rockers and cams, pulling the pan, checking bearings and cleaning all, it's getting close to buying a long block, and that would be without a year warranty that a long block would offer.
Total cost is $9000!!!!!