Low Compression - Low Power?

[Devjack]

Hey Guys

I recently have experienced a loss in power in the nav. I've got a 2003 D22 ZD30.
I carried out a compression test and the results are as follows:
Cylinders:
1: 410 Psi
2: 380 Psi
3: 330 Psi
4: 380 Psi.

My concern is obviously cylinder 3. I'm not getting any bubbles in the coolant. I also put some oil in the cylinder to do a wet test, but the compression didn't improve. So I'm leaning towards dodgy valves.
I'm going to do proper investigations this weekend. to determine if its valves, rings, piston, gasket or head.

My question is, would that amount of lost pressure cause a noticeable lack of power? Or is it likely to be another issues as well. I've noticed a putting sound which sounds like an exhaust leak, but I've inspected the exhaust manifold and pipe and its not that. It sounds like its coming from near the fuel pump though.

Any thoughts would be greatly appreciated

 

[Rabbit Chop 2]

Those are higher numbers than i have, yet mine was running really good until the pump shat.
Now they are telling me it needs a new engine because of the low compression.
I am looking forward to hearing more on this topic.

 

[Devjack]

Those are higher numbers than i have, yet mine was running really good until the pump shat.
Now they are telling me it needs a new engine because of the low compression.
I am looking forward to hearing more on this topic.

Yea the numbers are good, except for cylinder 3, which I'll be investigating on Saturday.

For understanding, my old 0-100 was ~18 seconds which I was content with, but now its blow out to 36s, literally double.

Reckon it could be the pump or injectors that are ****? Is there any way to test them or do you just need to take it to a shop?

 

[Rabbit Chop 2]

That is definitely not right^
Alls i know, is mine was pulling like a champ, and the pump failure was sudden.

Hopefully someone more knowledgeable will chime in with some insight

 

[tweak'e]

going by the book the 330 psi is below spec. i think minimum is 350 psi. there is also a variation spec as well but i can't recall what that was.
a lot of engines these days will reduce fueling on the other cylinders to keep all cylinder in similar performance. so one bad cylinder can reduce entire motor performance, however i do not know how much difference it would make. they usually have limits in how much it will derate the other cylinders.

 

[Erick]

Pull the tappet cover and check clearances. If u do have a tight/ burnt exhaust valve that would explain the ‘ puffing’ noise on exhaust side.
Did u do ur compression checks hot or cold? I’ve seen enough diesel motors u have to start wit aero start but once hot are as good as new.

 

[Devjack]

Pull the tappet cover and check clearances. If u do have a tight/ burnt exhaust valve that would explain the ‘ puffing’ noise on exhaust side.
Did u do ur compression checks hot or cold? I’ve seen enough diesel motors u have to start wit aero start but once hot are as good as new.

Hey Erick thanks for the tips.

We've got it booked into a mechanic in two weeks but my Dad decided to have a look at what he could last night.
The valve clearances are ok, one was tight - hopefully that's the putting noise as you suggested - I'm not sure what one it is, but does it have to be an exhaust valve to make that noise?
I did the comp tests warm.

We put compressed air into cylinder 3 and could hear a gurgling noise.
I bought a cheap borescope off of ebay and he did some poking around and could see an intake valve leaking as there was oil bubbling on top of the valve. So we've got to replace them.

Now deciding if we take the head off of it to investigate further, or leave it to the mechanics if I still decide to go that route.
Taking the head off is no trouble as we've done it before, but I'm just thinking it may be best to leave on and let the experts do it, as they may find something else.

I'll keep you all posted

 

[Devjack]

Update:

So we took the head off, cleaned it and inspected and it looked all good, including the gasket.

Then we inspected the valves. Some were covered in carbon gunk, but all the valves were still straight. We ended up getting them cleaned up and re-ground as well as their corresponding seats in the head, by a mate who did us a good deal.

After the head was off, we could see cylinder 3 was glazed and the honing marks were all gone, the others looked ok.

We then took off the sump and pulled out piston 3 to inspect for damage. The conrod was fine, but the piston had uneven wear on the back side (toward the windscreen) with carbon build up showing only there.

It looks like who ever did the engine recon, put the gudgeon pin and small end bearing in wrong, as the gudgeon was far too tight and the bearing wasn't aligned in the con rod properly. The bearing was worn, showing copper all around and the gudgeon had wear marks as well. Not sure how, but I'm sure this caused the uneven piston wear, which then lead to wearing on the piston resulting in low compression and therefor the lack of power which started this goosechase.

Now as I can't trust that the other bearings, pistons and conrods were installed properly, I'm tossing up between a bottom end rebuild or just replace cylinder 3 and its components as the others both looked ok and tested well in the compression test.

Any thoughts?