Please help me interpret this compression test: 1 - 165 lbs, 3 - 165 lbs, 5 - 130 lbs, 2 - 115 lbs, 4 - 115 lbs, 6 - 130 lbs.

To me, this suggests a broken head gasket and a leaky fuel spider. What do you think?

The test was done dry, engine cold, and throttle open. It's a 1998 Jimmy with 270,000 kms (165,000 miles).

 

Hard to say from where I am sitting with a beer just to the side of me. At 165K miles I am leaning towards head gaskets, but it may depend on the history of that mileage. I'm afraid you will be best off by pulling the heads, which you'll be doing to change the head gaskets anyway, but take a real close look at the cylinders. May end up needing to change the rings. If you bring it to a shop, I can almost guarantee they will say the rings, as they already pulled the heads. Unfortunately, that is how many shops operate these days. Not all, though.

 

I squirted some oil in Cylinders 4 and 6. Compression rose from 115 to 130 in Cylinder 4. Compression rose from 130 to 190 in Cylinder 6. To me this indicates worn rings in the rear cylinders and a bad head gasket on the passenger side.

How does the passenger head come off after the intake is removed? Thanks.

 

exhaust manifold off then the bolts on the bottom of head, in between the rocker arms and the Bolts toward top side of head. Reverse pattern of torquing them on is the preferred method.

 

It looks to me like there is a fuel leak. The fuel pressure regulator is located behind the fuel spider. The rear cylinders are worn from the compression test. Most of the washing seems to be on the driver's side from the pictures. Could this leak be anything other than the fuel pressure regulator?


Passenger side intake manifold.


Driver's side intake manifold.

 

Here's the proof, the fuel pressure regulator is leaking. The gunk on the bottom of the spider is washed clean at the connection. I wonder if this could be solved by just replacing the o-rings, rather than buying a whole new unit.


Fuel Spider

 

I would not put that spider back in. It is probably the original one especially with the poppet style. I may lean more towards a valve sealing problem with the 2 lower cylinders. Are you chasing a misfire down? What made you do the compression test? I would do a leak down and if air escapes into the neighboring cylinder then you know.

 

This is the best answer.

 

Thanks everyone for your helpful responses.

As far as I know there is no misfire. I did the compression test because I am replacing the spark plugs and wanted to know engine health. The compression test came back alot lower than I would like.

I removed the manifold because the intake gasket was leaking. I would like to do a leakdown test but don't have a test kit. Maybe I should get one.

I don't mind removing the head so long as the lower manifold is off.

 

A leak down tester is a good tool to have around. It helps with mechanical diagnosis as good as a compression tester does.