Compression test results on engine with dead cylinder

I performed a compression test on my 89 Ranger with a 2.9L this evening. I bought the truck back from the fellow I sold it to 9 months ago because it developed a horrible miss.

I pulled the plugs and every single one of them were black, except #2. The previous owner replaced all of the plugs when it developed the miss, so they were not in but maybe a week. The one he pulled out of #2 when he changed plugs looked bad, really bad. I couldn't tell from the image if it were damaged or just horribly oil fouled. So back to the plugs I pulled out. #2 smelled like gasoline. I changed all of the plugs and found the vacuum hose unplugged from the fuel pressure regulator. I figured it was just dumping a bunch of fuel in. Not the case, still a dead cylinder.

Time for a compression test...

The engine was run idle for about 5-10 minutes to get a little heat into the engine. Today was in the 80s, so it wasn't terribly cold. I propped the throttle open and let the engine rotate until pressure stopped increasing. This was probably about 10 revolutions.

#1 = 190psi
#2 = 0
#3 = 190psi
#4 = 185psi
#5 = 185psi
#6 = 185psi

Obviously a problem with #2. Other than the obvious, how do the rest of the numbers look? They are remarkably even across the board, which I guess confirms the engine was rebuilt at some point in it's life. The chassis has 300K on it now. What is the typical compression numbers from a stock 2.9L in good health?

There was a slight tick coming from the top end on the left bank when the engine was running. I figured maybe a broken valve spring or rocker issue. I pulled the valve cover and everything looks normal. I rotated the engine and nothing out of the ordinary.

So I connected the air hose to #2 and took a listen. I only had about 80 PSI available to me as it was past 10PM and I didn't want to disturb the neighbors with a loud compressor. Nothing from the dipstick tube, so rings seem to be OK. Nothing from the intake manifold either. I did seem to hear and feel some air coming from the exhaust. I want to up the air pressure to 120psi tomorrow and perform the check to verify. It seems like the exhaust valve could be bent or broken on #2. While performing the compression test, I covered the spark plug hole on #2 to make sure 0 was correct. I noticed it was sucking in through the spark plug hole fairly well, but hardly any air was pushed out during the compression stroke.

With the compression of the other cylinders, would it be worthwhile to pull the head off and have it repaired? No milkshake in the oil, so I think the heads and head gaskets are good. I'll have to inspect the bore on #2 to make sure nothing scored it. I was considering swapping to a 4.0L as they typically run $300-500 from the junkyards, but an engine swap is a bit more of an undertaking and this is just a daily driver.

I'm thinking I'll repair the head, put my JBA headers on finally, install the free-floating rocker shaft spacers, and port the intake manifold. It would probably be a good time to have the injectors cleaned too.

Are there any upgraded valve springs for the 2.9L? Should I have the other head inspected as well? It's going to be torn apart down to the head anyway.

What about head bolts? Are they re-useable?

2.9l Head bolts are TTY(torque to yield) so shouldn't be reused.
Anytime you see a head bolts torque sequence as "Final torque turn 90deg" it will be a TTY bolt.
Any head bolts are iffy to reuse, TTY or regular, once stretched(tightened) they never return to original length when loosened, regular head bolts often needed to be retightened after 100 miles

Yes, reads like a valve issue on #2 for sure.
With #2 exhaust valve closed and spark plug out put some air up the tail pipe, air hose and rag to seal it(I have used a Shop Vac), if air is coming out spark plug hole then exhaust valve is not sealing.

I have a broken head gasket on my´89 so im facing almost the same operation as you are. I think it´s a good idea to have the other head checked as well, doesn´t seem to be too much extra work once one head is pulled anyway.
Good chance to replace all gaskets that come across the way

RonD said:

2.9l Head bolts are TTY(torque to yield) so shouldn't be reused.
Anytime you see a head bolts torque sequence as "Final torque turn 90deg" it will be a TTY bolt.
Any head bolts are iffy to reuse, TTY or regular, once stretched(tightened) they never return to original length when loosened, regular head bolts often needed to be retightened after 100 miles

Yes, reads like a valve issue on #2 for sure.
With #2 exhaust valve closed and spark plug out put some air up the tail pipe, air hose and rag to seal it(I have used a Shop Vac), if air is coming out spark plug hole then exhaust valve is not sealing.

Click to expand...

Thanks, I wasn't sure if they were TTY or standard bolts. I hadn't looked at the torque specs in the service manual yet.

Any preference on head gaskets? I've always been partial to FelPro (using the blue metal core valve cover gaskets now), but Victor has some that are a little cheaper.

I'll pull the head this weekend. I'm hoping it didn't break the head off the valve and cause damage to the piston. Below is the plug that was pulled out when the miss initially started. It's definitely damaged from some foreign debris.



No, those aren't my fingers. I prefer to wear gloves so my hands aren't permanently stained

Got the head off tonight. Confirmed the valve is missing a chunk. The piston and bore are perfect. Not a bit of damage on either. The other 2 pistons and bores on the passenger side of the engine look great too. I haven't taken the other side off yet. I am hesitant to do so as the compression is great and there are no issues, but it's probably best to have the machine shop check them out which I have it torn down.

I also broke the heads off a couple exhaust manifold bolts and it seems that at least one had already been broken, so I'll have to get the machine shop to extract them while doing the other work. Probably another good reason to pull the other head. I'm sure I'll snap the heads off a few more bolts.

Anyone know if JBA heads will bolt up to the stock Y-pipe? It would be helpful until I can get the truck down to a muffler shop to make a larger Y-pipe. When I bought the headers used they didn't come with a Y-pipe.

No, any 3rd party headers should need a new "Y" pipe setup.
The point of Headers is to create a velocity at the collector, smaller pipe from head goes into lager pipe(collector), the transition to the larger pipe creates a drop in pressure in the other 2 pipes going to the head(V6), so has the effect of "pulling" out the exhaust when the next cylinder fires on that bank, which creates velocity.
So to make a Header correctly you need 3 pipes(V6) of equal length or pressure(on that bank), pipes need to be small enough to create velocity and large enough to accommodate volume of cylinder.
Too large a pipe will actually create back pressure, this is where the myth of "engines need back pressure" comes from, larger pipe lowers velocity which increases back pressure, so when people put on larger pipe headers performance went down, so their incorrect thinking was "oh, engine must need back pressure from smaller pipe", myth was born.
This is why you need a new "Y" pipe, can't do the above and make it fit to stock "Y" pipe



Exhaust valve failure usually has an underlying cause, lean condition in that one cylinder, i.e. fuel injector issue, or foreign object pinched between valve and seat when hot, i.e. spark plug electrode, you should see a mark on the seat if that happened.

If valve cracked from manufacturing defect, wouldn't take a lot of miles for that to show up, then crack would get bigger and cause a chunk to break off.

Yeah, it could be that the electrode from the spark plug caused the valve to break. Of course what caused the plug to fail? It could be a clogged injector. Unfortunately I didn't number the injectors as I pulled them off. I had planned on sending the injectors out for cleaning anyway. I've owned the truck for many years and have put a lot of miles on it so I doubt it was a manufacturing defect.