'98 Expedition 4.6 Random Misfire

[ctown2]

So I'm not sure if it's good news or bad news....
I check the fuel injectors and they are all good. I even pulled the #8 off and double checked that it was getting the right resistance readings.
While I was pulling the fuel rail off, I pulled the #8 plug. The #8 plug was black, and had a layer of oil that wasn't on the other plugs. After taking all the plugs off, I did a dry compression test. I did this with the engine cold.
Cylinders 1-7 were 125, Cylinder 8 was 0.
I then did a wet test with a small syringe of oil in the spark plug hole. Cylinder 8 still had 0 compression.

So, I'm guessing the cylinder head is shot?
This kind of sucks as we just bought this thing about 3 months ago and it 'was' running good until recently.

 

[stamp11127]

You could use an air hold tool to apply compressed air to the cylinder. If the air comes out of the intake or exhaust the head needs work. If it comes out of the crankcase then the rings are toast.

 

[ctown2]

I was looking up leakage tests as well, but I wasn't sure if it was worth measuring the specific amount of leakage, or to simpler understand if it's the head or crankcase. I'll fire up my compressor in the morning and see what I can come up with.

 

[ctown2]

So I tested #8 this morning, and I got air coming out of the #7 cylinder. I also had a little bit of air coming out of the intake, but it wasn't nearly as much volume as the #7 cylinder. I reversed the test by putting air into the #7 and got some air coming out of the #8. Not as much as from 8 to 7, but still enough that I could feel it on my finger. The next thing I did was to plug to go back to the #8 cylinder and plug the #7 with the spark plug boot. When I did that, I got a lot more air coming out the intake (pulled off one vacuum line).


Sounds like a head gasket replacement is in order? Or am I looking at two separate issues; head gasket and intake valve?

 

[ctown2]

To follow up from earlier today. My father in law came over, and we reran the leakage test. Neither one of us heard anything escaping from the #7 cylinder head, but we both heard and felt air leaking from the intake side. So, we started pulling off pieces to get the valve cover off to see if we could see anything wrong with #8. Ran into trouble with getting the EGR exhaust pipe off the exhaust manifold. Soaking the piece overnight to see if it will break loose. Is the EGR exhaust pipe a 26mm or 28mm head, as we were using an adjustable wrench and it kept slipping.

 

[ctown2]

Update on trying to find the problem. Pulled the EGR hose valve off after soaking overnight. Ended up buying a 27mm wrench to use, as the adjustable wrench just wouldn't get tight enough. Broke free after a couple of hard pulls. My FIL and I then tried to find TDC on #8 by hand spinning the crankshaft, and watching the camshaft (had pulled the valve cover off). When we thought we were getting close, we hooked up the compressor and blew air through the #8. We then spun the crankshaft, opening and closing both the intake and exhaust. As one of us spun the crankshaft the other guy listened for air leakage from both exhaust and intake sides. Through this process, we found that the intake side was leaking a lot of air. Although we never could pin point TDC, but we never once stopped hearing air leaking out of the intake. As we cranked through, we could feel the pressure difference from when the intake was open, and when it was closed. So, we are pretty confident that it's the intake valve on the #8 that is causing the loss of compression.

Anything else that I should double check before I start the process of pulling the whole head off? From what I've read online, it seems to be 'doable' to the average mechanic (myself), but just takes a lot of time to remove the whole front end.

 

[ctown2]

Pulled the head off after a couple of partial days of tear down. Found out today that the culprit is/was a bent #8 intake valve. In the process of cleaning the head to see if any visible cracks are present, but I may end up just getting rebuilt heads.

 

[Widdershins]

May I ask why you checked #1 when your CEL was reading #8 ?
and may I ask when allof this was starting were you having drivability issues prior to getting a CEL ?

 

[Widdershins]

Does ANYONE know of / or found a code reader that has Ford Specific codes?
We are a Ford Family and as hubby is old school, these new fangled machines are driving him nuts !
Thanks for your help

 

[ctown2]

May I ask why you checked #1 when your CEL was reading #8 ?
and may I ask when allof this was starting were you having drivability issues prior to getting a CEL ?

To answer your questions. I don't drive the truck on a regular basis, so I wasn't the one that would have noticed anything regarding driveability. The few times that I drove it before I pulled the code, I noticed a little loss of power at certain RPMs, but nothing I could pinpoint. If you read the whole thread from the beginning, you will noticed that I was having both a misfire code and a EGR code. I thought initially that the two were related.
The first thing I did was change plugs, wires and coils.
The second thing was to figure out why I got the EGR code. Found out that intake ports were clogged up, and the truck wasn't getting very much air. Cleaned that out, and the truck ran fine for a short while, before I got the misfire code again.
The third thing I did was to pull the plugs, double checked coils, and wires. Double checked to make sure that it wasn't an ignition problem. Solved the ignition step.
Then the fourth step was to figure out if it was a fuel problem. Checked all the fuel injectors and found it was fine.
Finally, I did a compression test on ALL cylinders, and discovered that #8 had no compression. Then, I did a wet compression on #8 to see if it was rings or valves. It came back to valves.
So than I ran a leakage test on #8, learning in the process how to find TDC for #8. Ran leakage test and discovered that it was leaking out the intake. So no compression = bad intake valve.

In order to pull the heads completely off, I had to get the timing right so that when I went to reassemble the valves wouldn't be hitting the cylinders. So that required finding TDC on #1.

I currently have both the right and left heads at the local machine shop were they are going to do a pressure and vacuum test. If they are good, I'm having them rebuild them.

Does this answer your question?