I have a '98 expedition with 144K miles. I need some help troubling shooting a random misfire in the #8 &#1 cylinder(s). About a month ago, I had the following CEL codes; #8 misfire, system to lean (bank 1&2). I changed out the plugs, wires, and coil packs, and reset the CEL. I never got any codes tell about a week ago. This time it was simply a #8 misfire. Changed the plugs and wires again, and tested the coils with my multimeter (showed the right resistance on both primary and secondary).

Now after reseting the CEL light again, my wife drove less than 50 miles and it came back on with the following. #8 & #1 Misfire, system to lean (bank 1 & 2), and EGR valve. I have not had the chance to pressure test the cylinders to isolate the problem, but that is next on my list of things to do.

Here's my question, are the misfires happening as a result of EGR? I noticed that it idles rough under 1000 rpms, but over 2000 rpms it seems to smooth out.

Here's the actual code numbers that keep popping up;
308 (Misfire on #8)
401 (Exhaust Gas)
301 (Misfire on #1)
171 (System to Lean Bank 1)
174 (System to Lean Bank 2)

I've replaced the following; plugs, wires, coils (under 1000 miles on the coil packs), EGR valve pressure sensor, EGR control solenoid. I bench tested the EGR and it holds a vacuum with compressed air ran through it.

Any idea what I'm missing? Or next steps to take?
Craig

 

At the back center of the intake manifold is a rubber elbow for the PCV system. This elbow is very problematic by either breaking, leaking, collapsing, or clogging. First verify that elbow is in good shape before doing anything else.

 

I cleaned out the throttle body after taking it all off. Both of the air intakes from the EGR were badly clogged, one was so bad that not even compressed air would blow through. I couldn't believe how clogged up both of them were!

So I cleaned everything really well and reinstalled. Truck ran a lot better, the rough idle is gone, and it a lot more power. However, after driving around the block and reving the engine a couple of times the CEL came on again, giving me the cylinder 8 misfire. I came home, popped the hood and pulled out my multimeter. Out of curiosity, I unplugged the #1 cylinder fuel injector sensor, and checked the voltage coming out. I haven't looked up the specs yet, but from the voltage readings it seems to be getting a signal (goes from 13-14v to 8v, to 10v).

I did get the freeze frame data from the cylinder 8 misfire.
Fuel System 1 CL
Fuel System 2 NA
Cacl Load % 56.47
ECT 71 degrees
STFT B1 7.81
LTFT B1 25.00
STFT B2 3.13
LTFT B2 25.00
RPM 1647
Speed Kmh 28

I haven't looked into what the data means yet, but I think I have cleared the EGR & lean code finally! So yes I did check the elbow in the back for cracks and didn't see any.

 

It's running way too lean, LTFT is full rich on both banks. This indicates a vacuum leak (check the rubber elbow alloro suggested), if no vacuum leaks are present you may check the MAF sensor, it might be dirty or biased.

 

So a too lean/rich could also cause a misfire? I will spray the MAF with MAF cleaner that I have on hand. And double check the elbow for cracks and leaks.

Any other suggestions for hunting down a vacuum leak?

 

If the mixture is too far out of wack, then yes it will cause random misfires. You should check the MAF readout, it should roughly indicate about 1g/s pr liter of displacement at idle. Ford does have a spec at cold idle, hot idle, and at I think 2000 or 3000 rpm or around there, but I don't have access to the book right now. If it shows much less than 4 or 5 g/s at idle, then you might have to replace it if cleaning doesn't help.

On the '05 I know the OEM manufacturer is Hitachi, so I bought a Hitachi sensor for mine (had a good sensor, but it was cracked around the seal). It was identical to the OEM Ford one, just had the logo and Ford part number scraped off. Not sure if Hitachi also was the manufacturer for the MAF in '98 but wouldn't surprise me:

Here it is at less than $82 plus shipping;

https://www.rockauto.com/en/moreinfo...304389&jsn=418

 

I'm not sure that the scan tool I have can read the MAF output (borrowing my father in laws).

Can I check with a multimeter?

Would a dirty air filter cause a bad reading on the MAF? I both this expedition about 3 months ago, so I'm not exactly sure what the previous owner had done recently.

Craig

 

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.

 

I ran a modified leakage test this morning. I simply stuck my air hose down into the #8 cylinder via the spark plug hole. When I did 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?

 

Did you make sure that you performed this leak down test on top dead center on the compression stroke? This is very important to get accurate results. You may have bad valves, the only way to fix this is to remove the head and overhaul it, or simply buy a new head.

 

I turned the engine over a couple of times as I was blowing in compressed air. I didn't thread the air hose into the spark plug socket, instead I simply pushed an open hose down. Would this make a difference?

 

Dont draw any conclusions before you perform a leak down test the proper way:
http://www.youtube.com/watch?v=ofSiTGeLXvc

 

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.

 

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.

 

In order to find top dead center on the cylinder, insert a long straw or stick of some sort into the plug hole, then watch as it rises up as you turn the crank, and you can easily see when it reaches the top and starts to go back down, zero in on the point where it's highest and you have found TDC.

This guy shows the "old school" way of doing it.


Eric the Car Guy shows another way to do it: