'98 Expedition 4.6 Random Misfire

[ctown2]

I have a '98 expedition with 144K miles. I need some help troubling shooting a random misfire in the #8
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

 

[Bedrck47]

Have you pulled the throttle body and cleaned out the exhaust port in the throttle body.
There is a good video on youtube about this.

Check the hoses that go to the DPFE sensor

 

[Bedrck47]

http://www.expeditionforum.com/f42/about-egr-pcv-dpff-evap-iat-tps-maf-23583/#post191356

http://troubleshootmyvehicle.com/ford/4.6L-5.4L/troubleshooting-p0171-and-p0174-page-1

 

[Bedrck47]

I would first pull the throttle body and clean the exhaust ports They are well noted for clogging up with carbon That should take care of the P0401 code and also may cure the other codes. After cleaning the TB clear your codes and drive the expy to see if any codes reappear.

 

[ctown2]

Have you pulled the throttle body and cleaned out the exhaust port in the throttle body.
There is a good video on youtube about this.

Check the hoses that go to the DPFE sensor

I have not cleaned out the throttle body, but I did notice when I pulled the EGR off there was some carbon build upon the EGR and the throttle body.

Could this be causing the misfires?

 

[Bedrck47]

Possible The TB on the 4.6 engine has two small ports thru it. They clog faster than the 5.4 which has one larger port. As I said earlier That would be the first thing I would do. Only needs two gaskets and throttle body cleaner. Not an expensive repair Just time consuming. Also while you have it off check the hose that connects to the rear of the TB. P0401 is low egr flow and if those ports are clogged that will cause low flow.

Keep the forum posted as to the results

 

[Bedrck47]

Read the information in the links I posted earlier. Some good information in them

 

[ctown2]

Thanks for the tips. I will pull apart the throttle body & EGR and clean them both. Should I use any special 'throttle body' cleaner, or would a general purpose cleaner like MEK work?

That link will point me in the right direction. I used that site earlier to try and trouble shoot the EGR code, and that is what lead me to bench testing the EGR. When I took off the EGR it has some carbon build up, but I wasn't sure if it needed to be completely clean so I cleaned it a bit. Sounds like I should have cleaned it a bit more and the throttle body at the same time.

Should I take the throttle body off to clean it, or just keep it on and clean the air intake side and EGR side?

 

[Bedrck47]

Use Throttle Body Cleaner in a Spray can. You can get it at any auto parts store. You most likely will need two cans if they are badly clogged. Wear gloves.

Watch the following video

https://www.youtube.com/watch?v=XvMyPL5d7kg

 

[ctown2]

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!