Service Engine codes P0304, and P0401
 

I have a 99 expy, Service engine light came on. Engine runs fine, except when climbing a hill or small acceleration, then it seems to be missing. Took it to AutoZone and The codes- P0304, and P0401 came up. I just had it tuned up at the dealership (ouch), about 3 months ago. Any one with any ideas?

Service Engine codes P0304, and P0401
 

Code 0304 is a continuous misfire code for cylinder #4. Cyl. #4 is the rear cyl. on the pass. side. Causes are a bad coil or a loss of fuel in that cyl. Do you have a 5.4 or a 4.6 liter engine. The reason I ask is that one has the coil-on-plug system, the other does not. (5.4 has the COP system). That particular coil, (cyl #4), is notorious for frying due to water in the plug well from a heater hose that runs above it. You may have a clogged injector too, have you recently run low or out of gas ? You may have picked up some dirt from the tank. Code 0401 is an EGR valve code. Check the EGR valve and its hoses/connections. Also, this code may be eliminated by repairing whatever is causing the other code.. Hope this helps...

Service Engine codes P0304, and P0401
 

Thanks Rtpjunior for your quick response. I have a 4.6 engine. It seems to miss more when the weather is hot (I'm in Texas so it is always hot this time of year). I have tried fuel treatments thinking it might be an injector, and I have heard of people having trouble with the coils on this 4.6 also. I will replace the coil and let you know my results. Thanks again

Service Engine codes P0304, and P0401
 

I have the exact same problem with my 97 expedition.I replaced the coilpack and added fuelinjector cleaner.I do not have the code anymore,but still feel misfiring when I get on it .Did you fix yours and if so what was the solution?
Thanks,
Pete.

Service Engine codes P0304, and P0401
 

I still have the miss. I have tried the coil pack and fuel injector cleaner also (3 times with different brands). I have also checked the plug and wire, and it does not miss when it is at an idle. I suspect it is the fuel injector, but who knows? I am going to have the injectors cleaned, and if that doesn't work, I will probably go to the stealership and let them try.

Service Engine codes P0304, and P0401
 

It was not the injectors. I gave up and took it to the stealership ($801.00 ouch). They replaced the EGR valve (may or may not have been bad), and the spark plug wires, and cleaned carbon deposits. I had 2 wires that were shorting out. I had checked these with a tester and thought they were OK, but I could only check them when the expy was at an idle. It seems that they only shorted out when I accelerated or drove up an incline. If I had it to do over, I would change the wires.

Service Engine codes P0304, and P0401
 

I have a 2001 expy and my service engine light has been on for awhile, I happen to stumble on this site and found out that auto zone will extrsct the code for me. Anyway i'm getting the 401-egr reading waht should I do to resolve this. The truck is somewhat slugggish when I get on the highway is this part of the problem?

Any words of wisdom will be appreciated thanks.

Service Engine codes P0304, and P0401
 

I also had this problem with my 1998 Ford Explorer, only cylinder number 4 is the first cylinder on the drivers side when facing the vehicle from the front (4.0 liter ohv V-6). Here is what I did to isolate the problem:

1. Exchange cylinder number 4 and 5 spark plug wires at the coil and plugs, clear diagnostic code, restart engine. Same problem, so it's not an ignition wire.

2. Using a digital ohm meter, I checked the primary resistance and secondary resistances at the coil. The 3 primary resistances at the coil were within specifications (.8 ohms). The secondary resistances between adjacent coil towers (left and right tower viewing from the front) were between 14,900 and 15,500 ohms, close enough. It's not the coil.

3. Okay now I'm thinking fuel injector, EGR valve or intake manifold. I ponder this for a moment and then it hits me. Could it be the spark plug. No way, I'm thinking....the last time I had a bad spark plug was back in 1977. I exchange the number 4 and 5 spark plugs, clear the diagnostic code and restart the engine. I run it around the block and sure enough the check engine light comes on. I read the code, P0305 (not P0304)...well what do you know, it's the spark plug. I install a new $2.50 spark plug and it's been purring ever since. The bad spark plug was an Autolite Platinum Plus.

Moral of the story. Check the simple things first. Switch adjacent spark plug wires at the coil and plug, retest. Switch adjacent spark plugs, retest. Then if that fails, check coil, EGR Valve, intake manifold and fuel injector.

Service Engine codes P0304, and P0401
 

Thanks for the input I'll sure try

2003 Expedition P0304 code
 

I have a 2003 Expedition, the code for a misfire in cyl 4 keeps popping up. I have had both the coil and spark plug replaced as well as a fuel system cleaned... What else could cause this issue?

I took it to ford to have them look at it and tell me the issus and they wanted to charge me 250.00 to do that so I left.

Any help would be great...

wadeseale@gmail.com

man you got taken to the cleaners ......YIKES!!!!!!!!!!!

what an EGR valve...$90 bucks?????
wires? 30-50 dollars?

can i do it next time?

Just from experience, the EGR flow code is a common problem with all Ford vehicles. Probably 80 percent of the time it is the DPFE sensor. Next in line is the EGR vacuum valve, and then the EGR valve. Make sure the EGR valve is not full of carbon. They also sell a carbon screen gasket for the EGR valves now, to help prevent the carbon build up. This is just FYI, nothing scientific; just my experience.

TommyJ

I've been looking up the parts you mention, but I can't find the DPFE sensor. I found an oxygen sensor, an EGR temp sensor, and a throttle sensor. Is one of these the same as the DPFE sensor?

Tommy -

Thanks for this post. My '97 Explorer failed emissions inspection last week. Over the weekend I had the DPFE sensor replaced. The check engine light did not come back on, and this morning it passed the emissions inspection. I really appreciate the information.

I just had the same P0304 code pop up. Truck shudders at low speed or at stop position - lots of vibration. At higher speeds it seems to be normal. Doesn't really happen when the truck is in Park.

I'm going to change all spark plugs along with the coil packs since I'll be under the hood anyway. My '03 expedition is at about 140,xxx miles - seems like it is about time for this issue to come up. I'll post once complete to let everyone know if the code goes away. Let me know if you have any other ideas. thanks!