Hi..... first off, I'm not a mechanic and don't profess to be. However, I'm a somewhat handy DIY guy. Having said that, this truck is driving me insane and it's now personal so I thought I would reach out to this forum. I've have read many posts concerning my symptoms, but have yet to resolve my issues. So now the story.....

I've been experiencing hesitiation when first pressing the gas, stall at idle, RPM fluxutating between 1000 and 500 at idle and loss of acceleration. Had the truck read at autopart store and received a P0402 error and misfire is cylinder 8. At this point, I've changed the the plug, COP, EGR valve, EGR Valve Solenoid and DPFE sensor and still have the exact same symptons. I've also changed the plug for cylinders 5,6 & 7 as well. The check engine light is on, went off briefly after changing DPFE sensor, but back within a day.

Given the fact the error code is P0402 and some of the threads I've read, I thought the issue was centered around the EGR system, but I've replaced many of the components.

I know it's a longshot, but wanted to see if anyone else has experienced this or may have a suggestion where to look next. Thanks.

V8
4.6 Liter (I Think)

 

First we need to get you into understanding a couple systems on the motor and some idea what they are all about so you can relate better to what is happening.
It sounds like you have an issue with the EGR system causing the rough and varying idle.
An open/ leaking EGR will cause these symptoms because exhaust gas does not burn the second time, leans the mixture and advances the ignition timing and cuts fuel, making the engine rough.
It only opens during OD or third gear and light throttle application at road speed over about 45.
Any other time causes drivability problems.
So getting that system under control by test and repair is the first order.
.
Next is getting the cylinder missfires solved if any exist after the EGR is solved.
Next is cleaning the IAC (intake air control) and throttle plate area to be sure it can control idle..
.................................................. .................................................. .....
The 402 code supports your rough idle problem because it is an "excessive" exhaust flow code indicating it is getting into the intake when it should not.
Look at the EGR control reglator to be sure it's not connected incorrectly keeping the EGR open full time.
Pull off the hose to the EGR to see it it settles the idle down.
If yes, there is vacuum being passed through the regulator causing the EGR to open.
If no, the EGR is leaking past it's seat for some reason.
Get this fault first so it does not cause confusion trying to solve more than one other issue at the same time.
It is quite possible this one fault will clear most or all the other issues you see.
Good luck.

 

Hey....thanks for the troubleshooting tips and educations. So many times, people love to blister you for touching things you shouldn't, etc..... I just appreciate the candid feedback and tips. Removing the hose from the top of the EGR valve did settle down the idle so I'm just leaving it off (just kidding - couldn't resist a newbie comment like that). Checking out more troubleshooting tips from here! Thanks again!

 

You have proven the EGR is allowing exhaust gas back into the intake when it should be closed.
Seems the EVR is leaking/allowing vacuum to get to the EGR.
The EVR is a 3 port device.
It has a filter at some location on it's body.
This filters air that has to be let in to allow the EGR to close once it has been opened by vacuum.
Get this cleared then go to any other issue.
Good luck.

 

Well it only took replacing everything in the EGR system and putting the vacum lines back on the correct ports to get things running properly. On a serious note, thanks for the input and patience as your tips put me on the right path! Best regards!

 

Noticed this thread when I logged on. I've been having the exact same issue with my Ranger, that arose after I went through a little mud. Strange thing is, my truck apparently is not equipped with an EGR system.. What was it that you finally did to fix the problem for sure?

 

Hi,

Unfortunately, I was in mass component change out mode vs. structured troubleshooting practice. However, I believe the plug and coil pack was bad which was the major fix. When I put things back together, I crossed up a couple of vacum lines that led me to replace many components within the EGR System. Thanks.

 

Ahh I see. Yea my truck is being totally awesome and not throwing any CEL's at all, which makes me wonder about where my problem is. It runs a little rougher than i'd like, but not all the time. It runs great when it's cold, but as it warms up, it just gets worse and worse to the point of shutting down at stop lights. It's almost as if the torque converter lockup system has a problem, but I'm torn between that and something with the engine because of the idle fluctuation. The plugs are original and at about 50,000 miles now. When I pulled them, the gap was outrageously high, but the plug condition was normal and there were no signs of running lean or rich. Doesn't necessarily mean they're good though. For now I re-gapped them and then put them back in until I can find some Motorcraft wires that don't cost an arm. Hopefully a plug and wire change will do me some good.

Thanks for the insight into your problem! It's good to know I'm not the only one having this issue. It's definitely personal for me too.

 

Check your crankshaft sensor line by the AC Unit under the truck and see if it has been warn down. Replacing it will fix the issue of stalling in mud puddles.