I have this 99 5.4L 4x4 (130k miles) that has been giving me fits for the better part of this yr. This thing has been putting out several errors one after another. Only condition I get is bad idle when the engine warms up, otherwise fine. The last few probs I got was that the o2 sensors were bad so they were changed. Still no improvement. Then the computer says the EGR flow insufficient. Pulled the intake and all and no probs. Vacuum on the EGR caused the engine to stumble so that was good. DPFE was also changed about 4 months ago but I got a new one anyway,- still no change. Keeping in mind that these probs came on right after my wife had wrecked the truck I thought that the computer might have gotten messed up. Some posts on here reflect that there were some problems with these PCMs. So I took it out today to look at it. The harness might have been slightly loose but no other obvious probs. Put it back in and now the system is saying that it has p0402 (excessive EGR flow). How does the system go from not enough to excessive flow overnight? I have changed just about everything emissions on this truck so far and am wondering if the computer has been bad all along.
So my question is do they just crap out all together or start throwing random errors when they go bad? Appreciate any advise on this one guys. -Bamadoc

 

anyone have any ideas?

 

Have you cleared the codes with the obdII reader? Might wanna try take off the neg post on the battery and turn on the high beams to drain the capacitors and let sit for about a half an hour, that will clear your PCM of codes.

 

Hi Xtrford, yeah I bought the OBDII code scanner. Have been clearing those thoughout testing.

 

Hey bamadoc.
If you are getting excesssive egr flow, the egr might be opening at idle. That will cause a bad idle. Has the egr vacume control solinoid be replaced? Can you post the code numbers or us?

 

Hey BossHoss, The code I was getting most recently was p0401. Keep in mind that I have been having a bad idle when warm all year despite having changed all o2 sensors, DPFE, IAC, MAF, plugs, COPs, all injectors, verifying correct fuel pressure per haynes manual, changed the intake manifold, and the pcv valve and harness all the way to back of TB. Checked the VSS too per haynes.
Took it to the dealer with P0174 code and got it back a week later with that code gone (after new O2 sensors)and now it had the p0401. He said just to clean out the port in the TB and that would prob be it. I had just done that the month previous but what the heck, did it again. Except this time I threw on a new EGR valve since it was the only thing old I could find. (It was checking ok with vacuum)
After that I drove it and right off came up with p0402 and p0401! Strange... So I ran through the checks again to find the recently chaged DPFE had 5 V in and 5 V out with the engine cold and KOEO. Warmed it up and same. So that got changed again tonight and it reads ok now. Havent run it yet though.
Question for you, the EGR vacuum reg should read betwwen 30 and 70 ohms right? Mine did but is there any other way to check its operation?
Thanks again for the help man, Bamadoc

 

Doc, slow down a bit.
You posts are hard to read.
Your doing a lot of shotgun work and not getting results for the efforts.
The 401 code reports a problem measuring exhaust pressure across an internal orfice in the pipe between the two small sample tubes.
If the EGR does not open enough or there is blockage into the intake 'after' the EGR, the flow won't measure right.
The problem could be the pipe, the DPFE, EGR channel.
It's easy the test the EGR control solenoid (EVR). at the hose port going to the EGR; is there substantial vaccum? If yes the EGR will be open and cause a rough idle 'if' the EGR channel is not blocked.
If the EVR has a vacuum 'supply' fault the EGR won't open under any circumstance.
All these different situations usually cause a related code.
The 406 code is usually a small DPFE attaching hose problem or a crack in a stand pipe. I won't go into detail about the 406 code because the last time I was critisized for being an engineer over it.
As for the rough idle and 174 codes, you need to very closely look at all the vacuum related hoses for deterioration and any leakage between the mass air meter and the throttle body..
Take a new look at everything and I think you will find most of the problems instead of spending money on hopeing to get it, and have money left over for a coffee..
Good luck.

 

Thanks for the tips Bluegrass, There isnt a tremendous vacuum going to the top of the EGR as far as I know. I am going to do the voltage check tomorrow on the regulator. The remaining items you mentioned were checked by myself and the dealer. Their only hunch was either the cats partially blocked or possibly the computer. Bamadoc

 

I'm really not to clear on what the status is.
Begin from the beginning and tell what conditions you have now.
Measiing voltages is fine but what are you expecting to find that relates to the problems.
Do you have a chart to tell you what you should be seeing.
Don't get me wrong I'm not trying to be difficult but you have to understand this truck is computer controlled and unless you have some idea about what is going on it will be difficult as your finding out.
The DPFE really needs to be tested using a pressure hand pump from 0 to 4.5 psi and record the voltage at each 1/2 psi level. This mimics the actual operation. Or replace it.
The voltage ranges from .45 to 4.6 volts +/- some tolerence.
Some extra infor; If you clear a 401 code by scanner or battery power removal, it takes 2 drive cycles for a failure code to return if not fixed. There is a reason it works this way. It you see the code right away there likely a hard failure before this test ever completes in a nomal manner.
I would suggest you visit the Motorcraft web site and down load the OBDII info for your year and study the EGR section until you have some understanding of how the systems works.

 

I hate to ask Bluegrass, but what denotes a hard failure? BTW, I am using the Haynes manual. I do have a basic understanding of motors after working for Ford a few years back but was just hoping someone might know something about possible PCM probs with this specific truck. Thanks again, Bamadoc

 

ok lets get to the baseaks first befor you spend more of you money

 

hard failure is like a broken wire that no mater what you do it keeps coming back or a internal failure with a sensor or moduall like if you were to clear the code it would not clear for you even if you take the -batt post of and clear kam-keep alive memory

 

Hi G-dog, thankfully I dont have that kind of problem. Codes are clear this am after driving to work so far. Idle is still a little rough though. Although I drove for months with bad idle and no codes before. The dealer was referring to soft codes when the computer would scan and give code but no CEL. Once the CEL came on it was hard code. Thanks for the info man. -Bamadoc

 

no problem we are all here to help hope you find out whats wrong

 

check to make sure ALL grounds are connected and clean and the bolts are tight

after the accident a ground may not have been reconnected properly

make sure the battery terminals are clean also