I have been experiencing a slight surge/hesitation at about 1400 RPM. Sometimes the idle gets a tad rough, but not very often. Fuel mileage has taken a turn for the worse.

Several days ago my "check engine" light came on and I plugged my scanner into the truck and pulled a "P0402 - Exhaust Gas Recirculation Excessive" code out of the computer.

So, now I know that the problem most likely lies in the EGR system. I've pulled my vacuum hose off the EGR valve and it appears to be working... I put a vacuum pump on it and it holds a vacuum. If I manually apply vacuum to the EGR valve while the truck is running, it starts running really rough until I release it.

Since I don't own the PCM troubleshooting manual (it's $160), I thought I'd ask someone here to see if you can shed any insight to my problem. Any help would be very much appreciated.

Oh yes, my truck is a 1998 F-150 5.4L.

--Steve

 

Steve,
An excessive EGR flow code can be caused by the EGR valve sticking open or by the DPFE sensor sending the computer an incorrect low voltage or by an EGR vacuum regulator not releasing vacuum(unlikely). The DPFE has 2 rubber lines going to the EGR tube. From memory, the DPFE voltage should be .6 to 1.1 with key on. You should pull a vacuum on the EGR while watching this voltage at idle. If erratic ,either the EGR is sticking or the DPFE is bad(likely). To determine which is the problem, turn off the truck and pull the valve open and close several times while you watch the EGR. You can usually watch the diaphram without taking the valve off. If the EGR sticks at all, replace it. Hope this helps.
Dan Kryszczuk

 

Dan,

Thanks for the information. I'll check the items that you mentioned and let you know the results. Thanks again!

--Steve

 

bluecrab:

Markmizzou has been looking for the egr valve in his 5.4 so he can replace it. You might want to drop him a note on one of his topics on the engines board.

--karl

 

Well, I replaced the EGR valve ($60) this afternoon and I am sorry to say that the problem still persists (I thought it might be the EGR valve sticking.) So, the problem is either the vacuum regulator solenoid or the differential pressure feedback sensor. Or, prehaps it is a blockage in the EGR valve tube between the differential pressure feedback EGR sensor tubes.

I plan to replace the regulator solenoid ($20) on Monday to see if that is the problem. Wish me luck!!

--Steve

P.S. After I replaced the EGR valve and made a long testdrive, I put my scanner back on the truck and the computer had registered another P0402 EGR excessive. So, I'm 99.99% certain that the problem lies within the EGR system. The money spent on the Auto X-Ray diagnostic scanner was worth it's weight in gold!!


[This message has been edited by bluecrab (edited 12-16-2000).]

 

Today I replaced the EGR vacuum solenoid and, I believe, the problem is solved! Before replacing the solenoid the truck was stumbling at 1400 RPM when driving about 35 MPH. Immediately after replacing the solenoid, I could not detect any roughness in the engine. I still want to drive the truck for a few days before I give a definitive answer, but I'm almost certain that the solenoid was the problem.

Also, as a side note, the solenoid appears to have fixed another problem that I have been experiencing since the truck was new... When I mash the pedal and give the truck everything she's got, after shifting from first gear into second gear and as the RPM's increased, I experienced a wavering of sorts which only lasted a second or two. The pitch of the engine would decrease slightly and then pick back up again and there was a slightly noticeable loss of power during this event. I always thought it was the torque converter slipping or something. With the solenoid replaced, the wavering is completely gone and now my truck accelerates steadily through second gear. I am one happy camper!!

So, it appears that my EGR system was not quite right from the factory. It took two years for the solenoid to get bad enough to be noticed and to register a "check engine" code. Better late than never!

--Steve

 

Which vacuum solenoid did you replace? I may have same problem....

 

I HAD THE ROUGH IDLE ON MY TRUCK FOR QUITE SOME TIME NOW. THE FORD TECH'S FINALLY CHANGED THE EGR VALVE AND NOW MY TRUCK IS RUNNING PRETTY SMOOTH. THEIR ARE LOTS OF THINGS YOU CAN CHECK FOR THE ROUGH IDLE. NOT JUST THE EGR SYSTEM.

 

The EGR vacuum solenoid is upstream from the EGR valve and is located immediately to the right of the throttle body (on the '98 5.4L). Locate your EGR valve (to the right and slightly rearward of the throttle body), then follow its vacuum hose to the solenoid. The solenoid looks like a small plastic cylinder with an electrical connector near the top and two vacuum hoses coming out near the bottom. My local Ford dealerhsip wanted $19 for the solenoid.

Back to my original message...

I do not think that the new EGR valve and vacuum solenoid have solved my rough spot at 1,400 RPM. It apparently did fix the slight wavering in second gear at WOT, so I am certain that the new EGR components have solved that problem (plus the fact that my PCM was repeatedly reporting "P0402 EGR flow excessive" codes.)

So, I have taken care of the EGR problem, but it appears that I am still stuck with the roughness at 1,400 RPM... which is most noticeable between 25 and 35 MPH. It only happens when I am maintaing speed and the throttle position is held constant. It does not happen at any other RPM range or if I am accelerating or decelarating... only if I am maintaing speed. My fuel economy is still much worse than before. I also get a good whiff of "rotten egg" out of my cats when sitting at a light (after light driving... never had this happen before.)

The "rotten egg" smell tells me that too much unburnt fuel is making its way into the cats... so the truck appears to be running too rich... which would also explain the poor fuel economy. I'm not getting any O2 sensor failures but I am beginning to feel that the O2 sensors are to blame since they measure the amount O2 in the exhaust gasses and tell the PCM to adjust accordingly. If the sensors were marginal, they could mistakenly tell the PCM that I'm running too lean which would then cause the PCM to make the mix richer.

Anyone have any other suggestions or comments?

--Steve

 

AFTER ALMOST A YEAR OF TRYING TO FIX MY TRUCK AND ALOT OF MILES LATER THE DEALER FINALLY CHANGED THE EGR VALVE AND MY TRUCK IS RUNNING GOOD. IT'S BEEN TWO WEEK SO FAR AND ALL'S WELL. GOOD LUCK


THE ROTTEN EGGS SMELL TELLS ME THAT YOUR CAT. CONVERTERS ARE NOT DOING THEIR JOB AND MAY NEED REPLACING.

YOU EVER TRY TO DISCONNECT THE BATTERY(NEGATIVE CABLE) AND LET THE COMPUTER GO BACK TO THE DEFAULT SETTINGS? RESETTING THE COMPUTER MAY DO THE TRICK.

 

I know of three F-150's that have had the rotten egg smell that was fixed with an O2 sensor replacment. I think it's worth looking into.

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Red '97 F-150 SC 4x4 off-road, 16" rims instead of factory 17"'s(borrowed from old '97 reg cab), BFG 265/75 16 all terrain T/A, K&N filter with modified air box, Flowmaster 40 with duals out back, Expedition center console, 3" rear seat lift, after market stereo seen at HTTP://members.sounddomain.com/red97
Got Superchip and velocity tube for X-mas too cold to put on as of yet.