I have a 98 Expy 4x2 4.6L with 115,000 miles on it. Recently I have started to experience the engine stumbling (more like a skipped heartbeat) through all engine parameters - idle through highway speeds. It is not continous, maybe 2-3 misses felt per minute and it is not real pronounced, but it is easily felt within the vehicle. It is more pronounced on acceleration. After about 20 miles the CEL will come on with code P0401 displayed (EGR Flow Insufficient Detected). I can reset the code and the engine will run a little better for a while then again after about 20-40 miles the CEL is back on again. CEL never does blink to indicate a mis fire.

I have seached the forum for P0401 and did most of the troubleshooting tips mentioned, but I do have a few questions.

When I checked the EGR regulator, I have 12 volts at the connector, but when I check the resistance of the regulator pins I get 26 ohms. I should get between 30-70 ohms. Is 26 a bad reading or is it "close enough"?

The DPFE connector has 5 volts supplied like the manual states. When I back probe the connector with the engine running I get 5 volts at the signal pin, whether the engine is stone cold or full hot. Stone cold shouldn't it be .2-.8 volts? If I apply a vacuum to the EGR, no change in voltage. When I back probe the reference pin, I get .6 volts, stone cold or hot, and when I apply a vacuum to the EGR valve it rises to about .8. With these voltage readings is the DPFE actually bad?

When I apply a vacuum to the EGR valve at idle, the engine does not necessarily run rough, but it does slow down. With the engine off, I can hear the valve opening and closing with a vacuum. I've checked the vacuum lines and they are in good shape with no leaks. When I run the engine at higher RPM's 2500-3000, I never feel much of a vacuum on the EGR tube, it is more like a pulse. Is that an indication the EGR regulator is faulty, or is it just that the PCM does not need EGR at that time?

I'm sorry this got kind of long. I'm trying to make sure I'm giong down the right path of troubleshooting here. I don't want spend $$ replacing things that aren't faulty. Based on what I've described, do you think it's components at fault or possibly clogged ports in the throttle body or both? Or do I have two seperate problems that are occuring at the same time?

Thanks

 

BTW your explanation is excellent, better than most all others posted, its appreciated. Try this link to see if it helps... https://www.ford-trucks.com/forums/2...-egr-flow.html

 

I took off the throttle body, IAC and an elbow leading to the intake manifolds. I got 3 gaskets from the ford dealership for about 16 dollars total. I also bought 2 cans of carb/TB cleaner. Ther ports from the TB to the EGR valve were clogged with carbon deposits that almost looked like burned popcorn or something. I cleaned all the ports out very clean( re-did 3 times to ensure i wouldnt have to do it again soon.) I used a old toothbrush and an air pick type tool I got at walmart for 5 bucks. The whole job took about 2 and a half hour while listening to some tunes and taking my time. It was a great feeing when the CEL did no return. 500 miles later still no sign along with slightly better MPG. Any questions let me know.
here is a great link throttlebodyclean.php it makes a lot more sense once you start tearing things apart. take the advice on the CC cable and detatch it from the other end.