Getting the dreaded 401 code on my 1996 bronco 351w and have tried just about everything I can think of.
List contains:
New EGR
New DPFE
New Vacuum lines
New Vacuum canister

What am I missing?

Bronco starts with high idle and sometimes stalls but after she warms up bronco runs like a dream.

Note:
Exhaust system has been cut right after the muffler and I am wondering if that will limit the back pressure and cause 401 code? Also had oem y pipe modified to fit around aftermarket oil pan and might have some exhaust leaks.

Thanks.

 

Another frequent cause of P0401 is a blocked or broken EGR tube.

 

I was thinking about that. The 2 smaller tubes are welded to the larger main tube and wondering one or both could be leaking from the welds?

Leaking exhaust cause 401 as well?

Thanks.\

 

Umm, isn't 401 a cylinder 1 misfire?

To answer about the exhaust, no. Leaks upstream of the 02 sensor could cause 02 codes or driveablilty issues, but they'd have to be pretty damn large

 

I applied vacuum to the egr while running and engine stalled, is that good or bad?

 

The OP has a 1996 model which is OBD-II. Code "401" is actually P0401: Exhaust Gas Recirculation Flow Insufficient Detected.

 

No a leaking exhaust is not a typical cause of P0401. The EGR tube can become clogged with carbon build up. A very common problem. A cracked EGR tube is a common cause of this code too.

 

That is neither good or bad. It just proves the EGR is opening.

You might find this troubleshooting procedure useful for your issue: FORD DPFE SENSOR TEST

 

The first thing I did was clean the egr tube and tube was not bad at all. How can the egr tube be checked for cracks? I think the welds that connect the 2 smaller tubes to the main egr tube look suspect but cannot confirm a leak.

Replaced dpfe sensor already several weeks back. I am thinking maybe the evp sensor(not sure I got the name right) but sensor is located down stream from the egr vacuum line on my 96. When the vacuum line is pulled off the egr at idle the vacuum is very weak, not sure if that is good or bad indication. Also code po401 usually occurs in stop and go traffic and on the hwy code is non existent. Any thoughts?

 

Physical inspection is the best way to check for cracks in the EGR tube. The old design with the accordion style section is well know to crack after years of use. Did you replace the silicone hoses leading to the DPFE?

The solenoid/sensor, actually upstream of the EGR, is the EGR Vacuum Regulator (EVR). There should be no vacuum at the EGR when the truck is idling. EGR is only applied under light throttle cruising conditions.

For reference: EVR

 

Funny no cel in several days but now have a slight hesitation under light throttle cruising conditions, think that could be the egr?

Did not replace silicone hoses yet.

What do u think?

Thanks.

 

Recheck for any stored codes. If the silicone hoses were bad you will definitely trigger a P0401 code.

 

Just bypass the EGR I've done that in my 95