Trucks been running great...New tune up, timing adjust, still shows code 335 that I'm not stressing about but will get to. Also throws 412 during the KOER test and had a tad of a high idle issue. Found and fixed a vacuum leak at the EGR. During the tune up I found a spark plug wire loose on a back spark plug, and by the looks of it it had been arcing for a bit. New wires.

well on an easy drive, CEL came on, code 172. It threw that code twice before last year but went away. So it's intermittent and just every so often. Has done it on both tanks so I rule out fuel pump. Would a bad O2 Sensor be that intermittent? That's kinda my first thought, buy the long periods between throwing throwing the code makes me wonder.

yes I'm gonna check fuel pressure, but like I said, it's done it on both tanks, did it towing the boat as well as empty, but long periods of time in between.

thoughts?

Dan
95 F150 XLT 4x4 5.8l E4OD 3.55 gears.

 

Code 335: DPFE sensor voltage out of Self-Test range.

Have you measured the actual DPFE output voltage KOEO and KOER? That code is an indication the EGR may not be fully closing when it is supposed to be. If it is slightly cracked open at idle it is an effective vacuum leak that can cause a high idle RPM as well as a lean code. A faulty EVR can also allow vacuum to be applied to the EGR at idle. This will open the EGR valve when it is supposed to be closed. That is why I suggest to measure the DPFE output voltage with the engine off and engine on.

 

I just learned something from you! How would I measure the voltage and what should the readings be? I'm pretty mechanical but the finer points of electrical are not my strong points.


This is my EGR setup. The sensor is fairly new.

 

That gray connector is the measuring point. This article should help even though the wire colors are different: https://easyautodiagnostics.com/ford...e-egr-system-1

It looks like the DPFE output should be around 0.9 VDC at idle/closed EGR.

 

As a side note, I just took a drive, and the idle sits at about 1k rpm after its warmed up.

While running I just disconnected the IAC and it made no change.

 

Great instructional. Here's my results.

The only thing that didn't go well, is the voltage. It started at 1.09v rather than 0.9v, and when vacuum was applied, the voltage went up to about 1.4v before the engine tried to die from applying vacuum rather that 3v to 4v as described in the instructions. Good 5v power and good ground. Vacuum seems good when the engine speeds up as well, with no measurable vacuum at idle (operating temp).

Bad sensor? This one is pretty new but wouldn't be the first bad sensor that's brand new.

Dan

 

Vacuum leak most likely. Or leaking IAC.

 

DPFE output KOEO?

1.09 vs .9 KOER is pretty close IMHO. Should not trigger a KOEO code.

 

I've looked a few times and can't find another vacuum leak. With the elevated idle and no changed when the IAC is unplugged, could it NOT be the IAC?

Would the potential DPFE issue be related or separate issues?

Are the voltage reading a concern with the DPFE?

 

Yes, I already stated that.


Could very well be related if the EGR is actually not closing all the way as stated previously.


Closed EGR DPFE output should be in the 1 VDC range, +/- a small factor that I have found. A good reference document from Tomco: http://www.tomco-inc.com/Tech_Tips/ttt36.pdf. Given your last DPFE output value I believe it is in range, but why is code 335 getting flagged?

I previously asked for DPFE output with the key on engine off, then again key on engine running. The output should be close to the same value.

Another observation is the hoses to the DPFE sensor are supposed to be two different sizes. In your photo they look the same diameter and the one on the left does not look like it is tight on the smaller nipple.

 

KOEO and KOER...didn't change when I started the engine. Sorry I didn't clarify.

 

here is the old one I took off. They seem slightly different. I will take the newer one off later today and compare more closely. Possibly wrong sensor?

 

That's a good sign the EGR Valve Regulator (EVR) is not allowing vacuum to get to the EGR at idle. That eliminates one item. Now trying to figure out why the DPFE output appears to be good, but you are getting Code 335.

Always difficult to troubleshoot multiple issues, but Code 335 is an indication there may be EGR flow when there is not supposed to be any, but the feedback voltage looks good according to the info I have. If this was a truck using the older EGR Valve Position (EVP) sensor on top of the EGR valve the closed EGR output from the EVP is supposed to be between 0.24 and 0.67 VDC. Which coincides with what a metal DPFE sensor should be. Perhaps you have the wrong one installed?

A photo from Steve83 for a 1996 F150/Bronco

 

One more thing I hope you can clarify...

When applying vacuum. The voltage went to about 1.4 volts before the engine tried to die. I read that it should go to 3.5 or even 4 volts. Should I be concerned that the voltage is not correct as vacuum is applied? I wasn't adding throttle, it was just at idle.

How do I validate the EGR is closing completely? It performed as expected on every test I've read about. And even bench tested it and cleaned it. (Ok...two more things)
Thanks so much for your help! I've learned alot!

 

Could be a sign the new DPFE sensor is not linear.



Simple test is to place a block off plate between the EGR valve and the intake manifold. If the idle RPM goes to normal you found your leak. If nothing changes you can effectively eliminate the EGR valve as the cause of your high idle an intermittent lean code. Now to also figure out why you are getting Code 335.