DPFE sensor question (Need to know)

[Silver Bullet]

My SHO's been bogging down and running really rough at various times the past few weeks. It runs fine, then out of nowhere begins running bad/misfiring. The car is at the shop as I write this for a failed starter, and my mechanic did a diagnostic on it today because when he got it started it was as he said "Running horrible". He advised me that the culprit is my DPFE sensor, and that it's not working at all. I figured I'd ask you guys if in fact the sensor malfunctioning would cause my poor running problem I described or not. I want to make sure he isn't just blowing smoke up my a$$ here... He also said the sensor is a special order from FORD costing $190.00!! For that much $$ I want to be certain he knows what he's talking about......................

 

[SHOtimer]

The Ford part may be $190.00 you can get the 'Wells' version at AZ for dramatically less, and i'm sure you can get it at all autoparts stores. You also, don't need to pay someone to install it. It is held on to the back of the intake manifold by two small screws and would probably take less than five minutes to change.

As to whether it would cause a problem like that I do not know.

Doug

 

[revhardSHO]

FWIW, I think the Wells part runs about $50.00

 

[Mr Anonymous]

As mentioned, the aftermarket versions of the DPFE are substantially less than you've been quoted, and it's a quite simple DIY install.

That being said, it's not likely that you would see a marked rough running due to a failed DPFE sensor. Worse-case scenario it would have the EGR valve opening early which might cause a slight stumble in idle when cold, but once the motor is up to temp it wouldn't be noticeable.

I'd recommend getting the car out of there and doing some further diagnosis on your own. I won't give you too much of a hassle for paying someone to install a new starter which is also generally a pretty simple DIY project but asking someone without a lot of SHO experience to diagnose rough running can get you into a lot of $$$ and still not fix the problem. Sounds like he just ran your codes and got a DPFE code, and just addressing the codes found by replacing sensors doesn't always solve the problem. You might just have a simple vacuum leak which could also have caused the DPFE code.

 

[karz]

My SHO's been bogging down and running really rough at various times the past few weeks. It runs fine, then out of nowhere begins running bad/misfiring. The car is at the shop as I write this for a failed starter, and my mechanic did a diagnostic on it today because when he got it started it was as he said "Running horrible". He advised me that the culprit is my DPFE sensor, and that it's not working at all. I figured I'd ask you guys if in fact the sensor malfunctioning would cause my poor running problem I described or not. I want to make sure he isn't just blowing smoke up my a$$ here... He also said the sensor is a special order from FORD costing $190.00!! For that much $$ I want to be certain he knows what he's talking about......................

I had the same problem it was oil leaking into spark plug hole causing the plug wires to arc out.I cleaned spark plugs and wires and applied dielectric compound on plug wire boots and problem solved.....

 

[jaded93atx]

As of 3 years ago the dealer cost ( my buddy worked there) was 65.00 for a new oem DPFE, anything over that is being marked up.

 

[rangerj]

How did the mechanic determine that the DPFE was the problem? Did he test it? The connector has three wires. The end wires are the VREF (voltage reference 0- 5 volts), and the PFE signal. The middle wire is the SIG RTN or signal return to the computer.

If the computer gets a signal return of less than .2 volts it will code 31 or 327 depending on the model year.
Key off disconnect the sensor connector
Jumper the DPFE circuit to VREF at the harness connector
Perform KOEO sellf test
Test results code 35 or 337 generated - replace the sensor (ignore other codes)
If NO Codes at all check the wiring to the control unit or the control unit is faulty OR
check the VREF which will vary with the vacuum pressure from .45v to 4.56 approximately.

for code 35 or 337 a DPFE signal of more than 4.8 volts
Key off - disconnect the sensor connector
Perform the KOEO self test
code 31 0r 327 generated (ignore other codes) replace the sensor
if codes not generated check the wiring to the control unit or the control unit is faulty

VREF test
key off - disconnect the sensor
KOEO measure the voltage between VREF and the signal return at the vehicle harness connector It should be between 4 and 6 volts, If NOT, check the VREF circuit (wire continuity, short, or bad connection)

The DPFE sensor
backprobe between the DPFE signal and the VREF with a digital multi meter set to measure DC current. KOEO apply a vacuum pump to the sensor vacuum connection and vary the applied vacuum from 0 to approximately 10 in.Hg (vacuum)
At 0 Hg vacuum the voltage should be about 0.45 V. The voltage will increase up to about 4.56 (at about 9 Hg) as the vacuum is increased.
This is how it should work. If the sensor does not work this way do the above tests and follow the recommendations if a test fails. rangerj

 

[Off Road SHO]

Wow! How do you know all that, RangerJ? Do you do this kind of trouble shooting for a living? Your depth of knowledge continues to amaze me, and I'm not easily amazed.

Tom

 

[rangerj]

Tom,
First of all thank you the compliment. No, I do not work on cars for a living. I work on them for pleasure. With every car I own I have a minimum of the Factory shop manual and usually get the additional manuals for things like the "Drivability Diagnostics" which usually includes the kind of tests described above.

I also have an extensive library including the following; "How to Understand, Service and Modify Ford Fuel Injection & Electronic Engine Control" by Charles O. Probst, SAE (Society of Automotive Engineers). Steve (Project SHO89) brought this book to our attention a long time ago (thanks again Steve).
It is an excellent reference source for our cars with the EEC IV distributorless ignition system and is about $23 via Amazon.com. The later model years have OBD II (On Board Diagnostics) but most of the sensors and the basic principles are very similar or the same so the diagnostic approach is the same.

Mechanics who take a WAG, even if it is an educated guess, drive me nuts. They often replace parts unneccessarily. Granted there are many good ones out there who will make an educated guess based upon their experience with a specific problem, and/or a specific make or model, but they ususlly also do at least some diagnostics beyond pulling the codes before they replace parts.

I have to know what is not working, why is it not workin, and what do I have to do to make it work, e.g. repair it or replace it?

If I have to turn my car over to a so-called "professional" mechanic I see it as a personal defeat. That runs against the ranger's code, "no surrender, no retreat, and never say die". So, what I do not know I go out of my way to learn. It's as simple as that. And I do not mind sharing what I've learned whenever I can. The beauty of this forum is that I can learn from so many other experienced and knowledgable folks every time I visit. I love it.

 

[SHOZ123]

Easiest way to see if it is the sensor is to pull and plug the vacuum line going to the EGR valve. If it improves then it is the sensor.

If it does not, then at idle when the engine is fully warmed up put a vacuum hose on the EGR valve and apply vacuum. If there is no change in the way the engine is idling then the EGR valve is leaking. A properly working EGR valve will cause the engine to stumble at idle when vacuum is applied to the valve.

 

[rangerj]

SHOZ123,

Those are in fact some of the "quick" test used to zero in on an EGR problem.
I responded to the DPFE (or PFE for pre 1993 model years) question without discussing the EGR system or its other components. I'll add a couple of bits of information to your post.

The EGR valve is NOT active when the engine is cold, nor when the engine is at idle, nor when the engine is at wide open throttle. So the first step in checking the EGR is to have an engine at normal operating temperature. Then tip the throttle a LITTLE off of idle and watch for the EGR valve stem to move as you open the throttle a little. It should open and close the valve as you open and close the throttle. The valve stem moves up and down.

Check the vacuum lines to and from the sensor. Make sure they are not plugged up or cracked, split, or otherwise leaking vacuum. It is not uncommon to find cracks or splitting at the ****** where the hoses are attached.

If you vacuum test the sensor be careful not to exceed 9 inches of vacuum for a DPFE sensor. The vacuum limit for a PFE sensor is 4 inches of vacuum. This could ruin the sensor. Apply only enough vacuum to the EGR valve to move the poppet valve stem. Any additional vaccum pressure can damage the EGR (vacuum diaphram). If the valve stem will not move, then the valve is either stuck, or the vacuum diaphram is damaged.

You should then check the PFE or DPFE to make sure you are getting vacuum to it and from it (to the EGR valve). You can test the lines with a vacuum gauge or simply place your thumb over the end of the lines, one at a time, and feel for the vacuum pressure.

Now check the exaust tube and the exaust ports (holes) in the exaust manifold and at the intake manifold. These commonly get plugged with carbon deposits (hard black deposits). Clean the tube(s) and the port openings. The EGR has to be removed for this and you will need a couple of gaskets to replace the old ones. So, get your gaskets before you take things apart. This is a very common EGR problem along with vacuum hose problems. Check these two common problems BEFORE replacing any parts.

The EGR valve should be inspected while things are apart. It gets carbon deposits built up on the inside of the valve. There is no practical way to get at the deposits to clean them off of the valve. If you find a way that works please let me know. I have tried scraping, and chemical dissolving products, with very little success. It is usually a short lived success.

Lastly, check the sensor and its wires and connections as described above.

When the EGR valve is not functioning properly you will usually have a poor or rough idle that starts to happen a short time after the engine has been started (as it warms up). If the EGR valve is being held open by deposits it could affect the idle even when the engine is cold and the EGR "system" is not supposed to be in operation.

The DPFE (DIFFERENCE in Pressure Feedback)sensor is used since 1993 (I think that was the beginning year). Actually the D stands for the engineering term DELTA which refers to the DIFFERENCE in pressure) It is different than the PRE (Pressure Feedback). The DPFE considers the exaust pressure in its measurements (the difference in exaust and intake manifold pressures).

NOTE: For you professional mechanics out there - the trouble code 34/335 could be triggered by a lack of exaust pressure caused by exaust extraction equipment, and/or a customer that has altered their exaust system so that the exaust pressure is altered. You could change sensors all day long and never correct the "problem".

The point here is that you can adversely affect the EGR systems operations if you alter the exaust pressures on a vehicle with the DPFE EGR system. If the manufacturer of the aftermarket exaust system does not mention this in their information ask about it. If you gut the cats, or put in "cut-outs", you may experience some problems.

The EGR system is very often neglected and often is the cause of that annoying rough idle, hesitation when the throttle is tipped as you start out, or in extreem cases some hard starting problems.

Any other thoughts and/or experiences would be appreciated. Jump in!
rangerj

 

[SHOZ123]

I have never seen an actual valve fail. Not to say they don't. It is almost exclusively the sensor that fails. I have seen where the two short fat hoses won't stay on too.

When I say apply vacuum I meant using your lungs. This is a very low level of vacuum but enough to move the valve.

Actually if you follow the codes then it is pretty easy to pinpoint the problem.

 

[rangerj]

I have only seen a few valves fail. The diaphram will develop either a pin hole, or they crack from age. The more common "failure" is the accumulation of deposits on the valve itself and/or in the chamber. This can either prevent the valve from fully closing, or restricting its opening. It would be great if you could take it apart and clean it, but they are sealed and the opening is not large enough to get at the problem (carbon build-up).

The most common problem is the blockage of the intake and exaust ports and/or the tube between them. Then the next most common failure is the vacuum hoses that develop a leak or get blocked. Lastly, the sensor or its connections cause problems. The aforementioned is based upon my experiences and is not in any way representative of any official sources.

The DPFE for late model Fords are operated with broader perameters built into the computer program. In essence the early perameters are too sensitive, so that it only takes a slight irregularity in the pressure differential to trigger one of the codes. Keeping the system clean and the vacuum and electrical connections in good shape is imperative.

You are ablolutely right about using your lungs to apply the limited amount of vacuum necessary to test the EGR, and the DPFE. However, doing so is a bit ackward and the stuff in the hoses tastes horrible. I use gauges because I have them but, you are right it can be done by sucking on the hose. (Good grief that sounds horrible).

 

[Mr Anonymous]

Guys, guys, guys!

I realize you're trying to be helpful, but please re-read his original post and consider its context.

He asked specifically about his mechanic telling him that his rough running was the result of a bad DPFE sensor which would cost $190 just for the part and if it was a reasonable diagnosis.

What's happened here can be compared to a patient asking his doctor if his eyeglasses could be causing his headaches, and the doctor explaining to him how to perform do-it-yourself brain surgery!

There's no doubt that there are some very, VERY smart people on the forum. That being said, sometimes simple questions require simple answers!

 

[rangerj]

Mr Anonymous,

The last sentence of the questioners post says that he want to be sure that the mechanic knows what he is talking about, right? We cannot possible make that determination.

So, what better way to do that than to know how to diagnose the problem yourself? Ergo the do-it-yourself lesson. That is what we are here on this forum for isn't it.

There is a reasonable presumption than more than just the original poster will read the responses, and in this case a discussion of the problem and the different points of veiw as to the easiest way to diagnose the problem.

If the poster discusses the matter with the mechanic he should now have a better idea as to how good the mechanic is based upon his new knowledge of the subject.

Lastly, I delved a little deeper into the subject because of other threads in the recent past, and currently, regarding the same subject, that is the DPFE sensor and the EGR valve. So, I thought I would help several SHOs with one thread. EXCUSE ME! rangerj :cry:

What was the question?

 

[SHOZ123]

Sorry, I guess just pay the $190???????

 

[rangerj]

SHOZ123,

An old adage about leading a horse to water comes to mind!

 

[Tommy's SHO]

Thank you rangerj.

I just got a code 327 and will do the tests that you mentioned above asap.

 

[hawkeye18]

If you want to pay a mechanic $190, then go right ahead, but I think this would be a lot cheaper. I feel the mechanic is blowing the proverbial oil down your spark plug wells. A DPFE will not cause the car to misfire. It is either a DIS, Coil pack, wires or plugs. 95% of the time.

 

[93rev2sev]

He took the car to a wrench for a starter. He's not a DIYer.

Edit:
FYI: own an SHO for long enough and you will either be a DIYer or very poor.