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CEL Light Intermittent Activation

FixingDaily

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Boise, Idaho
Year, Model & Trim Level
94 Explorer XLT
Hey Guys,

My 94 Explorer with the 4.0 6-Cyl, MFI motor is having the CEL act up again. Last time I had this many codes in the CM memory test (2011), I started down the line of recommended tests, replacements etc. After considerable time and dollars, all was fixed by replacing the PCM with one out of a twin "94". After reviewing my old posts, most of the codes are similar, but are dealing with different banks, etc. I am close to just ordering a replacement PCM before starting down the investigations road again. Before I do that, I thought maybe I should run this list by the helpful folks on this forum to see if you have any other ideas. I should say I my daughter and I have been driving this Explorer back and forth to her university about 3 hours each way at 80 MPH (yeah for Idaho) and it is running very strong. Here are the codes:

KOEO

335 (O) Pressure Feedback EGR Sensor Voltage Higher Or Lower Than Expected During KOEO

KOEO CM Memory Codes:

124 (M) TP voltage was higher than expected
176 (M) Oxygen sensor not switching - system is or was lean Left or Front HO2S
177 (M) Oxygen sensor not switching - system was rich Left or Front HO2S
336 (O,R,M) PFE sensor signal is/was high
337 (O,R,M) EGR feedback signal is/was high

KOER

336 (O,R,M) PFE sensor signal is/was high

Thank you in advance for any help you can give on clearing this up.
 


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FR-425

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It's just the DPFE.

335, 336.

All the other codes are due to the EGR failure caused by the DPFE. Except maybe the TP sensor. May be time for one of those.

Intermittent CEL is the only clue I needed to make the diagnosis on this one.

egr1512_zps58839912.jpg
 




FR-425

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Don't forget to reset the PCM with your scan tool or by disconnecting both batt cables..
 




mekelly

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1994 Ford Explorer XLT
Agree with FR-425 on the DPFE diagnosis. It will cause the CEL to light up and go off repeatedly. The gas re-circulation doesn't happen 100% of the time. The PCM doesn't call for re-circulation until the coolant temp is above 113 (the engine is beginning to warm up), TPS has to be above a certain threshold (not at idle) and the MAF has to be above a certain value.

In other words, you won't get a constant fault with a bad DPFE; it will come and go as your driving conditions change.
 




FixingDaily

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It's just the DPFE.

335, 336.

All the other codes are due to the EGR failure caused by the DPFE. Except maybe the TP sensor. May be time for one of those.

Intermittent CEL is the only clue I needed to make the diagnosis on this one.

egr1512_zps58839912.jpg

Great Advice: I will give that a try and report back.

Merry Christmas,

John O
 




FixingDaily

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Don't forget to reset the PCM with your scan tool or by disconnecting both batt cables..

I used the paperclip method to read the codes. Does disconnecting the paperclip with KOEO mode reset the PCM as well?

John
 




FixingDaily

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It's just the DPFE.

335, 336.

All the other codes are due to the EGR failure caused by the DPFE. Except maybe the TP sensor. May be time for one of those.

Intermittent CEL is the only clue I needed to make the diagnosis on this one.

egr1512_zps58839912.jpg

One more question: Can the DPFE be repaired/refurbished/rebuilt in any way? I noticed they are not the most inexpensive of parts.
 




FR-425

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Nope. $50 where I'm at.
 




FR-425

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I used the paperclip method to read the codes. Does disconnecting the paperclip with KOEO mode reset the PCM as well?

John

NO. and be careful. Key off before you pull the paper clip. You can fry the PCM!
 




FR-425

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I am one who does not advocate the use of the paper clip. bad juju

For ABS yes. For PCM no.
 




FR-425

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I have the Innova CAN OBDI & II. $185.00

It is smart enough to list codes in an order that makes sense.

It understands the cascading effect one fault can cause and weeds out the BS codes.

Can't imagine owning a modern car without one.

The 'clip' is guess work at best.

It is not possible to run an KOER with the clip, you get no cues for the required inputs, steering, brake, throttle. so all results from that are garbage.
 




mekelly

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2stroke

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I have the Innova CAN OBDI & II. $185.00

It is smart enough to list codes in an order that makes sense.

It understands the cascading effect one fault can cause and weeds out the BS codes.

Can't imagine owning a modern car without one.

The 'clip' is guess work at best.

It is not possible to run an KOER with the clip, you get no cues for the required inputs, steering, brake, throttle. so all results from that are garbage.

On the subject of scan tools, for most guys, they are out of the question. The paperclip method works fine if you know how to interpret the results. I, however, am pretty well invested in these old trucks. I already have a good OBD II code reader. I have seen some adapters for GM OBD 1, but only pictures of Ford OBD 1 adapters. Is there even such a thing? If not, I see they make a little plug that is more or less a display that memorizes the codes for about $30 on Amazon.
 




Centaurious

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mekelly

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I bought an Actron CP9190. It's not cheap but it does real time data streaming and graphing and includes all the old OBD I cables for Ford, GM, etc.

Works great on the '94 Explorer. Again, not cheap but I wanted one tool I could use for the Explorer and my other 5 OBD II enabled cars.
 




FixingDaily

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I have the Innova CAN OBDI & II. $185.00

It is smart enough to list codes in an order that makes sense.

It understands the cascading effect one fault can cause and weeds out the BS codes.

Can't imagine owning a modern car without one.

The 'clip' is guess work at best.

It is not possible to run an KOER with the clip, you get no cues for the required inputs, steering, brake, throttle. so all results from that are garbage.

Agree on having a good scanner for the modern vehicle. I have a nice OBDII for my other cars and it has made short work of a lot of issues (Bad COPs, etc.). Never purchased one for the OBDI though. Guess I am too cheap when a paper clip has been able to do most of what I need. I am wondering though about all the other threads where I am seeing them recommend disconnecting the paper clip during the KOEO mode to clear the CM part of the PCM (and looking back to my old posts in 2011, I may have fried my PCM in just the manner you are discussing, but it may have been a blessing as I replaced the PCM and all manner of ills were corrected).

Thank you for your help. Once I get a new DPFE installed I will report back.

Merry Christmas

John O
 




FixingDaily

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FixingDaily

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OK, Here is my report and request for additional HELP!!!!

I installed the new Wells solid state DPFE (and the two associated hoses) last winter into my 94 Explorer with the 4.0 6-Cyl, MFI motor (four wheel drive, XLT model). Aside from having to install a new radiator in July, there have been no issues since the install and through this summer and no CEL lights at all (even with shorter 1 hour drives).

I took my daughter back to her university last week (230 mile drive, all 80 MPH interstate) and the CEL problem re-appeared at about 2 hours into the drive, along with some engine sputtering issues after pulling off the freeway at our destination (even with CEL occasionally coming on and off - but not flashing, the Explorer still had plenty of power to maintain 80 MPH). Once we stopped at the off-ramp signal, the sputtering became obvious. We then went to her dorm, parked and unloaded.

I left the car with her and she reports that when the engine cooled, CEL light is off and the Explorer is driving well and strong. She has not had any issues at all this week during short drives.

The CEL issues, and as it has happened before changing the DPFE, only starts happening after about 2 hours of freeway driving. This leads me to believe that it is a heat related issue, and with a part that takes that long to get to the critical temperature before starting to act up (thus making this a more difficult issue to diagnose).

Without the benefit of being able to pull the codes (which I may be able to do next Friday when she drives back for Labor day), does anyone have another guess on which component would cause the CEL and engine sputtering symptoms when a peak operating temperature?

I look forward to any suggestions. I have a great bone yard about a quarter mile away with a good supply of Explorers, so picking things like a coil pack, MAS, etc for cheap to try and see is not a problem.

Let me know if anyone has some good ideas on what to try.

John
 




Centaurious

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If you want to do 80 on the Interstate I can't think of a worse vehicle to pick than a first gen Explorer. Codes are going to be the best clues but maybe you got some contaminated gas. Check for vacuum and intake leaks. I have a failed cruise servo and plugging the vacuum line smoothed out some rough running that was just becoming noticeable.

Good Luck
 


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