1993 Check Engine Light Is Lit

[Troll Slayer]

This is my first post. Okay, I am AMAZED and, frankly, overwhelmed, at everything on this forum.

If any of you can help me pin point what's wrong, I'd appreciate the help.

I knew it wouldn't last. Last September, I did some emission control system repairs on my 1993 Explorer so I could pass my emissions test and register my car. Now, a few months later, I've got a "Check Engine" light. I pulled the codes using a code reader. These are KOEO codes. They are as follows.

186 - fault in injector pulse width circuit/high

332 - insufficient EGR flow detected

335 - EGR sensor circuit voltage higher or lower than expected during self test

336 - EGR sensor circuit voltage higher than expected

336 - (Trucks only) exhaust pressure high

337 - EGR sensor circuit above maximum voltage

As most codes point to the EGR system, let me state that the EGR solenoid, EGR valve, Pressure Feedback Sensor (PFE) and PCV valve are all brand new. The oxygen sensors are new and the catalytic converter is only two years old.

Is this a case of the replacement component failing early on? Perhaps the new EGR valve died?

Truck is 20 years old with 110k miles.

It is running just fine but that light,...

 

[Troll Slayer]

I spent a few minutes checking some things today.

One strange thing is the colors of the wiring to the DPFE are different than those in the schematics I have. Nonetheless, with the KOEO condition, I probed most of the possible combinations and got only two readings - about 4.8V (center to bottom) and about 0.05V (center to top). My voltmeter is an inexpensive analog meter , so reading it to 0.05V (half a division) is "iffy".

The other thing, maybe more important, the engine was running rough at idle. It sounded as if a valve was letting gas back into the intake manifold. It was random and irregular, not constant, not consistent but it was persistent. It wasn't skipping a beat, there was an extra sound - a gassy, coughing sound. It went away at really high rpm but came back when the engine went back to idle speed. This one has me worried. I think this is a new symptom I've never seen before.

I tried listening for vacuums leaks but found none. The hoses are in surprisingly good condition.

One at a time, I tried unplugging and replacing all the emissions related vacuum lines and the wiring. Other than creating a vacuum leak, this affected nothing positively or negatively.

Is it possible I have a problematic valve that is causing the symptoms seen above, including the check

 

[FR-425]

It's the DPFE sensor. Part # EGR 151

"New" doesn't mean "good"

I had the last one I bought fail in 4 days. Bad right out of the box!

The next one I got is working better that all 6 I have replaced in three years.

You can expect to be replacing this regularly. I carry a spare at all times.
Just get the one with the lifetime warranty and they keep feed'n em to ya.

There is no permanent fix for this issue.

It is caused by moisture in the exhaust, eventually acids build up and poof it's dead. Cold weather makes it worse of course.

When they go haywire they cause all kinds of symptoms.

Pinging, rough idle, no power, black smoke, lean/rich, yata, yata.

Remember to disconnect both battery cables for two minutes to clear the codes.

Every one of those codes are related to the DPFE and all at the same time it way fried!

 

[arco777]

The DPFE sensor did change since original build. The stock DPFE sensors are usually silver and made of pot metal, and the updated versions are usually made of plastic. When you change from one to the other, the new one (from Ford) includes a new connector to replace the old one. Perhaps this update was performed and the wiring was done incorrectly?

 

[Troll Slayer]

Thank you both for the input. I will check on both ASAP tomorrow.

I can probably scrounge up my receipt for the DFPE, so I can get a free replacement. Perhaps I should get a spare, too, if things are as bad as you say (and they do seem to be).

I'll try to trace the wires to ensure the electrical interface to the DPFE is wired correctly (even if the colors are incorrect).

 

[Troll Slayer]

I did some more work on this but still have a problem.

I used solvent to clean the Idle Air Control valve. This smoothed out the rough idle quite a bit and the "coughing" sound is gone but I am still getting the following error codes.

They are fewer and perhaps more focused now (EGR system). Any ideas on what's next to check or do?

KOEO codes:

335 - EGR Sensor voltage higher or lower than expected.


Continuous memory codes:

157 - MAF sensor fault, low voltage

332 - insufficient EGR flow

336 - EGR Sensor voltage higher than expected.

337 - EGR sensor circuit above maximum voltage.

 

[Jason94sport]

Interesting you have a 93 & EGR......
Have you checked the EGR tube? Holes in it can cause these issues. Another member posted about it a few months ago.

 

[Troll Slayer]

Interesting you have a 93 & EGR......
Have you checked the EGR tube? Holes in it can cause these issues. Another member posted about it a few months ago.

No, I have not, not yet. I am at my wits end, though, so checking for leaks is my next and almost last hope. Everything looks okay as far as I can see - hoses are supple and no gross corrosion is evident, anywhere.

 

[Troll Slayer]

Can anyone tell me what voltages I should read on my vehicle's DFPE sensor output? The original reads 0.90V. The replacement unit reads 0.09 V.

 

[FR-425]

If you replaced the DPFE and you are still getting 332, 336, 337, 335

Then you most likely have a bad EGR actuator valve:

This dude right here:

The DPFE provides info to the PCM and then the PCM sends the call to this valve to adjust the EGR mechanical valve. If this thing is wonky you will still get high/low voltage and may also draw enough current from the PCM to cause all manner of strange unrelated codes.

It is a proportional valve; the more voltage the more vacuum to the EGR valve.

The rough running would then be due to the EGR being wide open or fully closed.

This is all assuming that you have checked and rechecked all connections; both vacuum and electrical.

 

[Troll Slayer]

If you replaced the DPFE and you are still getting 332, 336, 337, 335

Then you most likely have a bad EGR actuator valve:

This dude right here:

I put in a new one just yesterday, the third in as many months. I don't think that's it.

The funny thing about that EVR is the resistance across the terminals is too low to measure with my ohmmeter. In both directions, it reads as a short.


My favorite theory right now is a blockage/restriction/carbon build-up in the EGR tube restricting the flow.



Right now, I can't diagnose anything because the car won't start. It's as if the battery died or the starter motor shorted out. <-- It's one thing after another!

 

[Kesp4.0]

If none of the above works you might try using the Google custom search at the top and input the codes and see what comes up. There are many past threads here with the same problems and some good remedies. Good luck!

 

[Troll Slayer]

I believe I have solved the problems. It's been three days since I've seen a Check Engine light, so I am cautiously optimistic.

These were the problems -

0. EGR valve was not functioning properly.

1. I had to educate myself about the emission system, above and beyond what's in my Haynes manual.

2. ~50% failure rate on new parts purchased from parts store (measured out of spec right out of box).

3. Analog DMM gave inaccurate resistance readings on it low scale (right where I needed to measure).


I also replaced the idle air control valve with a new one but honestly, the older, dirty unit worked at least as well or better than the new unit (see item , above).

 

[FR-425]

Good work,

It is very rare for the EGR valve it's self to fail, probably why no one chimed in with that one.

 

[Troll Slayer]

Along the way, my starter motor and starter solenoid both failed. I replaced them and put in a new battery. The replacement units are working like a charm. Compared to the old motor, the new motor starts very strongly.