Replaced computer, still running rich

[mupmanyu]

History: I have a 95 XLT Sport and I have failed emissions twice before. Turns out I had an faulty, which was then replaced by an incorrect ECM. FI finally installed the new computer today, drove around for 10 miles, and then headed straight to the emissions center. No CEL on my way to the center, and the car was running a lot better.

Problem: I failed emissions again today - seems like CEL came on during the test, as I failed on that front as well.

The main problem is that I am still running rich. My HC was almost twice the limit, and CO was 3 times the limit. This is a LOT better than the levels in my past two tests - I was almost 10 times the CO limit, and 4 times the HC limit.

Got my ECM scanned for codes at Checkers. I got the following:

i) 452 - very good sign, as my speedometer is indeed not working.
ii) 332 and 335. EGR related problems, and I am hoping I can get some leads on what to attack (DPFE, valve).
iii) 177 and 173. I expect this to be tricky as well, as I recently replaced my O2 sensor.

Any ideas? I don't have any major idling issues, my mileage was quite bad, but have not measured it with the new ECM. Obviously, I am running rich, so it is not ideal yet.

FYI, I have cleaned my spark plugs, they were fouled out since I was running rich for so long. Replaced O2 sensor, spark wires are relatively new (replaced them 2 years ago). I have cleaned out my intake, new air filter.

I don't have access to the fuel pressure, but can someone tell me if this trick will work on my 95 explorer as well (Plan B)?

http://www.explorerforum.com/Singleton/web/pages/fuelpr.html

Any help will be greatly appreciated!

 

[MrShorty]

1st step with multiple EEC-IV codes is to identify the KOEO codes. My code list indicates that a 335 can only be a KOEO code, and the others would have to be CM (assuming you Checker didn't run the KOER test). Resolve the KOEO 335 first, then clear CM and see which codes come back. If those instructions aren't clear, I would suggest reading my notes on pulling EEC-IV codes thread and the other threads here that describe the basic test procedure.

Because KOEO codes almost have to be electrical in nature, a KOEO 335 points to a fault in the DPFE sensor circuit. I would start by checking the wiring between the DPFE and the PCM. If that checks out, then replace the DPFE sensor, because these fail fairly frequently.

I'm not certain which trick you are referring to on that page. The fuel delivery system operates on the same principles as the earlier models referred to, so most everything on that page can apply to your '95. Note that, unless you detect fuel in the vacuum line to the FPR, the best way to test the FPR is with a fuel pressure gauge. Fuel leaking through the diaphragm isn't the only failure mode for the FPR, though it is a common failure mode.

 

[mupmanyu]

update..

Thanks for the reply and tips.

I checked the voltage at the DPFE connector. My analog multimeter isn't good for that low voltages, but I checked the voltage while the car was running on the three wires that go into the connector (from the PCM). The light green connector reported very low numbers, while indicating that the DPFE was indeed bad.

I replaced it today, and scanned the codes again. The KOEO test passed without any error codes.

However, I still got three CM codes:

i) CM-173
ii) CM-177
iii) CM-452c (vehicle speed sensor, trucks)

CM-173 and CM-177 indicate that my oxygen sensor is reporting a rich condition, and I was getting them before I replaced the DPFE. I did disconnect the negative terminal of the battery for more than 5 minutes to erase the previous codes.

Any advice?

 

[mupmanyu]

another update..

I cleared the CM codes, and then drove the car around for sometime. The CEL came on after driving for a while, but then went away after 2-3 minutes, during the drive.

I decided to go ahead and do a KOER test. I got two error codes:

i) KOER - 137
ii) KOER - 173

As you can tell, my O2 sensor reports I am running rich...

 

[MrShorty]

Glad we got the EGR codes resolved.

1st thing I'd check with those rich codes, especially where they apply to both banks, would be fuel pressure and for gas in the vacuum line to the FPR. See Glacier's "fuel pressure test mini diary" thread.

 

[mupmanyu]

could the culprit be intake?

I invested in a fuel pressure gauge, and the accessories. Should get to measuring the fuel pressure tomorrow. Thanks for the info on Glacier's post, that was very helpful.

To be extra careful, I am going to i) disconnect the inertia switch connector, ii) remove the gas cap, and iii) work on a cold engine.

Regarding the intake, I decided to clean the MAF out today. I removed the intake, and the plenum appears to be incorrect for this vehicle. The disk that abuts the conical filter says ranger 3.0L, or something to that effect. The plenum body that has the MAF attached to this fits quite well. I had a spare disk lying around from an earlier visit to a junkyard, and it clearly says ranger/explorer 4.0, which logically should be the one on my truck. I tried fitting this disk to the intake plenum, and it was too big.

Can my rich condition arise because of an incorrect intake plenum diameter?

 

[mupmanyu]

clarification..

My choice of the phrase "intake plenum" may be inappropriate. What I mean is the metal body that the MAF attaches to....

 

[mupmanyu]

fuel pressure..

I) Finished testing the fuel pressure.

i) 35-40 psi at key on engine off.

ii) 30 psi at when I start the engine. No change in pressure upon revving, etc.

My Haynes manual says that these is as close to normal as you can get. I guess this out the fuel pressure regulator?

II) I also did a cylinder test on the car - firing on all cylinders, no problem there as well.

Not sure where to go from here...

 

[MrShorty]

Fuel pressure numbers look normal.

I don't know interchangeability on these or exactly what scenario you are describing with your "3.0" MAF. MAF is arguably the most important sensor in determining fuel mixture. It doesn't take much (if any) stretching of my imagination to see how the wrong MAF/MAF housing could lead to a rich condition. I hate to tell you to replace the MAF without knowing for sure, but that's what I'd be looking at.

 

[mupmanyu]

update..

I replaced the MAF body with one from 1997 4.0 - I couldn't get one for my year that easily.

The first I did was the KOEO test, and it passed without any error codes. I had cleared my CM codes, and I guess I did not error codes was because I had erased them. I then did a KOER test, and to my surprise, there were no rich codes.

I have driven the car a lot more, and still no CEL. I am a bit nervous, because I was supposed to at least get CM - 452, the malfunctioning speed sensor error.

I decided to scan for codes again, even though I did not have CEL. I got a KOEO-335 error, and a CM-452 error. Redid the test after unplugging and plugging the connector to the DPFE and clearing the CM codes - the 335 error went away.

I am a bit surprised at the 335 error, since my DPFE is a week old. I have checked the wires using my multimeter, and I get voltages in the right range. Just to be clear, I put the multimeter probe into the backside of the connector, into each of the three holes, to get a voltage reading.

I am also surprised that this error goes away after I clear the CM codes, and just move the wires a bit.

One thing on the performance of the car - once it starts, it runs quite while. However, when I am in open loop and when I release the clutch, the car buckles a bit, it has a small lag before it responds to the accelerator.

Could my EGR valve be an issue?

 

[MrShorty]

I decided to scan for codes again, even though I did not have CEL. I got a KOEO-335 error, and a CM-452 error. Redid the test after unplugging and plugging the connector to the DPFE and clearing the CM codes - the 335 error went away.

I am a bit surprised at the 335 error, since my DPFE is a week old. I have checked the wires using my multimeter, and I get voltages in the right range. Just to be clear, I put the multimeter probe into the backside of the connector, into each of the three holes, to get a voltage reading.

I am also surprised that this error goes away after I clear the CM codes, and just move the wires a bit.

I doubt the EGR valve itself is the problem, as the computer can't test the EGR valve KOEO. The fact that the KOEO 335 goes away by plugging/unplugging or otherwise wiggling the wires suggests a loose connection in the connector or possibly a broken wire inside the harness. Check the pins/connector that the metal contacts are clean and in good condition. It can be hard to check, but make sure the "pins" in the connector havent' pushed back and that they fit tight enough to make good contact. Look over the wiring harness for evidence of damage.