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Rough idle and running rich, have codes

WhitEngineering

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City, State
Windsor, VA
Year, Model & Trim Level
'97 XLT 4DR 4X4 OHV
Symptoms: very rough idle, enough to shake the explorer. Is running rich enough to leave a black spot on driveway after just a few minutes. Exhaust sounds like crap at idle, like a race cam lope. Mpg around 12-13 hwy. Runs smooth when driving, whether at 10 mph or 65 mph, only rough at idle.

Codes:
KOEO 513 - Replace processor (PCM) (internal failure)
KOEO CM 173 - Oxygen sensor not switching - system is or was rich - Single, Right or Rear HO2S - Fuel control
KOEO CM 177 - Oxygen sensor not switching - system was rich Left or Front HO2S - Fuel control

KOER 173 - Oxygen sensor not switching - system is or was rich - Single, Right or Rear HO2S - Fuel control
KOER 137 - Oxygen sensor not switching/system rich Left or Front HO2S - Fuel control

A little background: 176k miles. I just bought it, driven it about 400 miles total. It had an uneven/ weak idle when I got it, the rough idle and richness seemed to start suddenly a couple days ago. Was getting 18 mpg hwy before this.

I'm not sure where to start testing. The 513 leads me to believe the processor is bad and may be telling it to run rich, therefore setting off the O2 codes. But, searching the forums I see that some people had a bad battery or other problems that set the 513.
 


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WhitEngineering

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Did some thinking and reading on here which encouraged me to look at it as though the PCM code is also a result not cause of the problem.

Picked up a fuel pressure test gauge this morning. Before I left home I checked the Fuel Pressure Regulator vacuum line which smelled mildly like gas, though I couldn't really see any in the line. I hesitantly bought a new one against my better judgement.

Fuel Pressure as follows:
KOEO - 38 PSI (after cycling key several times it quickly built up and stayed at this)
KOER - 32 PSI idle
34 PSI @ 2k RPM
40 PSI with vacuum line removed from FPR
KOEO - 34 PSI (after shutdown)

I think these numbers are normal. Left gauge attached after shutdown and it stayed steady @ 34 PSI for 10 minutes. This leads me to believe the injectors are not stuck open.

I then replaced the FPR since I had already bought one, the original has 176k, and it was easy enough.

No change. I disco'd the battery for 15 min, then test drove 20 miles, check engine light back on with same codes in 1st post.

I also noticed an exhaust leak which started the same time as everything else. Appears to be leaking at the first cat. Could this be related or just a coincidence?

Any help or direction is much appreciated.
 




MrShorty

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You are correct, those fuel pressure numbers look normal.

SOP is to resolve KOEO codes first, then resolve KOER codes, then resolve CM codes. I would be inclined to focus on the KOEO 513. I haven't dealt with this one personally, so I don't know specific diagnostic steps.
 




WhitEngineering

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Pcm

Thanks for the order info, I hadn't thought about that. I ordered and installed a used PCM off eBay which appears to have solved the problem. Let it idle for about 20 min; I'll drive it to work tommorrow.

I started thinking it was bad since it was the only KOEO code and the other codes were just O2 rich codes and the fuel pressure was good. There weren't any maf, egr, etc codes.
 




WhitEngineering

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'97 XLT 4DR 4X4 OHV
Drove about 70 miles today with the "new" used PCM and all seems to be good.
 




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