CEL KOEO question

[wingnutkev]

Is there a separator pulse between codes? It looked like a longer pulse between each memory code. If it is a separator pules then my codes are 24, 72, 73 if it's a 1 then they are 124, 172, 172.

So either I'm looking at the MAF sensor TPS or O sensors. Right?

 

[MrShorty]

There is not a separator pulse between each code, and your '92 should output three digit codes. The separator pulse is a single pulse after the KOEO codes are all output twice and before the CM codes are output twice. I would expect all three of those codes to be CM codes, so I'm guessing you got 111 (pass) for the KOEO test? Any KOER codes? Some thoughts on the individual codes:
CM 124 -- TPS was high. Without accompanying KOEO 121/123, this indicates that the fault is either intermittent or is only seen by the computer when the engine is running. It could also be a fault elsewhere in the system that the computer is blaming on the TPS because it doesn't know who to blame.
CM 172 and 173 -- O2 sensor lean and O2 sensor rich. An interesting contradiction. Based solely on CM codes, we don't know which condition is more prevalent, or more recent. And, with any CM code, we don't know if one or more of these codes is an old code for which the fault doesn't exist anymore.
If this were me, my next steps would be:
1) KOER test. Be sure to follow the instructions (especially warming the engine up). We don't want any false lean codes because the O2 sensors were cold. If you get the TPS goose test code or the BOO code, repeat the KOER test until you know you are pressing the brake and throttle at the appropriate times during the test (it took me a couple of tries the first time to get it right). It can be easier to diagnose things from the KOER test, because these are hard faults that occurred during the test, rather than soft faults that occurred sometime in the past.
2) Clear CM codes (pull jumper wire during KOEO/CM code output) and see which (if any) return. This would be especially true if there were no other symptoms, and it passed the KOER test. This is just to see which codes are old, and which codes are currently being generated.

One thing to remember: Codes point to circuits not sensors. The computer can't tell the difference between a melted/disconnected wire and blown sensor.

 

[wingnutkev]

Thanks for the detailed reply, I'll update when I have the results.

 

[wingnutkev]

OK just re-ran a KOEO and a KOER here are the results, I need just a little direction here.

KOEO
After the 111 the memory codes are as follows.

124 (M) TP voltage was higher than expected
172 (R,M) Oxygen sensor not switching - system is or was lean - Single, Right or Rear HO2S
556 (O,M) Fuel pump relay primary circuit fault
185 (M) Mass Air (MAF) output lower than expected

KOER
412 (R) Idle speed system not controlling idle properly (generally idle too low)
172 (R,M) Oxygen sensor not switching - system is or was lean - Single, Right or Rear HO2S

The KOEO test after resetting the codes 124 and 172 have reappeared, the 556 and 185 are new. I'll probably clear the codes and retest tomorrow.

172 Suggest system is lean and could be the O2 sensor.

Where would you go from here?

 

[MrShorty]

1st thing, can I just say, "kudos" . That's how I like to see someone describe the results of the EEC-IV self-tests. With each code, you've indicated which part of the tests it came from, and you've included pass codes in your list. Well done!

SOP is to work on KOEO codes 1st (yours passed) then move on to any KOER codes, so we'll start there:

KOER 412: Often times, this code is more symptomatic than diagnostic. Basically, the computer had trouble getting the engine to idle correctly during the test. For now, we'll note that the code exists.

KOER 172 (and CM 172. as noted, SOP is to work from the KOER test rather than CM codes): This can be a challenge to diagnose, because there are so many possible reasons, besides a bad O2 sensor, that could cause the sensor to indicate lean:
1) Before blaming the sensor itself, make sure the wiring between the computer and the O2 sensor is intact. It's not unheard of for wires to contact hot exhaust parts and melt through or for connectors to break. The computer can't distinguish between a bad sensor and a bad wire.
2) vacuum leak: A vacuum leak could also make it difficult for the computer to control idle during the KOER test (see KOER 412). Check for vacuum leaks
3) low fuel pressure: Interestingly enough, you note a CM 556, which indicates a possible problem with the fuel pump circuit. Note that problem is intermittent enough to not show up as a KOEO 556. Could the fuel pump be intermittently cutting out, causing the fuel pressure to be too low? Check fuel pressure.
4) MAF is the primary sensor used to determine fuel mixture, with the O2 sensor providing data to fine tune that mixture. We have a CM 185 which points to the MAF (again, we don't have a corresponding KOEO MAF code, so any problem with the MAF only shows up during normal operation). When considering the combination of an MAF code and an O2 sensor code, we have to ask ourselves which is cause and which is effect. Is the MAF dealing out bad data causing the engine to run lean, or is a bad O2 sensor confusing the computer causing it to cast blame at the MAF. As any search for "engine ping" would show. A dirty MAF is a common cause of engine ping on these engines (causes MAF output to be lower than it should causing engine to run lean which causes ping). It's common enough cause of various driveability problems that you might consider opening the MAF up and making sure the filaments are clean (Decent instructions can be found in the Singleton site link in the useful threads forum). May not end up being the real problem, but it won't hurt (as long as you're gently cleaninig those filaments), and won't cost much.
5) Lest anyone accuse us of ignoring the possibility of a bad O2 sensor, if none of the above proves to be the problem, then we may have a bad O2 sensor. Try the above items and see if your problem is resolved. If not, then we'll pick it up from here.

(If you're still awake) Wow, that was quite a treatise! Probably a lot more information than you wanted. I hope it helps.

 

[wingnutkev]

Thanks so much. You provided exactly the type of response I was looking for. I'll get to work and let you know.