ok, someone help. my check engine light comes on pretty much every time i drive my car. i've done the code checks, but not sure i understand what they are telling me. its a 93 4-cyl vert
koeo
172 - lack of o2 sensor switches
186 - injector pulse width higher than expected
543 - fuel pump secondary circuit fail
koer
172 - same as koeo
411 - i think thats the boo switch fail code
538 - cannot control rpm during low rpm test
536 - not enough change in rpm during dynamic response test
521 - pretty sure that was the psps fail code.
secondary curcuit fail pretty self explanatory. found the circuit in wiring diagram but not on car. the boo switch is also not obviously placed under the hood, but not hard to understand what code is saying. same with psps but i'm pretty sure i know where that one is. the ones i don't quite get are the rest... does lack of switch mean o2 sensor's dead? what about the pulse width being higher than expected? is that because of the o2 sensors? so far i've gotten a mybe dead sensor and maybe dead cats... can anyone out there give me an answer thats better than a maybe or am i gonna have to just start replacing everything until the check engine light goes out? please help. tired of v8 mileage with less than i4 power...
the 172 code and the 186 code could be related. 172 indicates a a lack of switching, indicating a lean situation. Because of this lean situation, the pulse width (open time) on the injectors could be being forced longer then the computer ityanticipates, leading to the 186 code. These would definitely lead to a loss in fuel economy.
Another possibility, since I ran into a similar situation on my Escort, is to check the coolant temp sensor. I wasn't getting any codes for it, but since coolant temp directly affects fuel trim if the computer is seeing a constanly cold engine it's going to dump more fuel in in order to get it in to closed loop. By replace the ECT on the Escort, my mileage went from 22 highway to 35 highway. whereas the O2 sensor only gave me an increase of 18 highway to 22.
The boo failure could be because you didn't hit the brakes while running the KOER test same with the PSPS code. The KOER test looks for these cues to activate different portions of the test.
What sort of drivability symptom are you suffing from? The diagnostic info I have would seem to indicate a lack of fuel pump operation if the secondary circuit had a failure.
thanks brothat really helps! driving symptoms are minimal. slight surge when i got it floored from time to time, crappy idle, bad mileage, thats really all. oh, and the check engine light comes on every time. nothing happens when it does and nothing has changed, it just comes on... still drives like normal. my rad fan wouldn't turn off for a while so i wired a switch for it. don't knowwhy it stayed on like that. no strange temp readings. it came on and stayed on even after i turned off the car. i waited for it for half an hour once and had to pull the plug to get it to turn off. it didn't come back on when i plugged it back in later. maybe it is the coolant temp sensor. i really appreciate the advice! i'm gettin the o2 sensor today, may grab temp sensor too if $ allows. i'll let u know how it goes. thanks again!
The O2 is probably working because the computer is seeing a lean condition (pulse with higher) and trying to overcome it by adding fuel. Your surge confirms that fact. Things that can cause it
slight surge when i got it floored from time to time, crappy idle, bad mileage and the check engine light comes on every time.
The same thing happened to me after I changed my exhaust manifold and forgot to plug the o2 sensor back up. Drove it for 4 days like that until I got it on the lift at my mechanics shop and seen the unplugged sensor. Plugged it in and she drove fine. No surge, nice idle, lights off and I got my gas mileage back.
It might not be it though, but try it, you might be surprised.
swapped the o2 sensor and the ect sensor, no more light! yay! the o2 was covered in what looked to be white ash. its white and granular and looks exactly like the tips of my old plugs did. no more surges either. i think my o2 died stuck in a lean setting and my car was flooding it with fuel. kinda lost a little hp tho... not a big deal. plan to get it back with the ranger header and delete the cats. going with stock 2" pipes tho to try to keep a little backpressure going. thanks for all the suggestions! they really did help.
whats up with this check engine light? 
