This one’s got me stumped…
the car is a 4th gen civic with obd0 dohc zc turbo. it runs fine for the most part but it decides to go goofy every once in a while. sometimes when i spool the turbo, and then back out of it, my a/f starts jumping all over and it starts to miss and cut out (while driving) and it wont idle. it always starts back up right away but still wont idle as long as i dont shut off the key. if i shut off the key and start it back up the problem goes away, and usually doesn’t come back until i let it sit and go to drive it again. it sounds like a computer issue (that i reset when i turn off the key), but i’m not sure (pm6). it doesn’t have any map sensor codes in the computer or anything.
the cel is on, but i know thats b/c of the coolant temp sensor wire is broken out at the harness (temp gauge still works tho in the car). thats the only code it shows. it occasionally will throw a crank angle sensor code, but i cant figure that one out either since i’ve tried 3 different sensors on the cam and tested the wires to the ecu (but thats no big deal i dont think and not the point of this post).
also i have a dead spot in my rpm range…its around 2k-2.5k where the a/f drops to nothing (the car misses/hicups) and comes back instantly. its only while not under power, or while slowly speeding up and its only a momentary thing, but its really annoying.
i really dont trust this ecu tho, cuz everything i’ve stated its an intermittent thing and i’ve tested all the hardware. the pm6 seems to be kinda quirky, and i plan on trashing it asap. i have a p06, and dizzyto do the obd1 swap to it (so i can actually get a decent tune on it), but i still gotta get the conversion harness and 4w o2. thats the next investment…thanks
first thing’s first get rid of that cel. If your coolent temp sensor wire is broken then your ecu doesn’t know what your coolant temp is and it could be causing weird shit. (I think the gage is on a different sensor if I remember correctly) May not be related to your problem but it’s stupidity to try and diagnose problems with a honda with ‘unrelated’ cels.
2nd what are you using for management for that turbo. Stock pm6 won’t like boost so what do you have done to remedy that? Hack, check valves, etc.
3rd what do you mean the afr drops to nothing, what are you reading it with a a/f gage light show or do you have a wideband on it. If the car misfires the sensor is going to read full lean as it sees the unburned oxygen as a lean mixture.
yea the harness is broken right at the plug below the dizzy and i haven’t got to a junk yard to pick up another plug/harness. will the ecu detune if it thinks the engine isn’t up to temp?
you know, you make a good point…i only have check valves to remedy boost…they are getting pretty old and they could be leaking once the boost gets a bit higher (i’m running extremely low boost at 4psi right now cuz its not tuned the right way). that would trip the map sensor and possibly put the ecu in limp…ill check those out, cuz i’ll bet thats what it is…thanks, i completely forgot that those checks were in there.
also, i meant the a/f drops to full lean when it misses. so the sensor is seeing that extra oxygen? what might cause that
There are adjustments made in the ecu based on ect yes. Is that your problem who knows.
If you clear that ect code by fixing that short you would know if the ecu throws a new code when your problem happens, which it will if the MAP sees positive pressure.
an oxygen sensor reads unburned oxygen left over in the exhaust and based on that value calculates how much fuel had to be present in order to get that amount of unburned oxygen.
If the mixture doesn’t burn at all then the oxygen sensor thinks there had to have been no fuel cause no oxygen was burned.
That is why a/f reads lean when you have a misfire. If it is misfiring like you say.