strange misfire
Jun 13, 2017, 05:21 PM
#1
strange misfire
need help diagnosing a weird misfire on my 03 evo.
about a month ago was driving home from work and the car bucked and missed. Afr's shot completely rich which led me to believe it was or is spark related since i had an injector issue in the past that would randomly stop pulsing and the afr would go completely lean. First thing i did was change the plugs and made sure to gap them to where they needed to be. I also at that time threw a known good set of coils and wires on the car. The next day same problem. Under light load car bucks once or twice while cruising and afr goes rich down to 11 from 14.9ish. Get home and ordered a cam angle sensor and crank sensor just in case it was the crankshaft sensor going out. Also researched other sensors that could be failing and found that possibly the map sensor could be faulty. once i got the cam sensor in i threw it on as well as converted to an omni 4 bar that i already had (getting ready for sd) and the car drove fine for about a month. during that time i religously kept my laptop in the car and tried to make the car act up to get a log with no luck so i figured the cam sensor fixed the issue or the map sensor.
fast forward to yesterday and on lunch the car starts sounding weird at idle, and then starts its bucking again while cruising and afr shoots rich. Problem only happens maybe once or twice every five minutes. threw my laptop in the car again this morning and finally caught the problem while logging but just want to make sure that my suspicions are correct before throwing more parts at it. In the log the load goes from around 90 and suddenly spikes to 450 for no apparent reason, which is then telling the ecu to dump tons of fuel. this is the point that the car bucks and goes rich from what i can tell in the logs. So is that reason enough to believe that the maf is on its way out?
other related symptoms have been absolute horrible gas mileage, the obvious misfire, weird sounding idle (like its getting too much fuel) P0171 system too lean code has thrown twice, i had a P1400 manifold differential pressure (MDP) sensor circuit malfunction which i believe was caused by a mistyped value in the tephra rom scalings when i switched from oem to the omni that i caught yesterday while trying to diagnose the problem, a P0335 no crankshaft reference signal at ecu which im fairly positive came from doing a compression test yesterday as well.
things im sure its not, things ive done or tested. changed plugs with correct gap (old plugs were gapped correct and were not fouled), changed coils and wires, changed map sensor, changed cam sensor, boost leak checked the car (first thing i ever do when diagnosing problems), been through multiple tanks of gas from different stations, made sure everytime i filled up to tighten the gas lid until it clicks about 8 times, o2 sensor is fairly new, i also have a brand new one already i could throw in but would rather not just throw parts at it anymore, as well as a crank sensor, cleaned the maf sensor with alcohol and q tip.
attached is the log of the random misfire where the load spikes to 450 from around 90 and the tps reading stays the same while cruising but afr shoots rich leading me to think the maf is on its way out or has a short.
any and all help is appreciated and if mods think this should be in the ecu section feel free to move it. thanks.
weird misfire.csv
about a month ago was driving home from work and the car bucked and missed. Afr's shot completely rich which led me to believe it was or is spark related since i had an injector issue in the past that would randomly stop pulsing and the afr would go completely lean. First thing i did was change the plugs and made sure to gap them to where they needed to be. I also at that time threw a known good set of coils and wires on the car. The next day same problem. Under light load car bucks once or twice while cruising and afr goes rich down to 11 from 14.9ish. Get home and ordered a cam angle sensor and crank sensor just in case it was the crankshaft sensor going out. Also researched other sensors that could be failing and found that possibly the map sensor could be faulty. once i got the cam sensor in i threw it on as well as converted to an omni 4 bar that i already had (getting ready for sd) and the car drove fine for about a month. during that time i religously kept my laptop in the car and tried to make the car act up to get a log with no luck so i figured the cam sensor fixed the issue or the map sensor.
fast forward to yesterday and on lunch the car starts sounding weird at idle, and then starts its bucking again while cruising and afr shoots rich. Problem only happens maybe once or twice every five minutes. threw my laptop in the car again this morning and finally caught the problem while logging but just want to make sure that my suspicions are correct before throwing more parts at it. In the log the load goes from around 90 and suddenly spikes to 450 for no apparent reason, which is then telling the ecu to dump tons of fuel. this is the point that the car bucks and goes rich from what i can tell in the logs. So is that reason enough to believe that the maf is on its way out?
other related symptoms have been absolute horrible gas mileage, the obvious misfire, weird sounding idle (like its getting too much fuel) P0171 system too lean code has thrown twice, i had a P1400 manifold differential pressure (MDP) sensor circuit malfunction which i believe was caused by a mistyped value in the tephra rom scalings when i switched from oem to the omni that i caught yesterday while trying to diagnose the problem, a P0335 no crankshaft reference signal at ecu which im fairly positive came from doing a compression test yesterday as well.
things im sure its not, things ive done or tested. changed plugs with correct gap (old plugs were gapped correct and were not fouled), changed coils and wires, changed map sensor, changed cam sensor, boost leak checked the car (first thing i ever do when diagnosing problems), been through multiple tanks of gas from different stations, made sure everytime i filled up to tighten the gas lid until it clicks about 8 times, o2 sensor is fairly new, i also have a brand new one already i could throw in but would rather not just throw parts at it anymore, as well as a crank sensor, cleaned the maf sensor with alcohol and q tip.
attached is the log of the random misfire where the load spikes to 450 from around 90 and the tps reading stays the same while cruising but afr shoots rich leading me to think the maf is on its way out or has a short.
any and all help is appreciated and if mods think this should be in the ecu section feel free to move it. thanks.
weird misfire.csv
Jun 15, 2017, 10:00 AM
#4
EvoM Guru
iTrader: (1)
Seems like MAF. Should just convert it to speed density.. 
The following users liked this post:
Tommyfacekicker (Apr 17, 2018)
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