420A 2gNT Mysterious P0300 Random Misfire

[Zero6391]

Hello,
Well to start out the car is a completely stock 1996 Eclipse RS N/T 420a with a M/T. Only aftermarket thing done to it is a short ram air intake that I installed 3 years ago.
Anyways, so I was driving out of town one weekend when the car completely died on me and wouldn't start back up. I took a scanner to it and stated no signal from cam or crankshaft position sensor so I replaced both sensor with new pigtails and found the source of my problem, the old wires jackets broke and were arcing together.

After that was all fixed, the car started up but now I get the P0300 code but drives, starts and accelerates just fine no issues so I replaced spark plugs, no change, changed spark plug wires, nothing, replaced coil pack, nada, replaced fuel filter, nope, checked fuel pressure, held steady at 50 psi. I pulled the plugs they look fine and don't smell like gas on them and it shows normal wear and checked the gap they are fine, they are copper autolite plugs by the way.

I checked timing belt and it still lines up with proper tension. I've used the OBD scanner to check STFT fuel trims while idling and they are showing normal changes (less that 2% changes) I smell the exhaust and don't smell anything weird like the cat is clogged and I checked vacuum and it stays close to 20hg so I'm stumped.

I can accelerate to 80 mph just fine, its idles in stop and go traffic just fine, and accelerates with no hesitations whatsoever.

The only thing happening is the check engine light is on and when I'm cruising at a steady highway speed sometimes the light will blink then go solid again with no loss of power whatsoever.

This is my daily driver so I'm trying to get this thing running without the light on. Do you guys think it could be a misreading or that something else is going on? any help would be appreciated, been driving like this for 3 weeks now but no other codes besides the P0300 are popping up with no change to driveability

 

[Dsmkauai]

http://www.obd-codes.com/p0300

 

[Zero6391]

hmmm I read that article and watched the video last week after exhausting googles resources ive replaced practically everything except for the o2 sensor, EGR valve and the cat converter which all show as operational. I did an engine rebuild 7 months ago and haven't had any issues until those two wires started arcing. now I read up on a jeep forum that rerouting the ground wire for the sensor to the body helped?? ever hear of this?

 

[ohTONYoh]

Try changing your crank position sensor, again.

Back on my first eclipse I changed everything possible with the same code and then I changed the crank sensor for a second time and it worked. Apparently, they are very finicky and the aftermarket ones have a 50/50 chance of working. Try to get a better quality one or an OEM one.

 

[Zero6391]

hmmm I guess I can give that a try, the one I got has a lifetime warranty (autozone part) so it wont cost me anything but some time. I even thought about throwing the old one back on there but id have to resolder the old harness back on. I thought if there was something wrong with the crank sensor it would prevent me from getting spark completely? but since it was still driving fine I disregarded it....

 

[Zero6391]

Okay so update, i replaced the crank sensor a 2nd time but nothing changed... however i did notice that when cruising above 4000 rpm the check engine light will not blink but will occasionally blink at random times at any cruising speed that is under 4000 rpm. Should i replace the sensor a 3rd time??

 

[Dsmkauai]

Sounds like wiring or connector issue. Maybe somthing isn't plugged in all the way or a wire is shorting out every now and then. Are you sure nothing happen to the ecu when the wires shorted together?

 

[Zero6391]

Well i checked the wiring, and its showing continuity, and i checked all the wiring back to the ecu and nothing cracked or shorted besides where I repaired. Im leaving ecu last cuz some people say ecu is rarely the cause.... but it starting to become the last thing i can replace....

Here are the plugs

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Cylinder one is on the left and works it way to the right

 

[Zero6391]

Is there a way to test the ecu?

 

[Zero6391]

*Update* replaced spark plug wires... again and no change

 

[Zero6391]

Okay so someone came and told me it seems that im running a little lean based on the spark plugs condition. So i started looking at fuel system and read somewhere that the cam sensor is in charge of injector pulse so i warratied the part and to no avail it didnt fix my problem, so my next idea is to throw the old original cam and crank sensors back on and see it that clears my code. All this random misfire stuff started after i replaced those two sensors so maybe its got to be something with those two.... maybe..... by the way today marks exactly one month since i first got the p0300 code.... fml at least the car still drives normal

 

[burtonfl93]

i would look into an injector problem? injectors could be dirty causing the random missfire. run a quality injector cleaner in gas. Usally when engine light flashes while driving with a missfire means that cat is getting over heated.

 

[Zero6391]

I was debating on running some sea foam thru it again to see if that changes anything. Ill probably buy a bottle tomorrow and run it thru the gas and vacuum lines

 

[burtonfl93]

not a huge fan of sea foam, try a lucas fuel system cleaner, to remove deposits from injector pintles

 

[Zero6391]

Worth a shot, by the way what do u make of the spark plugs? Those are after 3 weeks. Do u think the problem is lying in cylinder 2?

 

[burtonfl93]

i feel 2 is running correctly porcelain has a brown haze to it, 1,3,4 are very lean very white porcelain

 

[Zero6391]

I concur with u on that, coincidence that the injectors clogged when the wires for the cam sensor shorted?

 

[burtonfl93]

unrelated clogged injector is mechanical side of injector

 

[Zero6391]

Well I bought 2 bottles of lucas fuel injector cleaner and then warrantied the spark plugs for a new set of autolite coppers and then gapped them to 0.48, gonna test it out on the relief route after work and see if that fixes the problem if not ill try out the old sensors and see what happens. ill report back with my findings!

 

[Zero6391]

Okay still no luck with the spark plugs and then i cam home and reinstalled the old cam sensor and car drove the same and still the check engine light. Only sensor left to revert back is the crank sensor so im gonna attempt reinstall that tomorrow night and then after that im back to square one. The car worked before with all these old sensors and parts so the way i see it just take off the new stuff one by one till i get to the culprit which if it doesn't work with the old crank sensor im gonna assume its the ECU

 

[Zero6391]

By the way i can hear and feel the injectors ticking so i know they work i think it just has to do with the pulse which from what ive read up the crank and cam both determine that sequence together

 

[burtonfl93]

its take a little bit of time to clean them out, at least 1/2 tank, just because they click doesn't mean they have good spray pattern

 

[Zero6391]

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so here are the plugs after one day, ran a quarter tank of of gas with 2 bottles of lucas injector cleaner and then switched the cam sensor back to the old one. what do you guys think? I think im headed in the right direction to solving this misfire code.... so I think from what I can figure one and 2 are burning nicely and 3 and 4 are semi burning right, what do u think?

 

[Zero6391]

Replaced the coil pack back to the old one and no change. Does anyone know if the computer stops looking for misfires while in open loop??

 

[Zero6391]

well I hate to have to give in like this but I think im gonna take it an auto shop around here and have them diagnose it and see what they can find out. gonna cost me $75 for them to diagnose it, maybe they can turn up something on their scanner. they have a high end scanner and ive been stuck using the basic bosch obdII scanner from oriellys so ill see if they can do it Thursday morning before I go to work.