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

 

[Zero6391]

okay so I took it to the shop and they tried diagnosing it for 4 hours and determined it is most likely an erroneous code from the computer as he couldn't pick up any actual misfire in the cylinders and he says it runs a little on the lean side but otherwise its a false code and he feels it might be the ecu as some suggested. I ordered my ECU"s from oriellys last week so they are sitting an waiting for me to pick them. not sure if that's gonna fix the problem but its nice to all my physical diagnostics were going in the same direction. so ill try that this weekend and see what happens or maybe tonight if it aint too cold

 

[Zero6391]

okay well after looking at the ECU's more closely I have discovered they are actually for a 97-98 eclipse rs and there is actually a separate ECU I can order for the 96 but is showing me as unavailable so they are not sure they can order it so my question to you guys is will a 97 computer work in my 96? from what I have read up is that in june of 96 I guess they switched to the OBDII system which I have so I would imagine it would work but just want to make sure before I buy it

 

[dustyboner]

As far as i know the only years that are interchangeable are 98 and 99.
For a 96 with MT the part # is MR4887051

 

[Zero6391]

alright dustyboner you were right the ecu isn't interchangeable. the guys at orielly's were nice enough to let me go for a test drive with the ecu and the ECU works for the most part but threw 9 codes they were Park/Neutral Switch bad, High speed radiator fan circuit 2, a P0300, a P0301, a P0302, a P0303, a P0304, another P0300 and forgot what the last one was, so I don't think the ecu was my problem but they ordered up the correct year ecu for me but wont be here till the first week of janruary, so today im gonna try throwing the old crank position sensor back on the car and see what happens

 

[dustyboner]

If you haven't done so already, do a compression test. Check the EGR too. Or since you dont have to pass emissions, just block it off.

 

[Zero6391]

yes compression showed good and the egr checked out good. but I threw the old crank sensor back on the car and before installing it I decided to see what the differences were and found that the old sensor is slightly longer than the new one. so I got it all old one hooked up and the check engine light is gone. took two trips out of town and nothing. so that fixed my problem there.

 

[Zero6391]

from what I have read up is that hall effect sensors like our cam and crank sensors are dependent on how far they are from what they are looking at. so with the new sensor being slightly shorter it wasn't as close to the crank as it should be so it was throwing the sensor out of alignment ever so slightly

 

[dsmcrzy]

Glad you found the problem. I have been watching this thread. The cam and crank sensors are usually best to go OEM on.

 

[Zero6391]

yea agreed so right now im gonna go to the junkyard and pull off another round pin harness and solder it up right and that should be the end of this nightmare darnest thing a whole month of scratching my head and it turned out to be the very first thing I replaced smh gotta love being a DIY'er mechanic

 

[rabenne]

I just read this from start to finish today... My first guess was sensor or reluctor related. I know nothing about the NT's but the P0300 code is usually thrown when the ECU doesn't like the signal its seeing from the cam or crank sensors. As I'm sure you have seen in your searches that code is common for 2g turbos with 6bolt swaps because the simulated crank sensor signal (provided from cam sensor) isn't exactly what the ecu is expecting to see. What shop did you take it to? They should have put an oscilloscope on the cam and crank sensors in the first half hour!!! Please tell me they didnt charge you 4 hours diagnostic time!?

 

[Zero6391]

yea this was first ever code with my NT since I got the car 5 years ago so I was really lost I have my other car that I did the 6 bolt swap and yea the misfire thing was a hassle till I got dsmlink hooked up. its a local shop around here and no they didn't charge hourly just the 85 bucks. this was the first time ever in my life I had to break down and go to a mechanic, always prided myself on being able to fix everything myself with the help of this site

 

[99DSMJoe]

Hello I have read your post and my car is crank but no start. Bought used ecm and still nothing changed. I would love some help and suggestions if possible. Thanks!

 

[Zero6391]

a no start huh, well did u just rebuild the motor or replace something or did u just wake up one morning to a no start??

 

[99DSMJoe]

a no start huh, well did u just rebuild the motor or replace something or did u just wake up one morning to a no start??

Thanks for quick response! I drove it for about 5 mins and all of a sudden lost power. No stutter no funy noises just turned off. Tried to start it and it would just crank hard but engine didnt turn. I changed battery, fuel filter, cam sensor, and ecm and still same thing. Also no obd codes or service engine on.

 

[dustyboner]

What do you mean by " it would just crank but the engine wouldnt turn" ? Like the starter is spinning but its not turning the crank?
If thats the case, the bendix probably isnt extending, so get the starter tested.

If the car cranks but wont start, check the timing belt and the ASD relay

 

[Zero6391]

and are u getting spark or fuel while it cranks? if your getting both my guess would be its a sensor. now with my problem my no start happened from two wires having their jackets crack on the cam sensor. the egr valve made the wires brittle. check the cam wires near the plug and see if anything is exposed. assuming you have a 420 a motor

 

[99DSMJoe]

What do you mean by " it would just crank but the engine wouldnt turn" ? Like the starter is spinning but its not turning the crank?
If thats the case, the bendix probably isnt extending, so get the starter tested.

If the car cranks but wont start, check the timing belt and the ASD relay

Dustyboner the starter was checked and was good. Also the fuel pump turns on and shoots out gas to injectors. Spark also good with timing correct. Now I do remember a multiple misfire code and insufficient egr flow sensor code but the gap was wrong when I bought the car and I cleaned egr valve and tube so codes cleared.

 

[99DSMJoe]

and are u getting spark or fuel while it cranks? if your getting both my guess would be its a sensor. now with my problem my no start happened from two wires having their jackets crack on the cam sensor. the egr valve made the wires brittle. check the cam wires near the plug and see if anything is exposed. assuming you have a 420 a motor

I do have 420a and I have not checked that but it could be possible since I messed around with egr valve. I can't check the car right now since im out of town but tomorrow I will be back and will double check my wiring. Thanks for that tip!

 

[Zero6391]

alright then yea check those out and let us know, if u have a digital volt meter u can check the circuit there are 3 wires for the cam and crank sensor. one is power and should read 8 volts with the key in the on position, one is a signal wire which should read 5 volts with the key in the on position, and a ground wire. here is a pic of the harness, wires are in the same order for crank and cam

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[99DSMJoe]

alright then yea check those out and let us know, if u have a digital volt meter u can check the circuit there are 3 wires for the cam and crank sensor. one is power and should read 8 volts with the key in the on position, one is a signal wire which should read 5 volts with the key in the on position, and a ground wire. here is a pic of the harness, wires are in the same order for crank and cam

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10 4 will do thank you for all the info and diagram to check wiring

 

[ilikejesus]

definitely if you have spark and fuel I'd say it would be the sensor as well. If you don't have fuel and spark.. that's easy

 

[99DSMJoe]

definitely if you have spark and fuel I'd say it would be the sensor as well. If you don't have fuel and spark.. that's easy

Thanks for the help! In all this where would the crank sensor be located? Its a 99 gs 420a auto.

 

[dsmcrzy]

Thanks for the help! In all this where would the crank sensor be located? Its a 99 gs 420a auto.

Right above your oil filter

 

[Zero6391]

yea its real easy to get to and replace as well, one 10mm bolt. just raise up the passenger side and your set to get at it

 

[99DSMJoe]

Right above your oil filter

Thanks for the location! Would I have to remove anything else? It just sounds to easy