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Discussion Starter · #1 ·
Hey guys. Gonna start this off by saying I am very much a car noob. I've worked on my old S10 a fair amount, capable of most smaller fixes, but nothing involving actual motor work. That said, I've had my ZX2 for about 3 years, I have pretty painfully neglected most of its maintenance aside from oil changes and such. Recently I was having trouble starting it and noticed that there was oil leaking pretty badly from a bad valve cover gasket. I started with replacing the battery, and well, this is a full list of everything that's been done.

Valve Cover Gasket Replacement, Air Filter Replacement, Serpentine/Drive Belt Replacement, Change Oil and Filter, Starter Replacement, Battery Replacement, Spark Plug Replacement.

After doing all of the above, I'm now getting really chunky acceleration, and popping two error codes, 304 and 117. I have a feeling that the two codes are interconnected, but I'm replacing my ignition coil next just to be sure before moving onto a vacuum test.

Question is, would you lovelies have any other recommendations for me after hearing what's going on?
 

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Instead of replacing parts, here are some free diagnostic methods you can do first (this will rule out one of your new spark plugs being bad as well). Also, in my experience sometimes these plug wire boots do not like to sit fully on the plug, make sure your boots are seated fully.

First, try a cylinder drop test, usually the easiest way to do this is to unplug the fuel injectors, if the engine does not change in behavior (no drop in RPM and runs the same) that is your misfiring cylinder. If there is absolutely no change when you unplug the injector to cylinder 4 you've confirmed that the ECU is recognizing the correct cylinder misfire. If you unplug cylinder 1 and there is only a slight change, and again only a slight change on cylinder 4 compared to cylinders 2 and 3 I would agree the most likely issue is a coil getting weak. Of course any cylinder that runs even more rough when you unplug it is contributing.

Next, try swapping spark plugs 3 and 4 (obviously check their condition, gap, etc. when you do this, cracks in the porcelain can be very hard if not impossible to spot, likely it will be wet with fuel due to misfire, clean it before moving it). Now repeat the cylinder drop test, if you unplug injector #4 and suddenly the engine runs worse or dies you know your misfire has most likely moved to cylinder 3, confirm this with the drop test. If the misfire is still on cylinder 4 you have another issue (and again, this doesn't even mean it's the coil, in fact you would likely have 2 dead or weak cylinders if it's the coil, 1 and 4 are paired, 2 and 3 are paired), but this is the simplest and easiest test you can do before you spend $100-120 on an OEM coil or cheap out on an aftermarket one.

Another easy test would be to check for spark at the end of the wire, if there is no spark there, check for spark at the coil, if there is a spark at the coil but not at the end of the wire you know you have a bad wire. If you have no spark at the coil (again, I would expect similar results on cylinder 1) then the coil is bad. This isn't a definitive test as a weak spark will jump fine in atmospheric conditions but not under cylinder pressures, but hey a free test is free right?

Try these tests first and report if you found your issue, I'll do my best to help with diagnostics. As I've mentioned a few times I would not suspect a bad coil if your misfire is ONLY on cylinder 4, but it is possible.
 

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Discussion Starter · #5 ·
Did you clean or replace the IAC, and check for vacuum leaks?


I haven't paid much attention to the IAC since the vehicle itself hasn't really had an issue of stalling. It will sound very off time (Out of rhythm?) if sitting at Idle, a lot of times I'll shift it into neutral to ease the rough idle if I'm stuck in traffic or at a long red light, occasionally the engine will "catch up" for a brief second, idle will settle, and then it will fall off time again. If that still sounds like it fits, I can look at replacing it. Smoke test is on my list of things to do but previous guidance lead me to believe temporarily that it was electrical in nature, which I no longer think is the case.



Instead of replacing parts, here are some free diagnostic methods you can do first (this will rule out one of your new spark plugs being bad as well). Also, in my experience sometimes these plug wire boots do not like to sit fully on the plug, make sure your boots are seated fully.



First, try a cylinder drop test, usually the easiest way to do this is to unplug the fuel injectors, if the engine does not change in behavior (no drop in RPM and runs the same) that is your misfiring cylinder. If there is absolutely no change when you unplug the injector to cylinder 4 you've confirmed that the ECU is recognizing the correct cylinder misfire. If you unplug cylinder 1 and there is only a slight change, and again only a slight change on cylinder 4 compared to cylinders 2 and 3 I would agree the most likely issue is a coil getting weak. Of course any cylinder that runs even more rough when you unplug it is contributing.



Next, try swapping spark plugs 3 and 4 (obviously check their condition, gap, etc. when you do this, cracks in the porcelain can be very hard if not impossible to spot, likely it will be wet with fuel due to misfire, clean it before moving it). Now repeat the cylinder drop test, if you unplug injector #4 and suddenly the engine runs worse or dies you know your misfire has most likely moved to cylinder 3, confirm this with the drop test. If the misfire is still on cylinder 4 you have another issue (and again, this doesn't even mean it's the coil, in fact you would likely have 2 dead or weak cylinders if it's the coil, 1 and 4 are paired, 2 and 3 are paired), but this is the simplest and easiest test you can do before you spend $100-120 on an OEM coil or cheap out on an aftermarket one.



Another easy test would be to check for spark at the end of the wire, if there is no spark there, check for spark at the coil, if there is a spark at the coil but not at the end of the wire you know you have a bad wire. If you have no spark at the coil (again, I would expect similar results on cylinder 1) then the coil is bad. This isn't a definitive test as a weak spark will jump fine in atmospheric conditions but not under cylinder pressures, but hey a free test is free right?



Try these tests first and report if you found your issue, I'll do my best to help with diagnostics. As I've mentioned a few times I would not suspect a bad coil if your misfire is ONLY on cylinder 4, but it is possible.


Full disclosure here, I'm not even sure where the injectors are to swap anything out for diagnostic testing. I'll sit with this comment and do some research until I can fully understand. It seems a bit above me but I don't want to stay ignorant on the subject, so I appreciate the direction you've granted me. I have a few questions to help build my foundation here.



"First, try a cylinder drop test, usually the easiest way to do this is to unplug the fuel injectors, if the engine does not change in behavior (no drop in RPM and runs the same) that is your misfiring cylinder. If there is absolutely no change when you unplug the injector to cylinder 4 you've confirmed that the ECU is recognizing the correct cylinder misfire. If you unplug cylinder 1 and there is only a slight change, and again only a slight change on cylinder 4 compared to cylinders 2 and 3 I would agree the most likely issue is a coil getting weak. Of course any cylinder that runs even more rough when you unplug it is contributing."



Would unplugging any cylinder not cause a drop in RPM's or destabilize the engine and cause shaking? (Which the car already does on its own, and it has always idled super heavy, since I got it 3 years ago anyways, there's just now a noticable "gap" in its cycle)



"Next, try swapping spark plugs 3 and 4 (obviously check their condition, gap, etc. when you do this, cracks in the porcelain can be very hard if not impossible to spot, likely it will be wet with fuel due to misfire, clean it before moving it). Now repeat the cylinder drop test, if you unplug injector #4 and suddenly the engine runs worse or dies you know your misfire has most likely moved to cylinder 3, confirm this with the drop test. If the misfire is still on cylinder 4 you have another issue (and again, this doesn't even mean it's the coil, in fact you would likely have 2 dead or weak cylinders if it's the coil, 1 and 4 are paired, 2 and 3 are paired), but this is the simplest and easiest test you can do before you spend $100-120 on an OEM coil or cheap out on an aftermarket one."



Now when you say "gap" are you referring to a physical gap or one in its running cycle? For porcelain and cleaning, are you referring to the cylinders themselves? Do I need to just get steel brushes and try to clean out what I can where the plugs are dropped in?



"Another easy test would be to check for spark at the end of the wire, if there is no spark there, check for spark at the coil, if there is a spark at the coil but not at the end of the wire you know you have a bad wire. If you have no spark at the coil (again, I would expect similar results on cylinder 1) then the coil is bad. This isn't a definitive test as a weak spark will jump fine in atmospheric conditions but not under cylinder pressures, but hey a free test is free right?"



The wires are fairly oil soaked from where the valve cover gasket was damaged, I'd like to assume you're talking about the wires running from coil to plugs, so pull the boot while the engine is running and check for a spark? Repeat the same with the plug and wire connected to each other but not in the engine to look for a spark on the end of the plug?



I spoke to my dad about it the other day and based on how it's behaving he thinks it's not electrical in nature at all but more likely has something to do with my sensors/intake.



Sorry for the super long reply, wasn't sure how to format, again I'm like a 5 year old when it comes to engines so just trying to learn as I go. Thanks for your replies!



Small Edit: It has 167k miles, it had about 125k when I got it and I have no idea what was done to the vehicle prior to me doing anything, but if I had to guess it was probably bare minimum care based on who the prev owner was, and has always had a really shaky idle in drive.



For history's sake, this is a screenshot of the services and parts that took place prior to the misfire starting(Or at least worsening) and some communications from the mechanic who performed the work






"Oil dipstick missing (It's literally in the tube but the handle is broken off so stuck inside. Rip.) valve cover gasket leaking into exhaust, coolant level very low hood latch not working"
 

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Give me a bit to read through your post and answer your questions individually, but just so we're clear don't remove your injectors, just unplug them for the drop test. I try not to disturb injectors unless I am prepared to replace the orings just in case they are damaged during removal.
 

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Discussion Starter · #7 ·
Oh also for the porcelain thing I realize you were referring to the spark plug haha
 

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Discussion Starter · #8 ·
Update: I got the oil dipstick out and holy SHIT. There was about an inch missing off of the top of it from the handle breaking I used pliers to lower the dipstick back down into the tube and it's still an inch over full.
 

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Injector Plugs

The connectors with the bit of orange where the wires go into each of them are the connectors for your injectors. When you unplug this the injector will stop spraying fuel. This WILL cause a misfire (shaking, running poorly, etc.) on a working cylinder. What I'm telling you to do is do this until you find that when you do this there is no change or only a slight change in how the engine is running. Theoretically when you unplug cylinder #4 (the one all the way to the right if you are standing in front of the car looking at the engine) there should be either no change or only a slight change in the way your engine runs, but unplugging any of the other 3 cylinders should cause the engine to run way worse.

To be clear, you should only unplug one at a time and plug it back in right away.

What we're trying to do here is correctly identify which cylinder is actually misfiring, I know on Ford V8s they are notorious for misidentifying which cylinder is misfiring and this can actually cause a 2 cylinder misfire (the computer will disable the injector on the cylinder if believes is misfiring, but this will actually result in 2 cylinders now misfiring).

Next, once you have identified which cylinder is misfiring (let's say it really is cylinder #4), what I want you to do is remove spark plugs 3 and 4 (the two on the right when standing in front of the car facing the engine) and switch which plug goes into which cylinder. When you do this, you should actually inspect the spark plugs.



If the ground electrode (labeled ground wire on this image) is literally touching the center electrode, there will be no spark, if it's way too far from the center electrode the spark will have a tough time jumping from one electrode to the other. The "gap" the spark has to jump is what I mean by the spark plug gap. There is a specification for how wide this gap should be which you would typically measure before installing a spark plug. When I say clean off the spark plug, I mean wipe off any fuel or oil, wire brush the threads, just clean it up. As for the boot I mean the rubber part that you stick onto the spark plug, if it's not seated fully on the spark plug it you may get a misfire just from that.

And yes, the porcelain is the insulator, the white part of the spark plug. If the spark plug was dropped it may have cracked, and sometimes these cracks can be so thin that you won't see it with the naked eye, but a spark can jump out of a crack meaning it didn't jump the gap down in the cylinder igniting your air/fuel mixture, if jumped out of that crack straight to the cylinder head. Sometimes you will see "carbon tracks" as a result of a spark jumping through the crack though.
 

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Are you on flat ground? Overfilled oil is not good for an engine. I would also make sure that is actually all oil, if you have a blown head gasket you could have coolant seeping into your oil which would cause the "oil level" to rise. This could also explain the misfire, but I hope that is not the case.
 

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Discussion Starter · #11 ·
Are you on flat ground? Overfilled oil is not good for an engine. I would also make sure that is actually all oil, if you have a blown head gasket you could have coolant seeping into your oil which would cause the "oil level" to rise. This could also explain the misfire, but I hope that is not the case.
I'm outside my job which is flat ground, no issues with leaking coolant.
 

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I'm outside my job which is flat ground, no issues with leaking coolant.
You mentioned that in your service notes that the coolant level was very low. If your car is losing coolant but it isn't dripping on the ground it may have an internal leak. If it is mixing with the oil it would cause your oil level to rise. What I'm getting at is you should probably get a new dipstick (junkyard will be fine for this) and confirm if your oil is overfilled.
 

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Discussion Starter · #13 · (Edited)
You mentioned that in your service notes that the coolant level was very low. If your car is losing coolant but it isn't dripping on the ground it may have an internal leak. If it is mixing with the oil it would cause your oil level to rise. What I'm getting at is you should probably get a new dipstick (junkyard will be fine for this) and confirm if your oil is overfilled.
Ah. Shit. Well, I haven't added coolant in over two years so hopefully it just evaporated off. I'm crossing my fingers and hoping he would have reported that there were signs of a mixture if that were the case for now. But I'll stop by an auto part store on my way home for a dipstick and probably drain some off. He refilled the oil but wasnt able to check levels as he did so I'm hoping that's why it got overfilled as well.
 

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Discussion Starter · #14 ·
@Apex As promised, I bought the dip stick and it turns out my engine is super heavy on oil. I guess the tech didn't think to at least try to google the capacity of my reservoir so he just yeeted a full 5qt jug into it, but I can't blame him for something I could have prevented. Still, I'm about half a quart to a quart heavy. Will deal with this first and then attempt troubleshooting you pointed me towards this weekend as well as look for signs of coolant leaking into the oil when I have some drained off.
 

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@Apex As promised, I bought the dip stick and it turns out my engine is super heavy on oil. I guess the tech didn't think to at least try to google the capacity of my reservoir so he just yeeted a full 5qt jug into it, but I can't blame him for something I could have prevented. Still, I'm about half a quart to a quart heavy. Will deal with this first and then attempt troubleshooting you pointed me towards this weekend as well as look for signs of coolant leaking into the oil when I have some drained off.
Depending on how long ago the oil change was, you might just change the oil. Obviously if your oil comes out like a milkshake or water comes out first (oil will sit on top of water, but it would have to settle), then you've found your missing coolant. Hope it's just overfilled.
 

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Discussion Starter · #16 ·
Yeah it was about a week ago, last Wednesday. Might not be a bad move, will update once done. Aaaaaaaand...you and me both! Fingers crossed!
 

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Yeah it was about a week ago, last Wednesday. Might not be a bad move, will update once done. Aaaaaaaand...you and me both! Fingers crossed!
If it's that recent I would probably just try to drain off the excess, but you won't hurt anything (except your wallet I guess) doing another oil change. Although I suppose the misfire COULD also have fuel wash down into the crankcase too... (though I don't think you would have a half a quart of fuel), so I guess maybe do the oil change and get this misfire resolved ASAP.
 

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Discussion Starter · #18 ·
Yeah I'm a little worried about it, on the note of overfilled oil, when I'm messing with my plugs, is there anything I should keep an eye out for? Everything seemed pretty oil soaked when I peered inside during spark plug change, just not sure how the inside of those motors are supposed to look when well lubricated vs overfilled. and uh...thanks so much for all of your help and guidance, seriously.
 

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Your spark plugs should not be wet with oil on top at all, all that should have been cleaned out when the valve cover gasket was replaced. Generally speaking they should not be wet on the threaded portion/electrode at all, but like I said they might be wet with fuel since you have a misfire.
 

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Discussion Starter · #20 ·
10-4. Got the oil changed off to an appropriate level, I no longer feel like Im driving underwater, no mixture that they could see, and the engine sounds way better. till misfiring and throwing codes, but massive improvement.
 
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