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I have P0301 and P0304 codes and switched out the spark plugs on those cylinders with the other two to rule out a spark plug issue. The spark was steady on all cylinders and an inline tester showed that the wires were good. I even pulled off each wire from the coil one at a time to check for spark there and that was also good.
A friend checked each injector and said that all four of them were working at idle but when I accelerated, the clicking sound didn’t increase as the rpm increased on cylinder 1. He said I should first try to either clean or replace the injectors on cylinder 1 and 4 to see if that fixes the problem. I got two from junkyard just in case but cleaned all six of them by running Berryman’s fuel injector cleaner through each one using my own made pump hooked up to a hose and powering the injector with wire and a 9v battery.
I used a lot of carb cleaner spray on the fuel rail, holes where injectors go into engine, and let the car sit. I reinstalled the injectors, with 1 and 4 not being reinstalled, but installed the junkyard ones on cylinders 1 and 4. The car ran fine for 25 miles on my way back and forth to work with no check engine light. Unfortunately, the check engine light did come on a few miles later for the same P0301 and P0304 issue but only comes on when I’m driving at higher speeds.
What else should I be checking and what else could be the problem?
Notes: I do not feel any misfire whatsoever. I do feel a rumbling under my seat but that may be due to the flex pipe/cat needing another gasket due to an air leak. This is part of another post and don’t want to keep adding different things to one post.
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It’s a 2001 Hyundai Elantra GLS, has 4 cylinders. I have not done a compression test yet. I’d also like to point out that the ignition coil has two parts, the left side controls cylinders 2 and 3 and the right side controls cylinders 1 and 4. I will try to test the right side connector and get the specs for resistance because this car is known to have broken pigtail connectors. I was told that I should also test the wires from there to the ECU but that’s beyond my potential.
Update: Compression came out to about the same value for all cylinders. I took off the rear catalytic converter/flex pipe today and there were chunks of black charcoal-like pieces that came out. I assume the front catalytic converter has broken up inside, which went down to the flex pipe area.
Review of what I did last week: The spark plugs and wires tested good but I have swapped them from cylinders 1 and 4 to 2 and 3 to see if the codes change, which they didn’t. I was told it may be the injectors so I cleaned them and swapped them like I did the plugs with no change.
I didn’t check fuel pressure because I figured it would affect all cylinders, not just 2. The coil that controls cylinders 1 and 4 has been tested a handful of times, I redid the connection, tested for voltage and continuity, and it tests good. The long-term fuel trim is about -8% and I figure I can rule out a vacuum air leak.
Could the broken up catalytic converter at the exhaust manifold, in any way possible, cause a misfire?
I am lost on what to do next or what to look for.
I have a few humble suggestions for you joeycava.
First, it doesn’t sound good regarding the cat for this vehicle. This should not cause a misfire, but is often symptomatic of a misfire. Unburned, raw fuel makes it through the engine and overheats the cat instead. Oftentimes it will restrict the exhaust. So as much as this stinks, you have to be diligent to find out the cause before replacing the cat. Otherwise, the same thing will happen.
Secondly, sometimes coils that are beginning to fail will show up only after they are warm. I’ve had coils do just fine, until driving the car for a while, and then it begins to act up. This can be difficult to catch unless you have a scanner that will give live data, etc., You may also notice that a bad coil begins to act up not only when heated up, but “under a load,” such as a steep hill while driving. A coil can “test” and act healthy at times at idle only to misfire at higher temps and rpm’s and while under a load.
Also, I might note that both cylinders throwing these codes receive fire from the same coil. If you’ve ruled out plugs, wires, injectors and fuel pressure this may be the most likely culprit. You’ll get some better advice I’m sure, but if she were mine and I didn’t have access to live data, I’d swap out that coil in a minute.
Best of luck with it…
I definitely appreciate your advice and I definitely must find the misfire before anything because I wouldn’t want to ruin a brand new cat.
This coil is fairly new and I even swapped it out with an older coil that has never given me problems. The same misfires on 1 and 4 come up, which happens to be the right side of the coil that controls cylinders 1 and 4 as you noticed.
I looked up the wiring diagram and made sure the wiring was correct, and tested for continuity on the wires that go to the ECU. The second pin of the connecter is a white wire (white on both connectors) and they tested good for voltage. The diagram shows that both white wires for power connect somewhere to each other in the diagram. These connecters have been known to break and turn brittle so I had to redo them in the past.
I do have a scan tool that I borrowed but I wouldn’t know how to look for any live data that relates to the coil. I see the 02 sensor voltages, short and long term fuel trims, load percentage, rpm’s, MAP, coolant temp, ignition timing advance, etc…what would show info about the coil?
I wonder, would it make a difference if I switch the white power wires from each coil to see what happens?
Also, being that some people with this car have had issues with the connectors having a strong connection to the coil itself, I wonder if just taking off the connectors completely and splicing the wires to a female connector where I would connect them to the male terminals of the coil would help?I’ll tap out on this one, as I honestly don’t have any experience with Hyundais. The wires in question may receive separate calls from the PCM in tandem with the crank and cam sensors, so this might not work to swap them.
Also, if the culprit was faulty wiring, it would likely show up at all speeds and not just higher rpm’s. Those DTC codes are cylinder specific, so hopefully you can track if down. This kind of issue can make you pull your hair out.
Have you addressed possible vacuum leaks, such as plenum or intake? I’ll be interested to know with the others what you find when you figure it out…
The white wires that supply voltage to the coil connectors both connect somewhere and then go right to a connector on the fuse box under the hood. I can see what pin and connector this white wire goes to. From this connector, it goes to a joint connector where the injector fuse and sensor fuse are connected to.
This is probably beyond my realm but one possibility is I could just switch those white wires on the coil connectors and see if the misfire codes change. I can also test for continuity and voltage at the connector in that fuse box.
I have a -8% as a long term fuel trim so the car is running rich, which I figured cancels out any vacuum air leaks.
I have a Mitchell diagram that says your primary coils are power side switched and those white wires you’re looking at actually ground wires. I have an OE diagram that says your primaries are ground side switched and you should only have one white wire for a coil driver circuit while the other driver circuit is green. That same diagram says both coils should get power from a brown wire. If we can trust the second wiring diagram, you can reverse the brown wires, but you’d be better off just back probing both wires with a good jumper wire. Before I ever commited to such shenanigans, I’d want to compare diagrams to the physical harness and verify what all the wiring actually does first.
My car and two other Elantras that I found at the junkyard have a tubing with 5 wires inside.
There are two white wires that connect to the left terminals of the coils, a yellow wire that connects to the right side of the coil that controls cylinders 2 and 3, a green wire that connects to the right side of the coil that controls cylinders 1 and 4, and the green and yellow wire are kind of inside the bigger brown wire.
The diagram I have shows a white wire, instead of yellow on the three cars I’ve seen, that connects to the left side of the coil that controls cylinders 2 and 3. It also shows that the brown wire connects to the ECU, terminal 55, and it’s for Ground.
The brown wire is at least 6 inches away from the coil inside the tubing and it looks like the yellow and green wires come out from inside that brown wire.
I don’t know if this is correct and could ultimately be the issue so I would like to compare the diagram you have with mine. I sent you a private message as well.
I have tested the 2 white wires for voltage at the connector and they did test ok.You can get OE wiring diagrams at this here website. I’ve used it a few times now and it seems legit. I can’t complain so far. They are copied straight out of the factory manuals just like alldata would do. I also attached the Mitchell based wiring diagrams too. Remember that the Mitchell diagrams don’t agree with the OE diagram. If there’s any confusion about which side would be power and ground, remove each connector from their coil and test for power with KOEO. Once you know absolutely which wire does what, remember to test for voltages with engine running. The real test of a circuit is how it behaves under a load.
Thanks for posting this. I do notice a difference with the Hyundai manual that I found online, as far as what terminals on the coil the wires go to.
Looking at the first diagram of the list, 1-3:
There is a White wire that comes from the engine fuse box at pin 7 of EC03 then on the right side of page is listed as WHT 2.
Pin 4 on the ECU to the coil that controls cylinders 1 and 4 is shown as Green and listed as GRN 3 on the right. Then it shows a White wire that goes from Pin 5 on the ECU to the coil that controls cylinders 2 and 3 and is listed as WHT 4 on the right.Notes: The Hyundai manual does list the same thing but unfortunately, I have 2 White, 1 Green, and 1 Yellow wires while this diagram and the manual both show 3 White and 1 Green. The Hyundai manual does show that Pin 4 on the ECU is a 0.5G wire and that Pin 5 is a 0.5W wire, while the other White wire from EC03 is 1.25W. Assuming that means the wires from the ECU are smaller in diameter and that Green is from Pin 4 on the ECU, then the Yellow wire on my car must be from Pin 5 on the ECU because it’s the same smaller thickness as the Green wire.
Now looking at the third diagram in the list, 2-3:
GRN 3 goes to the Left side of coil 1 and WHT 4 goes to the Right side of coil 2. Assuming this is true and that we can consider WHT 4 as a Yellow wire instead, this is not what the Hyundai manual shows because both of these wires are on the Right side of each coil.
WHT 2 can be seen going straight towards coil 2 on the Left side but connects with another White wire that goes to the Right side of coil 1.Notes: I checked for continuity from the White wire at Pin 7 of EC03 to both of the White wires on my car that go to the coils, which was confirmed.
These 2 White wires at the coil terminals supply the power and I tested for voltage with key in the on position and got 12.15 Volts.
I am not sure if it makes a difference which coil each White wire connects to because they both have voltage. With the engine running, both White wires had 14.40 Volts and so did the White wire at EC03.I did not make a strong connection on coil 1 yet because I wasn’t sure which wire goes to what side. I did try it the way this diagram shows, where the Green wire is on the Right side of coil 1, because mine was the opposite.
I did still get misfire codes for cylinders 1 and 4 but can be due to the connection where I just shoved a spliced wire into the harness connector and then attached a female connector to the other side of the wire where it’s connected to the coil terminal. I noticed that the wiring fell out of the harness for the Green side when I was testing for continuity the second because I want to test and make sure everything works before I go and make a strong connection.
The catalytic converter at the exhaust manifold is definitely broken up inside. When I idle the engine, the RPM gauge stays the same but it’s like a popping and sputtering sound.
From all of this, can you see anything about the wiring that I should have tested or if I misinterpreted something in the diagram?
A summary of what I posted to avoid confusion:
Coil 2 that controls cylinders 2 and 3 must be okay because I don’t get misfires from those cylinders. The wiring to that coil matches up with the diagram.
Coil 1 that controls cylinders 1 and 4, has wiring that was opposite of this diagram. The White wire on Coil 1 is on the right side of the coil shown in the diagram, while mine was on the left side.
Both White wires tested good for voltage and read 12.15 with key on engine off and 14.40 when engine was running. Also, the same voltage was given from where the White wire comes from at the engine fuse box.
Key on/engine off: Voltage was same for every wire.
Engine running using the diagram given: Coil 2 had 14.26V from the power wire and 14.19 from the ECU wire. Coil 1 had 14.26 from power wire and 13.9 from ECU wire.
Just for laughs I changed the wires on Coil 1 back to the way they were. Voltage with engine running was 14.26 from power wire and 14.19 from ECU wire. Not sure if it matters at all though.
A diagram that I found of the coil wires. I went to the junkyard and opened up the harness from where the Coil 1 and 2 wires go inside the bigger brown shield wire. I then spliced open the brown shield wire the whole way to the firewall and the yellow and green coil wires are not cut open or spliced at all under the hood. I wouldn’t know where to find the SC07, SC25, and SC26 on this diagram.
Here’s pics of where the Yellow (Coil 2) wire and Green (Coil 1) wire go inside that shield wire. According to the manual, the shield wire only connects to ground and it’s a “Radia Frequency Interferece” wire.
I tried to do a resistance test between ground and touching the shield wire but it looks like a hardened glue in that area so I got no reading.
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