4.0l V6 Ignition Coil Question

[djpope09]

Hi guys. I have a 2004 4Runner with the 4.0l V6. It has 189,000 miles on it. I had most of the engine disassembled recently to replace some things and I got it running again last week. It was sitting for over 4 months I think.

It ran fine when I put it all back together and I've been driving it about 20 miles a day while checking fluid levels for the last week.

Yesterday I was about a block away from home and the engine started idling pretty rough at a stop light. It seemed a little better once I was moving and then it seemed rough again as I pulled up to my house. I put it in Park and it idled fine again. I shifted back to Drive and the rough idle came back so I put it in Park. The idle speed dropped to below 500rpm so I shut the truck off. The Check Engine Light never came on so I don't think there will be any codes to pull. It definitely felt like a misfire though.

I started it up this morning and it's running fine again.

All the fluid levels are fine and I replaced the spark plugs about 2000 miles ago.

I've seen some threads on here suggesting it could be an ignition coil. One person said their 4Runner had the same symptoms where it would idle rough once the truck was warmed up. It finally threw a CEL a couple months later, they replaced the ignition coil and it fixed it. Others say the ignition coils either work or don't, they don't slowly die.

Is there a reliable way to test the ignition coils? I've seen people use multimeters, but I've heard that isn't reliable since the coil isn't in use while you're testing it. Any ideas?

 

[waypoint]

The ECM might have set one or more codes in Pending state...whip out your scanner and check for them.

From your description, it sounds like the idle problem only happens when the engine is up to temp and in closed loop mode. This is usually a malfunctioning mass airflow sensor or upstream oxygen sensor.

Scan the Long Term Fuel Trim values for both banks, both at cold idle and after fully warmed up. Post the data and we'll see what's happening...should range from +5% to -5% on both banks, with values within ~2% of each other.

 

[radlynx]

i think its one of the ignition coil failing. i guess its time to replace all of them. when one fails, all the rest will follow.

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[djpope09]

I wanted to give you guys an update since I haven't completely solved it yet, and I may not have time to for at least a week.

I found a heater core hose leaking onto the first cat (driver's side). It seems it was leaking enough to also get the A/F ratio sensor wet. I tightened up the hose and drove it and it was still leaking and I finally got a CEL. I haven't scanned it yet.

I think the most interesting thing was how the CEL came on. It would flash on and off with the VSC Trac lights on, then the lights would turn off even though the engine was running rough. Then all the lights would come back on with the CEL flashing. It cycled like that over and over. The Fuel Economy display went from ~15mpg to ~8mpg before switching to E00. I don't know what E00 means except maybe 0mpg? I'm guessing the heater core hose dripping onto the A/F sensor was causing the problem.

The heater hose only has fluid running through it when the system is warmed up so to me it makes sense that the A/F sensor would be dry and working until the vehicle is warm and dripping coolant right onto it.

I was looking at it in the dark so I couldn't see much, but the hose didn't look like it had any cracks in it. I think my plan is to first try a new clamp and if that fails then a new heater core hose. Once I have the leak fixed I'll test it again. I'll also post the CEL code once I scan it.

Thanks for you input guys.

 

[radlynx]

i think its one of the ignition coil failing. i guess its time to replace all of them. when one fails, all the rest will follow.

Sent from my SM-G930T using Tapatalk

in addition to this, you can test the ignition coil one at a time by removing the ignition coil one at a time when the issue happens. if you dont notice an extra engine vibration after removing it, that is the malfunctioning coil. i hope this helps.

it can also be a head gasket problem. keep us posted!

Sent from my SM-G930T using Tapatalk

 

[djpope09]

The ECM might have set one or more codes in Pending state...whip out your scanner and check for them.

From your description, it sounds like the idle problem only happens when the engine is up to temp and in closed loop mode. This is usually a malfunctioning mass airflow sensor or upstream oxygen sensor.

Scan the Long Term Fuel Trim values for both banks, both at cold idle and after fully warmed up. Post the data and we'll see what's happening...should range from +5% to -5% on both banks, with values within ~2% of each other.

I finally got a scanner out and it had a P0301 Cylinder 1 Misfire Detected fault. I fixed the heater core hose leak which was dripping on the bank 2 A/F sensor. I was expecting the misfire to be on bank 2 because of this. I did some swapping of the spark plugs and ignition coils on cylinders 1 and 3 to see if the misfire would move with them. It did not, the misfire stayed on cylinder 1.

I drove it some more and managed to get a P0171 System Too Lean (A/F Lean, Bank 2) fault. I checked the Long Term Fuel Trims and bank 1 was +27.3% and bank 2 was +7.8%. I should note that I had the negative battery disconnected earlier in the day and I drove it maybe 8 miles before checking the LTFT.

I'm guessing this means the Bank 1 A/F sensor is bad. Is the bank 2 sensor also going bad since it's outside of you +5/-5% range? Or does that not apply since the numbers seem to have reset with the battery disconnected. If I had time I would have swapped the A/F sensors to see if the misfire moved to bank 2. I guess I could try that later this week when I have time.

 

[djpope09]

in addition to this, you can test the ignition coil one at a time by removing the ignition coil one at a time when the issue happens. if you dont notice an extra engine vibration after removing it, that is the malfunctioning coil. i hope this helps.

it can also be a head gasket problem. keep us posted!

Sent from my SM-G930T using Tapatalk

I had never heard of this test, but it works pretty well. I found a DTC for Cylinder 1 misfire. I alternated taking the connector off the ignition coils on cylinder 1 and 3. Taking it off cylinder 3 caused a noticeable difference in misfiring. Taking it off cylinder 1 didn't cause any change.

In another post I mentioned that I believe the A/F sensor needs to be replaced.

I replaced the head gaskets earlier this year so I'm hoping I didn't screw that up and this is unrelated. Thanks for the suggestions!

 

[radlynx]

try to swap your 1 & 3 coils. see if the misfire moves to cylinder 3, if it does, your coil is bad, if it stays in cylinder 1, you might either have a head gasket issue (not likely since you did replace the head gasket) or have a fuel injector problem. maybe this time you can swap the injector between 1 & 3 and see if the misfire moves. if it does, it's the injector, and if not, it's the head gasket.

I had never heard of this test, but it works pretty well. I found a DTC for Cylinder 1 misfire. I alternated taking the connector off the ignition coils on cylinder 1 and 3. Taking it off cylinder 3 caused a noticeable difference in misfiring. Taking it off cylinder 1 didn't cause any change.

In another post I mentioned that I believe the A/F sensor needs to be replaced.

I replaced the head gaskets earlier this year so I'm hoping I didn't screw that up and this is unrelated. Thanks for the suggestions!

 

[djpope09]

try to swap your 1 & 3 coils. see if the misfire moves to cylinder 3, if it does, your coil is bad, if it stays in cylinder 1, you might either have a head gasket issue (not likely since you did replace the head gasket) or have a fuel injector problem. maybe this time you can swap the injector between 1 & 3 and see if the misfire moves. if it does, it's the injector, and if not, it's the head gasket.

Yeah I did the coil swap test too. Misfire stayed on cylinder 1. I did some more driving and eventually got a P0300 multiple cylinder misfire fault to go along with the P0171 A/F too lean fault. I had not considered a fuel injector being bad. I'll swap them this weekend and see what happens.

 

[djpope09]

try to swap your 1 & 3 coils. see if the misfire moves to cylinder 3, if it does, your coil is bad, if it stays in cylinder 1, you might either have a head gasket issue (not likely since you did replace the head gasket) or have a fuel injector problem. maybe this time you can swap the injector between 1 & 3 and see if the misfire moves. if it does, it's the injector, and if not, it's the head gasket.

I swapped the injectors on 1 and 3 and replaced the o-rings on both. I haven't been able to get the misfire to come back yet.

I do notice that at idle, the engine sometimes has more vibration than it used to. This engine was the smoothest idling engine I've ever had, but now it sometimes has a little vibration to it. I'm guessing the injectors are dirty or bad. I plan on putting some fuel injector cleaner in the next time I fill up the gas tank to see if that helps at all.

I also had an issue with what I think is a bad engine ECU relay. I tried to start it after work yesterday and when I tried to crank everything died. No crank, no lights on the dash. I pulled the C/Open (I think) relay in the engine bay fuse panel. Put it back in and the truck started up and is running fine again. It's one thing after another with this 4Runner. I'll be testing all the fuses and relays this weekend to see if I need to replace any.