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Discussion Starter · #1 ·
Hello,

I have a 2019 Dodge Grand Caravan GT.

It now has 91000 miles (got it around 30000 a little over a year ago - have done some Uber and Lyft driving in-between...)

Recently the check engine light came on, I read the codes and it was p0300 random/multiple cylinder misfire. After some googling, I found plugs could be worn and coils sometimes "pack up" around the mileage I have, so I went ahead and changed the plugs and coils. (The old plugs were nicely colored but all had a fairly large gap due to the negative electrode eroding. I couldn't see into the right side plug recesses, but the left side ones seemed to have a little bit (very small amount) of dried oil in the bottom - not sure if it was from stuff leaking from the coils or from the engine. The coils - all 6 - had a somewhat "burnt-ish" smell, but all looked dry with no oil or fluid visible on or in them.)

Also prior to replacing the plugs/coils, I had started to notice the engine running rougher and noticeable shaking at idle, with the engine rhythmically "rocking" or "pulsing" back and forth, which I hadn't seen earlier.

Another phenomenon before the repair was, that if I put it in gear but stopped, and just partially let up the brake (without pressing on accelerator) just to "crawl" forward, the van would be pulsingly lunge forward repeatedly, until I'd start to press the accelerator or the brakes more "decisively", at which time it would cease/smooth out.

The same would happen in reverse, EXCEPT that when it would star repeatedly lunging, it would also give a dull repeated banging sound, making me wonder if one or more of my engine mounts may now be busted.

Anyways, after the plugs/coils change, things seemed to "quiet down" and smooth out - the engine seemed/felt more "effortless" and more even, and even stronger (and no new codes). UNTIL like 100 or 200 miles later new check engine light, and p0300 back, both as confirmed and pending, with engine feeling more uneven again. (I have been checking repeatedly, with pending and confirmed p0300 code present on each scan, and no other code showing.)


So my questions:

Has anyone encountered and/or solved something similar, or do you have any ideas/pointers on where to look next?

I'm wondering if a bad O2 sensor might do this? (But then there should be more codes, right?)

Or could/would this be mechanical? Engine sounds "normal" with no unusual sounds/noises, at least to my ears. (I had a 2018 SXT previously, which had a somewhat louder ticking sound that didn't sound very even, i.e. not every cylinder seemed to have it, and the dealership replaced the lifters under warranty - without a noticeable change in the sound, but that would be another story... But this van doesn't have that same loudish ticking sound or anything else - has a fairly faint and very even/regular set of ticks that to me sounds like possibly the injectors firing.)

Any tips would be greatly appreciated!
 

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I assume this vehicle runs well above idle.

Free cheap things to try, clean the throttle body, clean the maf sensor if it has one, look for a small vacuum leak. There are plenty of youtube videos to help you.

You don't want to hear this...but
This appears to be one of those times that paying for a professional diagnosis may be the least expensive way to go. You probably need a scanner and or the knowledge to watch and interpret live data. Changing all the coils was an expensive move that could have been avoided. Posting about your problem on a forum such as this can help avoid unnecessary costs in the future. Lets hope you find something simple and easy to correct.
 

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You don't want to hear this...but
This appears to be one of those times that paying for a professional diagnosis may be the least expensive way to go. You probably need a scanner and or the knowledge to watch and interpret live data. Changing all the coils was an expensive move that could have been avoided. Posting about your problem on a forum such as this can help avoid unnecessary costs in the future. Lets hope you find something simple and easy to correct.
That's the problem with CEL OBD codes- like reading tea leaves, and cloud patterns. Were the coils expensive or cheap (aftermarket or Mopar)?
Forums will give you lots of stuff (guesses) to fire a shotgun at, and hope something hits. I agree the drunken elvis - can save you time and frustration to buy a diagnosis. Though that's not always absolute either.
 

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If you haven't thrown out the old coils, I'd try them, especially if you got cheap coils. They should be in top shape to at least 100k and still be decent until they give out at 150-200k.

Did you gap the plugs to .043"? Were they iridium plugs?

The carbon build up in the cylinders could be an issue, but cleaning it comes with a whole list of potential issues, including fowling the cats. Check your PCV valve to see if it's dumping oil into the intake and needs to be replaced. You might also want to consider adding a catch can if it continues to dump a lot of oil with a new PCV valve.
 

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Discussion Starter · #6 ·
I assume this vehicle runs well above idle.

Free cheap things to try, clean the throttle body, clean the maf sensor if it has one, look for a small vacuum leak. There are plenty of youtube videos to help you.

You don't want to hear this...but
This appears to be one of those times that paying for a professional diagnosis may be the least expensive way to go. You probably need a scanner and or the knowledge to watch and interpret live data. Changing all the coils was an expensive move that could have been avoided. Posting about your problem on a forum such as this can help avoid unnecessary costs in the future. Lets hope you find something simple and easy to correct.
Thanks, Drunken Elvis!

Cleaned the throttle body.
No MAF sensor, only MAP (I didn't clean that).
No vacuum leak that I could detect. But I hooked up a vacuum gauge, and to me it seems a little low, but not sure why:

For the coils, I decided to change them after a fairly extensive search on this forum (and some others), reading others' experiences with them (and given my relatively hign mileage of 91000).
( Spark plug(s) and gap size for a 2012 Town & Country... )
(And right after the new plugs and coils, for a brief period, the engine was very nice and smooth - I guess until the computer re-learned something stupid and decided to mess up the experience again?)

As for professional diganosis - I've had just enough "less-than-optimum" experiences with that, that I'm not looking at that as an option (given I don't know any good mechanics that I know I CAN turst, both thier knowledge and their integrity).
One "professional" (and paid) diagnosis - by a local "respected" and high-priced shop - when I had a "chirping" accessory belt, was to replace my belt tensioner (and that "should" fix it, but if not, we'll just have to keep looking and replacing things. At the time I couldn't afford what they were asking for the repair and decided to tackle the repair myself - and on taking off the belt, the first thing I discovered was, that if I turned the alternator by hand, it was chirping... Took me about 5 minutes, and the shop, having charged an hour of diagnosis, couldn't find that? And another, the latest "diagnosis" was, on my previous vehicle, a 2018 Grand Caravan SXT. Ticking noise from the engine, that I compared to a brand new vehicle, which didn't have it, took it in to the local dealer under my extended warranty, and was told, "no problem, it's lifters, they do this, piece of cake". They replaced my lifters (at least that's what I was told...) under the warranty, and - ticking sound unchanged. Of course they found some items that the warranty wouldn't pay, so I had to pay out of pocket, too... But I was leaving the country and I didn't have any more time to try and "argue" or "fight". The kicker was, right after the repair, as I was returning to the vehicle from a store, I noticed something hanging out at the bottom. When I looked under it, I found a red shop towel dangling off my right side front axle, kind of wrapped around, and a few others tucked into the subframe...
So maybe - and I DO hope - others have had better luck with such "diagnosis", but you could probably see why that is not my "first choice". Besides, I'd like to be able to understand and figure out as much of this by myself as possible - it's fun.

As for scanner, I have a BlueDriver, which allows me to look at some live data with limitations. Any pointers on what the data to monitor would be that could give me a clue?
 

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Discussion Starter · #7 ·
That's the problem with CEL OBD codes- like reading tea leaves, and cloud patterns. Were the coils expensive or cheap (aftermarket or Mopar)?
Forums will give you lots of stuff (guesses) to fire a shotgun at, and hope something hits. I agree the drunken elvis - can save you time and frustration to buy a diagnosis. Though that's not always absolute either.
Thanks, Cciman.
The coils I used (Standard Motor Products Blue Streak, More Information for STANDARD MOTOR PRODUCTS UF648 ) seemed okay both price-wise and performance-wise, based on others' experiences
I wish I had someone knowledgeable and reliable to turn to to help diagnose, but I don't, unfortunately...
 

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Discussion Starter · #8 ·
Boy those u tube mechanics are NEVER wrong
While they may not always be perfect, more often than not, they have helped cut down time necessary in getting to the bottom of, and fixing multiple issues. I certainly consider them a useful resource, and of course I also know better than not to take things they say with a grain of salt :)
 

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Discussion Starter · #9 ·
If you haven't thrown out the old coils, I'd try them, especially if you got cheap coils. They should be in top shape to at least 100k and still be decent until they give out at 150-200k.

Did you gap the plugs to .043"? Were they iridium plugs?

The carbon build up in the cylinders could be an issue, but cleaning it comes with a whole list of potential issues, including fowling the cats. Check your PCV valve to see if it's dumping oil into the intake and needs to be replaced. You might also want to consider adding a catch can if it continues to dump a lot of oil with a new PCV valve.
Hi Sienile,
I DID chuck the old coils and plugs as soon as the engine fired up with the new ones... Since in the front spark plug wells I did see some dried oil, which I concluded (possibly incorrectly) had leaked out of the coils (and they also had a burnt smell, but again, that may have been "normal" for those...)
I used Standard Motor Products Blue Streak coils ( More Information for STANDARD MOTOR PRODUCTS UF648 ) and NGK Ruthenium plugs ( More Information for NGK 94705 ) after doing some research and reading others' experiences ( Spark plug(s) and gap size for a 2012 Town & Country... , https://bobistheoilguy.com/forums/threads/ignition-coil-for-3-6-pentastar.347300/#post-5922524 ).
I didn't verify the plugs' gap (couldn't find my gauge...) but "eyeballed" them and they all looked the same (factory) setting, about 1/3 of what the old (eroded) ones had.

I didn't look in the cylinders (I don't have a scope) so not sure what carbon they may have (I do drive extended stretches of freeway between city runs, so I'd imagine things could regularly burn off pretty good). But the plugs all looked nice and tan - although, in retrospect, the one in cylinder 2, despite the nice color, did seem to have some kind of a little bit of soft build-up around the porcelain center insulator that the others didn't seem to have - maybe this could be a clue? (This would rub off easily as I'd touch it, but was not a whole lot.)

Now I've also checked and cleaned the PCV valve - wasn't too bad, some oil but not extreme, nicely "rattling", and the PCV hose was pretty clean too.

By the way, the engine doesn't use/burn oil, either.

Also cleaned the MAP sensor now - even though it looked clean to begin with...

I have also added a bottle of Techron to my tank recently - so much for "process of elimination" vs. "shotgun method" (changing everything and then wondering what it was...)

I guess I'll do some driving and see how we'll do... (Engine right now still seems to have occasional misses at idle, but no codes yet.)

As I mentioned in my previous post, my vacuum readings seem low:
Per my (somewhat limited) understanding, indicating vacuum leak or worn rings.

But with worn rings, I'd imagine I'd also be using up oil, plus there would be at least some gunk on the plugs, or am I off?

So maybe it IS some vacuum leak to try and chase down at this point?
 

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If this vehicle does not have a MAF sensor [ you confirmed it does not ] then an air leak is unlikely to be the problem as it would be detected by the MAP sensor and compensated for.
EGR valve problem, dirty, sticking?
The evap system must have a line that feeds the intake manifold fumes from the canister. Pinching that line off might be interesting to try.
Dirty fuel injectors is a possibility.
With engine idling, disconnect the wire to the throttle body. This will set a code but again might tell a story.
Look at fuel trims as well as O2 sensor outputs.
Does this happen engine warm or cold? Eng temp sensor out of whack?
 

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...
I used Standard Motor Products Blue Streak coils ( More Information for STANDARD MOTOR PRODUCTS UF648 ) and NGK Ruthenium plugs ( More Information for NGK 94705 ) after doing some research and reading others' experiences ( Spark plug(s) and gap size for a 2012 Town & Country... , https://bobistheoilguy.com/forums/threads/ignition-coil-for-3-6-pentastar.347300/#post-5922524 ).
I didn't verify the plugs' gap (couldn't find my gauge...) but "eyeballed" them and they all looked the same (factory) setting, about 1/3 of what the old (eroded) ones had.
...
Take them out and gap them. NGK Rutheniums come from the factory at .033", not .043". I did the same thing and mine ran great for a week and then lost 30hp because the gap was too close and causing the plugs to fire too soon which caused knock. Nothing like ruining an engine with a simple upgrade.
 

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I couldn't see the video... Don't have the codecs to watch Apple stuff on my PC. Low vacuum with no leaks does sound like rings. That could have been caused by the under-gapped plugs. Knock forces some of the combustion gases (more than normal) past the rings and this can dry them out and lead to cylinder scoring. Oil in the cylinders from worn rings is possible, but not guaranteed. No oil, no gunk.

Speaking of gunk on the plugs... you mentioned something soft on #2. What color? Have a pic?
 

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Discussion Starter · #14 ·
Thank you Drunken Elvis and Sienile!

Sorry for my slow response, as I was trying to go through these steps as I was also trying to work.

Take them out and gap them. NGK Rutheniums come from the factory at .033", not .043". I did the same thing and mine ran great for a week and then lost 30hp because the gap was too close and causing the plugs to fire too soon which caused knock. Nothing like ruining an engine with a simple upgrade.
Thanks for the tip, I never thought about this - I gapped them now, hopefully soon enough.

I couldn't see the video... Don't have the codecs to watch Apple stuff on my PC.
Bummer! I haven't figured out a way to convert them (yet), but working on it.

If this vehicle does not have a MAF sensor [ you confirmed it does not ] then an air leak is unlikely to be the problem as it would be detected by the MAP sensor and compensated for.
EGR valve problem, dirty, sticking?
The evap system must have a line that feeds the intake manifold fumes from the canister. Pinching that line off might be interesting to try.
Dirty fuel injectors is a possibility.
With engine idling, disconnect the wire to the throttle body. This will set a code but again might tell a story.
Look at fuel trims as well as O2 sensor outputs.
Does this happen engine warm or cold? Eng temp sensor out of whack?
Low vacuum with no leaks does sound like rings. That could have been caused by the under-gapped plugs. Knock forces some of the combustion gases (more than normal) past the rings and this can dry them out and lead to cylinder scoring. Oil in the cylinders from worn rings is possible, but not guaranteed. No oil, no gunk.
Speaking of gunk on the plugs... you mentioned something soft on #2. What color? Have a pic?
Okay, so a summary:

I re-checked the vacuum, and (since on the previous test yielding a low reading I had the A/C on) turned off the A/C, and actually got normal and "healthy looking" reading - steady needle, about 17-18 InHg, when blipping the throttle, it would drop and then rise and normalize, as a "healthy engine" should.
Turning A/C on would lower the reading to about 15-16 at idle (wasn't sure if that's normal or an irregularity, but didn't research that, but at least without A/C it seemed fine).

I then tested for vacuum leaks - with a propane torch as well as (instead of pinching) pulling off the EVAP hose, the brake booster hose and the PCV hose, one at a time, and plugging their respective ports - NO change.

No EGR on this one, has VVT instead.

Didn't look at injectors or pull the wire from the throttle body (yet), but instead:

Hooked up my BlueDriver scanner and looked at some live data over a period (fuel trims and O2 upstream sensors) while driving around.
  • O2 sensors switching up and down (didn't look deeper into whether "all perfect" or not).
  • Short term fuel trims all within a few points of 0 - more often below than above, but near 0.
  • Long term fuel trims: Bank 1 hovering around 0, Bank 2 between -7% and -10%, which I thought was strange, and "out of place". Started to suspect that Bank 2 has something going on, with fuel being "dumped in" or something.

Then I looked at some Mode 6 data, and discovered that the "multiple random" misfires of the P0300 were actually TWO cylinders, #2 (a bunch) and #6 (maybe "half a bunch" or "a third of a bunch", but still many). All Bank 2, of course!

I pulled the plugs to see/"read" them:
All (still) look nice and new (with 1-2000 miles on them now) - no deposits or soot. The ground electrode of #2 appearing ever so slightly moist compared to the others, which could be gas unburnt from misfires (I just moved the car in place to work on, with a fully cold engine only running briefly and then shut off).
(By the way, the "deposit" the old plug for #2 had, was kind of like the normal "crust" or "deposit" on a normal looking plug (the tannish color stuff), except slightly thicker, if that makes sense(?) Unfortunately I threw it out without taking a picture.)

I was going to check compression earlier (I had a suspicion this might be something mechanical), but didn't have a 10mm adapter to my gage - but I ordered one and now finally I was able to test:
  • Cylinders #1, #3, #4, #5 all reading a little over 150 psi dry/around 270 psi wet, and
  • Cylinders #2 and #6 around 90 psi dry and a little over 150 psi wet.
  • All cylinders - both the good and the "bad" were reaching top/"peak" pressure in 3-4 compression cycles, both when dry and when wet.
  • And ALL cylinders seemed to KEEP the peak pressure instead of gradually losing it.

So my current guess (and please correct me if I'm wrong or missing something) is, that it's indeed my ring(s) in cylinder #2 and #6 that are shot. But not sure if are they worn, broken or stuck - would there be a difference in how they'd act/respond differently?

(By the way, I doubt this had anything to do with detonation due to the small plug gaps before properly gapping them, as frankly, there has been minimal change between "before" and "after" the plugs and coil change - car essentially drives about the same.)

Given this engine has 93000 miles currently, I'm wondering how this is even possible, that those got busted - and only 2 cylinders. I got the vehicle about 1.5 years ago, with 31000 miles, and I have been using full synthetic oil (5W-30), never running it low, always changing it on schedule.

So now I'm looking at pulling off the Bank 2 head, pulling off the oil pan, taking out pistons #2 and #6, and putting new rings on them and putting it back together. Fun driveway project... (Not in the position right now to take it to a shop and throw $$$ at it, as I suspect that would be "hurtful" for something like this.)

Is there anything you think I should be aware of while doing this?
Or is there a simpler and/or less "messy" approach that you could recommend?
Any other insight you may be able to offer?

Thanks, and I do appreciate your pointers and help!
 

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I don’t think low compression causes misfires. At least not by worn out rings. Also, worn out ring cause oil consumption and usually blue smoke, but at the very least the spark plugs would be oily, but you said they looked fine.

However, what can cause both low compression reading and misfires is a problem with the valves, valve seats. That’s where I would start looking.
 

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Thank you Drunken Elvis and Sienile!

Sorry for my slow response, as I was trying to go through these steps as I was also trying to work.


Thanks for the tip, I never thought about this - I gapped them now, hopefully soon enough.


Bummer! I haven't figured out a way to convert them (yet), but working on it.



Okay, so a summary:

I re-checked the vacuum, and (since on the previous test yielding a low reading I had the A/C on) turned off the A/C, and actually got normal and "healthy looking" reading - steady needle, about 17-18 InHg, when blipping the throttle, it would drop and then rise and normalize, as a "healthy engine" should.
Turning A/C on would lower the reading to about 15-16 at idle (wasn't sure if that's normal or an irregularity, but didn't research that, but at least without A/C it seemed fine).

I then tested for vacuum leaks - with a propane torch as well as (instead of pinching) pulling off the EVAP hose, the brake booster hose and the PCV hose, one at a time, and plugging their respective ports - NO change.

No EGR on this one, has VVT instead.

Didn't look at injectors or pull the wire from the throttle body (yet), but instead:

Hooked up my BlueDriver scanner and looked at some live data over a period (fuel trims and O2 upstream sensors) while driving around.
  • O2 sensors switching up and down (didn't look deeper into whether "all perfect" or not).
  • Short term fuel trims all within a few points of 0 - more often below than above, but near 0.
  • Long term fuel trims: Bank 1 hovering around 0, Bank 2 between -7% and -10%, which I thought was strange, and "out of place". Started to suspect that Bank 2 has something going on, with fuel being "dumped in" or something.

Then I looked at some Mode 6 data, and discovered that the "multiple random" misfires of the P0300 were actually TWO cylinders, #2 (a bunch) and #6 (maybe "half a bunch" or "a third of a bunch", but still many). All Bank 2, of course!

I pulled the plugs to see/"read" them:
All (still) look nice and new (with 1-2000 miles on them now) - no deposits or soot. The ground electrode of #2 appearing ever so slightly moist compared to the others, which could be gas unburnt from misfires (I just moved the car in place to work on, with a fully cold engine only running briefly and then shut off).
(By the way, the "deposit" the old plug for #2 had, was kind of like the normal "crust" or "deposit" on a normal looking plug (the tannish color stuff), except slightly thicker, if that makes sense(?) Unfortunately I threw it out without taking a picture.)

I was going to check compression earlier (I had a suspicion this might be something mechanical), but didn't have a 10mm adapter to my gage - but I ordered one and now finally I was able to test:
  • Cylinders #1, #3, #4, #5 all reading a little over 150 psi dry/around 270 psi wet, and
  • Cylinders #2 and #6 around 90 psi dry and a little over 150 psi wet.
  • All cylinders - both the good and the "bad" were reaching top/"peak" pressure in 3-4 compression cycles, both when dry and when wet.
  • And ALL cylinders seemed to KEEP the peak pressure instead of gradually losing it.

So my current guess (and please correct me if I'm wrong or missing something) is, that it's indeed my ring(s) in cylinder #2 and #6 that are shot. But not sure if are they worn, broken or stuck - would there be a difference in how they'd act/respond differently?

(By the way, I doubt this had anything to do with detonation due to the small plug gaps before properly gapping them, as frankly, there has been minimal change between "before" and "after" the plugs and coil change - car essentially drives about the same.)

Given this engine has 93000 miles currently, I'm wondering how this is even possible, that those got busted - and only 2 cylinders. I got the vehicle about 1.5 years ago, with 31000 miles, and I have been using full synthetic oil (5W-30), never running it low, always changing it on schedule.

So now I'm looking at pulling off the Bank 2 head, pulling off the oil pan, taking out pistons #2 and #6, and putting new rings on them and putting it back together. Fun driveway project... (Not in the position right now to take it to a shop and throw $$$ at it, as I suspect that would be "hurtful" for something like this.)

Is there anything you think I should be aware of while doing this?
Or is there a simpler and/or less "messy" approach that you could recommend?
Any other insight you may be able to offer?

Thanks, and I do appreciate your pointers and help!
I would most certainly be running a borescope into this before pulling the engine apart. Carbon build up on valves can definitely cause low compression or quick leak down. It's like 30$ for a scope camera on Amazon. Also, check the timing marks line up and the timing chain/belt is tight.

Essentially, check everything else it could be before hap hazardly taking the engine apart.
 

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Negative fuel trims mean too much air, not too much fuel. (Fuel trim is how much fuel to remove. Removing a negative is a positive gain.) Bank 2 is either running lean or is cutting fuel to your misfiring cylinder causing the negative trim readings.

Low compression can definitely cause a misfire. I agree with Truckster that the problem is more likely in the top end. Pentastars are known for valve seat issues, especially the exhaust ones and especially on bank 2. The machine shop I use will not do a Pentastar head without doing valve seats.

Valve issues would also explain the fuel trims as it pushes the compression back into the intake or allows it to pull air in from the exhaust.

The crusty plug like you described is often from an exhaust restriction. If a valve isn't opening as much as it could because of a dropped, but still holding in the bore, exhaust valve seat; that can cause the exhaust particles to collect in the cylinder and on the plug.

Have you opened the valve cover to check for rocker issues? Rockers that are missing or severely worn could cause some of the same issues as issues with the valves themselves.

Pulling the heads on these is a ton of work. I'd try to figure out as much as possible before going that far.
 

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A negative fuel trim value shows it’s removing fuel because it was too rich. A misfire dumps lots of oxygen in the exhaust, which would cause fuel trim to be positive if it were reacting to a current misfire. I’d guess it wasn’t missing when those fuel trims were recorded. And I don’t think I’d worry too much about the fuel trim until everything else is right.
 

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Fuel trim is just an indicator of the running condition. Once everything is right it will fall into place.

I've really had it backwards all this time? :p Good thing I normally go by O2 voltage and lambda values. :p Just doesn't makes sense to me to use the word "trim" when talking about adding unless it's a negative.

Anyway, still seems like a top end issue.
 
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