tl;dr: I've been chasing an intermittent "cyl X misfire" (the specific cylinder seems to move around) on the ol' 2011 Dodge Caravan (formerly known as the TunaVan). The symptoms are a rough idle when hot, but doesn't seem down on power or noticeable MPG hit (still floating around around 21MPG which is what it's gotten since we picked it up 4(?) years ago). Perfectly fine on throttle.
Background: I recently replace all of the plugs and coils @ 165k hoping to get rid of it, and yeah, they were the original plugs. Which makes sense, since you have to remove the intake manifold to get to 'em and it costs nearly $100 in gaskets to do it.
That made it idle slightly better, and caused the cylinder reporting a misfire to now shift around. before the plugs, it was always cylinder 1. Now it's sometimes 1, sometimes 2..
The check engine light is on ~90% of the time. It occasionally randomly goes out.
While checking it out on Torque, I noticed that on the "emissions readiness" readout, the O2 Sensor shows "incomplete." Looking at the live voltage for the O2 sensors, it looks like the two upstream only bounce between 0-0.8V and a bit slower than I'd expect. If you disconnect one, it will read 1.3V. I believe the cats are working correctly as the downstream O2 hold a very stable 0.8-0.9V. The LT trims for the bank 1 is -3.12%, bank 2 is sitting at -5.47%.
Questions: I was thinking of firing up the parts cannon and throwing a set of upstream O2 sensors at it. How sensitive are these things? A Mopar brand o2 sensor is ~$85, whereas a NTK is $40. Any idea what brand is OEM?
By 2011, the O2 sensors have been tuned really tightly to who made them- the differences between the sensors have a pretty minor appearing shift in where stoich voltage is, but the change is noticeable between the front and rear sensors. So hopefully, someone will post that the original sensor is NTK.
The other factor that will be noticed is the heater power. For the same reason they would be tuned to notice a maker change, they would very much notice if the heater power wasn't the same. You may have to go with the OEM.
That all being said, the fact that they are oscillating that far suggests to me that they are fine. As they age, both the speed response and the amount they switch will change- to the point that the OBD system will pick that up.
The rear sensors are rather rich, though. Far richer than I would calibrate them to be on a regular basis. When you unplug the front sensor, what does the rear do? And is the .8-.9v while you are driving around, or just at idle? For that cert zone, I would have them running in the .7-.8V range at richest, and more likely just below .7V with it switching *sometimes*.
It also could be very dirty intake/ injectors.
In reply to alfadriver :
Thanks for the additional info. I've gotten burned before by buying "off brand" O2 sensors (i.e., I put Bosch in a car that wanted NTK if I recall correctly), which is why i asked :)
All of my measurements were done with it at idle with coolant temps above 210°, blipping the throttle. When I unplugged the front bank, upstream sensor, that one went to 1.3V, and the rear didn't really change, still in the .7-.8 range.
I'll do some logging tonight after my wife gets home with it and I can answer you better then.
Maybe I'll toss a bottle of snake oil in to see if it'll clean the fuel injectors?
In reply to WonkoTheSane :
if you can get Chevron snake oil- assuming that it's still the same Techron that it used to be, I have seen lab results that it works really well. Should also help with intake system deposits.
It probably does need a new upstream O2, 150k life limit typically.
I wouldn't be surprised if it's not injector related. Is the misfire a "soft" or a "hard" hit? Cottonball vs sledgehammer.
Ranger50 said:
It probably does need a new upstream O2, 150k life limit typically.
I wouldn't be surprised if it's not injector related. Is the misfire a "soft" or a "hard" hit? Cottonball vs sledgehammer.
Whoops, sorry, my reply must not have posted..
It's definitely a soft hit, mostly noticeable in a rough/low idle.
I put a bottle of techron in and drove it with very low fuel for about 20 miles before filling up. Then, before driving off, I reset the CEL, here's what it looked like at the end of my 15 mile drive home:
So I like the injector theory :)
Circuit fault? Didn't see that one coming.
