Follow up: Spark plug change yields more misfires

This is a followup to a post from a few months ago. I included the original post below this new post.

After a few months of intermittently monitoring my misfires I am still having occasional misfires. Misfires occur randomly on all 4 cylinders.There was never a time when the misfires were bad enough to throw a code. I never would have known they were occurring if I had not been monitoring them with VCI cable and software on my laptop. Even when I coincidentally glanced at the laptop while a misfire was occurring no perceivable power loss, lag or shuddering was ever felt. Typically a 30 minute drive in mixed driving conditions would cause no more than 5 or 6 misfires.

Although their occurrence is mostly random, it does seem that certain situations are more likely to cause them. Like when the car is just getting going in the morning while in stage 1. Also, when decelerating to a stop (especially after a bit of higher speed driving like on a 4 lane highway across town. There is little likelihood of any misfires on highway and never during any of my 0-60 full out acceleration tests.
Cylinder 4 seems to have the highest count (about 30% more than the other cylinders). Cylinder 2 has the least number of hits. I decided to switch ignition coil between 4 and 2. I expected to get 2 misfiring more and 4 to misfire less. Oddly, I am getting more misfires over a shorter period of time and seemingly a more even distribution now across all 4 cylinders. I can't say that 2 is doing worse but 4 seems to be doing a little bit better since the misfires are more evenly distributed. There doesn't seem to be any better or worse cylinder but there does seem a higher total of misfires occurring. Of course I'd rather have 0 misfires so my inclination is to put coil from 2 back on 2 and 4 back on 4 because the total number of misfires was less that way. My observations with the 2/4 switched makes no sense to me but maybe with all the other findings I am posting someone will be able to put together a suggestion of what I should try next.

I have 2 questions - one for those familiar with VCI and the software.
1. What parameters should I be looking at to determine if this is related to air/fuel mixture and what is the normal range that these parameters should be operating at.

2. We have (2) 2008 prius's(prii). Mine and my wife's with about 35K more than mine at 165,000 miles on it. I just changed the plugs on it. I did not hook up vci to it to see if she has any weirdness basically because I don't want to know about any more problems. Do you think I should scan hers and if her's displays 0 misfires should I pull her ignition coils and test them on my car. I find it hard to believe that I could have 4 bad coils but perhaps I have one or two that might be marginal. It would not be that difficult to pull hers for testing purposes.

Thank you in advance for any guidance you can offer me. I'd really appreciate it.

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With all due respect, I would think that if these were bad for any reason (and your reason is certainly plausible) that the total misfire count for a 30 minute trip would be higher than the single digit count that I am seeing. I just don't want to replace $200 worth of parts and find that they were not bad. I don't see many posts on the forum about people replacing ignition coils at 135K as standard maintenance protocol ? Spark plugs yes but 'cops' - not so sure.

 

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Thank you Patrick for your suggestions and for re-threading my comments tonight to the prior thread I created. I can see without pulling anything apart that the amber bulb is looking pretty grey so I guess I will go ahead and carefully clean it with CRC product. Probably do that first before cleaning the throttle body and valve. If it fixes things great... If not I'll clean the throttle body as well. By doing one service at a time I'll have a better idea where I messed up and where to look if things get worse instead of better.

Typically I can go about 30 minutes and only register 10 misfires but tonight I was able to hold the variables at their sweet spot or rotten spot so in about 30 minutes I had about 30 misfires but this is not a very real world driving simulation. Even at that, based on your information, that is nowhere near 2% or 108/200 revolutions. Real world would have the state of charge at closer to 75 % or better as visually graphed on the MFD display. At that level there would be less need for the ICE to come into play and fewer transition situations between ICE and hybrid power. I'm kind of guessing here - there are a lot of 'moving parts' and this is certainly a simplification and observation based.

The car is a long way from being new and has nearly 140K on it so I guess i should be more accepting of the fact that it is what it is at this point. I don't have any drive-ability issues because of this problem so I'm thinking I'll do the mass airflow sensor cleaning and throttle body and if that doesn't change anything I'm going to put the VCI cable and laptop away and just enjoy the time I have left with her until she throws a real code or two or three..... I'll keep you posted of how things go after the cleaning.

Thanks again.

 

So I've isolated similar events causing misfires. These situations will illicit a misfire on random cylinders. I am not throwing and CEL or MIL any am only aware of them because I see them on my laptop.

Let me start by saying that misfires don't ever occur while car is moving (ie. while speed is being maintained without any stopping). When car is just turned on and inspection mode whereby ICE is running constantly there will be numerous misfires on all cylinders occurring randomly. I replicated this condition on my wife's 08 prius as well. A similar situation occurs if parked and the heater is running and the car is in ready state (on). The ICE comes on to recharge the battery because of the drain being imposed by heater. This doesn't typically cause any misfires. There are also times that ICE comes on apparently just to heat up the coolant being used in the heater core to keep the cabin at the desired temperature for comfort. If you watch the MFD consumption chart you will see no activity - no ICE or MG1 MG2 spinning - basically looks like it would look in auxillary mode without being in ready stat. If you weren't paying attention to MFD you'd assume it was just recharging the hybrid battery but there is no recharging going on during this cycling of the ICE. This is exactly when my car begins registering random misfires. The car also will on occasion have a misfire on approach to stop sign or red light. This can be seen more frequently during warming up cycle because the engine does not cut off/disengage when stopped as quickly as it would if it was warmed up and/or had full SOC. So I'll be approaching a red light and i see on my laptop that engine RPMs are not dropping and stay hovering between 900-1200 RPM while stopped. While sitting at the light stopped with ICE running I'll see a random misfire on one or more cylinders. Once warmed up, the misfires on approach to stops are less of an issue. However if heater is on and the coolant temperature has dropped below 160F a misfire at stop may occur regardless since ICE remains spinning to maintain temperature of coolant in the heater core. This is my assumption of why it remains spinning based on repeated observations.

The spark plugs are new, i cleaned throttle body valve and throat and cleaned the dirty MAF sensor with CRC MAF cleaner. I moved some cops around but that didn't seem to make much difference. The cops were reinspected for rips and tears and signs of damage but none was obvious. I am wondering however if I should have gapped the Toyota Denso iridium plugs to prius spec before installing them. I purchased a new plug today for my worse performing cylinder #4 and will be carefully gapping it to prius spec and installing it over the weekend if gets warmer. I don't know if that will make any difference but I doubt it.

It seems that this pattern should help some of you, who are much more knowledgeably than me, to venture an educated guess at what might be going on or where I should focus any further attempts at correcting this.

In summary, the ICE performs without a glitch when it is running under load to propel the car and to recharge the hybrid battery (basically under load). It runs into issues when it is called into operation for what I am surmising is to maintain coolant temperature when car is at rest with heat on, when slowing down to a stop while in warmup phase and when parked and running in inspection mode for purposes other than recharging battery.

I'm guessing there is a vacuum problem or similar situation which presents it self while at rest, or maybe air fuel mixture issues or injector issues. I have not tired MMO yet but I did put Techron Complete into my tank several months ago. I was not aware of misfires at that point so I don't know if they were worse prior to doing so. I was trying to quiet some tapping down which now has pretty much subsided and sound much more healthy. Maybe another dose treatment of MMO, Seafoam or Techron should be attempted. Coincidentally I was discussing my problem with he parts guy at toyota today and he said try this and that. Then he said wait a moment and went into the back and came out with a can of Seafoam saying that the mechanics there use this now and then and it fixes a lot of different problems. Said I could probably get it cheaper than buying it from the dealer. While I was there I had him quote me the cost of a fuel injector. Not in front of me now but it was like $175 for one with the seal kits. LOL and a PCV valve i had him quote was $17.00. I told him I'd hold on to the quote and get back if I wanted to replace any of those items.

As always, thank you in advance for any suggestion and for your time.

 

I performed the idle check that valde3 recommended (true neutral without any HV battery recharging as compared to inspection mode). Luckily I was keeping an eye on both the laptop and the MFD. It drew the HV charge down like valde3 warned but I forgot his warning and when I saw one purple bar left I let go a bit longer thinking the car wouldn't let itself be damaged in this way. I guess it would have though.

I did the test 2 times. First was from a cold start and later after driving the car for a while and it had heated up. The second test I guess was the right way to test because the first showed an idle strarting at 1250 and creeping down slowly into the 900 rpm range. The observations on the 2nd test after car had warmed up and without shutting down the car showed the car hovering around 1000 RPMs. It would not really stay dead on 1000 rpm although it would touch on it briefly as it moved in a range of 15-20 RPM below and 15-20 RPM above. In other words the range was between 980-1020. Since there wasn't a mention of what correct range for prius idle is I'm not sure if these results indicate anything. Also, the fact that it would not stay on any one value for long may or may not mean anything. It did kick out a few misfires during the test (probably 15-20 during the 7 minutes or so I ran it. I did feel a tiny bit of very subtle vibration motion in the car during various points in the test - nothing major but the car wasn't dead still either. I guess it was kind of like a very minor idle problem 'feel'. The motion did not feel different during the misfires - certainly would not have known any misfires were occuring. Not sure what to look for at this point. I can reclean MAF and do a better job on the throttle plate (maybe lubricate it with some lithium grease on the pivot points), look for some loose hose fitting. Can anyone suggest which hoses I should inspect that would cause any of the symptoms I previously posted and these new observation. I could also just do nothing right now and see what happens after another bottle of Techron fuel injector cleaner runs through my tank ?

Thank you !!!