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Misfires jumping randomly from cylinder to cylinder

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rifrash

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Discussion starter · #1 ·
Hi all.

My minivan is currently in the shop with an issue of jumping misfires. About 2000 miles timing belt, valve adjustments, fuel injection cleaning, etc has been done and in September the transmission had to be replaced. I notice that idling is not as smooth as before the replacement. About a week after, the cel and tcs light come on again. I bring the car back to the shop and they determine that 4 cylinders misfire. Interesting fact is that the car would be running very badly with 4 cylinders misfiring. However after standing still for a day and a half, when the car is started in the morning it runs smooth and the cel does not come on. They check the plugs and coils. The plugs look good, clean, not wet or worn. They check the coils in the misfiring cylinders by moving them around, however the misfire does not follow and happens every time in a different cylinder. It appears the misfires are totally random. Fuel injection was checked and found to functioning normally. They will check the valve adjustments tomorrow, but they feel they are running out of options as to what might be causing the random misfires. Is there anyone who might have an idea what this might be?

Thx
 
#2 ·
First, what year and model van do you have and how many miles on it?

Second, when exactly did the rough idle just start? Was it after the timing belt/valve adjustment/injector maintenance or just after the transmission repair, and has it been that way since you picked it up?

Third, what are the DTC's that are coming up? When the check engine light comes on that indicates DTC's stored in the computer. I'd assume a P0300 which is a random misfire but is there anything else?

Fourth, I'd want to look at the fuel trims on a scan tool. Is it running too rich or too lean? Is it only misfiring at idle and not at higher RPM's? If so, and if fuel trims indicate it's running lean it could just be a vacuum leak.

When it's running rough I'd want to do a cylinder drop test where you unplug one coil at a time and see if the idle drops. That is the way to determine, exactly, which cylinder(s) is/are misfiring. The misfire counters aren't always accurate in telling you which cylinder is misfiring. I'd also want to do a compression check.

Really, without a lot more information from you with some scan data there's not going to be much we can do here except suggest things to check hoping we hit the right thing. A good diagnostic tech should be able to track it down in just an hour or two max.
 
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#3 ·
If you are getting misfire codes, first, off, COMPLETELY disregard the cylinder number of the code. P0300 for random misfire is probably a more useful code than P0303 for example supposedly points at cylinder 3 misfire, which is rarely correct in my experience. The _ONLY_ reliable way (IMO) to discover the ACTUAL cylinder that is misfiring is with the cylinder drop test that John describes. This of course assumes that it's misfiring when you're checking it - intermittent misfires are more challenging to diagnose.

Finally, if you discover it to be a faulty coil pack, stick with OEM on this particular item, even though they're WAY more expensive. But since you've done your diagnostics, you'll only be replacing one or possibly 2 coil packs I'm guessing. Still cheaper than shotgunning a set of 6 aftermarket coil packs into it and having 1 or 2 be failures right out of the gate, and another fail 3-6 months later. Ironically, I went through this a few months back - also not but a few months after changing timing belt and doing the valve adjustment. Went down the fuel pressure route which I regret, found the offending cylinder in 5 minutes with the drop test after fighting rotating cylinder misfire codes along with the random misfire code.

One other item - you said a valve adjustment was performed - were spark plugs replaced at that time as well? These engines are notorious for REQUIRING the OEM spark plugs. Another - fuel injector cleaning? Was this an additive to the fuel, or they actually removed the fuel injectors? If the latter, hopefully the orings were replaced - also, the injectors are not very durable - VERY easy to break the plastic tips off during routine removal even when extreme care is used during removal which would affect the spray pattern and likely result in poor performance.
 
Discussion starter · #4 · (Edited)
Thx for responding :), I also responded to John, howeversomething went wrong because I don't see that reply?

Anyway, car is from 2004 and has 180000 m. Never any major problems.Rough idling began after transmission replacement. Misfiring followed soon after. Technician checked plugs and has ruled out bad coils. He did the drop test. Misfiring is indeed cylinder specific according to code, but when codes are reset and cylinders are tested again, multiple misfire has moved on to different combination of cylinders. The weird thing is that the car does not run badly and the morning when it was brought in, CEL was off and idling smoothly, leading me to think it might a bad valve somewhere, something that should be closed normally, is not currently, and that one morning, just happened to be. Fuel injection appeared to be in order. Plugs have not been replaced with the valve adjustment.
 
#5 ·
First off, if the plugs are orig. then replace them.
Second off, sounds like the tech did musical chairs with the coils. That doesn't work. Take a new, OEM coil to substitute. As reported before, the computer has NO IDEA what cylinder is misfiring, only that the fuel/air mix in the exhaust is high.
 
#6 ·
Well, the computer does know but it uses crank position signal and rpm to determine which cylinder it thinks misfired. Usually, on the Honda, it's been pretty accurate when it's a real misfire.

You're going to need to get someone really good at diagnostics on this one. This could be anything from a pinched or broken wire from the transmission change to a failed part somewhere to a compression issue. You can't just blindly say "the fuel injection is OK." There are hundreds of parts that have to be OK in order for the fuel injection to be OK. If there is a misfire then, by definition, there is a problem in the fuel injection system. You've messed with a lot of stuff recently so there are lots of possible failure points. Injector problems are pretty rare on the J35 so I'm also curious what caused you to have the injectors cleaned and how you did that.
 
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#7 ·
Here is a great read on misfire detection on gas engines; written at the time era of the engines we have.
http://ilot.edu.pl/KONES/2001/JOK2001 NO 1-2/R39.pdf

It appears POSSIBLE to detect a misfire and ID the offensive cylinder, using the toothed wheel crank position sensor, but it takes quite a bit of processing. The CPU needs to detect a very small change in the instantaneous angular velocity, using a fairly small number of "teeth" on the sensor wheel. I ran an experiment a couple of years ago on my '02 Ody. I unplugged ONE coil. I got codes for 3 or 4 cylinders that it claimed were misfiring.
So, all I know is MY Ody can't tell. Maybe other, more recent Ody can, that have upgraded ECM's. The article does claim the EPA makes this feature mandatory, btw.
 
#8 ·
Yeah, that's probably true. I know the Gen 3's are fairly accurate at reporting the misfires that are caused by VCM. The Gen 2's probably don't have quite the capability.
 
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Discussion starter · #9 ·
Diver Dave, the plugs were replaced with OEM ones, but not at the same time when the valve adjustment was done. Technician did the drop test and he used a new OEM coil to test. He does not think coils are bad. The fuel injection was cleaned last June as part of service done for 180000 miles. I don't know how it was cleaned. But technician working on the car trying to solve this issue says it is working as it should.

The mysterious thing is that even though the car gives codes for misfiring, the car is not running as badly as would be expected with several cylinders misfiring. I have driven it to the local Honda dealership this afternoon and idling is rougher and there is some loss in power, but that's it.
 
#10 ·
Have they checked the timing marks on the crank and cam shafts to make sure the timing belt isn't loose or not on properly?
The standard compression and vacuum tests could help.
Heck, it could even be that whoever adj the valve lash didn't do it properly or left a locknut loose.
Any chance that the connections to the computer are not snug and clean and dry?
Buffalo4
 
#11 ·
rifrash said:
... I have driven it to the local Honda dealership this afternoon...
Click to expand...
Ugh. When I suggested a good "diagnostic tech" I sure didn't mean the dealer. Most dealers are not known for being good at diagnostics. They're good at parts swapping and changing out many parts that don't need to be changed, costing you a fortune, and not getting to the root of the problem. Let's hope your dealer is better than that.
 
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Discussion starter · #12 ·
I hope so too, because it's causing a lot of stress, not being able to rely on a well functioning car :(. Finding someone good is tough. I thought I had actually done so with the shop that did the transmission replacement...
 
Discussion starter · #14 ·
Buffalo4, that is actually what the tech suggested. Since valve adjustment was done last June at the dealership, he suggested they look at that first.

As far computer connections go, would that not result in other issues too?
 
#16 ·
How close are you to either Avoca, NY or Pennsylvania Furnace, PA? I know of a couple of really good diagnostic techs in those two places. South Main Auto in Avoca would be my first choice.
 
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#17 · (Edited)
Pretty hard to diagnose this engine from afar. So, was the vehicle down for a long time with the tranny repair? That is: how old is the gas? Beyond that, a "small" loss of power and "somewhat rough" idle is consistent with one cylinder out. The compression test, as mentioned, is a good idea. While at that, replace the plugs. $ is << than anything at a dealer. no mention of EGR, and carbon in the intake passages. If the valves were adjusted, then someone was looking at the passages. Are they now clean? If one cylinder gets all the exhaust, because many others are clogged, you will have issues with that cylinder. One more idea. Take it to the road with #1 coil disconnected, then #2, and work it to #6. Is there any that don't make a difference? Don't do this for a long time, since the cat runs hot with rich exhaust, but you can get away with it for an hour, lets say. Good luck.

ps; Wrong on the valve adj and the intake plenum. Unrelated. Remove the carbon if not done in the last 80k miles.
 
Discussion starter · #18 ·
No, car was only for a couple of days in the shop. I mentioned the EGR to the technician twice, however he insists it should have thrown a code related to, which it did not do. They also took out one coil at a time, and every time performance of car was worse.

Thx, sure can use some luck :)
 
#19 ·
rifrash said:
As far computer connections go, would that not result in other issues too?
Click to expand...
Maybe yes, maybe no. If one of the PCM connectors was totally off, the van probably wouldn't run. Otherwise, it would have to be a single bad connection on a multi-connection plug.

It's possible to have a bad PCM connection, but keep in mind it's rare. The reliability of the PCM is helped by its location inside the cabin, away from dirt and water.

Dave
 
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