What could cause misfire codes?

[Easywin]

I replaced my timing belt and all associated parts including water pump. I drove it for about 80 miles last Thursday. I got in to leave Friday morning to a blinking Check Engine light. I pulled codes and only got P0300, P302, and P303. I put new coil packs on cylinders 2 and 3 only to get the same codes again.

I pulled the #2 Timing Belt cover and checked my timing marks on the camshaft gears only to find them lined up perfectly with the marks on the cover.

I have searched the forums and have came up with a few possible problems. I would like to know if anyone has had good results that I haven't found. As of right now the car has just under 150K miles.

[93celicaconv]

So what car are we talking about here? Your 2000 Avalon? Does it have a V6?

First, if this is the right car, you are in the wrong forum. But, what else can cause these codes? You could have any of the following causes:

- bad spark plugs in cylinders 2 & 3
- bad spark plug wires in cylinders 2 & 3
- bad fuel injectors in cylinders 2 & 3
- poor cylinder compression pressure in cylinders 2 & 3
- ignition wiring the occassional open to short circuits

I'm assuming there could be more causes, but these come to mind now.

[Easywin]

Yes this is my car, yes it's a V6, and I know I am in the "wrong forum", but from what I have learned at ToyotaNation, the Camry and Avalons have the same V6. Thank you.

I have the coil packs which I swapped between cylinders to get the same codes. The spark plugs were changed early this spring, which I swapped between cylinders also to get the same codes.

The car ran fine for approximately 80 miles so I don't think it's bad compression.

What do you mean by "ignition wiring the occassional open to short circuits"?

And also, why would these problems arise so suddenly? Would the new timing belt have something to do with the misfire?

[93celicaconv]

Yes, but from a moderator standpoint, shouldn't an Avalon question be in the Avalon forum?

The item should have read "iginition wiring occassional open or short circuit". What this was trying to say is that there may be an intermittent signal loss in the ignition system due to the wiring providing this signal either occassionally open circuiting or short circuiting. Probably wouldn't cause misfires specific to two cylinders though.

I can't tell you why this situation developed so fast. But there may be something that happened during the timing belt change that triggered the opportunity for it to happen. I didn't do the work, so I don't know what items the person doing the change all came in contact with that could have started all this. All I was trying to do was to point out a few things to consider when misfiring is specific to a couple of cylinders only.

[Easywin]

What stumps me is that the only electrical conponents I disconnected were the three grounds around the engine support bracket, the rest was mechanical.

[93celicaconv]

Ground wires are very critical to correct system operation. The ECU works for the most part as a relay to ground certain circuits to cause systems to activate. If a ground is disturbed, I always make sure the wire and the ground surface are extremely clean, no corrosion around, and wipe the surfaces down with acetone or laquer thinner to remove any kind of residual oil or material that could have gotten on it, then reattach. Grounds around the engine area are very, very critical to the ECU operating correctly.

[Easywin]

Bump.

[Easywin]

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[73sport]

Q? Did you keep record of every coil pack move and related code?

1) even new coil packs can be bad.
2) if you kept track and there is no way the offending pack is on the engine, i'd move the new ones somewhere else.

Also, a loaded up plug from not firing can go bad. It is rare but they will misfire under load. IMO if the coil was bad I'd replace the plug under it for this reason.

I didn't see mention of how it runs. What does it do? Did you clear the ECM by pulling the EFI 15A fuse under the hood?

I went down a similar path on my 1MZ. I felt it running bad long before the CEL came on.

Just curious, do the old coils look like this inside w/white spots near the center electrode?



Next area would be the O2 sensors. They get sluggish way before error codes come into play. They're rated at roughly 100,000 miles and if those are 150,000 I'd repalce them.

How about valve train noise. Valves that get to tight would cause a misfire when hot only. This is a stretch but its possible.

- report how it drives. What do you feel, hear, see.
- get current codes, don't assume
- move NEW coil packs to known good cylinders 2,4,6 ect
- confirm all grounds are good and intact
- clear ecm
- replace plugs
- replace old O2 sensors

I have more ideas but let me know how it runs. . .

EDIT: oppsee, just saw its a 2000. It has 3 coils yes? And you repalced 2 or 3?