'97 Camry V6 misfiring?

[mitaux8030]

Hi all,
Got a well looked after 1997 Camry V6 3.0 manual (bit of a rare one) that has a minor problem that seems like its misfiring? Its only noticable at around 60 or 70 km/h on level road in top gear, the engine seems to miss quite regularly with a light but perceptible hesitation or 'bucking'.

This was mentioned at the last major service, but no cause was found, and there was no change after the service. The spark plugs were changed at that service too. Otherwise, fuel economy is normal, acceleration is normal, and everything else seems fine.

Got any tips on where to start looking?

[Godzilla]

A Miss or a sudden total loss of power and back to life type kick?

ie is it a small roughness like a cylinder or 2 are missfireing or is it a split second nothing then OK

What im trying to understand is if its 1 or 2 cylinders being problematic or all of them at the same time momentarily.

Tell me a little more about the engine, does it have a distributor cap, does it have ignition leads or is it coil on plug, have you tried a bottle of injector cleaner, is your fuel filter OK?

Could just be one of the coils....

[Joey]

We had a 96 Vienta V6 ,same motor and with exactly the same problem , it was always worse when it was cold.
Apparently this is not uncommon and like ours it was caused by water leaking into one of the cylinders ,the amount of water was so small it was only noticeable when the overflow tank seemed to be loosing water every couple of weeks.
We had planned to get rid of it anyway so it wasn't worth getting a motor rebuild / head replacement so used some Chemiweld which worked perfectly for 6 months .

We found out about the problem through a friend that had a 94 model that suffered the same problem but his got worse within a couple of weeks and then started overheating and running really bad, it turned out cheaper at the time to fit and exchange import motor than getting the original repaired.

Also worth noting we had the water system pressure tested but it didn't show up with anything wrong because the leak was so small , but it doesn't take much water vapor to cause the miss fire.

[mitaux8030]

Thanks Joey, I'll keep an eye on the water level over the next few weeks.

And thanks for your input too Godzilla. Its only a fraction of a second 'jerk', but happening quite often, say once every few seconds. So 'roughness' probably describes it best. My gut feeling tells me its an ignition problem with only one or two cylinders. Its an electronic ignition with no distributor, just a coil pack with HT leads to each spark plug buried deep within the heads.

Might have to research Toyotas OBD-II and see if I can put it into diagnostic mode and capture anything unusual. Is the OBD-II protocol easily readable by mere mortals like you and I?

(my old Mitsubishi had a very primitive ECI with diagnostics... count the number of pulses on the diagnostic port. 1 = knock sensor problem, 2 = air flow sensor problem, 3 = throttle position sensor problem etc. I imagine things have advanced very significantly since then!)

[Godzilla]

There are OBD2 scanners on fleabay, just check your model with the seller, pulling error codes is not hard and can help but can also be a hindrance if your not familiar with the workings of modern cars.

If you pull a O2 sensor code it could still be a ignition lead as a example so dont be miss-led, a scanner help but wont tell you exactly what to fix, it will tell you the fault code that got logged and its up to you to work out why.

Are your coils the twin spark type? One coil for 2 cylinders? So 3 coil packs feed 6 cylinders? If so id be looking into getting another one and swapping it with one of the coil parks at a time till i found the one that was playing up.

Water leaking into the cylinder could be a issue but as mentioned, your water level will be dropping, im guessing you would have seen that.