2006 Toyota Prius Engine Performance Issues

HI
I am working on our 2006 Toyota Prius. I has been having an intermittent cylinder 3 misfire when the engine is cold, losing fuel economy and diluting the oil with gas. The compression ranges from 115 psi to 135 psi. Plugs are new. Attached are snapshots of the fuel injector waveforms from my verus. Do they look good? I"m Not experienced with injector waveform yet.

Over fueling and oil dilution are common symptoms of an ignition or any other misfire. With computer controlled fuel injection the oxygen sensor cannot detect unburned fuel in the exhaust from a misfiring cylinder, it detects only the excess of oxygen in the exhaust and regards this as a lean mixture so adds fuel by making the fuel trims richer.

If you have a misfire code pointing at any particular cylinder or any signs that one particular spark plug looks different from the rest I would replace the coil pack for that particular cylinder. This is parts swapping but it is playing the odds rather than random guess work. For a proper diagnostic you would need a current clamp or a cop ignition probe.
There are other causes of misfires from a cold start including a cylinder head gasket but I would expect other signs.

I haven't much experience with higher mileage Prius but you would advise you keep an eye on the oil level my neighbour had couple of issues one which was caused by slightly high oil level, the other issues were caused by the engine 12v battery dying of old age.

Agree with Andy about oil level, as this is known to cause performance issues.

The injector waveform itself looks good, IMO. If you're working on an injector diagnosis, you could try swapping it to another cylinder and rechecking after a cold start. While you're there, I'd suggest pulling the plug and borescoping the cylinder before starting. It's not unheard of for head gaskets to fail on these, leaking coolant into the cylinder.

I have a low amp probe for my verus can i test the coil with this? Also I am not getting a Misfire Code but can feel the hesitation and see it on the counters.Do you think it is ok to have the 20 psi difference between cyl1 and cyl4?
Also what other issues were caused by your neighbor's 12v battery? I suspect mine also.
Thanks,
Elijah

if a cylinder is getting bore washed with fuel the dry compression test can show misleading results an oil wet test tend to be more representative. The Prius is a slightly odd ball engine the peak compression is lower than most modern engines but it sustains peak compression for longer (I would love to see an in-cylinder pressure scope capture of a Prius engine) so I think your compression are ok
Not sure of the best way to test the coil on this car I think if it is a coil fault it will be the secondary arcing to ground which won't always show up in the primary.

My neighbors Prius was looked after by the dealer so I don't know the exact symptom apart from it was running poorly and had other random issues apparently the dealer lplugged into it saw a long list of fault codes and immediately tested the 12v battery.

Thanks for the reply
I think SD has videos on toyota four pin coil testing on celica or camary. Not sure which. would this be the same toyota cop four pin coil?
Thanks,
Elijah

Eli wrote: Thanks for the reply
I think SD has videos on toyota four pin coil testing on celica or camary. Not sure which. would this be the same toyota cop four pin coil?
Thanks,
Elijah

Testing would be the same. Pretty much all four pin Toyota coils are gonna work the exact same way, thankfully.

Honestly, though, I doubt this is something you'd catch by scoping the coil. Unless the fault is in the primary ignition circuit, you're very unlikely to see the fault in the current ramp or in the IGT/IGF signals. Toyota coils are very heavily shielded, which makes using a secondary probe impossible without a plug extension.

If you're suspicious of a coil problem, I think you've have much better luck swapping the #3 coil to another cylinder.