Hot engine misfire

[JohnMc]

I had a single injector go bad, it would work when the engine was cold/cool/warm/normal temp. But if it got a little warmer than normal (like a hot summer day, A/C on, etc) it would stop working and run on 5 cylinders. Ran normally at other times.

I got another set of injectors from a 5VZ in a local PnP yard.

After trying a cheap set of 'new genuine OEM etc etc' injectors from eBay which were nice looking (seriously couldn't see any differences looking up close) they were crap. Poor cold start, rough idle, poor hot start. Clearly uneven injection amounts and leaking down. Luckily enough the eBay seller took them back.

 

[jorgecarbajal39]

My problem:

Cold start runs great, drive down the road, turn the vehicle off and then on again and I was getting P0301, cylinder 1 misfire. Like everyone I did everything and even tested the resistance on the injectors.

Solution:

When I tested the resistance on the injectors I had tested in when the engine was cold, today I decided to give another stab at trying to resolve this issue. This time the engine was warm. I pulled everything off and tested the resistance on each of the injectors. Sure enough the resistance on injector 1 was 226 Ohms!!! 10 min later 76 Ohms, another 5 min 46 Ohms. As the vehicle was cooling down the resistance was decreasing which makes sense, resistance increases with heat... physics. Anyway I am in the process of buying a full set of injectors for 100$ on FB marketplace. Ill throw some new seals on the one and see if this works (It most likely will).

Sorry for the length but I hope this helps someone with similar issues. Test resistance with warm vs cold motor.

 

[phattyduck]

My problem:

Cold start runs great, drive down the road, turn the vehicle off and then on again and I was getting P0301, cylinder 1 misfire. Like everyone I did everything and even tested the resistance on the injectors.

Solution:

When I tested the resistance on the injectors I had tested in when the engine was cold, today I decided to give another stab at trying to resolve this issue. This time the engine was warm. I pulled everything off and tested the resistance on each of the injectors. Sure enough the resistance on injector 1 was 226 Ohms!!! 10 min later 76 Ohms, another 5 min 46 Ohms. As the vehicle was cooling down the resistance was decreasing which makes sense, resistance increases with heat... physics. Anyway I am in the process of buying a full set of injectors for 100$ on FB marketplace. Ill throw some new seals on the one and see if this works (It most likely will).

Sorry for the length but I hope this helps someone with similar issues. Test resistance with warm vs cold motor.

In this case, hot stuff expands - and the bad connection internally starts to separate when warm. The change in resistance with temperature is MUCH smaller than you were measuring.

But one part is correct - if the issue you are having happens when hot, you have to diagnose/test when hot!

Motorwest has 'upgraded' injectors for the 5VZ - same flow, same air assist but from a newer Toyota. Worth investigating. That's what I did for mine before I put on the supercharger recently.

-Charlie