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- - Cold start misfire (https://www.toyota-4runner.org/3rd-gen-t4rs/282928-cold-start-misfire.html)

Cold start misfire

Hey guys,

Been a while haven't posted since my rig has been running good only a few small things. Recently I have been having an issue with cold start misfire.

Back information: previously had P0420 I cleaned my maf, code went and stayed away for almost two weeks now. Truck feels more responsive and running stronger. In that time I had to replace bottom radiator hose, it was slowly dripping making a mess. Swap was straight forward. I thought I was having an issue with air in the coolant system afterward, I've burped it twice since, truck ran for 25 minutes coolant temp didn't get up to 190, ambient temps in the 20sF thou so who knows. But I've checked coolant twice a week in the morning since and haven't lost any coolant (radiator filled leaving little room for expansion).

Now onto my recent issue: cold morning start, truck starts to misfire, only for a few seconds, then runs fine. It's been cold 20s so white smoke from exhaust is normal for me, old rusty NE truck could have small holes that aid in condensation making more white smoke not sure. But again I haven't lost any coolant. The truck also never overheats with longest drive 40-1 hr highway speeds which leads me to rule out head gasket. (truck has new head gaskets, rebuilt heads etc with less than 15k miles)

Pulled the codes this morning P0300, P0440, P0446, P0441.

I did search a bunch, leaning towards VSV but not sure. Looking for some advice. I plan on checking plugs and wires but both are relatively new 1-2 years old. Also MAF just cleaned no issues all wires intact when I cleaned and put back. Could coolant system have bubble? I do hear some gurgling from time to time inside cabin. I may have to try and smell exhaust for sweet coolant if I'm somehow getting coolant into my exhaust. Hope not.

Any insight greatly appreciated.

Thanks
Alex W

Quote:

Originally Posted by 4runnerWiniarski23 (Post 3441509)

What type of plugs and wires? If I may ask?

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If there is a steady miss you could start with the basics start with a spark plug inspection and then go to a compression test wet and dry. If you can isolate a cylinder maybe it's a bad wire plug or coil pack. If nothing at all you have ruled out some problems.:shrug:

Cold start misfire

The cold start missfire and the 420 code to me is antifreeze and you know what that means. Been there twice with two different 4Runners.

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Quote:

Originally Posted by 19963.4lsr5 (Post 3441862)

The cold start missfire and the 420 code to me is antifreeze and you know what that means. Been there twice with two different 4Runners.

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Oh no. I hope it's not the head leaking.

I know on the one I have it dosent misfire. However, the white mist will not go away. So I know I was leaking antifreeze into the head.

[ plus antifreeze got into the oil and I drain that out and flushed with motor oil]

Let's hope its something else. Like a bad plug or wire at or over 25k ohms. Causing the misfire..:)

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I would do a leak down test. Misfire on a cold start often is a failing head gasket.

The leak down test will 100% rule out or confirm if you have a bad HG. All you need is a decent air compressor and the leak down tester. Shouldn't take you more than 20 minutes or so to do the tests.

I had a cold start misfire on my original engine. I tried various tests to see if I had a bad HG (coolant dye tester, bore scope, pulled plugs, smelled exhaust etc etc). None of these tests confirmed I had a bad HG until I did the leak down test. Once I pressurized cylinder #3 (the cylinder with the misfire code), I saw bubbles came out of the radiator confirming my fears.

Good luck either way!

Wow, I had to look up some of those codes since they are so rare. Here's my assessment of each:

P0446 - Most likely the gas cap is leaking or not seated correctly. Just went through this with our Nissan Altima. Very rare code to pop up.
P0441 - Most likely the gas cap is leaking or not seated correctly. Also very uncommon to have this code.
P0440 - Hmm, another gas vapor code? Have you checked or replaced your gas cap yet?

This would also explain the stumble you get on cold startup. The gas cap seals the fuel tank so when the lines are pressurized by the pump, they can't drain back out once you turn the engine off. The fuel lines will hold their pressure until you go to start again. If the gas cap is leaking then instead it allows air to enter the tank which allows the fuel lines to drain out. When you go to start in the morning, the pump has to not only purge the air but also build pressure again. It takes around 5-10 seconds for it to do this. That's most likely your stumble.

The P0300 (multiple cylinder misfire) is probably the engine sensing that the injectors are injecting air, not fuel at startup. Replace your gas cap and clear the codes, they should not come back.