P0300 (Random misfire) only after sitting a couple days **SOLVED**

[the walrus]

Hey guys,
282,000 miles on the clock now. Vehicle is very well maintained, new plugs, wires, timing belt, etc last year at 264k. I have the V6 auto 4WD.

I have noticed that if the truck sits for a couple days like over the weekend and I start it up it will run with an obvious misfire and throw code P0300 but no other codes. If I re-start the car a few times the misfire will stop and it runs smooth. Cleaned the MAF and TB but no difference. All coils tested fine and spark plugs look good. If I drive multiple times in the same day it doesn't do it, only after sitting a couple of days.

Thinking of testing injectors next.

What else should I look at?

Fuel pressure regulator?
Fuel pump?

Any other ideas?

Thanks,
Justin

**Appears to be resolved with new NGK wires and new OEM plugs. See post 18.**

 

[thegipper]

Are you losing any coolant? I would also check your oil and see if it looks milky or anything. My 97 was doing the same thing and it eventually got worse (started blowing white smoke out the exhaust).

Unfortunately, it was a failed HG on cylinder #3. What happens is when your truck sits for a few days, coolant pools up in the cylinder. When you start it, it will run rough and misfire until the coolant burns off. Once its warmed up, it will run fine if the leak is small.

You can do a leak down test to be certain, that is how I knew for sure my HG blew (air bubbles coming out of the radiator when I pressurized the #3 cylinder).

Lets hope its something else.

Good luck

 

[spartacus]

Hey guys,
282,000 miles on the clock now. Vehicle is very well maintained, new plugs, wires, timing belt, etc last year at 264k. I have the V6 auto 4WD.
Justin

You cleaned the maf also check the resistance should be 2.2 to 2.7 kilo ohms at 68 f and 0.5 to 0.7 kilo ohms., check camshaft and crank shaft connectors are secure and wires are in good shape, replace the the pcv valve and hose if not done for a while, check for vacuum leaks. engine coolant temp sensor could also cause this kind of issue by false temp input at startup.test the iac valve,engine idle should be around 750 rpm at idle. lean fuel could be a factor* so the next step would be to check the the fuel pressure could be the fuel filter. Now the more complicated stuff check the resistance on the injectors. valve clearance or timing might need adjustment or worse head gasket leaking coolant so a compression test. if you have obd scan tool you can look at the fuel trims at idle and at 2500 if the engine is running lean at idle only, then most likely vacuum leak could also be the cause of random misfire when cold.

edit: 0.5to0.7 kilo ohms at 140 f.

 

[the walrus]

Just checked coolant and oil. Levels and colors look good thankfully. No smoke out of the exhaust. I should let it sit for a couple days, pull the plugs and stick a camera down in there to check for presence of coolant or a really clean piston. That or do a leak down test.

Looks like I have some things to check out anyway.

 

[thegipper]

I would do a leak down test before you buy any parts. It doesn't take long and is pretty simple to do. If it all checks out, it will give you great peace of mind and you can do some other tests as stated above.

If there is a problem, you will have a much better understanding of what's going on and how to proceed.

Let's hope its something simple like a bad injector or something.

 

[Hockeyjock]

Have a leakdown done, and have coolant tested for signs of combustion.

 

[curryT4R]

Being that it's a P0300 code and not a singular cylinder misfire code, I am hard pressed to think it's a blown head gasket, but like others have said, go ahead and do a leak down test for the peace of mind. P0300 makes me think it's an issue for all cylinders, not just one, so i don't think it will be ONE injector, or ONE spark plug, etc.

 

[Hockeyjock]

Curry makes a good point. Generally speaking a p0300 will come with other individual cylinder codes. But it only happening after sitting still has me thinking head gasket. It’s possible the general vibration of the engine from missing is making the sensors not able to pick up which individual cylinder it is coming from.

 

[curryT4R]

Curry makes a good point. Generally speaking a p0300 will come with other individual cylinder codes. But it only happening after sitting still has me thinking head gasket. It’s possible the general vibration of the engine from missing is making the sensors not able to pick up which individual cylinder it is coming from.

Yeah you're absolutely right. From my experience P0300 is not a head gasket, but it doesn't mean it's not. Best to go through all the steps and be sure before throwing parts at it.

 

[the walrus]

More codes showed up.

Last night I was pulling onto the freeway and it was starting to misfire a bit, CEL blinked 3 times but then went off and ran ok the rest of the way home.

When I got home I pulled the codes and in pending faults it had P0300, P0303 and P0304, so that's random misfire and misfires in cylinders 3 and 4. Honestly I was hoping for some more specific codes to show up so this is a good thing.

Oreillys does not rent out a leakdown tester so I have not yet done a leakdown test but I will do that soon. Also going to check injectors, re-check coils and MAF, crank pulley bolt for correct tightness, vac lines, etc.

Fuel filter and PCV were new as of a year ago. The tube from the PCV is original and slightly loose. I can see oil residue around it.

Interesting that it would misfire cylinders 3 & 4 as they are not on the same coil and obviously they are different injectors. I remember that when I did the timing belt and VC gaskets last year that one of the injector clips was loose so that could be a contributor.

 

[LittleCaesar]

How about the plug wires?

I am with Mike though with the leak down test being an ultimate litmus test of how well the engine is performing.

 

[the walrus]

How about the plug wires?

I am with Mike though with the leak down test being an ultimate litmus test of how well the engine is performing.

Plugs and wires were new a year ago. Plugs are OEM from the dealer. Plug wires were from Autozone.

I will do a leakdown test as soon as I can get a tester.

 

[LittleCaesar]

I would be nothing short of leary using plug wires from AZ. I would say either NGK or OEM wires through Amazon. I am thinking wires only because there hasn’t been any coolant loss nor do you see any white smoke billowing from the tailpipe.

Regardless, find the leak down tester. You must have access to a compressor to use such.

 

[the walrus]

I have a compressor so good there.

I should be able to test the plug wires for resistance as well, no?

 

[LittleCaesar]

Yes, but I would check more for looseness at all connectors as well. Also pitting in the insulation. If the CELs are intermittent, and not temperature based, then I would say wires.

 

[the walrus]

Yes, but I would check more for looseness at all connectors as well. Also pitting in the insulation. If the CELs are intermittent, and not temperature based, then I would say wires.

Man it would be great if it turned out to be something simple like wires.

I'll be sure to post whatever I find out.

Thanks,
Justin

 

[Hockeyjock]

Yea for your sake I hope my guess is wrong.

 

[the walrus]

I would be nothing short of leary using plug wires from AZ. I would say either NGK or OEM wires through Amazon. I am thinking wires only because there hasn’t been any coolant loss nor do you see any white smoke billowing from the tailpipe.

Looks like we have a winner. I put on NGK wires and OEM plugs from the dealer about 3 weeks ago and it hasn't misfired since. No more CEL or anything.

Even after sitting a couple days at a time over the weekend it fires right up. At least for now it appears that we may have this one in the bag.

Thanks very much for the assistance. :biggrin2:

Justin

 

[Hockeyjock]

NICE! Glad my guess was wrong!

 

[LittleCaesar]

Well I am glad I am right some of the time, though time will be the real test. Glad the new NGKs are working for you Justin.

Having done shade tree mechanic work for 25+ years, I have found that plug wires now made in China and sold through AZ, AA, and the like just don’t have a long service life. Plus the usuage of wires today has been replaced by coil on plugs, thus aftermarket stuff just doesn’t have the quality control and durability it used to.