P0301 when hot

[Brian1973]

Seems I'm getting a misfire on #1. Last fall, swapped coils around and replaced wires and that seemed to fix it... A few weeks ago it ran fine for a 500 mile trip. Last week the truck did go about 30 miles fine and then for the last 2-3 miles of my trek, started missing when it first showed up again after a few months. The problem usually pops up the flashing CEL and P0301 code on the scangauge II.

So, this time, after swapping coils around, does not seem to phase it as it seemed to the other time. I also checked fuel injector resistance and all 3 on passenger side are around 15 ohms. Pulled #1 plug and it looked fine, no carbon tracking or anything looking wrong. New plugs just a couple months ago when mechanic did timing belt job, as well as new crank and camshaft sensors for other issues... I believe I replaced the downstream 02 sensor 2-3 yrs. ago when I replaced muffler system from cat back... Just thinking out loud. Soooo, currently, the truck starts fine after cold, and seems to run fine for saaaaay, a ride to the local grocery store (don't use truck every day)... but come back to the truck and start it and the misfire is there! Seems related to being warmed up and restarting truck? 200k+ miles.... Ideas?

 

[JayRolla]

Seems I'm getting a misfire on #1. Last fall, swapped coils around and replaced wires and that seemed to fix it... A few weeks ago it ran fine for a 500 mile trip. Last week the truck did go about 30 miles fine and then for the last 2-3 miles of my trek, started missing when it first showed up again after a few months. The problem usually pops up the flashing CEL and P0301 code on the scangauge II.

So, this time, after swapping coils around, does not seem to phase it as it seemed to the other time. I also checked fuel injector resistance and all 3 on passenger side are around 15 ohms. Pulled #1 plug and it looked fine, no carbon tracking or anything looking wrong. New plugs just a couple months ago when mechanic did timing belt job, as well as new crank and camshaft sensors for other issues... I believe I replaced the downstream 02 sensor 2-3 yrs. ago when I replaced muffler system from cat back... Just thinking out loud. Soooo, currently, the truck starts fine after cold, and seems to run fine for saaaaay, a ride to the local grocery store (don't use truck every day)... but come back to the truck and start it and the misfire is there! Seems related to being warmed up and restarting truck? 200k+ miles.... Ideas?

The injector resistance will only be low if the injector is misfiring at that time. I just had the exact issue as you and it was the #1 injector. When running fine the injector passed ohms test. I stopped one day when it was misfiring and ohm test failed.

I bet your #1 injector is failing. I bought 6 OEM cleaned injectors with all new o-rings for $60 on ebay. Been running great since swapping all 3 injectors on passenger side.

 

[Buckaroo]

Another forum member verified a bad injector that was only failing at operating temp by putting it in a toaster oven and then checking resistance - good at room temp and failed at operating temp.

Buckaroo

 

[LittleCaesar]

One has to ask how the coolant level is?

I'd remove the plug and see how it looks.

 

[Brian1973]

JayRolla, Thanks for the input! That makes perfect sense. I did test it prior to running the vehicle up to operating temp so I'm hoping to test in next 24 hrs after it starts it's shenanigans! Great aha moment! Hope that's it!

Buckaroo, great idea.... as long as you don't BAKE the injector, haha. Seeing as I'd have to remove the throttle body to remove and test, I think I will just try JayRolla idea and run her until she misses and test... then when I know for sure, can order some reman'd or new injectors (have opinions on that?). Probably just get 2 and replace the bad one and have a spare for jic? They normally shouldn't go bad I thought? Will weigh whether to replace the oem that are working fine after I start shopping fuel injectors I guess. Suppose could just replace the 3 on the passenger side since that is easiest.

Little Caesar, coolant level is fine... however before having timing belt replaced, water pump was leaking and I was refilling with water last fall... A few times temp got a little high before I could refill but never redline. Watched temp on scangauge II as well. Perhaps that may have had something to do with initial occurrence but I'm thinking probably not? I did have a P0125 in codes at one point when it was missing and believe that points to an ECT sensor... Sooooo I'm keeping that in mind but it has not shown up again after the one time... Think the ECT sensor is behind the timing belt cover and is merely a $20 part.... related to a misfire? dunno.... I did pull plug as mentioned in OP. Seemed fine. Now I feel like pizza!

Thanks for all the input, will be back with follow up shortly!

 

[Buckaroo]

Lots of discussion on this forum about counterfeit injectors off ebay so take care. I removed all my OEM injectors and sent to Witchunter.com to be flow tested, cleaned and rebuilt. Very cost effective.

Buckaroo

 

[Brian1973]

Solved - As JayRolla stated... checked after the misfiring and #1 injector had no resistance.

I "second" the junk that can pop up on fleabay. I usually do a search thru rockauto of some respectable parts and then find on ebay or amazon...

Wonder if there is more heat near #1 injector that causes it to fry? Seems #1 is the majority of issues for folks...

 

[Brian1973]

Seems Witchhunter.com is more for flow problems? Seems my issue is electrical in the injector? Would they just tell me I will have to buy a new one? Seeing as turn around time will take over a week, probably try a 3 injector set and send out the originals if they can fix the resistance problem?

 

[Buckaroo]

The bad injector is toast - needs replaced. Witchhunter would rebuild/clean the other five. About a year ago, when I had the same problem as you, had the five rebuilt and he sold me a used rebuilt/cleaned OEM injector for $35 which matched up with their flow rate. You could inquire if that would be an option for you. Important that the six injectors have similar flow rates.

Buckaroo