P0301 misfire, replaced "everything", still a misfire, but no CEL...what next?
Howdy, I've been lurking and using the search function for the last year when I got my 1999 4wd/AT/v6/SR5/200K miles. I love the truck, and this is a great forum, I haven't posted much because just about everything has been asked and answered before, and the search function works well.
This one is getting me down though...
After 1 year of ownership, I still love my '99 SR5, it's a great mule, but a couple weeks ago I got the dreaded intermittent misfire P0301...
The misfire occurs only after the truck has been driven a while (hot), then is parked for 10-30 minutes, then restarted. It's definitely hitting on only 5 cylinders.
When it's not misfiring, it runs great. Starts easy, idles smooth, accelerates like new, basically nothing wrong with it most of the time, it's only after a good heat soak that it misfires. If I give it a little time, ~30+ minutes, it acts normal again.
So far I've replaced/installed...
3x new coils Toyota/Denso
6x new sparkplugs Denso
1 set new plug wires NGK
1 new MAF sensor Denso
6x reman. injectors from Five0motorsport
2x new O2 sensors Denso
Not related but because I want to get another 200K out of this truck...
2x Upper & 2x Lower balljoints - Toyota
2x Outer Tire rod ends - Toyota
1x Reman A1 Cardone steering rack w/inner TRE's
etc, etc
Before I replaced parts I was getting a CEL and the P0301 code. On a hunch, when it misfired I poured a little cold water on injector 1 while it was running, the misfire would clear up.
3 times I did this and I was convinced it was an injector. fiveOmotorsport is well liked around here so I took the plunge on all 6. I checked them on the bench at ~16ohms each, all my originals were 18+ ohms, which is just a little over spec.
I hit the originals with a heat gun to get them closer to operating temp and they were all ~21-22 ohms. All, I was hoping for 1 to stand out as a culprit, none did.
Now after all these new parts I can tell the motor is running more smoothly, and hopefully more efficiently, but the same problem persists.
And I'm NOT getting a CEL.
I'm at a loss for what to do next.
A couple of possible culprits come to mind...
One - Maybe a vacuum leak, but I can drive 100 miles without a problem, so long as I don't turn the motor off, that just doesn't make sense to me, it would run like crap more often - I think.
The other - One of the female injector connectors on the wiring harness broke it's locking tab. I didn't repair it while I was in there, but I zip-tied it in place so it can't move. This could maybe be a problem, but I would think the problem would be more random, rather than just after a good heat soak.
I'm about ready to throw in the towel and take it in...<shudder>
Oh yeah, compression in all 6 cylinders is ~190-200psi
What do you think...?
Thanks
-stumbling in Texas
Howdy, I've been lurking and using the search function for the last year when I got my 1999 4wd/AT/v6/SR5/200K miles. I love the truck, and this is a great forum, I haven't posted much because just about everything has been asked and answered before, and the search function works well.
This one is getting me down though...
After 1 year of ownership, I still love my '99 SR5, it's a great mule, but a couple weeks ago I got the dreaded intermittent misfire P0301...
The misfire occurs only after the truck has been driven a while (hot), then is parked for 10-30 minutes, then restarted. It's definitely hitting on only 5 cylinders.
When it's not misfiring, it runs great. Starts easy, idles smooth, accelerates like new, basically nothing wrong with it most of the time, it's only after a good heat soak that it misfires. If I give it a little time, ~30+ minutes, it acts normal again.
So far I've replaced/installed...
3x new coils Toyota/Denso
6x new sparkplugs Denso
1 set new plug wires NGK
1 new MAF sensor Denso
6x reman. injectors from Five0motorsport
2x new O2 sensors Denso
Not related but because I want to get another 200K out of this truck...
2x Upper & 2x Lower balljoints - Toyota
2x Outer Tire rod ends - Toyota
1x Reman A1 Cardone steering rack w/inner TRE's
etc, etc
Before I replaced parts I was getting a CEL and the P0301 code. On a hunch, when it misfired I poured a little cold water on injector 1 while it was running, the misfire would clear up.
3 times I did this and I was convinced it was an injector. fiveOmotorsport is well liked around here so I took the plunge on all 6. I checked them on the bench at ~16ohms each, all my originals were 18+ ohms, which is just a little over spec.
I hit the originals with a heat gun to get them closer to operating temp and they were all ~21-22 ohms. All, I was hoping for 1 to stand out as a culprit, none did.
Now after all these new parts I can tell the motor is running more smoothly, and hopefully more efficiently, but the same problem persists.
And I'm NOT getting a CEL.
I'm at a loss for what to do next.
A couple of possible culprits come to mind...
One - Maybe a vacuum leak, but I can drive 100 miles without a problem, so long as I don't turn the motor off, that just doesn't make sense to me, it would run like crap more often - I think.
The other - One of the female injector connectors on the wiring harness broke it's locking tab. I didn't repair it while I was in there, but I zip-tied it in place so it can't move. This could maybe be a problem, but I would think the problem would be more random, rather than just after a good heat soak.
I'm about ready to throw in the towel and take it in...<shudder>
Oh yeah, compression in all 6 cylinders is ~190-200psi
What do you think...?
Thanks
-stumbling in Texas
