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...

Oh yeah, compression in all 6 cylinders is ~190-200psi

What do you think...?

Thanks
-stumbling in Texas

It is an injector. One of them is leaking after you shut the engine off. Open your hood before shutting the truck off and then turn it off and get as close to the intake manifolds as you can. If you have a stethoscope or some other listening device even better. You will hear something similar to a squirting sound. I had the same problem. Replaced everything including injectors and somehow got a bad injector.

That's not what I wanted to hear...

Before I tear into it again, does anybody know if a OBD scanner (more that a ScanGauge2) would help pinpoint the problem?

I'm not impressed with Toyotas missfire detection. I had a coil go bad on two occasions on my 97 and the 97 puppy hauler and both times no missfire code.

It took 35mph to get a code on my sr5. The puppy hauler never gave me a code.


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It does sound like an injector, but here's another possibility: the evap system. I had a similar issue, ended up being a hose going from the evap system into the throttle body had slipped off. Check those hoses to make sure ones not split or slipped off.

Good news (since I like banging my head against the wall), misfire happened again today at lunch after a 15 minute drive and a 20 'rest'. it was misfiring at hot startup and threw a code P0304 - which is the same cylinder as the broken electrical connector.

I'll try swapping the coils again, but I'll bet I'll be pulling the manifold again...

Thanks for the comments - I still would like to know if a shop with a scanner could see this sort of thing.

You guys were right, 2 bad 5-O motorsport injectors.

The long version is here... Injector wiring harness?

I suspected them all along but I gave them the benefit of doubt, figuring their quality control and the favorable reports I saw here, that chances were they weren't the problem. But they were.

If the problem crops up again I'll replace them all with OE

Thanks again

glad you g9t it fixed. good work trouble shooting. others will benefit from your experience.