High RPM Misfire

My 99 (4x4, Automatic, 5VZFE engine)Tacoma has developed a misfire at high RPM that limits it to about 4300 RFP. It ONLY happens when the engine is warm and occurs under any engine loading condition (in Park, pulling a load, going downhill with no load, etc). There are NO engine codes. I have changed the plugs, plug wires, coils, PCV valve, fuel filter, air filter, gas types, etc. The dealers have NOT been able to isolate the problem and found no problems with fuel pressure. They offered to "experiment" by replacing the computer, fuel pump, or "other" components. I don't want to pay for anyh more of their play time. When cold the engine will rev to red line with no problem but once warm it misfires. I have even exchanged the plugs, coils, etc with another 5VZFE engine and mine continues to misfire with the "new" parts while the other engine functions properly with my "suspect" parts. Any suggestions????

 

Do you have points and have you checked under the distributor cap lately. What is the milage on the 2 trucks is it close to the same.

 

No points, no distributor cap. Both engines have about the same mileage.

 

you want to make this hard. Have you checked to see if its from one cylinder or random cylinders.

Check your injectors might be dirty

 

Cannot isolate the problem to a single cylinder. Disabled each one in sequence by disconnecting plug wire/coil connector. No clear difference in the overall performance in any once cylinder (of course, the engine ran badly with a plug disconnected). The dealers' computers could not isolate it to a single cylinder either. They did confirm that fuel pressure remainded adequate (don't remember the figures) when the problem occurred. I would think a clogged injector would perform about the same whether warm or cold. By "warm" I mean the engine has to run at least 10 minutes at highway speeds before the "miss" occurs. Thanks for the suggestion....other ideas?

 

How old is your cat and is it getting very hot. If its getting very hot it could be getting pluged up could be causing issues when its getting hot. The o2 sensors reading the exhaust wrong but i think that would set a check engin light. Have you gotten any codes read yet cause with the miss fire it should set a check engine light

 

I can't tell the difference in the temperature of the cats in the two trucks (the one that is misfiring and the one that runs normally). I will see if I can find a way to measure them. There are NO engine codes. I had two dealer repair shops check when they were "experimenting" with repairs. There were no codes either before the misfires happened (while the engine was cold) and after the misfires (once it warmed up). Thanks again for the suggestions. I will work the cat temp now........

 

What brand of plugs did you put in?

 

Currently using Denso but have tried NGK and others.....no change. I pulled nearly new Denso plugs for a similar engine with no problems and put my "suspect" plugs (and wires, and coils, etc) on the "good" engine. The result was that mine still missed at high RPM and the other engine with "suspect" parts ran fine. Beginning to think it is the ECU but need to do more work to check that out. Thanks for the suggestion......

 

yea you might want to swap ecu that would help with ut spending 1500 bucks for a new one you dont need

 

Thanks AudiTech. Will do the ECU swap and check the cat temp. My company sent me to the Middle East for a couple of weeks so my troubleshooting has been put on hold until I return. The folks on this forum have been very helpful. Will update when I get back to the States.......

 

be safe

 

JMtrap. sorry to resurect a old post. But man I am banging my head on the wall. I have changed everything under the sun and still a high rpm miss. Bout to pull my hair out... So, did you ever find a solution? I have the exact same dang problem and am to a point of having to buy a new computer just to try it but wont be able to send it back :-(

Any ideas?

 

Unfortunately he has not been in 5 years going on 6 now sorry dude

 

Just getting back from 5 years in Saudi Arabia. Truck survived being stored that long. My misfire turned out do be a crack in a vacuum line. Sorry I don't remember just which one it was. $2 worth of rubber hose ended the problem!

 

Lol, thanks for coming back and verifying the repair!

 

WOW, Thanks for coming back. Well I'm well over a thousand$$$ now...

So, maybe I'm crazy but I was thinking a vaccum issue would become less of a problem at higher RPMs so I've somewhat ignored it... Am I nuts? I thought you'd see the vaccum issues at the lower RPMS???

I'm bout ready to set it on fire

 

Check all the vacuum hoses as he mentioned, just to be safe. After that the way we always zoned in on a potential cylinder was to use a scope and check the Kv on the coil wires. If memory serves me correctly, the 5VZ uses a waste spark system, so you should be able to narrow down the misfiring cylinder IF it has anything to do with spark. Once you rule that as the failure or still good, then you can go from there. I have seen poor grounds cause some strange things like you have mentioned as well.