If you have to disable the alternator in order to increase the engine RPMs to beyond a certain point then either the alternator or the voltage regulator has a problem.
I’m the OP , in my case # 4 injector shorted out & fried the # 4 injector driver in the PCM . I replaced the injector & PCM & solved my problems . I still have no idea what the alternator had to do with it but after replacing those parts everything’s fine .
I havent messed with it to much figured I could get the op to tell me what he did to fix his. But if you first start it and rev it up past 2k it will go all the way to rev limiter but then as soon as you let t go back under 2k its like the ecu lowers the revlimiter to 2krpm illgrab a voltmeter tomorrow and see what it reads
Just sent you an email .
Along with checking the DC voltage at 2k RPM, check the AC voltage also. It should be less than .1 volt.
I still have no idea what the alternator had to do with it
Maybe when the engine computer sees the alternator not working it enters some kind of “safe mode” and whatever that mode does, likely it ignores certain sensors it normally pays att’n to, it somehow masked the injector/ecu problem that was preventing the engine from exceeding 2000 rpm. Sort of an unintended consequence of letting the engine-computer rule the roost.
Hi dear, i ve got the same issue with my jeep. When i disconnect the alternator i can rev above 2000 but when i connect i get the same code for injector 4 and oxygen sensor. Tried every thing but nobody can figure out the actual problem.
I would be curious to know what the charging voltage is at the battery when the alternator is connected and the engine running at the limited 2000 RPM. What the DC and AC voltage readings are.
Since you are getting a code for # 4 injector this is what I would do first . Unplug the wires on # 4 injector & plug a noid light into those wires . If the noid light flashes with the engine running the pcm is sending the ground signal to fire that injector & battery power is being supplied to the injector . There are 2 wires that plug into the injector . 1 of those wires provides power from the battery to the injector all the time when the ignition is on . The other wire is an intermittent ground sent from the pcm to fire the injector .
If the noid light doesn’t flash with the engine running , either there’s no power from the battery on 1 of the wires or no ground signal from the pcm on the other wire . If there’s no power on the power wire it’s very likely it’s a defect in that wire & not a battery problem . If there’s no ground signal on the wire going to the pcm it could be either a defect in that wire or a pcm problem .
I took ohm readings on several injectors including # 4 & found all injectors except # 4 read very nearly the same . # 4 gave me a vastly different reading than the others . After saying all this , take ohm readings on several injectors & see if # 4 is different than the rest & plug a noid light into # 4’s wiring connector & see if the light flashes .