YJ will not rev past 3500rpms ????

[67bbc]

1067303

I need some help...my 91 YJ, 2.5l fi, will not rev past 3500 rpms and then sputters at that range?? I am not sure, so I changed a few sensors and ciol with no luck. It also is idleing rough. I also cound not find any vaccum leaks. Anyone have any ideas???? Timing chain??? :-? :-? [addsig]

 

[dingus]

1067322

my XJ did that when i unplugged some box under the dash, but i would have no idea as to how to diagnose something like this...[addsig]

 

[MudderChuck]

1067333

High speed miss is often ignition related, when it craps out totally it´s usually fuel related (or crank position sensor or distributor pickup). Sensors are expensive (can also cause ignition problems), but before changeing any, I usually check my ignition system for good function.
Plug wires are always a good place to start, take one good cable and replace each cable one at a time (with the motor off) see if it makes a difference. Take a look at the plugs and check the gap. Take a look in the distributor cap for corrosion, carbon tracking and wear. Unplug all the related connectors, coil, distributor, spark plug, distributor cap plug and sensor and check for moisture and/or corrosion in the connector (takes very little of either to mess things up). Sensor connectors use very low voltage, WD40 or equivilant will mess them up, as will oil.
Before changing a suspect sensor, such as 02, MAP, throttle position or with the TBI idle motor, I unplug them just to see if there is a difference. Unplugging the distributor pick-up or the crank position sensor will stop the engine. But I have seen oil in the distributor pickup plug that caused problems, with starting and missfires.[addsig]