Making this post to save the headache that this issue caused me.
For the past 2 years I have had relatively good luck with my 91 land cruiser with 256xxx on the clock, but there has always been a nagging issue at the mid RPM range only when in gear. The truck would surge with a burst of power like I wasn't firing on all cylinders than all of a sudden I was and it would surge forward with power, but it really wasn't causing a problem in day to day driving
Fast forward to this month where I finally bit the bullet and decided to do my exhaust manifold gaskets and downpipe donut gaskets.
After the job was done and verified everything was plugged in, reconnected, smoke tested for vacuum leaks, etc. I took it for a test drive. New something was wrong immediately. Rev's in first were fine, shift to second fine, start to go through the powerband the truck fell on its face...no power....pressed more on the gas and still barely moving...truck shifted to third and was loping around missing like crazy at 35 mph and falling on its face sputtering. I shifted the lever to 2nd and went pedal to the metal and the truck lurched forward with full power? So lower RPM range good, mid RPM range terrible, high RPM range good?
Brought the truck back to the garage and verified everything that needs to be unplugged when doing the exhaust manifold was still plugged in and checked all injectors with a long screwdriver that I used as a stethoscope, then I started verifying all sensors and meters were in spec with a multi meter. Everything check out, AFM, IAC, TPS, coolant temp sensor for ecu, etc. Even start unplugging vacuum lines to make sure they weren't in the wrong place. Checked fuel pressure regulator with old one I had lying around. Unplugged each sensor one at a time taking test drives in-between, still NOTHING. Still couldn't figure it out.....Figured if I did exhaust manifold gaskets I might as well check the exhaust sensors as well....unplugged each o2 sensor, check engine light came on, took for test drive anyway.....THAT WAS THE ISSUE......the truck drove like brand new.......I had no check engine light prior to the unplugging the sensors?
Currently driving around with a check engine light on due the unplugged o2 sensors but I don't care cause I can actually drive the thing.....if I had to guess, my leaking exhaust manifold threw off the air/fuel ratio at the o2 sensor starving the truck of fuel due to fresh air entering through the blown out exh gasket. The ecu must have stored the data and didn't clear it when I started the truck after doing the gaskets and kept the same parameters OR the sensors are bad and this has been my problem for the past two years....
will keep updated, hope this helps someone!
For the past 2 years I have had relatively good luck with my 91 land cruiser with 256xxx on the clock, but there has always been a nagging issue at the mid RPM range only when in gear. The truck would surge with a burst of power like I wasn't firing on all cylinders than all of a sudden I was and it would surge forward with power, but it really wasn't causing a problem in day to day driving
Fast forward to this month where I finally bit the bullet and decided to do my exhaust manifold gaskets and downpipe donut gaskets.
After the job was done and verified everything was plugged in, reconnected, smoke tested for vacuum leaks, etc. I took it for a test drive. New something was wrong immediately. Rev's in first were fine, shift to second fine, start to go through the powerband the truck fell on its face...no power....pressed more on the gas and still barely moving...truck shifted to third and was loping around missing like crazy at 35 mph and falling on its face sputtering. I shifted the lever to 2nd and went pedal to the metal and the truck lurched forward with full power? So lower RPM range good, mid RPM range terrible, high RPM range good?
Brought the truck back to the garage and verified everything that needs to be unplugged when doing the exhaust manifold was still plugged in and checked all injectors with a long screwdriver that I used as a stethoscope, then I started verifying all sensors and meters were in spec with a multi meter. Everything check out, AFM, IAC, TPS, coolant temp sensor for ecu, etc. Even start unplugging vacuum lines to make sure they weren't in the wrong place. Checked fuel pressure regulator with old one I had lying around. Unplugged each sensor one at a time taking test drives in-between, still NOTHING. Still couldn't figure it out.....Figured if I did exhaust manifold gaskets I might as well check the exhaust sensors as well....unplugged each o2 sensor, check engine light came on, took for test drive anyway.....THAT WAS THE ISSUE......the truck drove like brand new.......I had no check engine light prior to the unplugging the sensors?
Currently driving around with a check engine light on due the unplugged o2 sensors but I don't care cause I can actually drive the thing.....if I had to guess, my leaking exhaust manifold threw off the air/fuel ratio at the o2 sensor starving the truck of fuel due to fresh air entering through the blown out exh gasket. The ecu must have stored the data and didn't clear it when I started the truck after doing the gaskets and kept the same parameters OR the sensors are bad and this has been my problem for the past two years....
will keep updated, hope this helps someone!