89 4.0 cranks up with misfire after sitting all night and running super rich

[Hudy]

 

On 12/28/2021 at 1:08 PM, Ωhm said:

Couple of could be's.

Leaky Fuel Pressure Regulator (FPR). Check for fuel in vacuum line. Slow leak.

O2S Heater circuit. O2S is a maintenance item. Replace ≈87.5kmiles.

 

Did you check these items yet? My crank issue was the FPR. 

 

I was also running super rich until a couple days ago and found a faulty O2 sensor. Use an analog multimeter to measure the output. 

 

Dan 

[oleskool]

On 1/3/2022 at 10:20 AM, Hudy said:

 

 

Did you check these items yet? My crank issue was the FPR. 

 

I was also running super rich until a couple days ago and found a faulty O2 sensor. Use an analog multimeter to measure the output. 

 

Dan 

All have been checked and verified but for a disclaimer the truck has been running perfect for days with no cold start up issues what so ever haha.  I need it to have the issue again sadly to re-measure all the sensors with a voltmeter to better understand what is happening.  Right now everything checks out 100% good