1994 ODB1
O2's, FPR, Plugs, Leads, Coil, Dissy cap & rotor are all less than 1 year old
No EGR or PAIR. Throttle body and intake manifold recently removed and cleaned.
All vacuum lines are new OEM
PCV lines are new.
O2's relocated into manifold
Background - You can skip this and go to the main event
Since last October I have had a code 25 (Constant Lean) which I have been trying to fix. I have followed the FSM to the letter. Troubleshooting pointed towards the O2 sensors. These are OEM and less than a year old. In any case @beno sent me a replacement set which didn't clear the fault. The FSM says to measure the voltage at VF2 and then you from there with the troubleshooting flow chart. I have done all of this including changing out the ECU. None of the steps resolved the Code 25 or the 0 volts on VF2 (O2 Signal wire). The only troubleshooting step left was to check the wiring for the O2. I did a continuity check on the wires and everything was fine. Yesterday I decided to try a new, shorter cable.......
RTH Needed For This Part
Yesterday I decided I was going to rerun the O2 signal wire (OX2) since it was still it original length from when I relocated them. I peeled back the main harness insulation as far as is shown below.
I also disconnected the harness at the ECU and the 3 terminal blocks next to the ECU that are part of the engine harness. That end of the harness was pulled through the firewall so I could work with it all in the engine bay.
I traced the blue signal wire to the disconnect further up the harness, cut the wire and spliced in a shorter piece of shielded wire. This in effect got rid of all the cable that was previously routed over the transmission tunnel reducing the circuit to around 18". I also did the same to the OX+ wire but left the 2 remaining wires..
I re-wrapped the harness, fed it back through the firewall and reconnected the terminals and the ECU.
When I fired her up she started as usual and for the first time in 8 months I was able to confirm the #2 O2 sensor now had a signal (Hurrah).
Took her for a test drive only to find she has very heavy stumbling and a misfire. She is pretty much undrivable.
This morning I pulled the harness back into the engine bay, removed the cable wrap and checked every wire - feeling them, wiggling them etc but nothing changes how the truck idles or runs.
I should mention that the idle is rough but nowhere near as bad as it is when she is in Drive.
I have checked as much as possible that all voltages at the ECU are per FSM values. I also do not have a code (CEL Works)
I am at a loss right now - I only messed with short piece of harness. What could I possibly have disturbed that would cause this sudden bad running?
O2's, FPR, Plugs, Leads, Coil, Dissy cap & rotor are all less than 1 year old
No EGR or PAIR. Throttle body and intake manifold recently removed and cleaned.
All vacuum lines are new OEM
PCV lines are new.
O2's relocated into manifold
Background - You can skip this and go to the main event
Since last October I have had a code 25 (Constant Lean) which I have been trying to fix. I have followed the FSM to the letter. Troubleshooting pointed towards the O2 sensors. These are OEM and less than a year old. In any case @beno sent me a replacement set which didn't clear the fault. The FSM says to measure the voltage at VF2 and then you from there with the troubleshooting flow chart. I have done all of this including changing out the ECU. None of the steps resolved the Code 25 or the 0 volts on VF2 (O2 Signal wire). The only troubleshooting step left was to check the wiring for the O2. I did a continuity check on the wires and everything was fine. Yesterday I decided to try a new, shorter cable.......
RTH Needed For This Part
Yesterday I decided I was going to rerun the O2 signal wire (OX2) since it was still it original length from when I relocated them. I peeled back the main harness insulation as far as is shown below.
I also disconnected the harness at the ECU and the 3 terminal blocks next to the ECU that are part of the engine harness. That end of the harness was pulled through the firewall so I could work with it all in the engine bay.
I traced the blue signal wire to the disconnect further up the harness, cut the wire and spliced in a shorter piece of shielded wire. This in effect got rid of all the cable that was previously routed over the transmission tunnel reducing the circuit to around 18". I also did the same to the OX+ wire but left the 2 remaining wires..
I re-wrapped the harness, fed it back through the firewall and reconnected the terminals and the ECU.
When I fired her up she started as usual and for the first time in 8 months I was able to confirm the #2 O2 sensor now had a signal (Hurrah).
Took her for a test drive only to find she has very heavy stumbling and a misfire. She is pretty much undrivable.
This morning I pulled the harness back into the engine bay, removed the cable wrap and checked every wire - feeling them, wiggling them etc but nothing changes how the truck idles or runs.
I should mention that the idle is rough but nowhere near as bad as it is when she is in Drive.
I have checked as much as possible that all voltages at the ECU are per FSM values. I also do not have a code (CEL Works)
I am at a loss right now - I only messed with short piece of harness. What could I possibly have disturbed that would cause this sudden bad running?
