winkosmosis
NAXJA Forum User
- Location
- Maui, Hawaii
The EE version made more sense. It sounds like the ECU is too smart for its own good
Sorry, I only have a '99 FSM. I'd assume '98 and '99 would have the same colors, but it's entirely possible that they're different. My wires were pretty burried in that loom and required some considerable digging around with a dental pick to pull them out of the bunch.
I did not use a new fuse in my wiring set up. The old relay retains fuse protection via the original circuit and the new relay gets it's fuse protection through the ST-RUN circuit that you tap into.
I believe I used either a 30 or 40 amp fuse, however it really doesn't matter as there is very little load being passed through it. I used the same size and type of relay as many of my other accessory circuits use so that I can carry fewer spares.
As an update for anyone interested in this thread, 4+ months later and this set up is still working perfectly for me. The fan still cycles on and off with the A/C, turns on and off at the appropriate engine temps, turns on and off with a flip of the switch, does not trigger any CEL's, does not blow fuses, no problems at all...
You're partially correct. The ECU does switch the relay on by grounding the terminal - but what you're missing is that the ECU will notice if you ground the same terminal by yourself. It'll throw a CEL saying that the fan relay is stuck low for some reason.
What this mod does is turn the relay on without forcing the ECU fan relay control wire to ground, so the ECU never realizes you're doing anything.
Interesting. My 98 fsm tells me the ECU will trigger a CEL. Another strange bit of info - looking at my fsm wiring diagrams, my wiring harness matches that of a 2.5L. I have a 4.0. This only pertains to the fan wiring, I haven't checked for any other differences.
I tried the simple grounding of the wire, and it threw a code. I used a relay (NO/NC) to open the PCM side and ground the relay side, to prevent that, but it would still throw a code when the PCM wanted to run the fan. I gave up as the cold weather arrived. I've read numerous posts on other forums where guys said this mod (the simple grounding of the wire, not fyrfytr's variation) didn't throw a code on 97+ Jeeps, but that wasn't my experience.
So it doesn't throw a code when you have the fan forced on, and the AC on? I just assumed (don't know why I never bothered to check) that it watched the voltage/grounds of the entire fan circuit, not just the wiring between the PDC and PCM. I need to tear into the dash again soon- I might just try that.
My info says this is wrong, extended idle is just a switch that grounds a pin on the ECU when the switch is turned on. The ECU uses this to change its idle RPM setpoint from 750 to 1000 and turn the fan on when required. Covered in section 14 and wiring schematic on page 8W-14, at least in the '98 FSM. If you ground pin A12 in C1 (connector 1) of the ECU wiring harness on any 4.0L XJ this should be enabled.When I installed my relay I cut the blue ground wire at the fan and pigtailed a wire to terminal 87 and connected it to the other end of the cut blue wire going to the fan motor. Then attached another wire to terminal 87a and then to ground. Wired in the relay to actuate by grounding the relay coil with a toggle switch on my center console. this seup has worked flawlessly for many years with no codes thrown. When grounding the wire from ECM to the PDC relay this is something similar to what the Police Dept XJs have with the additional (4th) switch on the bezel beneath the climate controls in which there is also an additional relay to also actuate the IAC to increase RPMs during prolonged idling with the A/C on. I researched this modification many years ago and then consulted a well respected local Jeep dealer tech to verify my findings were correct.
My info says this is wrong, extended idle is just a switch that grounds a pin on the ECU when the switch is turned on. The ECU uses this to change its idle RPM setpoint from 750 to 1000 and turn the fan on when required. Covered in section 14 and wiring schematic on page 8W-14, at least in the '98 FSM. If you ground pin A12 in C1 (connector 1) of the ECU wiring harness on any 4.0L XJ this should be enabled.