Fuse 22, help reading FSM wiring diagram

Hoping someone can help me understand the wiring diagram in the FSM? I keep blowing F22 fuse, which from what I can tell fuses A61 which has the fuel pump relay, but also via C107, pin 14, it could be blown by either O2 sensor.

My main question is whether this can also be blown somewhere else? On the other side of the fuel pump relay, of course we have the Fuel Pump itself, which seems to be a candidate, but the dashed line from C100 over to what appears to be the combo flasher. What is this dashed line? Can it blow F22?

Any other ideas? Another note, the fuse blows if I just start the jeep and let it sit there. Sometimes 5 minutes, sometimes 30 minutes. The O2 sensors are brand new and I checked all their wires under the truck, nothing seems to be rubbing.

I am on page 8W-10-31 of the 1999 FSM

fuse 22 (15a) is for the fuel pump. for the 4.0l and also supplies 12v to pin A22 of the PCM


AFA the dashed lines go, typically there will be a notation stating another engine, transmission or trim package. So it is likely a routing that is used for the 2.5 engine that you are seeing.

For clarity, I'm using michell's diagrams... which will have any corrections that were made after the fact.

Digger87xj said:

For clarity, I'm using michell's diagrams... which will have any corrections that were made after the fact.

Click to expand...

WTF are mitchell's diagrams?

The reason why I got my heep so cheap was because it was having that exact same issue, it would blow that fuse at the most random times. the previous owner put a new ecu and a fuel pump in it and it still didn't fix it. One day I was helping my boss move something and in backing up his driveway the fuse blew. When I went to put another fuse in it blew that fuse instantly as well. so hooked up a test light (a spare headlight bulb) and unplugged the ecu and the fuel pump. No change, so I started moving the engine harness around and I had found the harness had slipped below the fuel rail and had been chaffing against it and it ended up chaffing into the dark green with black that supplies constant power to the ecu. I put the harness ontop of the fuel rail and it hasn't popped a fuse ever since.


As for the dashed line in the FSM, that denoted that other circut is in the C100 connector as well.

MoFo said:

WTF are mitchell's diagrams?

Click to expand...

Seems like this probably:
http://www.eautorepair.net/Marketing/html/wiring_diagrams.asp?VID=&Count=Y

sidewaysstarion said:

The reason why I got my heep so cheap was because it was having that exact same issue, it would blow that fuse at the most random times. the previous owner put a new ecu and a fuel pump in it and it still didn't fix it. One day I was helping my boss move something and in backing up his driveway the fuse blew. When I went to put another fuse in it blew that fuse instantly as well. so hooked up a test light (a spare headlight bulb) and unplugged the ecu and the fuel pump. No change, so I started moving the engine harness around and I had found the harness had slipped below the fuel rail and had been chaffing against it and it ended up chaffing into the dark green with black that supplies constant power to the ecu. I put the harness ontop of the fuel rail and it hasn't popped a fuse ever since.


As for the dashed line in the FSM, that denoted that other circut is in the C100 connector as well.

Click to expand...

I have read a lot about this, there are a lot of really random things that can blow this fuse. Different components, or wire harnesses in multiple places in the vehicle shorting to ground. I am also getting a P1694 code along with the fuse blowing.

I am not looking forward to this, especially since I am moving to Nashville in less than 2 weeks

Re: Re: Fuse 22, help reading FSM wiring diagram

MoFo said:

WTF are mitchell's diagrams?

Click to expand...

WildcatRider said:

Seems like this probably:
http://www.eautorepair.net/Marketing/html/wiring_diagrams.asp?VID=&Count=Y

Click to expand...

Close. www.prodemand.com ... the professional subscription of michell1.

WildcatRider said:

Hoping someone can help me understand the wiring diagram in the FSM? I keep blowing F22 fuse, which from what I can tell fuses A61 which has the fuel pump relay, but also via C107, pin 14, it could be blown by either O2 sensor.

My main question is whether this can also be blown somewhere else? On the other side of the fuel pump relay, of course we have the Fuel Pump itself, which seems to be a candidate, but the dashed line from C100 over to what appears to be the combo flasher. What is this dashed line? Can it blow F22?

The dashed line indicates that the Combo Flasher goes through C100 as well, pin F5.

Unless your XJ has been submerged and water soaked C100 (and C200 for that matter), I wouldn't focus on that connector(s) at this time. Nor would I suspect the O2S' at this time.

Any other ideas? Another note, the fuse blows if I just start the jeep and let it sit there. Sometimes 5 minutes, sometimes 30 minutes. The O2 sensors are brand new and I checked all their wires under the truck, nothing seems to be rubbing.

As you mentioned in your last post, you would indeed get a P1694 if F22 blows because it is the main B+ feed to the PCM (through PCM C1, pin A22). Collateral damage.

As you see in 8W-10-31, A61 taps power from the Battery Bus off the FP relay, pin 30 (D2), on its way to the PCM. I'm assuming that F22 doesn't blow with the engine not running so I would think that the A61 circuit to the PCM is not shorted to ground.

With the engine running, it's obvious the FP relay has been activated and power is flowing to the FP. This is the circuit in question.

The way I would check this circuit is to fabricate a jumper switch rated at least to 15 Amps, remove the FP relay, and jump the FP relay socket from pin cavities 30 (D2) to 87 (D8) and see if F22 blows. If so, detach the FP connector and try it again. If it doesn't blow, the pump is bad, if it still blows, the short is between FP relay 87 (D8) and the FP connector.

In the past I've checked my FP by doing this jumping with a switch and a 10 Amp fuse in F22 to do the FP Amperage test instead of using a DRB, as the FSM states.

I am on page 8W-10-31 of the 1999 FSM

Click to expand...

The FP circuit is also in section 8W-30.

Here's a pic of jumping the FP relay socket with a 15 Amp On-Off switch.

Great posts, thank you! I am not sure if I will get to this before I move, but I will definitely post back with the results.

Been a while, but I just had my first free weekend since I moved a few months ago. I blew about 20 fuses before I decided to work a little smarter. Through my poor troubleshooting, I did determine that the short was intermittent. I blew a bunch of fuses without the fuel pump even connected, so I ruled that out.

Once I got smart, I disconnected the fuel pump, removed the fuse, put a test light in place of the fuse. This way, a short to ground will cause the light to be on, if the short is removed, the light will go off. I read through the FSM and wrote down the exact path with connector locations of the related circuits and just started following the wires and wiggling everything along the way.

Discovered that there was a short being caused by the bracket holding the connector end of the Crank Angle Sensor, it was rubbing against the harness right where it takes a 90 degree turn to go through the firewall near the center/driver side of the engine bay.

As soon as I separated the two and put some tape around both sides to protect it, the Jeep started right up for the first time in almost 3 months. Drove it around the neighborhood a few times with no problems.

Sadly today, I made the mistake of trying to drive it to work. The fuse blew in the middle of a busy intersection halfway to the office. Luckily I had thrown the box of fuses in the Jeep before I left, so after blowing the first replacement, I was able to wiggle the harness a bit and get back home to swap vehicles.

Back to the drawing board on how to put a more permanent repair in place, but it seems like it is probably either grounding out inside the harness where the cut was, or at some other point.

I'd start by stripping all the tape off the harness at that point, reinsulating and/or resplicing any damaged wires, then rewrapping the harness. And bend over anything that's cutting into the harness or move the harness out of the way and remount it.

iirc the same circuit also runs the o2 sensor heaters (if it's the one that powers the alt field coil, injectors, ignition coil, ECU, etc... that is the one) so check to make sure the harness to the rear o2 sensor and VSS isn't getting crushed between the tranny/tcase and the trans tunnel or (what happened to me) hasn't come disconnected from its mounting points and fallen onto the rear output shaft of the transfer case, which wears through the insulation and intermittently grounds it out.

Hopefully the final update on this. I found that one of the looms coming from the PCM which was zip tied to the place I thought was causing the problem was grounding out on the fuel rail. The loom had rotated and separated in such a way that allowed the wires to rub on the fuel rail, and it rubbed through the insulation on a green wire (maybe green/red? This was like 10 days ago). I managed to cause sparks to fly out and the fuse to blow, so it was easy to find after that.

Just lucky I didn't start a fire I guess.

Green/red or green/orange (can't recall which) is power from the fuse for the ASD relay and fuel pump relay to most of the engine control system, so that makes sense. It's the circuit I mentioned previously, I remember that much.