Fuse trouble after water misting

[Taylor]

This is a 96 jeep grand cherokee with a 4.0. Well I blew a fuse like two months ago it was a 20 amp, but when blown the fuel pump comes on to prime as normal but doesnt turn off and vehicle wont start. so i traced down the fuel pump wires and right before the connector two wire were exposed. I fixed that and all was fine, well today I misted water in my intake, I noticed water "puddling" in the indentations in the intake boot. I then decided to switch to the brake booster line also due to sensors on the TB. all was good then i was driving down the road and my jeep just shut down in the middle of traffic. well it was this fuse again so i replaced it jeep turned on idled at the stop light as soon as i hit the gas it blew. so i changed it out with a 25 amp in hopes to make it to the parking lot. well i made it changed it back to a 20 amp and headed to advance auto grab some more fuses. died once again so i put the 25 amp back in so i could make it home. and thats where im at now. Is this a coincidence??? or is this related to the water?

 

[Gary Allan]

Check for more exposed wires (or your original repair point). You should be able to take a garden hose ...heck a pressure washer to the engine bay. I do it routinely (well, when I get annoyed at the dust accumulation).

 

[mechtech2]

Whether it is related or not is a subject for future bench race sessions.
You need to check and clean all the connections and wiring for the fuel pump. This includes any relays.

 

[Taylor]

i jiggled the connector and the repair spot while running with no results. I pulled the PDC checked all wires coming and going. switched the relays, pulled interior fuse panel checked all wires coming and going. I gave the wires running to the fuel pump a good look over. guess im going to have to pull the carpet up when i get a chance. I recently had the tank out and all wires looked good before i put it back in. i too have power washed my engine countless times, this is the second or third time i have misted the intake...

what are bench race sessions, they sound very interesting....

 

[eljefino]

Bench racing is like monday morning quarterbacking, a bunch of guys who weren't there 2nd guessing the ones who were.

 

[brianl703]

Does the fuse look like it blew due to a short or due to an overload? An fuse that blew due to a short has metal splattered inside of it.

 

[mechtech2]

Can you hook up a multimeter in series to test the amp draw [fuel pump]when running? And under different loads if possible?

And like mentioned by eljefino, bench racing is guys theorizing and not actually participating hands on.

 

[Taylor]

Well the first two were blown pretty bad the third you could barely tell, but maybe that was b/c it was more on top. right now i have a 25 amp in so i can get to work as I dont yet have time to check everything. if i recall correctly when i got it there was one or two fuses that were a step up so i drove it for a long time with a step higher fuse then discovered it, so i switched it to a 20 lasted a couple months thats when it blew and i found the short near the fuel pump connector. fixed that and it lasted prob 2 months thats when i ran into this problem.. thanx for all the help.

 

[AcuraTech]

Be careful running extra amp fuses. I was diagnosing a car a couple months ago that had a shorted door handle. (Acura RL with keyless entry and proximity remote, all you have to do is walk up to the car and touch the door handle to get in, as long as the remote is within a few feet of the car, IE your pocket)

The stock fuse was 10 amp. It kept blowing so I threw a 15A fuse in for further diag. The door handle (plastic) started to melt and smoke! Not a little smoke, a lot. And a big melted bubble on the handle.

Point of all this being just stay on the diagnosis track and find the problem, instead of leaving the higher amp fuse. Fine for emergency use, not fine for extended use.

 

[brianl703]

You can wire a lightbulb in place of the fuse. Something like a 50-watt sealed beam headlight bulb would work well for most circuits. Start disconnecting stuff until it stops glowing brightly and you've found the problem.

The lightbulb will limit the current so you don't damage any wiring. It might still allow a component that has an internal short to finish dying. I'd view that as a good thing, though, especially if it makes it obvious what's bad.

 

[mechtech2]

brian - That light tester is a bit of trouble to make and hook up, but is a truly GREAT idea. I wish I used that idea over the years!

 

[Taylor]

so i found my short.....it as my downstream o2 sensor. it was sitting on the rear driveshaft...all im wondering is if this would mess up the sensor? my CEL cam on after i grounded out the 02 sensor to make sure it was blowing the fuse.

21** Left O2 Sensor Shorted to Voltage Left oxygen sensor input voltage maintained above the normal operating range
21** Upstream O2 Sensor Shorted to Ground; or Upstream O2 Sensor Heater Failure; or Upstream O2 Sensor Slow Response Upstream O2 sensor voltage too low, tested after cold start; or Upstream oxygen sensor heating element circuit malfunction; or Upstream oxygen sensor response slower than minimum required switching frequency
21** Downstream O2 Sensor Shorted to Ground; or Downstream O2 Sensor Heater Failure; or Downstream O2 Sensor Shorted to Voltage Downstream O2 sensor voltage too low, tested after cold start; or Downstream oxygen sensor heating element circuit malfunction; or Downstream oxygen sensor input voltage maintained above the normal operating range

How to turn OFF the Check Engine Light
First of all, your Check Engine Light probably came on for a good reason. However, if you were doing something funky on the trail, the problem has most likely already corrected itself as soon as you got things back under control. Therefore, as stated in the Powertrain Control Module discussion above, "if the problem is repaired or ceases to exist, the PCM cancels the code after 40 warm-up cycles and the Malfunction Indicator (check engine) Lamp will go out." This means that, depending on how many times you stop and restart the engine during the remainder of the ride, the light may very well go out before you hit the trail end. Otherwise, it will go out during the next few days (or maybe weeks). To get it to do out sooner, I'm told that if you disconnect the battery for a few minutes, that will reset the computer and turn off the light. However, if there's still a valid malfunction, the light will most likely come back on again, and you should probably take your Jeep in for a professional diagnosis and service.


i have the battery disco'ed now just wanted to make sure i didnt need a new one cus its they are only 15k mi old if that..

 

[brianl703]

Fix the wiring to your O2 sensor, clear the codes. If no codes come back the O2 sensor is fine. If they do, then the sensor may have been damaged when it got shorted out. If the sensor output is shorted to 12V then that could damage the sensor.

 

[chevrofreak]

That could potentially damage the computer as well.

 

[Taylor]

yikes hope thats not the case, i cleared the code and it stayed off for a couple hours. but its now back on, so looks like i need a new sensor.

 

[Gary Allan]

Just unhook the sensor and clear the code. If you get the same code ..it's the wiring. If you get "no heater circuit" (or the proper code - but a different one) then it's the sensor.