4.8 2008 in a jeep stock ecu stock modded oem wire harness
I used the jeep starting relay for cranking the ecu has separate main relay and sep relay for fuel pump, the fans are independent power separate killed by key switch,

Ok with above in mind it's been running with minor teething pains for 8000 miles
Today I went into a store ,outside temps around 89 deg jeep had been running around 205. turned off jeep went in for about 15 to 20 min went I came out there was a HUGE puddle of water under they jeep, as I get closer I can tell Its Running!!!!!!!!!!!! WTF!!! No key naturally the fans are off so it very over heated pegged the gauge over 260 and all the water had appeared to blow out the recovery bottle, the only thing I could think get this thing off now!!! I unplugged the battery cable , still running! Crap forgot alt still providing power, it's running like crap so I'm thinking its already bent a valve or something bad, then I think pull the plug the ecu ! Now it finally goes dead, I let it cool a little and it cranks but then dies after 30 sec , I'm thinking oh crap , I think all the things that could be for non start . I then notice the indicator led I have for the fuel pump is not on, no wonder not start. It's plug to its relay looks like its been hot and is discolored . After moving it around the engine is running. I fill the rad with one gallon of antifreeze and it drives home normally. I know I dogged a huge bullet here.

Any ideas how could this have happened? I'm scratching my head looking for anything that's common between the main and the start cir, or maybe the jeep key ? Idk

What all ideas to prevent this from occurring again?

I'm thinking at least to add a loop cir to the brake pedal to disable the start cir unless its pressed is one thing , another might be add a power loop to the fan cir with diode that if engine is running the fans are on,

Anyway crazy jeep day for sure.

Has anyone ever heard of a starting itself?????

 

Who did your harness work? It is possible something shorted out and started powering things up. Maybe water getting into something, maybe a wire chaffing through the insulation and shorting out.

I would check every wire and every connection to make sure nothing is wrong.

 

I would start with the starting relay circuit...something had to activate the relay..that would be the only way for it to crank over in the first place.

Do you have a Alarm system with a remote starter ?

I'll be watching the one !

BC

 

how did you use the jeep relay? is it the relay itself or is it still mounted in the jeep fuse box and wires spliced there? what fuse box are you using for motor? as for the safety brake loop idea it would only work if the loop is after the "problem" part of the wiring. do you wheel your jeep in wet conditions? if so how long was it since you was in wet conditions and this problem happened?

 

Yes I had been in a creak just 3 hours before. Not deep just a few inches only. But could be a factor I suppose.

The stating circuit: I used the jeep block and relay with the existing cir from the key. I ran a independent ground from the relay straight to the battery. ( The reason I ran the separate ground is either the clutch sw and or wire was faulty ) I suppose I should check if it has the original ground also and if so delete it so its only ground should be this new one. But it still would have had to receive power. this wire is the one I was thinking of adding the brake loop to. Going to pull out jeep fuse block and check it for wire chafing.

Alarm and remote start: No dont have either ,

Harness : Local Guy in Ark ses performance , And the starting cir is has little or no contact wire the 4.8 harness . But I am thinking the main relay on this side had to have power also , and there is the very slim possibility I must consider that the main relay stuck ON and when I got out of the Jeep turned key off , the fans cut off , the radio that was blasting goes off, and because im in a noising parking lot I don't notice the engine is still running. I cant believe I would not have noticed that , but I have to consider that possibility


I need to see why the fuel pump wire was sooooo black is one clue , its pulling too much current or was just loose at the connector, it couldn't be this cause as its only powered by the main

it helps to have someone to bounce these ideas around with. I will do some further checking this afternoon.
Thanks

 

I did a bunch of checking today , I found no chafing and the key switch acts normal. I did change how the always on low speed fan the gets its power, it was from a random wire that was hot with the key on, to getting power to engage slaved from the fuel pump relay. Im thinking that way if this thing does this again at least it will not be running without a fan lol.

This week also adding the Park safety neutral safety switch , a kill switch (overkill maybe), and a brake pedal switch loop for the stater relay. ( I already have the TC lock up relay I could just tap off it)