Cherokee 94 Auto Shut Down relay overheated (difficult)

[Gabo]

Hi there

I have a problem that still unsolved by the experts.. My standard 94 4.0L shuts down after 30 min, the problem is narrow down to the "auto shut-down relay" which overheat and when I want to restart doesnt start, when I change the relay start fine and the cycle continue...

Actions and status

• all the relays are changed twice in 2 different brands (germans and Americans) thats why I can change them all the time
• The balast resistor relay overheats aslo but does not cause the problem unless is very related with the problem
• the balast resistor has 1.1ohm is ok but runs hot (I dont know if this is normal) the drop voltage is at 10V to the pump.
• The most important part: if I open the balast resistor the engine does NOT stops just run with difficulty but never stops, as per the diagram this is imposible a low rpm because the balast resistor relay must be off, then there is a problem here...
• The radiator fan runs all times with the coolant sensor new and A/C off

This is a difficult problem, I would appreciate you expertise here Thanks a million

Gabe

 

[FloridaCherokee1988]

Im not the best with electric parts of engines so hopefully some1 else can help u more, like steelheadz lol but is it possible that you have a short somewhere that's causing your ballast resistor relay to over heat and cause these problems?

 

[MudderChuck]

I'd use the key method and pull the MIL codes from your PCM. If you have a shorted sensor it should show up there, though theses codes can and will lie to you.
A likely spot to overheat the ASD may be the O2 sensor heater. It should have a resistance, though I sure can't tell you what it should be, no resistance is likely a bad sign.
The ballast resistor is bypassed during cranking, so the fuel pump gets full voltage during starting.
Disconnecting the ballast resistor and jumping it for a test may put you on the right track. They are supposed to get hot, but from what I understand their sole function is reduce noise in the pump during normal operation.
I've heard an open circuit for the engine temp. sensor (in the thermostat housing) will cause the aux cooling fan to run continuously. Though this also makes me suspicious, a shorted sensor can cause all sorts of grief.
I'm not sure where the PCM grounds, but grounds are always worth a look see. Likely near the dipstick holder like earlier models.

 

[Gabo]

OK this problem still very very difficult
Yes of course I pulled out all MIL codes and all of them are the expected..
Oxygen sensor circuit
A/C clutch relay
Colling fan relay circuit
Fuel pump resistor bypass relay circuit
Fuel pump relay

In few words all the problems that I already know... no too much help

This model came with the O2 sensor and the O2 sensor heater removed from factory (no US model)

The ballast resistor still jumped

The fuel pump relay, Ballast resistor relay and ASD still over heated after 1 hr in cold weather, power distribution center and hood opened... after that If I stop the engine doesn't re-start, I have to put a cold ASD relay then start.

I found a second temperature sensor very small that goes near the firewall driver side, was broken and I replaced it, same problem... this sensor is not listed in the Haynes, is for turn on the cooling fan as per OEM sticker.

The cooling fan still starting at 140F, this is not possible that whys the relay fries, I removed the colling fan relay to the see relation with the other relays overheat but still the same thing, is not related.

I did not check for open circuit in the engine temp. Sensor because the system is starting at 140F and stops if the temp goes under that

The PCM is in the Driver side

Regarding the Colling fan ruining after 140F the only thing that left is replace another brand new sensor and if not change the the problem is the PCM in this specific output that send the negative signal much before when should be. ANY other IDEA?

The overheated relays the only thing now is rewire externally and see what happen, but this is big job that I am reluctant to do....

Guys I think is this is a real challenge I normally solve all kind of problems of this nature but this overpass the normal problems. have some body another logical idea? Thanks a million

Gabe

 

[SteelHeadz]

I'm not all up to par with this setup but i'll give it a shot. The ballast resistor you speak of, is the voltage supply circuit wire also a resistor wire?, If so, in thoery and from personal experience on a different Jeep, If the resistor supply voltage wire is shorted to battery voltage, the ballast resistor will exceed it's max. tolerance and overheat. I'm thinking maybe a short somewhere in the engine harness that's causing all of the other issues as well as opposed to an actual component failure like a sensor, although i would not eliminate that out of the equation but it's better to verify the integrity of the circuits before condeming the component.

 

[MudderChuck]

I'm with Steelheadz, three distinct Possibilities, either a short in a harness, an odd ground path or a component that is supposed to have resistance that has low resistance (or almost no resistance) and shorting the ASD circuit to ground.
My 96 will run very poorly with the ASD circuit open. My best guess is there is a wiring fault in the circuit someplace that allows this to happen. I've never found the cause, never bothered because it has never caused me any serious grief.
I'm thinking about what the aSD relay powers up, the coil, the Alternator, the injectors, the O2 sensor heater (I think) and power to other relays.
Some places you may wish to check, the harness where it runs down the front of the motor behind the power steering pump, a likely spot to get cooked on the exhaust manifold.
Another spot is under the insulation on the injector harness where it makes the bend by the firewall. This area flexes a lot.
140 degrees is right around where my motor idles down and the other sensors start to kick in for closed loop operation. A common misconception is it is either closed loop or open loop, though in my experience closed and open is a stepped process not a either or process.
The reference voltage for most sub systems (sensors) are shared by multiple sensors. Like the CPS and the sync sensor share a supply voltage. Likely the fan relay and others share a supply voltage, most sensors and relay are switched at the PCM in the ground side and have constant power.
It once took me, on and off, almost a year and a half to find one ground fault inside my harness (TPS) that was a faulty crimp. On another occasion I got lucky and found one fairly quick, an injector feed wire that was fatigued almost all the way through.

Is your XJ an export model? Does it have the anti theft module, that is usually wired in with the remote door lock?

 

[carnuck]

too much draw at the fuel pump could be a pump going south or bad connector causing too much draw (my son found that out AFTER replacing his pump twice!)