Dead 96 ZJ

[DaveB]

My son was out driving yesterday in the rain and a few miles after going through some deep puddles our 96 ZJ died. It will turn over just fine and has plenty of fuel pressure at the fuel rail. The gauges aren't working and the computer won't flash any codes at all. The fuel pump runs all the time rather than priming the system then shutting off. I am going to check for spark and injector firing tonight. Do you think he fried the computer or should I look for anything else ?

 

[iamsparticus]

sounds like a major connector or the computer is fried. Check the wiring diagrams for it and see if all the stuff that is not working is possibly all on the same circuit, check the fuse box for blown fuses or relays and cross your fingers that it was not the computer that got fried

 

[Bart]

Is it a 4.0 or V8? If it's the 4.0 it may be the CPS.

 

[DaveB]

Is it a 4.0 or V8? If it's the 4.0 it may be the CPS.

Its a 4.0. Would a bad CPS cause the loss of gauges and no error codes ? I know they won't run with a bad CPS but I would think the computer would still be able to show codes.

 

[iamsparticus]

Did any water make it into the cab?

 

[DaveB]

Did any water make it into the cab?

Not that I am aware of.

 

[mbryson]

I've had similar issues with a CPS. Get a dealer one.

 

[Cody]

I think the ecu is behind the washer fluid bottle on the passenger side firewall. Definitely sounds like a PITA electrical issue. If you had something grounding out I could see it causing the guages to stop....maybe check to see if any water is resting in the bottom of the fuseblock under the hood?

 

[DaveB]

I checked all of the fuses for continuity and voltage and they all look good. I also verified that there is no spark to the plugs and no voltage at the injectors while it is cranking. All accesories work fine. I believe this obd2 ecu runs the gauges through a serial interface so if the serial wires or the ecu are damaged that would explain the guages and the lack of codes. I know the ecu fires the ignition and injectors but requires a good cps to fire them properly. I'll have to see if I can find the cps and ecu at one of the yards fior a test.

 

[DaveB]

Well I did some more testing and verified that all of the ground wires are good, the fuel pump comes up to pressure if I manually enable it at the fuel pump relay. The fuel sending unit has reasonable resistance for the amount of gas. I disconnected the crank position sensor which some on the net claim will kill the gauges but it had no effect. I finally crawled under it to look at the oxygen sensors and found that the mount for the sensor after the cat must have come off in the water which allowed the wires to get caught in the driveline and cut them in half. The bare wire ends were shorted together. I re-connected the wires but it still won't start. I'm leaning towards the computer at this point, it has voltage, good grounds, good sensors as far as I have tested them but still I get no gauges, error codes, spark, or injector firing. I even verified the ASD and fuel pump relays and they work as they should if they are enabled manually.

 

[iamsparticus]

Well Dave im glad you are actually diagnosing it most just through parts. If all the stuff you checked is good, then i think it must be the computer for what ever reason fried it's self i would do as you said and pull a junkyard one, as well as a cps. Everything that is not working does go through the ECU so it makes total sense

 

[mbryson]

I'm still thinking CPS. Just my opinion

 

[DaveB]

I'm still thinking CPS. Just my opinion

I found some info on checking the CPS and the cam position sensor so I'll be trying that before swapping out the ecm. I will also try using one of my oscilloscopes to watch for waveforms from the two sensors to see what is happening. I am also going to check some of the control voltages from the ecm.

 

[Darwin]

often times if the computer has gone bad, the check engine light on the dash will not illuminate when the key is turned on. if you have no CEL with key on i'd look a little further into the computer by checking for a 5 volt reference on throttle position sensor, map sensor, cam sensor and crank sensor. if there is no 5 volt reference and no CEL you may have a bad PCM.

 

[DaveB]

often times if the computer has gone bad, the check engine light on the dash will not illuminate when the key is turned on. if you have no CEL with key on i'd look a little further into the computer by checking for a 5 volt reference on throttle position sensor, map sensor, cam sensor and crank sensor. if there is no 5 volt reference and no CEL you may have a bad PCM.

Those are some of the voltages I was planning on checking tonight.

 

[4Runner]

it could have water in the distributor.this is different but it also could be you oil pressure sensor. that will cause it to not through a spark. to test the oil pressure sensor use an ohm metter. i couldn't tell you about the lights in the dash. just a thought. did your ECU get submerged in the water? just another thought.

 

[DaveB]

it could have water in the distributor.this is different but it also could be you oil pressure sensor. that will cause it to not through a spark. to test the oil pressure sensor use an ohm metter. i couldn't tell you about the lights in the dash. just a thought. did your ECU get submerged in the water? just another thought.

I checked the distributor right after it died and it was dry. I don't think the ECU was submerged, it might have been splashed on however. I am going to continue testing each sensor and I'll check the oil pressure sensor too. I would have looked at it last night but I didn't want to get my electronic test equipment wet in the rain.