No fire, Not the CPS, i think

[cushdaddy]

Well, it was the PCM. I got one from a guy on craigslist and plugged it in and it fired right up. Thanks for the help limiting the possibilities for what could be wrong. I think that changing the current setting on the charger while it was hooked to the battery might have spiked a higher voltage then the PCM could handle. I watched the voltage as I switched it and it jumps up to over 15 VDC. Could have been higher, but its hard to tell with a Digital meter. It runs rough at idle so I pulled and cleaned the IAC valve and it is still rough. I put some fuel system cleaner in as well to help clean the injectors that have been sitting for 3 years. Full tune up has been done.

 

[wall04]

Thanks for your posts. I'm going through a similar thing. I replaced the spark plugs (after 100kmi they were totally gone, I know, I know...) with new NGKs and Bosh cables. Jeep ran like new for about a day. Then it slowly died as I was rolling into a parking lot and subsequently wouldn't start. Before dying it gave me a check engine light but there's no code when I go to check it.

When I started the jeep right after I replaced the plugs and cables, the cable from the ignition coil to the distributor popped off and caused an arc. I re-seated it and the jeep ran for a day afterwards with no problems.

I discharged the capacitors to reset the computer after I replaced the plugs. So, I disconnected the battery and put the key in accessories and turned the lights on. Again, ran like new after that.

I get 12v spike at the power to the coil when it's started then it dies to zero. I checked the ohms on the coil and I actually just replaced the coil and it still won't start.

It has to be related to swapping out the plugs and cables and resetting the PCM. I can believe it's the crank sensor and I'm working through the recommendations in this post to troubleshoot.

Any insight is greatly appreciated. 1999 Classic 150Kmi.

Thanks!

 

[MoFo]

I have pulled every sensor connector and my gages still don't come back to life.

I still haven't put a new battery in it, but I am trying to figure out how that would kill the 2 gages. I pulled the dash and reseated the gage cluster and everything under the dash looks clean and tight. I keep testing for 8vdc at the CPS, and will all the sensors disconnected, I only get 1.25vdc.

I don't think anyone suggested you replace the battery yet. The recommendation was that you take the battery to your favorite auto parts store and have it load tested.

I keep testing for 8vdc at the CPS, and will all the sensors disconnected, I only get 1.25vdc.

I think your problem is still with the 8V supply. Leave your alternator, coil and all the other stuff alone to concentrate on this. The battery is critical in the respect that you must spin the crank fast enough to satisfy the PCM, through the CPS, but it won't work without 8V. WHERE are you testing for the 8 VDC?. You should have the CPS unplugged and be measuring from the ground pin to the power supply pin on the chassis side of the connector, with the plug disconnected. The reason the supply voltage is passed through the PCM, is so the PCM car regulate it and know exactly what voltage is supplied to all the sensors. This is why this is sometimes referred to as a "reference" voltage. It is also current-limited, so a short on the line will not damage the PCM internal voltage regulator.

I keep testing for 8vdc at the CPS, and will all the sensors disconnected, I only get 1.25vdc. This is the same voltage I get when I check the PCM ground to chassis ground.

I am not sure exactly what to make of this without knowing EXACTLY where both the red and black probes were attached when you took both of these measurments. The 1.25V drop from the PCM ground to chassis ground only says that that particular ground wire is drawing significant current, assuming the meter connections were good. The troubling piece is when the voltage drop at the ground being equal to the the loaded (presumably shorted) supply voltage being 1.25V also. This could only indicate a direct short of the PCM internal (current-limited) voltage regulator. The probability is HIGHLY unlikely. You should repeat these 2 measurements with all other sensors connected, making note of exaactly where the meter probes are touching. If you get similar results, measrre the voltage between the CPS ground wire and the 8 V supply wire.

I have cleaned the grounds by the PCM, the coil, and the battery. I think I am going to pull the kick panel off and check the wiring around the fuse block.

I believe the PCM and sensor grounds are on the passenger side of the engine, over by the oil dipstick tube.

This jeep did get hot and blew the radiator, I don't see any chaffed or melted split loom or loose wires. If the alternator got drenched, could there be a problem there? IS there a fuseable link somewhere that could be blown? I am still getting the no buss OBDcode as well.

Thanks for the help. This really shouldn't be this difficult.

Don't get lost in the noise. Get back on the 8V!

Are you still trying to work with that Haynes "manual" If so, it will only waste your time when working on an XJ electrical issue. Get an FSM. The officail CD manual are a little difficult to navigate, but you can trust the information.