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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
I am trying find definitive answers about where the pcm is. My cherokee cut off while driving the other day, the pcm fuse kept popping, I cleaned the fuel pump connector and that stopped the fuse popping. The fuel pump turns on, it turns over but doesnt start. I replaced the relay and still nothing.
Before condemning the computer, I would first consider the possibility that the fuel pump itself might be involved.
You need approximately 49 psi of fuel pressure for your 99 to start. I have a 99 so I know this system pretty well. You can easily test it with a fuel pressure gauge which you can often rent inexpensively from many parts stores; call around for availability. Just because you hear the fuel pump "energize", doesn't mean that the fuel pump is working properly.
If you are past blowing fuses, you need to verify your fuel pump operation. And that would mean testing fuel pressure. And if fuel pressure is around 49 psi, then you need to test for spark. You can test spark this way. Pull a spark plug. Keep it attached to the plug wire. Place the plug electrode near a good engine ground. Have a buddy crank the engine over from the cab while you watch. You are looking for a strong, snapping, BLUE spark. Yellow/orange/white indicates a weak spark which is usually caused by a weak ignition coil.
You can test for spark before fuel first if you wish, but you gotta test for quality spark and proper fuel pressure. This WILL yield clues as to root cause. Using a testing based strategy will get you back on the road. Don't throw parts at this on a hunch. It's terribly inefficient and gets expensive in a hurry.
Good luck and keep us updated!
Last edited by tjwalker; May 27, 2016 at 06:45 PM.
Before condemning the computer, I would first consider the possibility that the fuel pump itself might be involved.
You need approximately 49 psi of fuel pressure for your 99 to start. I have a 99 so I know this system pretty well. You can easily test it with a fuel pressure gauge which you can often rent inexpensively from many parts stores; call around for availability. Just because you hear the fuel pump "energize", doesn't mean that the fuel pump is working properly.
If you are past blowing fuses, you need to verify your fuel pump operation. And that would mean testing fuel pressure. And if fuel pressure is around 49 psi, then you need to test for spark. You can test spark this way. Pull a spark plug. Keep it attached to the plug wire. Place the plug electrode near a good engine ground. Have a buddy crank the engine over from the cab while you watch. You are looking for a strong, snapping, BLUE spark. Yellow/orange/white indicates a weak spark which is usually caused by a weak ignition coil.
You can test for spark before fuel first if you wish, but you gotta test for quality spark and proper fuel pressure. This WILL yield clues as to root cause. Using a testing based strategy will get you back on the road. Don't throw parts at this on a hunch. It's terribly inefficient and gets expensive in a hurry.
Good luck and keep us updated!
Thanks, I will do that this weekend! Starting to frustrated, I also have an 88 xj with a bad transmission. The wife is not happy about to broken jeeps.
I have solved the fuse blowing issue, the wires to the ignition coil were bare as well as the fround wires that go on the studs beneath the ignition coil, insulation melted off. Cleaned the wires, coated them with liquid electrical tape and moved them away from the engine block. Now it starts if the throttle is opened manually and dies as soon as the throttle is let go. Any suggestions?
1999 Cherokee pcm replacement
