My kid's Jeep now starts and run for 1-2 seconds, then stalls. I checked the ohms on the CPS and it's infinite as be between 2-3 pins. I also check the TPS voltage and fuel pressure and both were fine. The fuel pressure doesn't drop when the engine cuts out. I'm not sure if the injectors are shuting down cutting off fuel or the spark is quitting, or both.
I'm thinking of replacing the pickup coil, but wonder if there's a test for this. It's a 3 wire model.
1-2 second run indicates a sensor/relay fault is shutting down the engine or the computer isn't getting an indication the engine has actually started. This can be from a failed camshaft position sensor or crankshaft position sensor. In some cases it can also be a failing ASD relay or a blown fuse. Some times a faulty ignition coil can do this as well.
The ASD relay is in the engine relay center
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can swap it with the AC relay Have you checked the distributor for oil?
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The camshaft position sensor is in there, but to replace it you have to remove and dissasemble the distributor. If the distributor has oil/sludge and the rotor can be moved side (which it shouldn't be able to do) then the bushing is shot and your better off just putting a new unit in, as they come with a new sensor.
Now before replacing any sensors, disconnect and reconnect the harnesses to the Crankshaft and camshaft position sensors, remove and reinsert the ASD relay, remove and reinsert the coil feed, and check the distributor for oil.
Also if your measuring sensors use a digital mulitmeter. Analog multimeters are not safe for use on sensors these days.
Just a thought, this happened to me when the battery went dead and we jumped started it some seven or so years ago on my old 93 GC 4.0. It was the alarm system. Once the alarm was (reset) it was OK. If you know this, please forgive the post. Bob
I thought the sensors too. The CrankshaftPS ohmed out infinite with a Fluke digital meter. I also checked all the fuses and swapped around relays to eliminate this.
There was just a little slop and a little oil in the distributor so I replaced it. It was close to the same price of the sensor alone.
I did all these things.
I didn't know that, but I use a digital meter almost all the time now anyways.
I'm still stumped. I'm beginning to think a computer problem.
This makes wonder. I guess I'll play around and put the distributor on both sides of my mark. There scary thing is that I saw other marks in the distributor that I didn't put there.
Thanks for the input. This already happened to me before so I know the hard way. I didn't notice the 'security' lamp lit so I assume this isn't it. I don't remember it starting for a second when this happened before.
I use a Fluke 87 to back up by my trusty little Tektronix TDS2002 :) Ok.. so that is a bit nuts.
The crankshaftPS is just your basic hall effect sensor. It outputs a 5v pulse once every rev. There should be
8V between the center pin (Black/light blue (ground)) and the White/Black wire. with a 5v pulse coming out the grey/black wire.
There isn't an "ignition module", just the ECU/Computer. If it was fragged I doubt the engine would start at all.
Just a thing to check, look on the engine block forward of the right engine mount where the O2 sensor wire goes up to the front of the wiring loom that runs along the injector rail. (man what a run-on sentence) Check the metal clip that holds that wire to the block to make sure it hasn't been pinched or burned/shorted out.
You could remove/clean/replace the ECU connector. Just have to move the overflow bottle out of the way. If you do this, DO NOT.. use the center screw on that connector to suck it back in, that will crack the connector and that is $bigbucks$. Make sure the battery is disconnected. And when you go to hook the battery back up, put the key in the ignition and turn it to ON. That will tell the alarm system it's ok and your not some nefarious car thief. ;)
It's not advertised on the site but sometimes the temp directory has interesting things.
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If you need tech info the 93ZJ service manual is out there, I strongly recommend getting on. Not cheap but they pay for themselves in the first few jobs.
Ohmic check of the CPS is a waste of time unless you do it right - it is a Hall Effect switch which is basically a transistor that is turned on by the change in the flux field. You may get some info if you make all your measurements the repeat with reversed leads. This causes some "0" readings to go to open while other open leads will indicate a small current flow. The only reliable way to measure it is with a scope while it's under power, altho some better digital VOLTMETERS (not OHMETERS) have a fast enough response time to show whether it is actually pulsing or not. An older analog VOM will also work to check the voltage.
I guess I'm half blind. The third or fourth time of taking out the fuses, I spotted the burn in the 40 panel fuse. I should have known that the absence of any bells was wrong and I never tried windows, heater, radio, etc. I was too focused on the fact that the dash gauges/lights were working.
It seems the thing is running better than before. I just wonder when the cause of the blown fuse will rear its ugly head again.
Thanks, for all the help. Great stuff on the web site Doug, thanks.
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