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Unread 07-14-2014, 09:58 PM   #1
dylanshawley
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engine trouble

Hello all, I'm new to the site but have done a decent amount of reading on here and I haven't quite come across anyone having the same issue that im dealing with. To start off I drive a 1994 limited grand cherokee 5.2L V8 with 1603m miles on her. During the summer months while I'm driving down the road typically the first drive of the day as long as it is a drive longer than 2-3 miles, my RPMs will drop and peak around 2000-3000 depending on the speed I'm travelling at very erratically. The engine will back fire and cut out and I can hardly gain any speed but I can keep the jeep moving but it sounds like it is on the verge of dying. It seems its happening once the engine is up to temperature and if I continue to drive it will eventually work itself out and I won't have an issue for the rest of the day. Now I have replaced my fuel pump, O2 sensor on the engine block, TPS, camshaft sensor, but I have not checked cap and rotor. Has anyone dealt with this or heard of this problem before? Any help is greatly appreciated

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Unread 07-14-2014, 10:00 PM   #2
merc07
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id check your crank sensor
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Unread 07-18-2014, 10:54 PM   #3
dylanshawley
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Thank you merc07, I got to the crank sensor, thankfully im a dude with small arms, I ran a meter over it to check resistance on the three ports it had on the sensor unplugged, between port B and C it had 1.83 resistance, however I read online it was supposed to be 0 or as close as possible? I also did the same on an auto store's new sensor and it read 3.78. Was I off in thinking it should read 0 and say my sensor is fine?
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Unread 07-18-2014, 11:00 PM   #4
dylanshawley
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Also today as I was back there I checked out the distributor and cleaned all the plugs, they had build up on them so I plan on replacing the cap and rotor along with my spark plug wires once I attain the funds. spark plugs are 2 months old and ignition coil is about a year old if that helps any diagnosis.
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Unread 07-19-2014, 03:55 AM   #5
Uniblurb
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You're correct the resistance between pins B & C on the crank sensor should read '0' or no resistance. Make sure you have the black probe on the middle B ground cavity and the red probe on the C (power) cavity pin or you may get some wonky readings. The test is in my signature along with a video.

You shouldn't be buying a crank sensor at a typical parts store and only buy Mopar or you'll be sorry. Wouldn't doubt the one you tested there is bad and I installed 2 brand new bad cranks sensors from Advance and never again.

If you don't want to pay the high dealer costs for a Mopar crank sensor you can find them on Amazon and/or ebay for less.

Note: here's a Mopar 56027272 crank sensor on Amazon for $63 which should be the correct one for your 94 5.2.

http://www.amazon.com/Mopar-56027272...&vehicleType=6
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-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread Yesterday, 10:22 AM   #6
dylanshawley
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Uniblurb, I watched your video but did not see a test like I was doing. if I put my meter set on 20k ohms with the black pin on port B and the red pin on port C I don't get any kind of reading my volt meter still reads 1. I can only get a reading on ports B and C if I have the red probe on B and black on C. If it doesn't register anything when I placed them how you recommended would that mean the sensor is completely bad even though it still starts?
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Unread Yesterday, 10:40 AM   #7
PolkaPower
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02 sensor on the engine block? The 02 sensor is in the exhaust pipe before the cat.
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Unread Yesterday, 11:26 AM   #8
dylanshawley
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You're right my apologies, meant to say coolant sensors on engine. I have done the O2 sensor on the exhaust
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Unread Today, 01:13 AM   #9
Uniblurb
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Quote:
Originally Posted by dylanshawley View Post
Uniblurb, I watched your video but did not see a test like I was doing. if I put my meter set on 20k ohms with the black pin on port B and the red pin on port C I don't get any kind of reading my volt meter still reads 1. I can only get a reading on ports B and C if I have the red probe on B and black on C. If it doesn't register anything when I placed them how you recommended would that mean the sensor is completely bad even though it still starts?
The crank sensor test you're doing above is a resistance test with the link to it also in my signature to the left of the video test. And as mentioned in the test you have to put the black probe on the middle B pin (ground cavity) and the red probe on the C pin (power lead/cavity). Your test is reading no-resistance (1), same as the probes aren't touching anything, which means in this application the crank sensor is testing good.

As also mentioned in that test if you reverse the probes you will get some wonky readings which you cannot go by. It would make sense to have the black probe attached to the ground cavity (B) and red probe on power (C) to do a proper test. Reverse this order and the hall-effect crank sensor with magnet inside just won't test right. This is why you were getting resistance with the probes backwards and you just need to ignore this reading.

This resistance test is not fail-safe even though it's listed in most all ZJ FSM's (factory service manuals). What they were doing in the video was testing to make sure the sensor is getting power while the crank sensor signal is carried through the sensor itself onto the PCM/ECU. Have you meter set to voltage. You do this by pinning the wire, or back-pinning the connector, with the red probe going to the wire connected to the C pin (power) and black probe connected to to the signal wire which leads to the A pin (signal wire). This is where a cheap pair of alligator clips come in handy for going from the probes to the pins. Just don't have the red/black pins/clips touching each other.

Then remove the ADS relay from the PDC and just knock the starter over in clicks using the ignition key. Helps to have 2 people to do this but what you're looking for when your meter will read 5V once in a while. This indicates the crank sensor is working by taking the 5V of power, passing it through the sensor itself, then passing 5V back to the PCM in the form of a signal. You can also turn the crank by hand with the key on to check this and an analog meter may be better for watching the needle jump up to 5V once in a while.
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-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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