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Old November 17th, 2019, 09:38
BALTANAKT BALTANAKT is offline
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How to bench test '91 CPS

Hey guys, I have a 91 with the round plugs. Since buying a NAPA sensor that didn't work, I've been collecting different CPS's and I'd like to bench test them if possible.

There are three terminals inside the plug. If I orient the plug in the same way as in the image below, with the tab facing up, would the terminals (a,b,c) still be located in the same order? Is the test then to check for no resistance between B + C?

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Old November 17th, 2019, 09:38
BALTANAKT BALTANAKT is offline
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Re: How to bench test '91 CPS

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Old November 17th, 2019, 16:13
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Tim_MN Tim_MN is offline
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Re: How to bench test '91 CPS

I have never owned an OBD-I Jeep, but everything I recall seeing, the tab is UP and left to right is A-B-C. Is this different than what you are finding in your Jeep Factory Service Manual ?

CPS Testing
TESTING PROCEDURE 1991 –2001 4.0L H.O. engines
1. Near the rear of fuel rail, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C or 2 and 3 (See Image). Ohmmeter should be set to the 10K-or-2OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.
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Old November 19th, 2019, 09:56
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8Mud 8Mud is offline
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Re: How to bench test '91 CPS

I check for open between B and C. Then I check the C for power (C to ground volts) with the key on.

Different years have a different supply voltage, believe yours is 8V (some years 7 or 5). If the Cam position sensor has a short it can affect the CPS input voltage (low voltage). A tipoff can be when the Check Engine Light doesn't light when the key is turned to run, before start.

If either the CPS or the Cam position Sensor have a short the motor is unlikely to start.

While the CPS is the most likely culprit for a no start, it isn't the only reason.
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Old November 19th, 2019, 21:03
BALTANAKT BALTANAKT is offline
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Re: How to bench test '91 CPS

^ Huh. Interesting. Thanks for the info.
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