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I've read that drilling out the upper mounting hole will get my cps a hair closer to the flex plate BUT that is just close enough to  improve the voltage to a much more respectable reading. 

My problem is, I haven't read anything that clarifies which hole. Am I drilling the mount hole on the bell housing or the one on the cps bracket. And this is my first post so I'll let y'all get the flaming out of your systems now with a second question. 

What in the wide wide world of sports are us early 2.5 (1987) TBI remix guys supposed to do when we need a MAT (NOT MAP) Sensor? NLA 

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Hi, 54bobby...There would be no way to move the 2.5L CPS closer to the flexplate or flywheel.  However, if the goal is to modify the spark timing or possible make it more accurate, the CPS's winged flange holes could be elongated with a file or burr grinding bit to move the sensor slightly in either direction on the bellhousing/converter housing.  The sensor would still mount on the same arc as the original position.

 Fuel-Spark-218-21.jpg Fuel-Spark-238-21.jpg

At left is the 2.5L Jeep TBI Crankshaft Position Sensor (CPS).  Shifting the sensor slightly in the left or right direction would change the base spark timing and the entire spark curve.  This would "trick" the computer into thinking the modified CPS sensor pickup position was #1 piston at TDC or top dead center.  (Normally, the CPS indexes the TDC or #1 cylinder timing position, which is the same as "0" degrees at the crankshaft.  The ECU or computer receives this TDC signal for #1 piston.  All spark timing is adjusted by the computer/ECU.  

 Fuel-Spark-235-21.jpg 

The ignition distributor is in a fixed position.  Modifying or trying to change the distributor base location is futile.  Spark timing works from the CPS and the computer.  The 2.5L TBI engine requires that the distributor housing lines up in this position with the rotor pointed correctly toward #1 spark wire position in the distributor cap;  #1 piston is at TDC of its compression stroke when indexing the rotor and cap.

Moving the center point of the CPS pickup with relationship to the flywheel/flexplate and crankshaft would either advance or retard the overall spark timing curve.  The bell housing/converter housing threads are in a fixed position and need to remain that way.  Do not attempt to modify the housing threads.

There should be no reason to move the sensor "closer" to the flexplate or flywheel.  This is a hall-effect, magnet based pickup method.  The flexplate or flywheel generates a signal pulse at the pickup tip.  The gap between these two points has some flexibility;  the factory position and gap for the sensor is acceptable for normal purposes. 

The one exception is when the flywheel or flexplate surface gets dirty with a combination of dirt and engine oil from a weeping rear main seal or oil pan lip.  Before modifying anything, I would clean the flywheel/flexplate face and the sensor tip of the CPS.  If difficult to access the flexplate/flywheel, consider removing the CPS and cleaning the flywheel or flexplate surface through the sensor pickup hole.  If there is a major oil leak (oil pan or main seal), fix it.

As for the MAT sensor, this is actually called the AIT (Air Intake Temperature) sensor by Mopar.  In the Mopar catalog, instead of including this sensor with all the other sensors and switches, the part number is buried at the intake manifold listing for 2.5L TBI engine parts (1987-90 Jeep XJ Cherokee/Comanche).  The OEM Mopar part number is:  33002382 SENSOR, Intake Air Temperature.  When I looked this up online, more common Dodge engines also use the same sensor.  One example is the 1990-91 Dodge Monaco 3.0L V-6 gasoline engine and apparently the Renix 4.0L inline sixes.

Make Model Year Body & Trim Engine & Transmission
Dodge Monaco 1991 ES, LE 3.0L V6 - Gas
Dodge Monaco 1990 ES, LE 3.0L V6 - Gas
Jeep Cherokee 1990 Base, Laredo, Limited, Pioneer, Sport 2.5L L4 - Gas, 4.0L L6 - Gas
Jeep Cherokee 1989 Base, Laredo, Limited, Pioneer, Sport 2.5L L4 - Gas, 4.0L L6 - Gas

As for a source, I did a look-up and found some interesting possibilities:  

1) AutoZone refers to this inexpensive CompCams part:https://www.autozone.com/electrical-and-lighting/temperature-sensor/comp-cams-air-temperature-sensor/891301_0  [You need to confirm the Ohms readout range and also the wiring connector type.  The CompCams catalog may have the specs on this sensor.  Look it up in the online catalog.]

2) Standard offers the AX1 and AX40 air intake temperature sensors.  The AX49 is also a possibility but would require a connector change;  connectors are listed in the Standard online catalog, so any sensor connector can be found if it matches the number of wires.  This is not rocket science:  You need a sensor with the correct ohms readout, wire count, thread size and the right electrical connector.  If a new type connector is needed, you can splice into the existing wiring.

3) The OEM part number turns up this Omix-ADA part at Summit Racing:  https://www.summitracing.com/parts/omx-1722101?rrec=true  [Same fit-up rules apply.  Confirm fit.]

Do some homework here.  Standard, Omix-ADA, Crown and others offer tech support.  Ask about the ohms readout for these sensors and confirm their thread size and sensor length.  If the sensor matches the 2.5L TBI Jeep engine's thread size and the OEM sensor's ohms rating, you have found the holy grail of sensors or a solution for 1987-90 Jeep 2.5L TBI engines.  Post your findings here in a reply, and be a 2.5L TBI hero!

Here is an article I provided some time ago to help 2.5L TBI owners with troubleshooting and tune-related issues:  https://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four?r=1

Trust this helps...

Moses 

 

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  • Moses Ludel changed the title to Jeep XJ Cherokee 2.5L TBI CPS Modifications

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