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Old 10-08-2011, 10:24 AM   #1 (permalink)
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1989 4.0 bogging and back firing

I was given an 89 cherokee with a running problem. I replaced the throttle position sensor but don't know how to set it. I have moved it into every position and have had no luck. The engine when you step on the throttle boggs down and some times back fires. Anyone have any ideas or suggestions?
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Old 10-10-2011, 06:14 AM   #2 (permalink)
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A bit more info so that maybe some one can steer me in the right direction, I ohmed my cps and it was fine. I then tested voltage to the cps and did not get any volts. However the engine does run.
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Old 10-10-2011, 06:41 AM   #3 (permalink)
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Check ur plugs and wires it might b as simple as a tune up a lot of times u can tell what's going on inside by what's on ur plugs if u search jp magazine tec archives they have a good article whith great pics of what the plugs should and shouldn't look like and tells u the corresponding problems u could b having
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Old 10-10-2011, 07:22 AM   #4 (permalink)
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I'll give that a shoot. But if I hold the throttle down long enough the engine will bog and stutter for a bit and the go to full throttle.
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Old 10-10-2011, 08:47 PM   #5 (permalink)
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Look at ur wires in the dark first if they r cracked or split u will c flashes
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Old 10-11-2011, 07:15 AM   #6 (permalink)
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I did not find any problems with the spark plugs or wires. Why is it that it runs at low idle, and if you hold the throttle to the floor and wait a while it will then run up to full throttle?
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Old 10-13-2011, 07:54 PM   #7 (permalink)
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The Renix CPS is a voltage generating device, it makes AC voltage, should show above .25 volts AC while cranking, better if it's higher. Ohms is around 235.

The TPS can be set with a volt meter. there are three wires to the ECU and four more to the TCU if you have an automatic. We need to check the sensor volts at idle on the three wire connector. One wire is ground, one is 5 volts, the other is the sensor return to the ECU, this is the wire to back probe with a pin to read the voltage. Set the closed throttle volts to around .83V by rotating the sensor. Check the sensor, the voltage reading should sweep smoothly from your idle setting to around 4 volts. Any gaps or skips, the sensor is bad.

It wouldn't hurt to clean and tighten up the pins in the ECU connector. Many driveability issues are due to poor connections in the Renix EFI system. The ECU connector is not sealed, the ECU mounts above the gas pedal inside the XJ, under the dash.
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Old 10-13-2011, 09:37 PM   #8 (permalink)
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Set the TPS voltage.

Then replace the map sensor and vac line to the map sensor.
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