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Old February 15th, 2019, 12:56
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kastein kastein is offline
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Join Date: Jul 2009
Location: Central MA - keep going till the road turns to dirt, then listen for banjos
Posts: 14,193
Re: differences in 91-95 xj

91-95 are pretty close. The only things I can think of off the top of my head:
- 91-92/93ish have a 2 wire VSS that's just a reed switch to ground. 93/94ish-up have a 3 wire Hall effect VSS. Same number of pulses per revolution and the ECU *may* have a pullup resistor built into it, I'm not sure, so it might not matter, or you might have no VSS signal.
- I think the brake light switch changed at a certain point, not sure when. If it did, the ECU may not read it right but it probably will read it fine.
- 91-93ish had a fuel pump ballast resistor and a relay to bypass it during starting and wide open throttle, 94ish and up don't. If this gives you trouble you can just bypass the ballast resistor. I believe the O2 sensor heater might be involved in this circuit as well, might want to compare the wiring diagrams and see if it'll affect the O2 sensor.
- there are a few TCU changes in that year range but I don't believe they'll matter for the ECU.
- cruise control is different 91-94 vs 95-96. Old ones used the GM steering column and cruise switch, 95 used the resistor multiplexed setup similar to 97-98 and 99-01, but each of those year ranges has different multiplexing resistors.

I'm 99% sure everything else will work. I haven't checked the resistance curve on any of the sensors but I'd be pretty surprised if they actually changed them instead of just changing the connectors occasionally. For example 91 through 01 use the same CPS reluctor slot pattern on the flywheel and the same (or compatible) CPS electronics, but they changed the connector like 3 or 4 times over the years. I know people who have spliced old CPS connectors onto new sensors and vice versa as an emergency repair and had it work just fine.
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