Ok guys, my XJ has been running like a champ... Till now. Oh, '99, 4.0/auto/4X4.

Was driving the other day when out of nowhere the check engine light comes on. When I went to leave from a stop, she revved, but was just creeping along. Put her down in 1, she took off fine. Got her to autozone, had the codes pulled. "VSS malfunction".

Ok, reached under, jiggled the wires. Started up, light turned off, drove fine the rest of the day. That night started her up, light comes back on. Then the check gauge light comes on, sure enough, alt gauge spikes to 19. Then goes back down to normal. I eased her to the shop and left her there.

This morning I changed the large VSS, the alt, cleaned and tightened EVERY ground. Visually checked every harness I could get to.

No change. Start it, fine. Rev it once or twice and the check gauges light comes on, alt spikes, speedo sweeps to 100 and back to zero, other gauges twitch around, and domelight pulses to the rpms. Check engine light is on whole time. Verified when the alt gauge spikes, the alt is pushing 17+ at the battery.

HELP!!!!

 

Ok, update.

Replaced the input speed sensor, new battery for good measure. Cut back the insulation, found the main ground cable to be badly corroded, replaced that. Still in the same boat, though since last night the check engine light no longer comes on. Even though the torque converter still won't engage in drive, unless you put it manually in 1st.

EXCEPT...

When I hard restart the pcm. After two and a half days of chasing my tail, that's what I've found to be consistent. Disconnect the battery for 15+ minutes, reconnect.

Starts perfect, gauges behave like normal, transmission engages like it should, drives great. For about a minute. Then the bull**** starts all over again.

It's clearly acting like its not reading the input speed sensor, but the check engine light no longer comes on. Check gauges light comes on, but that's it. The gauges going nuts starts at the same time the trans stops engaging properly.

I'm starting to think my PCM has taken a dump? I'm really running out of ideas here, definitely open to some input guys. Any way I can test the pcm itself?

 

Thanks for all the help buttheads!


Got it figured out, FINALLY, Golden Badger is back on the road! I'll write it up a bit later in case somebody else ends up with a similar problem.

 

Ok, the following is a list of things I did/tried in my attempts to figure this mess out.

Output speed sensor
Input speed sensor
Input ss pigtail
Alternator(X2)
Battery
Battery cables
PCM($ent that sucker back)
Cleaned all grounds
Cut back & rewired most grounds
Unplugged and cleaned all connectors

A whole LOT of time and money, not exactly down the toilet, but could have waited.

Then I tested the field leads for the alternator... Bingo. Two wires, green with an orange stripe, and a solid dark green one. The solid green was showing a ground. Sunuva*****.

Of course, this wiring goes right into the massive main harness, then comes out at the PCM. I cut the wires of at the alt plug, and at the PCM(after double and triple checking they were the right ones!).

The green/orange wire got spliced to itself, and to the new lead going to the alternator. The connection to the main harness is needed, or you will immediately get the "check engine" light.

The solid green wire was the grounded out one. Makes no stops along the main harness, straight shot to the PCM. Cut, spliced to the new lead to the alt.

Wrapped the new leads, routed em over the motor, zip ties to secure it. Later, I'll crack open the main harness and repair it properly. But this repair will last as long as I need it to.

Gauges, trans, all performing perfectly, tested the alt output idling... 13.8V done and done.

 

This happened to me once, check gauges light came on and battery gauge was pinned. Dome lights, gauge lights , headlights etc.. all were based off the revs. Turned out it was a loose battery connection with the negative post. Glad you were able to fix yours aswell.