Speedometer weirdness and engine hesitations

[DaveF]

So weird issue with my 06 LJR Saturday... started it up in the morning, ran fine, no codes... got on the highway and noticed the speedometer was swinging up and down by like 10-20mph, and reading way higher than I was going. Confirmed from others on radio that I was doing about 50 and the guage was bouncing between like 65 and 85mph.

Then the engine started hesitating or cutting out for like a split second seemingly randomly as I drove.

We stopped at a meet up point, revved the engine up to like 2500rpm and left it there, no hesitation or anything. We then drove down the road to the trail (max 35mph) and the speedo was still acting weird but no hesitations. 6 hours later (we were working with DNR to pickup trash on trails, so spent that 6 hours in low range stop and go) and I hit the highway to head back to camp, low and behold speedo was now dead on (no swings) and no hesitations.

Curious on what could have caused it, and the seeming correlation makes me wonder could the speedo swings cause the hesitation somehow?

 

[tr21triton]

Yep, I think you're about to be another @Wranglerfix customer.

 

[Wranglerfix]

Auto or manual transmission?

 

[suicideking]

You're not running a speedohealer are you? If not, likely need a PCM from Wranglerfix.

 

[macleanflood]

Good job on the trash pickup!

I'd be looking for wiring issues. Definitely a visual inspection on the wires from the transfer case to the PCM.

-Mac

 

[Apparition]

When my VSS failed the speedo did some crazy things.

 

[DaveF]

Auto or manual transmission?

auto 42rle

 

[DaveF]

You're not running a speedohealer are you? If not, likely need a PCM from Wranglerfix.

no, haven't touched anything with the speedo previously, or the tranny... closest was installing the rubicrawler

 

[Wranglerfix]

How is your shifting from 1st to 2nd in the morning? Are you getting any codes?

 

[DaveF]

How is your shifting from 1st to 2nd in the morning? Are you getting any codes?

a bit of a hard shift at times before it warms up (needs a bit more rpm before it shifts) but no codes

 

[Wranglerfix]

The hard shift from 1st to 2nd is the transmission side of the computer failing you… It will not cause a check engine light and usually happens twice until up to operating temperature. The instrument cluster is controlled by the Pcm. It is not a common occurrence but could be the cause of your speedometer issue.

 

[DirtDawg]

Agreed that the root cause might be related to the speed sensor or wiring harness connector for that. In my case (2005 TJ), after removing the prior old-school Superlift speedo calibration box in combo with changing from 35" to 33" tires, I discovered the speedo sensor connector latch had been damaged previously and wouldn't stay engaged even when secured temporarily with gaffers tape. That was a few weeks after replacing the OEM PCM with one from WranglerFix (proactively). At the start of one trail run (subsequently aborted), the trans flared into false neutral a few times concurrent with no speed displayed on the dash, along with CEL and code. I suspected the sensor harness connector being briefly disengaged had "confused" the PCM, which apparently requires consistent speed signals. Ordered and installed a new Transfer Case Speed Sensor, along with SpeedoHealer and no more issues in roughly 1000 mostly off-pavement miles.