Tachometer
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Tachometer
OK so maybe someone can explain this. On the way to work this a.m. I'm driving my '98 Ranger Supercab 4.0L Automatic at 73 mph on cruise control and the tach is registering 2600 rpm which is normal for this speed. A few seconds later a gauge scan reveals that the tach is registering 3000 rpm, with no increase in vehicle speed, while on level ground, and with no apparent increase in engine noise.
Additionally, the O/D light was not illuminated nor was the check engine light. I slowed to 60 mph then increased speed back to 73 mph, set the cruise control and waited. A few minutes later the tach dropped back to the normal reading of 2600 rpm without a change in engine noise and still no check engine light nor O/D light.
Haven't had the chance to pull the codes but wondering if anyone had any ideas. By the way it didn't do it for the rest of the day and the transmission was flushed by the Ford dealership about 10k miles ago.
Thanks in advance for any ideas.
Additionally, the O/D light was not illuminated nor was the check engine light. I slowed to 60 mph then increased speed back to 73 mph, set the cruise control and waited. A few minutes later the tach dropped back to the normal reading of 2600 rpm without a change in engine noise and still no check engine light nor O/D light.
Haven't had the chance to pull the codes but wondering if anyone had any ideas. By the way it didn't do it for the rest of the day and the transmission was flushed by the Ford dealership about 10k miles ago.
Thanks in advance for any ideas.
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From: SW Va
Bet you were running in some hills & the tranny down shifted on it's own when the engine began to lug in OD.
After the engine load eases. it'll shift back into OD & the rpm will drop.
The tranny is normaly in OD, every time you start it up.
The only time the OD is off is when you switch it off with the button on the end of the shift lever. When you do this, the "OD OFF" dash light will illiminate.
The OD will remain off until you push the switch again, or shut the engine down.
You can also implement a downshift by lifting off the accelerator for a half second or so, then getting back on it.
I find this handy when towing in hills & want to keep my speed & rpm up so the engine doesn't lug. Again, once the engine load has eased, it'll up shift on it's own.
After the engine load eases. it'll shift back into OD & the rpm will drop.
The tranny is normaly in OD, every time you start it up.
The only time the OD is off is when you switch it off with the button on the end of the shift lever. When you do this, the "OD OFF" dash light will illiminate.
The OD will remain off until you push the switch again, or shut the engine down.
You can also implement a downshift by lifting off the accelerator for a half second or so, then getting back on it.
I find this handy when towing in hills & want to keep my speed & rpm up so the engine doesn't lug. Again, once the engine load has eased, it'll up shift on it's own.
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Originally Posted by dhag911
the 4.0 can pull some major hills and not down shift
Sorry if I confused some of you. I do know when the transmission downshifts for load, the only problem is that when it does, there is a corresponding increase in engine noise that is associated with the increased rpm. In this case the engine was still making the same level of noise and the vehicle was on straight and LEVEL road so no down shift was warranted. I am convinced that the transmission did not downshift.
There are no hills on my route to work that require a downshift. When I had transmission servo problems (repaired by Ford) two years and 100k miles ago the O/D light came on to signify that the transmission was experiencing difficulty. At that time there was an issue with the upshift/downshift and the O/D light was valid for that problem. Also, once this problem surfaced it did not just go away like it did this time.
Hope this clarification helps.
Thanks
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This is kind of out there, but, maybe the vss is going bad/loose or something. If it reported a lower speed, the cruise may have upped the rpm to maintain speed, the speedo was maintened at the same speed, and you didn't notice a slight speed increase. Then as it started reporting the right speed again, the cruise brought the rpm down to the correct speed. The vss signal provides drive for the speedo and the cruse, but the tach get its reading from the PCM based on the engine. (I think).. Just a guess.
Dave
Dave
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Originally Posted by Dave257
This is kind of out there, but, maybe the vss is going bad/loose or something. If it reported a lower speed, the cruise may have upped the rpm to maintain speed, the speedo was maintened at the same speed, and you didn't notice a slight speed increase. Then as it started reporting the right speed again, the cruise brought the rpm down to the correct speed. The vss signal provides drive for the speedo and the cruse, but the tach get its reading from the PCM based on the engine. (I think).. Just a guess.
Dave
Dave
Thanks,
Mike
