Tachometer / Transmission (4D56)

connorwhite.online

connorwhite.online

Active Member
My tach has been out of commission since I bought the van, but I assumed it was a 'read-only' value that had no correlation to the A/T shifting. It wasn't until recently that a friend indicated a point in my acceleration where my transmission was hesitating. I'd assumed this was just a dip in power before the turbo spooled up but now that he's said it, it's quite obvious my A/T hesitates jumping from 2nd to 3rd. My question is, does the tachometer (crank position sensor? or wheel speed sensor?) output control the transmissions shift points? This is obvious on newer engines, I just assumed the ECU was too archaic for that level of communication.
 
You've got a diesel, the rpm is taken from the IP pump and it doesn't talk to the transmission. More likely it's the throttle position cable.

Automatic transmission kickdown or throttle cable adjustment.

Our primitive mechanical automatic gearboxes' shifting is regulated by a hydraulic "brain", a complex arrangement of pistons and springs and valves. To decide when to shift, the "brain" looks at engine speed, road speed, and accelerator position. Accelerator position is indicated by the throttle...
delicaforum.com delicaforum.com
 
sk66 said:
You've got a diesel, the rpm is taken from the IP pump and it doesn't talk to the transmission. More likely it's the throttle position cable.

Automatic transmission kickdown or throttle cable adjustment.

Our primitive mechanical automatic gearboxes' shifting is regulated by a hydraulic "brain", a complex arrangement of pistons and springs and valves. To decide when to shift, the "brain" looks at engine speed, road speed, and accelerator position. Accelerator position is indicated by the throttle...
delicaforum.com delicaforum.com
Click to expand...
Sweet, thanks Steven. Any insight into common faults of the tach gauge? Hoping it's just the gauge itself and not the input.
 
I think the most common fault is a bad electrical connection, often the harness plug at the IP/sender. Might need to clean or replace that connection.
 
Interesting. I came to the forums to mention that today I started and drove my van after it sat for 3 weeks. Before the three weeks I drove it a few times over the course of 5 days, and before those 5 days of minimal driving it had been sitting for 3 weeks again. Anyway, I noticed today I have no life in the tachometer. Then a little ways into driving it started bouncing like it was coming back to life. 10 mins later it was reading again and from what I could determine, accurately.

Don't mean to hijack the thread, just thought it was too relevant to start a fresh thread and was curious why the tach might die on me, then come back to life.
 
prayforsurf0 said:
Then a little ways into driving it started bouncing like it was coming back to life. 10 mins later it was reading again and from what I could determine, accurately.
Click to expand...
Yeah I'm getting a bit of a bounce. I just cleaned out all the IP wiring connections with contact cleaner and the tach has a range of motion now, but its still hanging well below the 0 mark (like -30deg). I may have to go behind the gauge-cluster. Tried reading the multimeter on the wiring but I'm either dogshit at using it or fairly certain the meter is faulty. (Klein Tools M400)
 
I also have a tachometer that was bouncy and now is dead, temp needle also doesn't work. The electrical feedback to the plug seems fine and ive cleaned and tightened things up. I'm kind of at a loose now for what could be wrong.
 
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