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2000 Suburban speedometer is reading 2x as fast

Kay86K5

Kay86K5

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I own a 2000 Chevy Suburban 2500 with an LQ4 6.0L and 4L80E. About a year ago I rebuilt the motor, put a cam and lifters in it, swapped out the 3.73 geared diffs for some 1 tons with 4.11:1 gearing. During the process I sent my computer off to be tuned. The tuner knew my new parameters and gearing. When I hooked everything back up everything worked great except my speedo.

My speedo reads exactly 2x faster than I am going. Once I hit 50mph the speedo just pegs out at 100mph and I have to tell speed via rpm's. I contacted the guy who tuned the computer and he swears he put the gear ratio in correctly, he keeps records of what he does to everyone's computer I guess.

I am at a loss as to what could be causing it.

Your experience is appreciated.
 
The VSS should put out 40 pulses per revolution. Verify that or have someone check the ECM to verify how the speed sensor input was modified.

Does it shift super early?
 
Update... I had wayne hartwig retune it for some 8.1L injectors as replacements for the stock 6.0L. He confirmed that the pcm is set for 40 pulses per revolution for the vss. The speedo still reads exactly double.

One thing that I failed to mention is that i swapped out the original front 9.25" ifs and rear 9.5" semi float that were stock (3.73's) to a 9.25" ifs front and 11.5" aam rear with 4.11 gears. I picked up the axles out of a 2001 2500HD and I don't remember if it had autotrac or not. My Suburban has autotrac. I just plugged in the 4wd actuator harness/connector into the new actuator on the 4.11:1 9.25 ifs front. There are 5 prongs in the connector on the actuator side (donor), and just 4 wires/female connections in the harness (stock burban). I am not sure if this is significant or what that 5th, now unused, connection is for. Currently everything, including the autotrac, works like a charm.

Wayne recommended that I check the 4wd low switch circuit because he thinks that the transfer case control module thinks that I am in 4Lo all the time. I disconnected connection C153, which is supposedly breaks this connection and the speedo still reads double. My transfer case control module (tccm) is tucked way up in the dash and is a pain in the A$$ to get to.

If there are some good 2000's silverado/tahoe/suburban techs that know these systems well your input is appreciated.
 
Blue85 said:
Low range is exactly 2:1?
Click to expand...

No. The chain cases are 2.73:1

Do you have the ability yo read sensors on a scanner? I haven't dealt with your issue but would be niceto see what all tthe output speed sensors are doing. I know the autotrac tcase is weird about having a load of the front shaft to move the rear shaft. Probably unrelated
 
blazinzuk said:
That was you huh? Lol my buddy Josh is skinny pedal on there. Wayne knows the problem now he should be able to get ya squared if not pm skinny pedal on pirate
Click to expand...

This whole thread was actually started by my brother (kayjef on pirate) just using my username and sign-in. He's not on ck5, so wanted to use my login to get more opinions. I didn't even know he put this on here. And I think for future people looking on ck5, he wanted to kinda wrap it up.
 
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