Speedo and tach problem
Thread Starter
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Senior User
Joined: Mar 2005
Posts: 214
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From: Nottingham, MD
Speedo and tach problem
Hey, I have a 01' Expy that I just finished swapping the engine from a 4.6l to a 5.4l. I immediatly noticed the speedo and tach are off. Reading slower than I am actually going. I took it to a local dyno shop and the owner said the speedo is off by 5 mph at low speed and increases in difference as the speed is increased. As well as the tach. Reading 200-300 rpm lower then normal when at idle. The only thing i'm worried about is the shift points since the PCM uses the tach to determine them. When I swapped the motor I didn't do anything to the tranny and kept my PCM that came with the truck. The tuner didn't mess with the tranny either. Would the VSS be the culprit? Thanks for the help. Chris
Thread Starter
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Senior User
Joined: Mar 2005
Posts: 214
Likes: 0
From: Nottingham, MD
My tuner said the PCM is getting a bad signal from a sensor. So it's not my PCM. He just finished tuning it and WOW what a difference. I brought it in and she had 133hp and 260ish ft/lbs at the wheels. When he was done she has 205hp and 280ft/lbs at the wheels. Big difference. He was able to correct my speedometer but can't do anything with my tach. The trucks runs great and the shift points are on and firm. Just the display is incorrect. I think I'm just going to leave it be since the speedo is reading correct now. But eventually it will bother me enough that I will fix it. See ya, Chris
