Tachometer and Boost Lights seemed reversed?

[btroadman]

I just bought another Grand national for very cheap. One problem is that when I started it up the Tachometer is maxed out and stays there, and the boost lights seem to rev with the engine. Is it possible that these were somehow reversed when someone worked on it? If anyone knows what I can check out please let me know. TIA.

 

[stealth908]

Not reversed... BROKEN

my tach and boost gauge did the exact same thing. exactly! the tach climbs from 0-redline gradually after you turn the key? the boost gauge reads like 2-3 psi at idle, and it goes up as you accelerate? that's what mine did.

i didn't really worry about it, but it bothered me a little. i replaced the whole gauge cluster. the new tach and boost gauge on the new gauge cluster work perfectly. your gauges are bad!

the tach and boost are digitally controlled on the same circuit board. you could probably just replace that portion. it has two screws on it. probably cheaper and easier to replace the whole cluster though. you'll have to take the cluster out and disassemble it to get the circuit board out. good luck getting the connector for it unplugged. it's almost impossible to get to.

 

[Turbo Ryan]

As old as these cars are, most don't have boost and tach gauges that are even close to accurate. However, it sounds like maybe you have two plugs plugged together that shouldn't be. Behind the alternator there is a couple of white wires with on one green connector and a grey wire with a black connector. They should not be connected. When they are connected they cause the problem you discribed with tach. Then boost guage is a whole nother issue that can only be fixed with a lot of money and aggrivation.

Ryan

P.S. If what I discribed "fixes" your tach problem, don't expect it to be accurate. It might be close or be off by as much as 1000 rpm or more.

 

[GNVenom]

Send the boost/tach assembly to Caspers. We can recalibrate the unit. It involves replacing both of the calibration IC's and bench testing the unit.
It's a REAL common problem with the boost/tach modules to go out of calibration and show abnormal indications of boost and RPM.
-John Spina
Casper's Electronics Inc.

www.gnspyder.com

 

[btroadman]

It is more than just being out of calibration to me. stealth908 hit it right on the head, it is doing exactly what he said. You turn the key on and the Tach jumps up all the way to red and stays there. Then the boost idles at 2 or 3 psi and jumps up when I rev the engine in or out of gear. The extra boost autometer gauge works perfectly though.

If I send it to Caspers do they guarantee it will work? And do you know the median price range for this type of thing?

 

[spooky]

mine too

see GMVenom for quality fix

 

[Vendor Defendor]

Originally posted by Turbo Ryan
Behind the alternator there is a couple of white wires with on one green connector and a grey wire with a black connector. They should not be connected. When they are connected they cause the problem you discribed with tach. Then boost guage is a whole nother issue that can only be fixed with a lot of money and aggrivation.

Ryan

Ryan, or anyone for this matter, correct me if I am wrong, but if that Black connector gets a hot wire to is (12v) it begins to run the fuel pump... that way if you take your fuel gauge off, or if you don't have one, the shrader valve out, it runs the fuel pump so you can drain the gas tank? I did it once, worked for me... but my car is a freak...

 

[Dan Thompson]

The single black connector is for the fuel pump. If I take the connector off the under hood light, 12v, and touch it to the single black connector behind the alternator, the fuel pump runs. I check my fuel pressure this way and when I want to drain my fuel tank I can turn the pump on and off this way.