83 Chevy C20 Suburban 454 engine wiring

[blakeduren]

Hey square body fans,
Two questions:
1. My 454 HEI distributor has a factory wire running to the TACH spot on the cap...but this is not a truck with a tach...what is this for? AND I want to add a tach...is there a great place to splice into this?

2. On the drivers side valve cover, there is a electronic thingy bolted down...factory wiring harness...is this part of the cruise control or the turbo 400 down shifting?

Thanks in advance

[Dead Parrot]

I had an aftermarket cruise that used the HEI tach signal for speed control. I thought most of the square factory cruises used the speedometer cable for speed sensing.

My 68 Impala had the TH400 kickdown as part of the throttle cable bracket on top of the intake. I think shortly after that, the kickdown switch moved inside the cab near the gas peddle.

[blakeduren]

I believe that 83 was the first year not to use the speedo cable for the cruise control. My speedo cable is a one piece and I have factory cruise.

The kick down cable on the throttle is there for the 400 and the orange wire is there for the 400.

[THI]

GM used the speedometer for the cruise control through 1989, it used an optic on the back of the speedometer that also doubled as a speed sensor for the computer. They changed to a VSS when anti-lock brakes were added to the rear axle in 1990.

As for the wire to the HEI tach terminal, the only time I have seen a factory wire there is when it also had a factory tach. Might want to investigate where it goes.

[blakeduren]

I have not traced the tach wire yet....but this suburban is pretty original and I don’t think someone ripped a factory tach OUT of this truck. I will look into it more though.

Here is a pic of the electronic solenoid in question. It is 2x2x1 or so. Bolted to driver side valve cover. Emissions equipment related??? After looking, maybe it is not related to the cruise control.

[blakeduren]

Engine idle speed switch. Gm part 477322? Maybe?

[blakeduren]

The electronic thing, engine idle speed...seems to be for emissions. #51 in this picture. Still...I have no idea what it does. All of the other emissions things are run by coolant temp or vacuum...but this one is electrical.

[blakeduren]

Ok....so my plan is to unplug this thing.(engine idle speed switch?)..and unplug the tach wire and see if something stops working.
My 454 is stripped of all the emissions equipment but does have the solenoid that bumps up the carb idle for when A/C is on. I will check to make sure the cruise control still works too....
Any other thoughts?

[blakeduren]

So...the tach wire leads to the speed sensor to help activate the solenoid to send vacuum to the pot on the carb to bump up the idle for the A/C.
This system was for 78-84 I believe.

[LT7A]

Originally Posted by blakeduren

So...the tach wire leads to the speed sensor to help activate the solenoid to send vacuum to the pot on the carb to bump up the idle for the A/C.
This system was for 78-84 I believe.

Thanks for running this to ground and reporting back. I would have probably had the same questions on my Suburban at some point.