87 Suburban temp gauge reading max

[KeyBlazer]

I just rebuilt the 454 motor and now the temp gauge is pegged all the way to the max even when the ignition is off.
I broke the plastic connector to the sensor in the right head(Pass side), but it reads the same connected on not.
Also there is a grean wire that comes out of the harnes near the firewall that I am unsure about... its a single grean wire. There is a temp sensor on Left head too, but I unsure if it goes there...
Any ideas?

 

[4X4HIGH]

The green wire is the temp sender wire and it goes on the driverside head.

 

[KeyBlazer]

Ok, Thanks.
So what is the other one on the pass head??

 

[4X4HIGH]

Ok, Thanks.
So what is the other one on the pass head??

I've never seen a sender on the passenger head of any SBC or BBC but i'm not saying yours doesn't have one. Stranger things have happened before and people do all kinds of different things to their rigs over time. Get a pic of the wire and the sender and maybe someone can help you figure out what it is and if it's factory.

 

[cuervo]

My 87 Jimmy also had a sensor in the passenger side head as well. There was never anything hook up to it. I'll check my 91 today and see if it has the same thing.

 

[k20]

what did the plastic connector look like on the pass head? Could be a knock sensor or something. When the guage is pegged it means its grounded out somehow, that is actually the gm test for the guage, to remove the wire and touch it to the exhaust manifold and see if it makes the gauge go to full hot.

 

[KeyBlazer]

When I pulled the motor I thought I had labeled everything, but the motor was out longer than I thought and my memory faded a little!
Here is the really stupid thing... the green wire that came out of the harness that we think maybe the drive side temp sender ended up trapped between the trans and motor when i connected the two... the choice was pull the TH400 out.... or snip off the connector! I chose the latter.
The connector on the other side broke apart as it was so brittle. It maybe a knock sensor... the single green(also) wire comes out of the engine harness above the middle of the pass side head and drops down to the sensor.
I will take some pics tonight and post.
I cant get the motor to run well... it starts good and runs, but sometimes it bucks and surges at idle. It just does not feel right. My gut feeling tells me a vac leak.
Its throwing a code 32 and 33, so I checked the EGR valve and it seemed to be fine, but I cant seem to get the 6" of vac at the pipe it says it should have... I get 12" at the booster tho at idle.

 

[Thunder]

Code 32 and 33 together usually point to MAP sensor problem. Is the vaccum line hooked up? or maybe broken?
Also you need to hook up the knock sensor. The ecm wont allow full timing advance without the KS hooked up.

 

[KeyBlazer]

I looked into it again today, and decided to swap the gauge, just to see if that was it...
It reads normal now!
The gauge clearly went bad!
Thanks guys!

I reset the codes by disconnecting the battery. I spotted that the vac hose that goes to the canister was off, so I reconnected that.
It runs good when cold, but then it still begins to hunt at idle when warm.
I will drive it tomorrow and see if the check light comes on again.