gta_knight

Hi all,

Ive got an 84 Trans Am and im just wondering what the two sensors in the thermostat housing are called so i can find them on rock auto.

one of them is snapped off and not connected to anything and the other looks questionable and has electricians tape wrapped round it !

Drew

iTrader: (58)

The one with wires is probably the coolant temp sensor, the other is the vacuum switch that controls the EFE valve.

NoEmissions84TA

iTrader: (1)

Yes, coolant temp sensor for the ecm, not the gauge.
Years ago, GM updated the sensor and pigtail (connector) because a hose (I think) laid
right across the wires, bending them at 90 degrees, causing an intermittent connection.
Get the matching pigtail for the new sensor that you buy.

sofakingdom

iTrader: (1)

Make sure to get the coolant temp sensor that comes with the replacement pigtail. The original pigtail is ALWAYS crumbled to dust and self-destructed, even when the sensor itself is still good. It was in fact originally wrapped in some kind of black gooey tape, different from normal electrical tape. Disgusting.

EFE valve is the "flapper" thing in the right exhaust manifold. The vacuum switch in the water outlet sends vacuum to it, to operate it, when the engine is cold. Full name of the switch is EFE thermal vacuum switch, abbreviated TVS.

gta_knight

I will have to double check on rock auto for the right one then. so the other one, can i just leave that then saying as that stuff doesnt appear to be connected up anyway ?

NoEmissions84TA

iTrader: (1)

If the ECM is still controlling the engine, then you need it.

gta_knight

Dang. I don't even know what it does. Why does a flap open on the exhaust ? Also my EGR valve is disconnected. And I also noticed the vac sense that bolts to the top of the firewall has no vac line going to it either when looking at the exhaust flap thing

NoEmissions84TA

iTrader: (1)

Is your carb still the computer controlled version - E4ME?
It sounds like someone tried to disable all the emissions components.
You can't just go half way. Everything else must be changed to manual like a 70's musclecar.

gta_knight

It is yeah. The only emissions thing that still appears to be hooked up is the charcoal canister. I got rid of all the emissions crap on my 87 which is a 5.7 TPI but I had to have my chip redone when I removed the egr valve.

I'm not sure if this is the case for a carb even if it is electronic

stahrman0612

Hey...just checked out your face book page....WOW your Kitt car is amazing!!! Brings back a lot of great memories when I was a kid watching Knight Rider.

sofakingdom

iTrader: (1)

The flap in the exhaust is there to make it warm up faster: it only does anything when the engine is cold.

If the thing that looks like a vac sensor is in the center of the firewall, just under the lip where the hood seals to, and has a connector that's a different color (blue if memory serves) then it's not a vac sensor; it's the baro sensor. It gets no vac line, and is actually measuring ambient air pressure. Given that "vacuum" is THE DIFFERENCE BETWEEN the pressure in the manifold and the pressure in the atmosphere around it, to really accurately measure "vacuum", the ECM needs BOTH of those parameters. The manifold absolute pressure (the other half of the "vacuum" measurement) sensor is on the left side of the engine compartment right near the brake booster.

gta_knight

Thanks man, i had a look today and your right, so this one just hangs here as it is and does its own thing ?



And here is the other one by the booster, which has no vac line on it. So im wondering if this is why im getting a code 34. I dont suppose you know where the vac line for that comes from do you ? that would be a nice easy fix if it gets rid of the code 34 !

NoEmissions84TA

iTrader: (1)

I believe that is a vent. When new, they sometimes had a filter on that nipple. They deteriorate and fall off easily.
The vac sensor by the brake booster should have a vac line connected to it.

gta_knight

Oh right I thought it was a vacuum sensor therefore should have a vac line. I'm not sure what's causing the code 34 then

sofakingdom

iTrader: (1)

There should be a vac line going to that, somewhere. Maybe on the bottom.

If there's not one, then yeah, the ECM is going to complain. It normally hooks up to a port the base of the carb, facing the rear, on the US passenger side.

gta_knight

Ah right. I will check that later then thanks.

gta_knight

Got it ! the vac line had been tucked back into the wiring harness near the firewall. connected it up, started the car and it idled high for a little bit then came down to what sounded normal and then after a few minutes the idle went back up again and stayed there, maybe around 1000-1100 rpm.

So its obviously made a difference plugging this vac line into the sensor. I wonder if it being unplugged when ive done the timing its been over compensating or something. I will redo the timing tomorrow and see how it goes

NoEmissions84TA

iTrader: (1)

DID you still have code 34?

gta_knight

Not with it just idiling in the garage. The SES light only came on after I drove the car to the end of the road and back the other day so I will try moving it again tomorrow. (Won't shift out of 1st so can't drive it properly) so many problems !