Ok, so I live in CA, and I have to get my car smogged, but you will fail if the Service engine light is on.

I have a 1986 Z28 Camaro, Carburetor, Manual transmission, 5.0L 305 V8.

Heres the deal:

Ive given the car a complete tune up, new spark plugs, wires, distributor cap, rotor (found out the firing order was wrong as well so fixed that) replaced oxygen sensor and thermostat. Went to junkyard and replaced the radiator overflow tank, but the cap still doesnt seem to lock air tight...

The fan wouldn't come on at 220 degrees like it was supposed to so I added a switch to the relay just so I could drive it without overheating.

The car had a gas leak at the fuel filter near the carb, just needed to tighten that bolt. so fixed that.

After that i replaced the ignition cylinder, so I had the battery disconnected for a couple of hours so it had time to reset as well, but it came back.

Now my mechanic said he was pretty sure it had something to do with the fan not coming on, and believed that this small electrical plug right in front of the carb was a pressure sensor for the fan, and that it wasnt working, But im not quite sure if he is right...I check the manual and Under the Engine Coolant Temperature Sensor (What he was pointing at) it says that a failure of this sensor will get a code 14 or 15, so im pretty sure he is incorrect.

Now this whole time the check engine light has been on...I just got around to checking the code and this is what i got:

CODE 34

According to my Haynes manual:
Code 34: Carburated models:
"Differential Pressure Sensor - Leaking or restricted vacuum hoses; poor electrical connection, open or short in circuit; defective ECM."

According to this sites tech articles:
Code 34:
" Low voltage (high vacuum) at mass air flow sensor (or MAP sensor)"

Does anyone have any idea what to check or where to start on troubleshooting this problem?

i should note that I am not a mechanic,, but like to think of myself as mechanically inclined, and bought this car to learn all of this stuff, so detail in any explanations or suggestions would be greatly appreciated.

 

Code 34 on a carbureted car comes when the MAP sensor vacuum reading is too high (voltage is too low) at low engine speed, or is too high at high engine speed while the throttle is open. Make sure the MAP sensor is connected correctly.

 

Ok checked the manual, and you were right, MAP sensor is the same as differential pressure sensor...

So I ran out and checked the MAP sensor on my car, and it looks like the tube next to the MAP sensor quick connect electric plug is missing...theres a housing there for a tube to be inserted, but its open to just the air.

Now right next to it i noticed some tech flex, T(The black plastic stuff used to wrap wires, IDK what its called), and comin out of that was a TINY tube not connected to anything, maybe 1/16 of an inch think, but the input on the MAP sensor housing is about 1/4 of an inch thick...

are these two supposed to be connected?

if not, where can I find the tube that goes into the MAP sensor housing? where does it go?

THANK YOU!

 

It should just be hooked up to manifold vacuum. Here is the diagram, see "vac sensor"

 

Thatnk you that diagram helped a lot.

Ok so I traced that tiny vacuum hose to the right place, but the thing is, that hose is too small for the housing...I dont think it was stock like that, Ive never seen a vacuum hose that small..

My question now is will it affect the vacuum if I replace that with a normal smaller vacuum hose and run that between the carb and the sensor?

Also, If I reset the light after replacing the hose and it doesnt go away, does that mean I need a new sensor?

 

The factory lines are small with a large rubber connector ( usually a 90 degree ) on the end that goes on the fitting.You should be fine to run any sized vac line

 

With the MAP sensor disconnected, it should be reading vacuum too low, not too high.

 

Well im not sure what happened then, because when i hooked the new hose up, the light disappeared!!!!

Thank you guys so much!