Sensors in heads?

[ehjorten]

What are the two sensor for in the side of the heads?  I have a one wire sensor in between the middle ports on my 1991 V3500 with the stock TBI 454.  There is one in each head and it has one green wire coming out of it.  I have the two wire coolant temperature sensor in the manifold just below the thermostat.

[zieg85]

I am pretty sure one is for the temp gauge in the dash and the other tells the temp of the engine for the air/fuel mixture to run the throttle body properly. 

[VileZambonie]

The coolant sensor is in the intake manifold near the t-stat housing and is for the ECM. The one in the cylinder head is the coolant temp sending unit for the temp gauge. The other is the EFE switch (Early Fuel Evaporation)

[ehjorten]

Thanks Vile!  What does the EFE do exactly?  The connectors are kind of messed-up so I will probably be buying new sensors and pigtails.  Also...would it be possible that my '91 never came with Air Injection?  The truck has headers and no CAT or air pump.  The port for the air pump (J in the diagram that you gave me I think) is not there in the TB.  It doesn't exist and it doesn't look like it was ever there.  All of the emissions stuff is hooked-up and looks pretty stock.

I failed emissions and the truck keeps getting a periodic code 44.  I did have a vacuum leak at the TB where the hose is suppose to go to the Charcoal cannister.  I rectified that and put a new O2 sensor in.  Replaced the spark plugs (#8 was pretty black...need to keep an eye on that one).  Put a new coolant sensor in too and replaced all of the vacuum lines...some were looking pretty bad.  Haven't checked the MAP sensor yet and need to check fuel pressure too.  I think I can get a waiver though once I have a shop do $150 worth of diagnosis and/or work.

[ehjorten]

TTT!  Anyone?

[VileZambonie]

What did you fail emissions for?

Yes it may not have been equipped with A.I.R.

EFE - Means early fuel evaporation. Evaporation is vaporization. Cold start up fuel does not atomize well so it condenses rather than vaporizes and doesn't burn. This means high levels of HC's leaving in the exhaust, driveability issues etc. So with your era computer control system the EFE controls the thermostatic air cleaner and cold start enrichment program.

[ehjorten]

Hey Vile;

I don't have the stock air-cleaner (crappy Edelbrock open-element), but am looking to get one.  So...the thermostatic valve on the air-cleaner is gone!  The headers do however have a tube welded on for the heat-riser!   That shouldn't be a problem though with a fully warmed-up engine.

Question...what models of chevy can I get the correct air-cleaner from?  I am assuming 87 C/Ks and 88-91 R/Vs with the 454, but I don't know that for sure.

Thanks again for all of your help!

[ehjorten]

TTT...anybody with an answer to the air-cleaner question above?

Thanks,

[ehjorten]

The coolant sensor is in the intake manifold near the t-stat housing and is for the ECM. The one in the cylinder head is the coolant temp sending unit for the temp gauge. The other is the EFE switch (Early Fuel Evaporation)

Got my factory service manual, unit service manual, and electrical diagram/service manual yesterday!   Actually, the one in the LH head is the temp sender for the gauge and the one in the RH head is for the optional electric fan in front of the radiator that my truck has.

[Captkaos]

am assuming 87 C/Ks and 88-91 R/Vs with the 454, but I don't know that for sure.

That would be correct.