merrillgtrs

I am just about done with rewiring an 86 C4 but have a question as to the EGR diagnostic temp switch wiring. the factory service manual dated late 1985 shows the wire coming off the switch to be a .5 dark green when the one on the car is a larger 3.0 black with the same connector as the O2 sensor. the car is a late 86 with aluminum heads. the only other connector left is the same size and color down on the block that feeds out with all the other harness grounds next to the oil temp sending switch, and is shown as a ground on the fsm schematic. would this be correct for the EGR diagnostic temp switch, which would make the switch basically be a heated ground for the rest of the EGR system? if this is correct an extension wire would be needed, and I do have the correct connector with the wire cut off from someone in the past.
thanks in advance for any help

Cliff Harris

The connector near the oil temperature sensor is for the O2 sensor.

The connector for the EGR temperature switch is buried in the wiring behind the distributor. It tells the ECM when the EGR valve has opened to verify that the EGR system is working.

gman35

that is correct.. i just fought that bugger to get it connected.. mine had been disconnected before i aquired the car.. I had to use two pairs of very long needle nose because i could not get my hand back there..

merrillgtrs

thanks for the help. I have it backwards because of the EGR diagnostic wiring I have being the same color and gauge as the O2 sensor, maybe being made up by someone in the past. I have located the wiring for it behind the distributor and will now make up an extension for the O2 sensor, which must be the other connector with the cut off wire that I have. too many years of too many people working on this car not knowing what they were doing. thanks again

HlhnEast

Sounds like you have the preliminary or "white cover" '86 FSM. It is basically a copy of the '85 with the few things that GM knew were different for the '86 MY. Since our C4's were a constantly evolving critter the prelim or white cover FSM's are not the best source for intricate information. Since the '86 also had the aluminum heads and convertibles added during the years production, no telling what info may be lacking.

All I have to add is "Good Luck!!"

Cajun CB

You can go to Harbor Freight or similar place and get some medical clamps that are 12" long. These will help in getting the connector closed.

Cliff Harris

A lot of information in the FSM is generic stuff that applies to all GM cars, especially the section on AC charging, etc.

All '86s were supposed to have aluminum heads, but there was a problem with cracking on the aluminum heads, which is why early '86s have cast iron heads. The FSM writers apparently didn't know about this or it was too late to change it because everything refers to aluminum heads.

The table that shows the 700r4 pressures in various gears has a huge table of transmissions, but the MD8 version used in Corvettes is NOT listed.

The FSM has a lot of problems and some of the information is just plain wrong. The section on how to adjust the TV cable shows pictures of carburetors...

The HVAC section is pretty weird. There is a picture in my '86 FSM that shows the '84 heater water valve, which is unique to '84s so it's obviously wrong. On the very next page is a picture of the correct setup. The section on how the C68 HVAC controller communicates with the HVAC programmer is completely wrong. I think there was a design change and the writers never got notified.

Here is one of my favorite examples of FSM problems. The first picture is a heavily modified version (by me) of the second picture directly from the FSM (FP fuse is not shown, fusible link H is not shown, the circuit number of the fuel pump voltage going into the ECM is wrong. I added connector numbers.):