Rod Bender

On my 96 Z28 what is the sensor in the engine block just above the oil pan on the right side of the engine? What does it do? Mine has a broken red and black wire coming from it. It is in a spot where I cannot locate where it was connected.

Injuneer

By right side, do you mean passenger side? A single red/black wire, or a pair of wires, one red, one black?

A single red/black wire is used for the A/C pressure sensor, but that's on the A/C line, not on the block.

The only sensor mounted on the passenger side of the block it the knock sensor, but that has a single dark blue wire.

Rod Bender

Thanks for the quick reply, Injuneer. Sorry, I was not more specific. Yes, the sensor is on the passenger side. It looks like a temperature sending unit and the one very small wire is black with a red stripe. Yes, I noticed in the Haynes wiring diagram the wire was to an air conditioner connection. Weird. Also, the engine has developed a misfire. It seems to run normal only for a minute or two after start up. Then it alternates between running rough and smoothing out. Sometimes it accelerates normally and other times seems to be missing on more than just one cylinder. It finally gave a "service engine soon" light, but when I took it to Advance Auto Parts to read, it gave a "Circuit high voltage, Bank 2 Sensor 1 Passenger side" which they said meant oxygen sensor. The engine has headers with the oxygen sensors installed, but no cats. Spark plugs have only about 10,000 miles and wires are MSD. The engine starts and idles normally.

Injuneer

Code sounds like P0152 - HO2S Circuit High Voltage, Bank 2 Sensor 1. Always a good idea to ask them for an exact numerical code and write it down.

That code if for the pre-cat O2 sensor on the passenger side. It sets when the O2 sensor sticks above 774mV for more than 30 seconds. Did the engine seem to run better when the code set/SES light came on? When the code sets, it puts the PCM AF ratio control back in open loop.

Possible causes can be high fuel pressure (but would affect both banks), leak in the fuel pressure regulator diaphragm leaking fuel into the intake manifold via the vacuum line (will affect both sides, but the passenger side worse), leaking fuel injector (one of them could be sticking open, could affect only one bank), EVAP canister purge stuck open, and canister saturated (would affect both banks), MAF sensor (would affect both banks), external contamination of the O2 sensor preventing outside air from entering the sensor thimble via the opening for the wires (would affect only one bank), erratic readings from throttle position sensor (would affect both banks), or an intermittent short in the sensor wires to the 12V sensor heater supply wire (would affect only one bank), faulty O2 sensor (would affect only one bank).

As far as the red/black wire, look at Shoebox's harness photo to see what other wires the A/C pressure sensor wire is bundled with. Note that the connector has two wires attached to it, the red/black wire and the black wire.

95 wiring harness, but yours would be similar:

1995 Z28 A4 Engine Harness

Enlarged area of A/C pressure sensor harness:

http://shbox.com/1/harness4.jpg

One difference on your 96 would be the presence of an EVAP canister vacuum switch. I think that' on the front of the passenger side valve cover (part #11 in the diagram below). But that has a 2-wire connector with a purple wire and a black/white wire. The EVAP purge solenoid (part #7 in the diagram below) is on the bracket on the side of the passenger valve cover, has a 2-wire connector with a green/white wire and a brown wire.

http://shbox.com/1/1996_evap.jpg

Rod Bender

Thanks Injuneer for input and references. The SES light started flashing and the engine ran better when the SES light stayed on - for a few minutes. I thought I was home free. Is the problem the sensor? Could replacing the sensor solve the problem, or is the sensor just the purveyor of bad news?

MyfateZ28

so this sensor that you are asking about-- being broken-- one wire running to it, it is a knock sensor, has a grey plastic clip that looks weird. i just did my starter the other day... i know the one you are describing.

https://www.google.com/search?q=knoc...YXhjSMD1JQ4%3D


Sorry for the length of the link, but is this the sensor you are talking about?

Injuneer

Interesting, but he said it has a red/black wire, and the knock sensor has a dark blue wire, as I noted in post #2, when I explained that was the only sensor on that side of the engine block.

MyfateZ28

Mine is black with a red strip, just jacked her up and looked mine might be aftermarket?... but it Definitely is red and black and is right above the oil pan mid way on the pass side on my 96'

shoebox

Hmm...factory manual says it is dark blue.

Rod Bender

Yeah, Myfate. That is where the sensor with the broken black/red wire is located. The sensor does not look like yours, however. Mine is for an lt4. Would that sensor being disconnected make the car run so erraticly when driven normally? It seems to run normally for the first minute or two after cold start up. Eventually it will surge and alternate between about what feels like two or three cylinders missing and then everything firing ok for about two seconds. Tomorrow I will jack it up and try to get the wire connected.

Injuneer

The LT4 uses the same knock sensor as the 96/97 LT1. Only the knock module is different in the LT4, but the knock module is in the PCM.

If the knock sensor is disconnected, there should be a code set, and the PCM will pull up to 15° of ignition timing, varying with engine operating conditions. It is possible to use a resistor to eliminate the code, but that also eliminates the PCM's ability to respond to knock (detonation).

I checked the 1996 factory manual numerous times, and it shows that wire as dark blue.

Rod Bender

Thanks Injuneer. Then what the heck is that thing?

Injuneer

If it's screwed into the block, jut behind the motor mount, it's the knock sensor. Why there is a difference in the wire color is not clear, but apparently another OBD-2 LT1 (96/97) has the same red/black wire.

If yours is in that position, but does not resemble the photo, then you have to post a picture of it so we can try and figure out what it is.

The photo in the link above is Shoebox's photo of the knock sensor on his 95:



This is for an LS1, but yours should look similar:

Rod Bender

The part of interest looks similar and is in the exact same position as in the photo. I looked closer at the wire coming out of the connector and it is black with a light blue stripe - just as it is supposed to be. However it is joined with a connector to the black with red stripe wire. It looks like someone had spliced it into the air conditioner lead. When I looked to find the wire it had been connected to I found a broken off black/red wire which could, if really stretched, reach. But will no current going to that sensor make the car run so crappy under normal driving conditions?

Rod Bender

I see in the Haynes book that a blue/black wire goes to an idle air control valve, a fuel injector and a brake switch. The wire to the knock sensor is dark blue (as has been noted). Where do I find the dark blue wire coming from the PCM?