Cyl. head CTS drill+tap size needed....

[Spankdamonkey]

Hey all,

I had asked this once before on Bstuff.com, but there was an 'incident' involving a hacker.....and said topic was lost.

Anywho, could someone re-enlighten me to the necessary drill and tap size I will need for my 3x00 heads? (the single wire sensor for the gauge)

Also, for my own knowledge, what year did GM stop using the cyl head sensor and switch to the 3-wire version in the LIM?

[3100 MPFI]

not sure exactly when they swapped, but my 1996 Grand Prix had the 3 wire sensor.

Why not use the 3 wire sensor? Or is this in something like a Fiero?

I am using the 3 wire sensor in my 1990 Grand Prix STE with the 3.1 MPFI, and it works fine. I also used the 3 wire sensor in my 3100 swapped into my 1988 Cutlass Supreme, and it is calibrated correctly for my cluster as well (1992 analog cluster).

[Spankdamonkey]

Nah, the car is just a '95 Beretta. Personally, I've always like the cyl head sensor, IMO gives a better reading of temp seeing as it's placed right next to the heat source lol. The other reason.....my buddy and I tried the 3 wire sensor in his z24 and it ended up doing funky things on the gauge (fluttering up and down) so I;d rather keep it the way it is.

I BELIEVE the information given to me on bstuff was a 3/8" drill bit and 7/16" tapered tap. But I really wanted to confirm this.

[Superdave]

I'm running the 3 wire.. in the rear head, haven't noticed a difference between that and when it was in the LIM. Never had any fluttering, maybe he had a bad ground wire?

IMO it's better to have in the LIM right next to the Thermostat that way you get a true reading of the overal coolant temp, not just a hot spot in the head. I'll be moving mine to there on the 3500 this year.

[treeZ24]

arent the gm sensors 3/8 npt??

[Spankdamonkey]

Most likely, I'll probably end up going to the boneyard to pick up a spare sensor to confirm the size and the 3-wire pigtail (just in case)

[IsaacHayes]

Just got done driving with the 3 wire CTS. Reads exactly the same as the old one in the head did. Fan comes on in the exact same spot the old gauge would read. Used ScannerPro to read what the engine was seeing and now I know what the gauge points are.

1/8 = 170F
1/4 = 200F
1/2 = 220F
Little over 1/2 when fan kicks on = 227F

I grabbed 3, 3-wire pigtails today at the yard. All from a 96 grand am. TPS, CTS, and one was by coolant recovery tank.. If you need one just holler. Oh yeah I found out a 95 dodge neon uses the same sensor (had one lying around lol). Physical size is the same, I bet the pinout/readings are too. I could throw it in my car to test in 5mins but didn't bother. Only had 20k on it, but I'm running the 97 3400 one that came in my manifold.

[Barry]

I answered you on bstuff. Its a 1/4 inch pipe tap(tapered).
Sorry if Its to late, I dont get on here often.

[merlot566jka]

7/16 drill bit and 3/8 pipe thread tap, been there done that

[Spankdamonkey]

Well then thank you again Barry

I'm playing with the 3-wire idea at the moment (picked up 2 connectors at the J/Y).....how does the pinout go for it? I'm electrically handicapped

Isaac- I was curious about your find on the Neon, and sure enough, I managed to find one with the same connector as well!

[IsaacHayes]

Pin A = Black ECM (from 2 wire harness)
Pin B = Yellow ECM (from 2 wire harness)
Pin C = Green dash sender wire.

[Spankdamonkey]

Thank you sir!

[IsaacHayes]

If you want to snip the single wire sensor off and use it's wiring harness pigtail and route it under the plenum into the wiring loom that the 2 wire CTS wires are at so you can disconnect it up by the injector bulkhead like stock would, the wire you might find hard to solder to.

Mine was it was a high temp wire with some weird alloy. So what I did was take apart the connector, un-crimp the wire and solder in a new wire to the pin and re-assemble it.