Trinten's SBC/F23 build - The work has begun! (Page 76/76)
fieroguru AUG 25, 06:54 AM

quote
Originally posted by Trinten:
Okay, so his sensor might have worked because - if I understand things right, it doesn't need the ground except to kick on the warning light?



Both the sensor wire and the switch ground through the body of the sensor. So no ground wire is needed. The 2 wire sensor has 2 signal wires and 0 ground wires.


quote
Originally posted by Trinten:
The FAST temp sensor we have in the head is kind of a pain to get to, and having a third point to see temp / temp differences at various points is not a bad thing.
If we go with the Camaro unit, which pin is the correct one for the gauge? (thank you for the link to the right part!!)



Pin C is the analog signal wire for the temp gauge.



quote
Originally posted by Trinten:
For the speedometer, I have the FAST software set to do an output at 4k PPM for the gauge. What is the function of the circuit?



It changes the type of the output signal to what the Fiero speedo needs to see. The ECM will create the 4000 ppm output, but the shape of the signwave will likely be incorrect and not work with the fiero speedo. This buffer circuit changes the shape of the output signal so it works with the fiero speedo. Every OBD2 GM ecm needs this circuit as well as the Haltech Rebel LS, so odds are your FAST unit will need it too.

[This message has been edited by fieroguru (edited 08-25-2025).]

Trinten AUG 25, 08:19 PM
Got it!

So I have learned a disturbing amount on how coolant sensors work this week. For those that don't know.

1. There is the "GM Curve", where 0 ohms is hot, and 90 ohms is cold. Odd, but okay.

2. There are sensors made specifically for "short sweep" - which is the 90ish degree arm sweep of our coolant gauges (compared to 270 degrees, the other most common). One must make sure their sensor is for the right 'sweep'.

3. This one was a dead-stop... oh hell that make sense moment... even if you buy a sensor with the right 'curve' and 'sweep', the sensitivity might differ based on the max temp your gauge shows! So a sensor meant for a gauge that goes up to 300 (for example) will not show a correct value when feeding a gauge that goes up to 220!

It's wild stuff. Unfortunately it seems the LS1 sensor that FIeroGuru recommended has a thread of M12-1.5, and the opening currently on my water manifold is 3/8" NPT. This is likely why Mike grabbed a GN sensor, because the stock Fiero sensor is 5/8"-18 UNF (and yes, I did buy, and find, my stock coolant sensor and PICO connector).

I don't recall how much space is on the water manifold on each side of the existing port to know if we can drill/tap it open to take the LS1 coolant sensor, so in the meantime I'm trying to find another sensor that checks all of the 3 points above. It is not as easy as it you'd think.

I did find out that the speedo output sender is using a "Square wave" signal. So if that is the wrong type, I will need to build that buffer, as Red Devil shows it on back order.

Trinten SEP 26, 08:54 PM
Due to work kicking my butt and just generally feeling gradually defeated by my car, I'm going to do a combo recap and maybe correction.

My current cooling setup is using a dash -16 fitting on a 1.5" tube, coupled to the hard tube under the fiero with a standard coupler and clamps. The inlet is running that -16 line all the way up to a central inlet port on the current manifold, a -12, connected to it by a reducer. The output is via a single -12 line (this manifold has one -16 inlet, two -12 inlets, and two -12 outlets (on the sides).

We think we are having a flow issue, as mentioned before because the upper radiator hose would collapse from the suction until the coolant got hot enough and pressure popped it back out.

So, we decided to step things up a little.
Peterson Fluid systems makes a -20AN to dual -12AN Y adapter. This will give us some flow increase. We will make a new coupler, putting the -20 end on that to/from the tubes under the car. These were not cheap, because -20AN to dual -12AN is not a big demand thing.

https://drive.google.com/fi...Yky/view?usp=sharing

Of course.... AFTER I buy these, and extra -12 hose, etc etc... I discover that now there are many more affordable 4 port -16AN LS water manifolds out there. *sigh*. Anyway. I figure we can try what I bought. So we go about trying to set all this up.... and discover that even with the current 1" spacers, the AN fitting for the port on the side will not clear the accessory adapter plate and bolt. So it needs to come out another 1.5" (2.5" in total). I can't FIND a 2.5" LS style spacer. Just a 3".

https://drive.google.com/fi...4uO/view?usp=sharing

^ offending bolt removed in that picture

So we may need to see if that will fit, and if not, buy it and take them to a machine shop to put in a portland and shave the damn things down.

At least after all this, if we still have issues, I know I can save up for another $300-500 manifold that has quad -16 ports (and -20 to -16 Y adapters are much more common and affordable). Downside is most of them only have 1/8 NPT ports besides those, which will be a restriction from the surge tank, and mean I'll have to change up the coolant sensor I put there (I think).

Ooooor.... I need to see if I can convince FieroGuru to plasma cut/mill out something awesome for me. *cough* plan c *cough*.

On the upside, I found my Aux gauge cluster! So we can check to see if the oil pressure sensor is working properly. OH, and I saw on ebay someone was selling a new faceplate for that cluster that hoses three 2.125" ports. So I might get that and pick up other gauges to put in that, along with my transmission temp gauge I got from speedhut a few years back.

The upside is, with the colder weather around the corner, we can do longer drives like we did at the start of this year and Mike can smooth out all those spots in the tune.

Also, sorry for not embedding the pictures... I am just kind of at zero-Fs right now, so I just linked them from my google drive. If you guys can't see them, I'll fix it when I have the energy.