Ok so here are the details:

1988 Fiero 2M4 Auto (originally) - now has 4.9L PFI V8 and 4-Speed Muncie transmission.

the harness was made by "Rockcrawl"

the car runs and drives great without issue...except...

Speedo doesn't work and the Coolant Temp Gauge doesn't work.
to add the Odometer doesn't work either, so it's like there is no signal from the VSS. I'm going to swap in a spare to see if it's just the sensor. but if it isn't what can I do.

as for the coolant temp gauge not working. I have found 2 harness connections that are unused that I can't identify. there are a few ac tually but they are all labeled and not needed do the the manual trans and no A/C

the oil pressure gauge works fine the tachometer is the original 4 cylinder one so I need to get it calibrated (I'm clueless as to how, except using a resistor or something)
the Fuel Gauge works as well.

anyway, I await some good helpful responses. Thanks!!

------------------
F.I.E.R.O. - Fantastically Imaginative Engineering Racing Object

I'm here to Help, just ask

www.fquick.com/GTXBULLET
Tech/Mechanic (Restorations, Modifications, and Maintenence)
1988 FIERO 3.4L Getrag Base Coupe (the show car ;-) )
1986 Fiero SE Auto (parts car, still in Tenessee )
1984 Fiero SE 4-speed with A/C and Trunk Pop
Size 13 Feet with Cracking Ankles and Tired Knees

if the speedo isnt getting a signal then the odometer wont work so check the wiring filter as per mickey mooses thread. if anythign you can run the VSS directly to the speedo rather than run it through the computer, although i do believe the computer needs a signal input for that

i had my coolant temp not working but it was in my 84 and it was wired to the idiot light and not the gauge but that was my own fault.

i still havent gotten my tach to work and ive read the guide on how to do it i just cant follow it very well.

You need to replace the coolant temp sensor with a three wire if it isn't and run the green wire to the c500 C2

You can hook the speedo directly to the c203 pins G and R and splice G into the speedo input on the ECM

Tach

http://fieros.de/en/main.html

If the VSS connections are reversed to the ECM as compared to the speedo, that can short out the VSS signal and make neither get the signal. If you find the VSS signal bridged to both the ECM and speedo, but the speedo is still not working, try pulling the pins from the ECM connector. If that brings the speedo back to life, then try reinserting them reversed.

Question - Does the ECM see the VSS input?

I guess the easiest thing to do is take a few pictures and post them.
Give me a little bit.

Phonedawgz- the previous owner had a scan tool and while parked it read the mph as 0.0. Dont know if that means anything.
im going to check the pcm connections and i also thought maybe just the vss itself is bad.

Let me get some pictures.

The engine runs beautifully! Idles at 800 instead of stock 600 (programed in)

Try a scan tool and check it while driving to see what MPH the ECM is seeing. If none, then the ECM will be confused. It might put the ECM in 'Limp' mode.

I'm going to see if I can borrow the PO's scan tool for a day to check out the VSS signal.







NO CLUE as to what this is...?


says "oil sender" but with this is where I would think the "water temp" would be...
the engine temp can be read with a scan tool. the temp gauge just doesn't work.

No clue what the small connectors are but that sensor in the head is the temp switch for the temp light. Don't need it

The two prong in the thermostat housing has to be changed to a three wire sensor and the green wire on the new plug is connected to c2 of the c500. This will give you a working temp gauge

quote Originally posted by FriendOfYours: No clue what the small connectors are but that sensor in the head is the temp switch for the temp light. Don't need it The two prong in the thermostat housing has to be changed to a three wire sensor and the green wire on the new plug is connected to c2 of the c500. This will give you a working temp gauge

got a part number for that sensor?

also, if I can read temp through the computer already, shouldn't that wire go straight to the temp gauge?

The c2 of the c500 connector next to the battery IS the wire directly to the gauge

GM P/N 10096181

Well if the harness is already wired up to use the Fiero temp gauge and light sender (the top two pics) why not just screw in a Fiero temp gauge and light sender and be done with it? That two wire temp gauge/light sender is what is screwed into the head on a stock 2.8 Fiero right next to the coil.



You can cut off the yellow/black connector, and then splice on the 3 pin connector (yellow/black/green) - Yellow to yellow (cts signal)- black to black (CTS ground) - and then wire the green of the CTS to the temp gauge. (a 3 wire CTS is actually a combo CTS AND temp gauge sender built into a single housing) But again, if it were me, I would just screw in the Fiero CTS.

The sensor you are pointing (third pic) to on the side of the head is a two pin temp light (only) sender. You can screw in the Fiero temp gauge & light sender right into that hole.

The connector marked "oil sender' has the right color wires to be the (2 wire) CTS connector. The sensor it is plugged into is the CTS. So I must conclude that it is just mislabeled. (It sure looks like the CTS to me)

[This message has been edited by phonedawgz (edited 04-30-2012).]

quote Originally posted by phonedawgz: Well if the harness is already wired up to use the Fiero temp gauge and light sender (the top two pics) why not just screw in a Fiero temp gauge and light sender and be done with it? That two wire temp gauge/light sender is what is screwed into the head on a stock 2.8 Fiero right next to the coil. You can cut off the yellow/black connector, and then splice on the 3 pin connector (yellow/black/green) - Yellow to yellow (cts signal)- black to black (CTS ground) - and then wire the green of the CTS to the temp gauge. (a 3 wire CTS is actually a combo CTS AND temp gauge sender built into a single housing) But again, if it were me, I would just screw in the Fiero CTS. The sensor you are pointing (third pic) to on the side of the head is a two pin temp light (only) sender. You can screw in the Fiero temp gauge & light sender right into that hole. The connector marked "oil sender' has the right color wires to be the (2 wire) CTS connector. The sensor it is plugged into is the CTS. So I must conclude that it is just mislabeled. (It sure looks like the CTS to me)

great!
when I saw that sensor and the unused plug what you said is exactly what I was thinking to myself.
I'm going to see if I have a good sensor in my electrical bin.

as for the speed sensor I will be checking that today.

the car currently has no engine strut/dogbone. so I bought some 1/4" steel at menards and am going to make a mount/bracket to goes from the right side of the rear head straight to the engine cradle. either going to make it solid or use and dogbone/sturt bushing. wish me luck!!!

so I broke the temp sensor and switch...

I put a new temp sensor in. but here's the catch. the lower "sensor/sender" is actually just a switch. and the hole is WAAAY too small to put the Fiero Style sensor in...do I dare drill and tap it? I don't think so...lol

I'm going to just use an aftermarket gauge and do an Auxilary gauge set up instead (triple pod) oil pressure, Water Temp, and possibly a wide band or just a Volts gauge, haven't decided yet.

I'm going to put a build thread up as I'm switching to a Gold 1986 SE body and making it into an 85 GT look-a-like. it has a 4-speed afterall
though I've never seen a GOLD 85 GT...

also going to be making a new cooling system and possibly adding an Auxilary Radiator (coolant) mounted under the driver's decklid vent with an elextric fan. 4.9L's are great engines, but even in their original vehicles they could've used help cooling. so I'm going to improve efficiency.

I still would like a part number for the 3-wire style temp gauge so I can atleast have a functional gauge cluster.

also the speedometer still doesn't work.

There are other one wire temp gauge sending units also.

The 3 wire TPS PN is Delco 213815 or 10096181 or equivalent.

Also on the 4.9, the high speed fan ECM output can be used for the TEMP light. When you do that the ECM has to be properly programmed, however that also means that the temp on and off light is ECM (chip) programmable.

[This message has been edited by phonedawgz (edited 05-01-2012).]

quote Originally posted by phonedawgz: There are other one wire temp gauge sending units also. The 3 wire TPS PN is Delco 213815 or 10096181 or equivalent. Also on the 4.9, the high speed fan ECM output can be used for the TEMP light. When you do that the ECM has to be properly programmed, however that also means that the temp on and off light is ECM (chip) programmable.

so if I buy the 3 wire will it function correctly with my ECM?

Not to sound harsh, but, do not try and reinvent the wheel - this swap has been around for a long time and what is in my wiring thread works: https://www.fiero.nl/forum/Forum2/HTML/098096.html

1) if you want to temp gage to work you NEED the 3 wire temp sender. The 1 in the head is a SWITCH only (not needed if you are using a gage) - it is either on or off as in temp light on or off. You can NOT install a temp sender in it's place. The 3-wire sender goes in the thermostat housing. If the ECM is reading the temp right then the wiring at the thermostat housing is correct despite it saying oil pressure. The oil pressure would be a 4 pin plug anyways and the sender for that is located by the oil filter assembly.

2) speedo - depends how it is wired - where does the VSS wire on the C203 go to? If it goes to the ECM there should be a 'conversion' circuit in between. If it goes to the VSS sender it should be wired directly there with a branch off to the ECM VSS input.

3) easy to do, follow the directions in the link posted (not sure if it is the same as the one posted in my wiring thread).

pictures posted - be alot easier if you trace them to see where they go to - there is no point in guessing. Simple to do with a multimeter (preferably one that beeps on contunity check), no need to pull the harness apart. Put 1 lead on the mystery wire and with the other lead go through the C500/C203/ECM connections 1 at a time until your meter beeps. Look in the pinouts what that is for and your good to go (probably no need to check the other wire as they are a pair).

No need to add another rad - the stock system works just fine, just wasting time and money plus the added hassle of trying to burp the system. The ECM controls the cooling as does the thermostat - it will still get up to the set point in the ECM program code before the fan turns on regardless of how many rads you have. What makes you say it runs hot?

Maybe adding an oil cooler if it doesn't have one is a good idea.

[This message has been edited by Mickey_Moose (edited 05-02-2012).]

quote Originally posted by gtxbullet: so if I buy the 3 wire will it function correctly with my ECM?

Yes



Ignore the PCM pins in this pic - This is just to illustrate the 3 pin CTS electrically

[This message has been edited by phonedawgz (edited 05-02-2012).]