86GT 93LX

i have a 85 gt vert with a 86 gt motor and maf conversion. a few things dont work and im looking for someone who has dealt with this before. how to rule out the gauge or sending unit.or is it a ecu issue. i have an A9L ecu.my gauge cluster has some neon crap installed but the stock bulbs dont light up. on the conversion i wired up all my other gauges and they work fine. im assuming the fuel sending unit wires in to a relay then the gauge so no reason i would have needed to splice anything in. i might just swap in a 87 dash and consel since mine is beat

U S Marine

There should be no need to splice. Does the gauge read full or empty? Full=sending unit. Empty=wiring, gauge or possible IVR. The early foxes have an IVR instead of the anti slosh module that came out in 87. USUALLY if the IVR is bad none of the gauges work, if I remember correctly. The IVR is a silver rectangular canister looking thing on the back of your gauge cluster.

86GT 93LX

it reads empty. theres no silver thing on it nor does my 86 have that thing either.yes i know 87 has a differant fuel set up as far as wiring.so youre sure if it reads empty that it cant be the sending unit?

U S Marine

Well, the IVR is on my 84 SVO and both of my 86 SVO's had them. I know the sending unit is different on the SVO's, but I'm under the impression that all Mustangs had them previous to 87. Perhaps someone else can chime in for clarity on that. I know there is a solid state conversion for the 'stangs of the 60's and early 70's. As to the last part of your question; 100% of the time, for me, it has been that way. When I say for me, I mean mine and others that I have fixed in the past.

Ohm the fuel gauge that you have and I will Ohm the two that I have to see where they are in regard to resistance. I would *think* that if the resistance is infinite, the gauge would be bad. Post your reading here.

mjr46

ECU will have nothing to do with the gas gauge the system is not related to or part of any ecu function...........the sending unit in tank is a variable resistor and by looping in the appropriate resistance value you can make the gauge go up or down, some use reistors in series from radio shack, here's how to test it
1.Disconnect wiring harness at sending unit and connect an ohmmeter between ground terminal and resistor terminal on sending unit
2. meter should read between 8-86 ohms..if reading is infinate , check ground connection on tank, and if ground connection is okay but reading is still infinate..intake unit is defective or float is sunk......
3. at empty, resistance value on the sender will be 60-86 ohms and full 8-12 ohms.....hooking a resistor with these values in series on the harness connector will make the gauge move, I use a special decade gauge box/tester I have, to do all this, I can dial in whatever resistance value I want and diagnosis prob in two secs, hope this helps

U S Marine

This might be a good item to post in the "tech articles" section. I'm pretty new here and I see this question has come up numerous times before.

86GT 93LX

yeah i agree too tech article quality mjr46!
i did some resaerch svo's are differant as well as the carbbed cars. so all 85 cfi cars and 86 efi cars wouldnt have the silver box.
im going to test the gauge here soon. i also need to findout why my dash doesnt light up. i might put my 86 cluster in it for a second to see what i get

mjr46

85 cfi car and carbed cars both have an IVR that snaps on like a 9 volt battery, my 85 cfi had one and I have a 85 gt carbed cluster, whether or not it is efi has no bearing on it having an IVR

86GT 93LX

well this car doesnt have one

mjr46

it should, that may be half the problem for your instrument cluster gauge malfunctions