bird93bill

i have an 87 gta that i put an older carbed sbc 350 into.the swap went fine and after some time and money i learned the 350 had multiple problems that would require a rebuild.I lucked into a 95 formula with the lt1 intact for $300 and rebult it instead.i put the gmpp carb intake and hei from the sbc and it runs super.the problem i have is the gta has a digital dash and the only thing working on it right now is the speedo.i was told at the beginning of the switching to carb process i would no longer need the ecm or ecm harness to run the engine and the digital dash would work fine.well it doesn't and i've come to find out the oil pressure sender is run thru the ecm and i don't see an odometer reading anywhere.the temp gauge slowly but surely goes to 260 and stays there seconds after i start it.the amp gauge sits at the bottom and never moves,of course the oil pressure gauge is blank.the gas gauge doesn't work either and the tachometer moves a little but seems to move more when i press the brake than it does when i press the accelerator.i have the cooling fan hooked up on a thermo switch and works fine.the fuel pump is wired thru a toggle switch and it works fine as well.i see now the ecm and some of the harness is necessary but i don't want to put any more wires back into the engine compartment than i absolutely have to but since i'm putting some of it in to hopefully fix the dash issues i would like to also run the wiring back to the trans for lock up and overdrive to operate.the issues were present when the sbc was in the car so it's not a new problem.i get overwhelmed when i look at this harness and try to figure out what to keep and what to cut.
HELP!

RBob

iTrader: (1)

None of the issues you are having is due to a lack of ECM. There is a separate coolant temperature sensor for the dash, same as the oil pressure sensor. Neither of which go anywhere near the ECM.

Same for the gas gauge, right from the fuel tank.

The VIN S (V6) cars digital tach is from the minus side of the coil. The VIN F & 8 cars have the tach coming off the EST line, which is from the ECM. Can see if the coil - works.

RBob.

RBob

iTrader: (1)

I've had second thoughts on trying the coil - for a tach signal. The V6 digital cluster is different as they used a different oil pressure sensor. May be different in the tach area too.

The EST line is a 0-5 V square wave signal, and is clean. While the coil - is 0-12 V with a high voltage spike on it when the coil fires. That signal can be cleaned up with some resistors, a capacitor and a diode or two, which is likely what I would do to feed it to the cluster.

RBob.

bird93bill

well thats what i thought,too.is there a ground for the dash i can check?I've tried three different temp sending units and one stayed at the bottom of the gauge.the other two just go from cold(bottom) to the top of the gauge in a few seconds.also isn't the oil pressure tied in with fuel pump somehow?The only oil pressure sending unit plug disappeared when i removed the ecm and harness.

bird93bill

my reply was to first post.the tach does respond to accelerator but it reads 0 rpm at idle and only goes to around 500 or 600 rpm when i rev it up.

RBob

iTrader: (1)

There are a bunch of dash grounds and power feeds. Seems each gauge has it's own of each.

If the oil switch was a three prong plug, that is both the fuel pump back up and the oil pressure sender.

RBob.

RBob

iTrader: (1)

The tach input is likely not connected to anything. It is picking up electrical noise and responding to that.

Be sure to check the 10A CLSTR and the 20A CTSY fuses.

RBob.

bird93bill

fuses are good.the plug for the oil sending unit is a single wire,at least until it goes into the loom,tan in color.i thought i remembered reading somewhere that some thirdgens had a protective circuit that would shut off the fuel pump when the oil pressure went low or to 0.

bird93bill

i finally was able able to get the ecm and partial wiring harness back in.now the gas gauge works properly,the temp gauge seems to be working well and the amp gauge is showing proper readings as well.even the tach is responding better than before,I'm still not sure its right.i dont have an oil pressure reading yet.when i followed the wire from the the sending unit(tan) it went to a two wire plug the other wire(green)went back to the ecm so i just spliced the two together and plugged it in but i still get no response.the speedo seems to want to stay in the km/h reading for some reason now and while i see some number-like things appearing in the middle display,they seem to change in the number of digits and in digits displayed quite often.it is usually unreadable,though.does this sound familiar to anyone else?its better than it was but i still have some stuff to go.

bird93bill

Update. the trip odometer now displays and miles roll up accurately.no other changes so far.thanks.