curious if this could still be a bad alternator diode or headlight relay. with the fuel pump fuse pulled battery doesn't drain. with fuse in it will drain and not turn over within 5 hours. could this still be symptoms of a bad alternator or do I focus only on the fuel circuit? SC3800 swap in a 1986 GT.
------------------ 1986 Fiero GT fastback SC3800 3.4 pulley, LS1 TB 1986 Fiero GT Fastback 3.4Lpr with 4T60 - SOLD 1998 Jeep Grand Cherokee with "big boy" 5.9 motor 1983 Honda Goldwing 1100 Interstate
If you're using the old style Fiero oil pressure sender, disconnect it. There is a constant 12V going into it. If it fails, it goes to ground. Second thing is to disconnect the single blue wire on each of your headlights. With the aid of a helper put a multi-meter on your battery terminals and one at a time, disconnect the items to see if the voltage changes.
It sounds like a shorted oil pressure switch. Does the fuel pump continually run when the car is off? You can disconnect the plug from the oil pressure switch to see if the problem goes away. You will lose the functionality of the oil pressure gauge, but as long as you know their is oil in the crank case, no problem.
I'm really not hearing the fuel pump running with fuse in or out or ignition turned to on or off. Do I need to be right next to it to hear it? I'm thinking it's got the stock SC3800 pressure switch.
[This message has been edited by Grantman (edited 05-11-2014).]
on second thought it looks like what's on a 2.8. haven't done a swap, bought the car with the 3800 already in it. so the GTP oil pressure sender is replaced by the old style because of the fuel circuit?
When my oil pressure switch/sender went bad and caused the fuel pump to run all the time, it was so quiet that I ONLY heard it when I removed the gas cap and put my ear to the opening.
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Originally posted by Grantman:
I'm really not hearing the fuel pump running with fuse in or out or ignition turned to on or off. Do I need to be right next to it to hear it? I'm thinking it's got the stock SC3800 pressure switch.
I couldn't hear my pump running, either but I found i had a bad oil pressure sender and that was what was killing my battery. Ironically, it was the newer style sender that I'd just installed to get away from the problems of the old style. Just happened to get a bad one. Rock Auto replaced it at no charge.
I was just about to edit my last post to ask the question even though the fuel pump isn't running if the switch is going to ground it will drain the battery without telling the fuel pump to pump. So I should be able to hook up a mult meter, unplug the sender and see my amps drop to confirm the switch is bad.
Bad fuel pump relay...on the rear firewall. There are 2 cube shaped relays...one is AC and one is fuel pump. Sounds like your points inside it are sticking.
The oil pressure sender should be a 3 wire sensor. On3 terminal, the orange with black, is the 12V. The others are fuel pump and gauge. They ground through the base of the sensor
thats what I expected to find, instead it's a single wire. sender is still screwed into the GTP oil filter holder but the sender is definately not from a stock fiero. The harness is from Dan but maybe the PO took some liberties? Filter points down and the sender is screwed in pointing to the front and the back end points to the back of the car.
I'm expecting it to be some kind of relay gone bad or switch, although everything so far works, so if a relay it hasn't completely failed. The PO had it running fine for about a year and a half after the swap was done and then it started draining the battery so sure seems as though something failed, or came loose. Since it's on that fuse sure seems as though it should be something on that circuit vs the headlight relay although I didn't take a reading with the fuse out. maybe more than 1 thing.
[This message has been edited by Grantman (edited 05-11-2014).]
here's a picture of what looks like my sender except I dont have the T and instead of a plug in mine has a thread on it so the wire is on a eyelit and secured with a nut. PO said he put in a different oil pressure gauge which it is that needed the different wiring and not the stock
Link didn't work
here's the thread that went along with that picture
I can't see the pictures in the other thread, but it sounds like you have one of the button style sending units like the Dukes use. Since you're dealing with a 3800 conversion, I'm not experienced with what harness makers do. I am probably of no more help.
I suppose this type of sender could come apart inside just like a stock one and ground out causing a drain. started to unscrew the wire to check and didn't finish it. dumb SC newbie. going to take it to a local electrical guru and see what he finds. radiator fan comes on all the time and the PO said it didn't do that for him so something else to check.
