well i had basically given up on the car and let it sit for about 6 months since i bought a new daily driver, but now that i'm about to move, i HAVE to be able to drive it. so i really need some help.

it started out just happening once as i turned into a steep driveway, the ecm fuse by the battery popped. took me a while to figure it out, and i had been snooping around checking wires a bit by the firewall, so if there was an exposed wire someplace back there i may have knocked it away from whatever it was grounding on. replaced the fuse, good to go.

then a couple months go by and it pops as im turning, and now it pops everytime i try and start the car.

what i need to know is, is an exposed 12v lead the only thing that could do this, or could a bad maf power, maf burn off, or fuel pump relay do the same thing? what about the oil pressure switch? bad ecm ground? i have a gm service manual and am looking at the electrical diagrams but have only a very basic understanding of reading it.

what i'm really afraid of is that theres an exposed wire where the power lead runs through the firewall to the ecm, way down under everything on the passenger side. could that be the cause of it, or would an exposed lead there burn up one of the relays before popping the fuse by the battery?

 

I thought the fuse by the battery was a fuel pump fuse?If not though,my guess would be like you said abad ecm ground,or an exposed 12v lead.The wiring diagrams won't help you much there,(time to dig in&start tracing wires)also,I'm no expert here so don't qoute me on this but I don't believe a bad maf relay could cause this.Good luck man Timmy

 

pretty sure its for the ecm itself, havent tested the 12v wire at the ecm harness but when i turn the key the check engine light doesnt come on at all.

 

headers? check the wire coming off the starter that powers your ecm at start up

 

that fuse shows to power up the ECM, the fuel pump relay to power up the fuel pump, power through the oil pressure switch, the MAF power relay, the MAF burn off relay & the MAF sensor. a short to ground in any one of these will pop the fuse, also a short to ground in any of the wiring for these will pop the fuse.
you can get a some fuses & unplug all the relays, the MAF sensor & the oil pressure switch and put a good fuse in & turn the key on & see what happens.
if the fuse pops unplug the ECM & try it again, if it still pops go through all of the wiring & look for any bad spots.
if the fuse doesn't pop with just the ECM plugged in, start plugging the other things back up till the fuse pops.
there may also be a problem with the fuel pump, its wiring from the relay running back to the fuel pump, or the sending unit.

this may help, open it in windows picture & fax viewer so you can zoom in to read it, you may need to save it to your computer to do it.

 

great info, thanks denn. it never occured to me to try it with one of the circuits at a time unplugged to see what happened. have the 87 ta service manual with that diagram in it, was looking at it the other day, just that i only have a basic understanding of electricity. appreciate it, pretty sure i can track it down this weekend now, will post back with results

 

no problem good luck

 

it only pops with the fuel pump relay plugged in. about to pull up the carpet and start checking wiring. you said it may be a problem with the fuel pump itself, how so? i can hear it start to prime for a split second before the fuse pops. where is it grounded?

edit - its not the fuel pump. i unplugged the harness in the rear where the pump plugs in and the fuse still popped.

 

try a new fuel pump relay & see what happens.

 

already did, no dice.

is there a harness i can unplug at the ecm to disconnect it from the fuel pump and figure out if its grounding between the battery and ecm or between the ecm and fuel pump?

 

You mentioned that this first happened when you made a turn up a hill. Just a guess but I'd almost bet you have a problem in your fuel tank. Was your gas gage working properly. If not your fuel retention bowl may have broken loose in the tank. GM is famous for this problem. You can usually disconnect the Fuel pump and sender without dropping the tank. If you unplug it and the problem goes away it's in the tank. When I have a problem like this one I usually replace the fuse with a light light duty light bulb like the ones used in the dash lights. So rather than blowing a fuse you just light up the bulb and the draw is low enough that you don't burn up wires etc. Good luck!

 

yeah gauge worked fine. already tried unplugging the pump itself, fuse still popped, so the problem is forward of the pump. going to do more investigating tomorrow.

 

you can put the wire out of the ECM connector which would keep the ECM from supplying power the the relay, but it would probably be easier to pull the terminal at the fuel pump relay, instead of doing that, try pulling the terminal for the wire that goes to the fuel pump & see what happens.

 

oh so the 12v lead goes from the battery to the ecm, from the ecm to the fuel pump relay and directly from the relay to the fuel pump?

 

the 12 volt feed from the battery splits off & goes to everything.
the ECM turns the fuel pump relay on by sending power to terminal C at the relay.
terminal A at the relay sends power to the oil pressure switch, MAF power relay, MAF burn off relay, ECM fuel pump input & the fuel pump.

 

i tried to find that exact info in my service manual but couldnt, where is that located in the manual?

edit - never mind i found it

i'm a little confused as to how the ecm, relay, and fuel pump all work together. plug A1 on the ecm harness goes to the C terminal relay and turns it on, i've got that. now for the fuel pump signal, the A terminal sends power to the B2 plug on the ecm harness, but where is the power lead for the fuel pump itself? i can't find any plugs on the harness in my service manual showing output to fuel pump.

am i just wasting time trying to narrow down where to look? i just can't think of any easier way to track down where its grounding and i dont really want to pull all of that wiring out to find it.

 

terminal A to B2 is the input to the ECM so it knows that the relay turned on & power is being sent to the fuel pump, somewhere in the harness is a splice where the wire for the fuel pump & MAF system branches off.
the power feed to the fuel pump relay is terminal E on the relay.
terminal E is also the power feed to the MAF power & burn off relays, it comes from the same power source as the fuel pump relay & the ECM keep alive power comes from.

im thinking because you hear the fuel pump come on to prime, the problem isn't in the wiring to the pump, if it was the pump wouldn't come on.
you know its not the pump itself. i think you may find the problem some where with the MAF wiring, relays or the MAF sensor.
try this, with the fuel pump relay plugged in, unplug the MAF burn off relay, the MAF power relay & the MAF sensor & see what happens. if it doesn't pop the fuse, plug in the MAF power relay, if your still good, plug in the burn off relay, last plug in the MAF sensor, you will need to turn the key off for about 15 seconds & then back on each so the ECM will power up the fuel pump relay.

 

HEY 1MEANGTA HAVE YOU GOT YOUR PROBLEM WORKED OUT YET?I WAS JUST CURIOUS.I HAVE AT LEAST LEARNED SOMETHING.(NO,THAT FUSE REALLY IS FOR THE ECM) NEVER KNEW THAT BEFORE,THANKS TIMMY

 

well i never did figure out exactly what it was, but when i pulled up my carpet, found the fuel pump power wire runs on the driver side and not the passenger, followed it up, and bumped some of the wires under the dash around looking for anything suspect, apparently i moved whatevers grounding away from the ground point, because now i can turn it to acc and prime the fuel pump without blowing the fuse. which is cool with me, i only need it to start twice and be run for maybe 30 seconds each time, to pull onto and off a trailer.

however, when i try to start the car, it cuts all power? no fuses under the dash blow, the ecm fuse up by the battery is ok, it just kills the power. like theres no battery hooked up at all. what the hell?

 

Sounds like your vats system acting up. Use an omh meter and put one lead on each side of the chip in your key. write down that reading go to radioshack or a near electronic store. but a resistor that is 20-30 more of less around the number you got from your key and wire the resitor in parallel on the ecm side of the 2 wires runnign down the column Not the two little yells ones but the ones on the other side of the plug.

If you have vats that is.

Im shure somone can add to it i just did it myself 3 days ago 99 cents and 20 mins to solder it in. Cranks every time now no more tripping the alarm.

What size fuse does the ecm take i had 20 in mine and it was blown when i got it so i put a 20 in it and on it worked for a days and a half mashing around town and then it finnaly poped on a hard accselleration.... so i have a 30 in it now ill see what happens.