caseyZman

OK, so its an Camaro 1987 v6 MPFI all stock. Its blowing fuses at the ECM/FUEL PUMP 20A under hood location (see attached). I can usually put a fuse in, turn the ignition to the ACC position but right as I'm turning to crank the engine over BAM! the fuse blows. I've been through dozens of fuses trying to figure this out. I started by disconnecting individual sensors and wire harnesses in the engine compartment to try and determine the source. At one point during this process I blew a fuse, went to place a new fuse in to check the next sensor, but it wouldn't even let me put a fuse in, blew immediately when I touched the fuse to the inline. So I went through the entire engine compartment (and tranny, fuel pump), disconnected every sensor/harness...still popped. So I figured I'd try connecting everything back again...popped again. Frustration. So i give up and the next day I go out and tackle it again but it lets me put a fuse in? Still blows on crank. The only time it DOESN'T pop is when I have the ECM/FP relay out (see attached). Anything, I mean anything would help!
-Thanks in advance

Ward

iTrader: (1)

Unless I'm mistaken, that fuse only powers the ECM and fuel pump. The ECM itself doesn't draw much current, but it does power the injectors directly. I would check resistance of the fuel pump (check at the fuel pump relay connector), and also of each injector. I know TPI injectors are supposed to be around 16 ohms, I assume the V6 ones should be about the same. I'm not sure what the fuel pump resistance should be, but if you're blowing a 20 amp fuse, it would have to be like 1 ohm or less, almost a dead short.

BigBadLou

iTrader: (3)

That specific fuse powers only the ECM memory, fuel pump and fans. Not injectors or anything else.

I would suggest unplugging both relays by the brake booster (the one for the fuel pump and the one for the fan). If the fuse still blows when cranking, try also disconnecting the ECM. You don't need it for the cranking itself.

It could be as simple as a bad relay but it could be also wiring, hard to tell on a car that old. I've seen a wiring harness from an '85 and that thing crumbled apart between my fingers. Scary.

Did you just acquire the car? Or have you had it for a while and it just started happening? My educated guess would be that it's a shorted fan circuit or fuel pump circuit but we need more information to determine that.

Let us know what you find!
Lou

Ward

iTrader: (1)

The fan(s) should be powered separately, through the fusible link also near the battery.

caseyZman

Thanks for the ideas. Just a little more background on the car. It was parked for about 6 months (I've had it for about 10 years), when i went to start it, no fuel pressure, no fuel pump even when i gave the pump a direct 12v source. So i dropped the tank, replaced the fuel pump and now this... Initially i thought, maybe a bad fuel pump, but i gave it a 12v source and it worked fine, so I hooked it back up and it started for about a minute, then blew the fuse. Now it can't hold the fuse for a single crank, even when i disconnect the fuel pump entirely. The engine cranks over fine but when that fuse pops...no fuel pump/no fuel. I can disconnect the fuel pump relay and crank the engine as much as i please, feed fuel to it manually and it'll spark. I've swapped the 2 relays by the brake booster (since they have the same part #) but no luck. I think I'll have to just get a couple new relays to cancel out that possibility. I'll try that "disconnecting the ECM" and turning it over, but I'm wondering if that won't give power to the fuel pump?

I also found this thread:
https://www.thirdgen.org/forums/elec...-ecm-fuse.html

sounds like the guy had a problem with his cooling fan switch. I'll check that as well.

Thanks everyone

BigBadLou

iTrader: (3)

Now THAT's some good info!

If you disconnect the fuel pump relay, you won't have power to the fuel pump and the car won't start, granted. You can bypass that with a paperclip, though. Take a paperclip, straighten it out, bend it into a U-shape and insert into the relay socket/connector, one end into the orange wire terminal and the other into the tan/white (or grey) wire terminal. (sanity check: both wires should be THICK)
That will turn on your fuel pump (without the relay in the socket) and you can try cranking. If the fuse blows, the problem is not in the relay.

Hope this helps.
Lou

caseyZman

Thanks Lou and Ward.
I tried disconnecting the the ECM...but it still won't even let me put a fuse in without sparking like crazy. Tried the trick with the paper clips, same result. I soooo hate wiring. So I was thinking my next steps would be to just open up the harness and trace back the Orange and Tan/White wires. Does that sound right? Any other suggestions before I drown in wiring?
-Much appreciated

caseyZman

OK so I checked out the wiring diagrams off of Autozone to see if they could give me insight. I don't know much about wiring diagrams but I can trace lines. From the diagram (see attached highlighted section) it looks like there are only a couple of places a short could be (other than the wire itself),

The Fuel Pump Relay
The Fuel Pump Switch
The Fuel Tank Unit

I've tested the Relay as explained earlier, I've tried it with the Pump disconnected, so it seems that the Pump Switch is the only other thing? Is there a pump switch or is it inside of the pump? Maybe a stupid Question. If so, where is it?
-Thanks again

TIMMYS89GTA

iTrader: (28)

caseyzman,I just read through your post and have 1 question.
Are your fans/fan still wired to the factory harness?

caseyZman

Yep, its a single fan, and stock w/stock wiring as far as i can tell.

BigBadLou

iTrader: (3)

True, my mistake!

BigBadLou

iTrader: (3)

You will need to give us a little more detailed answers. We can't unfortunatelly be there to see what exactly happens and when, so we rely on your words.

When you used the paperclip, did the fuse blow as soon as you put the paperclip in? If not, did the fuel pump run? Then did it blow while you were cranking the engine?

I'm not sure where the fuel pump backup switch is on your V6 but on the 90+ V8's, it's right above the oil filter, on the driver side of the block. It will have an orange wire and tan wire sticking out of it. It is possible that the switch is bad and shorting out internally or the wires could be touching ground or something.
This Fuel Pump Oil Pressure (FPOP) switch is a backup switch that turns on the fuel pump when your engine builds up oil pressure. It's a backup system for when the fuel pump relay fails. If it does, you wouldn't normally have fuel then. But this switch will help you get back home instead of making you stranded 100 miles from the nearest Vatozone where you can buy a replacement relay.

One more question: so if you leave the fuel pump relay disconnected completely, the fuse won't blow while cranking? (I realize the engine won't start immediately without the fuel pump relay but it SHOULD start eventually once you build up oil pressure)

Lou

caseyZman

Hello hello,
Sorry about not being specific last post. Here we go!

Without the key in the ignition, As soon as I put the paper clip in, the fuse popped. I tried the same thing again (this time with the Fuel pump disconnected at the rear harness) as soon as I put the paper clip in it popped.

I tried cranking with the relay out, cranked for about a min until battery was week, no luck, didn't seem like it was getting any fuel. Maybe it could be that switch? I never realized the Oil Pressure switch worked like that. Looks like its only about $5 at the "Vatozone" (LOL, thats great, never heard that one).

I'll Let you know what I find, Thanks for all the help!

BigBadLou

iTrader: (3)

Sounds like you're right, it might be the tan/white wire that carries the current to the fuel pump. Try finding the switch and disconnecting it. If the fuse keeps popping, it's the wires (probably pinched somewhere). If it stops popping, the switch is shorted inside. I believe the FPOP switch itself is around $35. The relays are $5. Sorry for the confusion.

If it's the wires that are shorted, it wouldn't be easy to find without tracing every part of the wire. A common location, though, is by the driver door, under the carpet. The fuel pump wires (and a lot of other wires) run there to the back of the car. I've seen many screws put through the doorsil or carpet. And some screws might find a wire and screw it right to the chassis. :-)

Let us know what you find! I'm very curious.
Lou

P.S.: Btw, you can live without the FPOP switch if it's shorted. Just leave it in but keep it disconnected.

caseyZman

Whew, well after tracking back wires through the harness, I started tugging on the part of the harness that rest on top of the Transmission (where the Orange and Tan wires run). Went back to try the fuse....IT WORKED! Runs fine now. For how long is undetermined. Since the wires lay on top of the transmission, back under the firewall, I can't really see what the problem really was, a crimped wire, exposed and grounding, etc. I guess it could happed again, but at least I've identified where it is occurring if it comes back, thanks again for everyones suggestion to help me narrow down the location of this pesky thing.