What does the fuse pull actually do?

[Lee123]

I've been curious about this ever since I first read about it. Does the fuse pull do anything different than unhooking the battery for the same length of time (other than the fact that is doesn't mess up date and time in the radio and require resetting the windows)? The only way I could see it would have a different effect is if there was another battery or capacitor that maintains power to the ECU when the battery is unhooked.

On a similar subject - After my tune the car wouldn't idle at all until he hooked up a GM hand held device and set the "idle relearn." That fixed the idle. Can that be accomplished some other way? Maybe by unhooking the battery?

[jtzako]

I'm not really sure but I thought someone tested that and unhooking the battery didnt clear the ECU.

[SSDan]

Originally Posted by Lee123

I've been curious about this ever since I first read about it. Does the fuse pull do anything different than unhooking the battery for the same length of time (other than the fact that is doesn't mess up date and time in the radio and require resetting the windows)? The only way I could see it would have a different effect is if there was another battery or capacitor that maintains power to the ECU when the battery is unhooked.

On a similar subject - After my tune the car wouldn't idle at all until he hooked up a GM hand held device and set the "idle relearn." That fixed the idle. Can that be accomplished some other way? Maybe by unhooking the battery?

I think you are right in that pulling the fuses for the ECM powers just it down leaving everything else powered up and set. When powered back up by putting the fuses back in - the ECM is suppose to go back to all the factory default settings including the high octane table. For you and me since we have tuned cars now its a moot point as I'm pretty sure the tune no longer has the low octane table enabled. At least I'm comfortable thats what my tuner did.

I can't help you on the idle relearn question. I wasn't there for the inital fire up for my cam install. When I picked it up it idled fine and has ever since. It just lopes and chops along at around 900 rpm with a little shaky shake here and there.

[The Stig]

fuses 5 and 20 are for the ECM. By pulling them out you break the circuit going to the ECM - turning off the ECM. When it starts back up (aka you put the fuses back in) it rereads the fuel in the gas tank to determine if it's high or low grade.

[orangejuice]

steiger said it all. Basically just adjusts it from 87 or 89 to 93 (which you should be putting in it regardless)

[Lee123]

Thanks for the replies. I knew that pulling the fuses removed the power from the ECU and that caused it to reset the octane table. I was just wondering how that could be different than unhooking the battery which would also removed the power unless there is some axillary power source for the ECU.

[SSDan]

Originally Posted by Lee123

Thanks for the replies. I knew that pulling the fuses removed the power from the ECU and that caused it to reset the octane table. I was just wondering how that could be different than unhooking the battery which would also removed the power unless there is some axillary power source for the ECU.

Inquiring minds want to know!

For the heck of it before I had the car tuned I did the fuse pull. I did that because its a lot easier than disconnecting the battery and then resetting everything. I'm basically lazy!

So, I'm posting to keep your thread alive in case someone has a real answer to your question. Because bottom line is

[daveagogo1]

Cannot say for sure but the ecm handles and reads the exhaust. Pretty much all of the exhaust manufacturers tell you to disconnect the battery before the work so that on initial startup it will learn the new exhaust. Why wouldn't it relearn octane tables also.

[The Stig]

Originally Posted by daveagogo1

Cannot say for sure but the ecm handles and reads the exhaust. Pretty much all of the exhaust manufacturers tell you to disconnect the battery before the work so that on initial startup it will learn the new exhaust. Why wouldn't it relearn octane tables also.

because the camaro ECM is dumb and once it reads an octane table its stuck there. Unless you do the fuse pull, which resets the octane table.

[PQ]

There is in fact a battery back-up between the battery and ECM.

A brief history in the 'Fuse Pull'.....

Some of us realized our cars weren't performing the way they should 0-60mph and 1320' so we pitched a fit here on C5.

GM brought a car and engineers to Alabama to look at Scotts car. They ran the car, datalogged it, and studied the results. In no time they had Scotts car running the way it should. (it was losing to a V6 there on the lot in Eufala AL)

In the meantime the rest of us were still pissed. We hadn't got any word.

Well, member GMRULZ had his car tuned and worked on and before they started they pulled those two fuses. Scott noticed this in a video and called me to tell me. Now I had dynoed my car. Pulled the battery, dynoed again, tested it on the street and everything I could do and still was around 6.2 secs 0-60 and 14sec 1320' so I was pretty pissed and getting madder. Scott called and at first I refused to pull them. I had tried enough backyard tricks. GM was going to fix this or I was gonna put my car through the window at the dealership.

Ok, not really, but I had threatened at that point to try and turn the car in somehow.

I finally relented to Scott. And the rest is history.

So the battery disconnect did nothing. As is evident in my dyno sheets and timed runs. The fuse pull opened this car up like crazy.

I have looked into schematics of the Camaro electric system but am too stupid to read it correctly. All I know is that pulling those fuses was the only thing that did the trick.

For the record it has never been confirmed how long they HAVE to be left out. The reason 3 hours came about is because that day I was busy in the yard and I just pulled them out and went back to work in the yard. The 3 hours was by chance.

Here is the thread explaining what happened after I pulled them if anyone is interested.

http://www.camaro5.com/forums/showth...552#post834552

[PQ]

After the first pull we disconnected the battery and left it for a while. Don't remember how long but the AFR was still rich as hell. The tuner thought at the time that something was wrong.

Dynoed at a ricer shop. He said GM must just love to waste fuel. lmao

http://www.camaro5.com/forums/showth...507#post662507

[geaux_tigerss]

Originally Posted by daveagogo1

Cannot say for sure but the ecm handles and reads the exhaust. Pretty much all of the exhaust manufacturers tell you to disconnect the battery before the work so that on initial startup it will learn the new exhaust. Why wouldn't it relearn octane tables also.

I don't think that's why they tell you to disconnect the battery. I think it's more of a safety issue. No battery = no start = no moving parts = no mangled fingers/damaged parts . Maybe I'm wrong, though.

[Lee123]

Originally Posted by geaux_tigerss

I don't think that's why they tell you to disconnect the battery. I think it's more of a safety issue. No battery = no start = no moving parts = no mangled fingers/damaged parts . Maybe I'm wrong, though.

I think your right. They didn't unhook my battery when they installed the exhaust.

[Pistol-whipped]

Originally Posted by Lee123

I think your right. They didn't unhook my battery when they installed the exhaust.

I think you disconnect the battery while working on the exhaust (at least the headers) because you will be in very close proximity of the starter. One slip of a wrench and you could get jolted.