HELP! Electrical issue driving me nuts.

Follow the harness first looking for anything not normal like a stud poking into it. It is very unlikely a wire inside the lume is shorted. Most likely it has to do with the cam install.(something out of place)

Hi Shoe salesman, Went through the wiring. Couldn't find any issues there. This started before I put the second cam in. (Had the 502 cam in there first and no matter what GM said it was lousy. Computer never did find it!). After installing the new cam I was hoping to find a short. Nothing though. It was mentioned that the computer controls the voltage to the system. And I needed to replace that! But this was the same tech from GM that said he cam would work. (Think he's the only one who answers emails up there.). So I have my doubts. Read about a Burn off relay. But even after unplugging it . The fuse is still poped. Not sure where else to look. Was even debating on pulling the fuse block and seeing if something happened underneath it. Again any suggestions would be appreciated. The cost of this so far is getting to the point where it's taken the fun out of using my truck! (Wife doesn't appreciate it either!)

get a hold of a wiring diagram to see what all that fuse feeds. Unplug those things to isolate. I made a tool out of a 5 amp circuit breaker to plug into where the fuse goes. it will click on and off while there is a short. this way you can isolate it. I have in the past bypassed a wire with a new one to eliminate a short (out of desperation and in the interest of time) again, a wiring diagram is invaluable in a case like this.:)

I did buy a full 2 book service manual on the truck when I first got into the engine work. Always nice to have that to fall back on. Wiring diagram in it is sketchy though. Guess they expect you to know which page to jump to for the next picture. I like the 5 amp breaker idea. Have to make me one of those when I get home. Sounds like a very handy tool. Thanks for the idea! Will let you know how the next investigation goes.

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Later in the thread you said you schematics for the truck.

~~SUGGESTION~~ Cut the 5vlt signal wire at the MAF......cut it at the ECM, run a 5 amp fused jumper wire and go for a test drive.

post the results

~:~ MarshMonster ~:~

======== ======== Dave, you said you had schematics for the truck.

Suggestion..... cut the signal wire at the MAF and at the ECM, run a 5amp fused jumper wire to bypass the circuit and go for a test drive.

post the results

~:~ MarshMonster ~:~

Well I've tried the suggestions. Got all the wires put back where they belong. Guess the computer is the next shot. Although someone I work with mentioned a relay might be stuck for he MAF burnoff. I can't find the relay though. Thought I did but it still poped the fuse when I left it unplugged.

Anyone out there have an old motor computer they are willing to part with. # 16244210 ! Dealer want $450 including the burn for my Vin number. My truck fund for this year is already shot. So that price can't happen for awhille.

I think you must be missing something. It doesn't seem posible that the ECM could cause a fuse to blow and the truck still run...know what I mean? Looking at the wiring scematic what ALL does that fuse feed? Be SURE you didnt miss something. If you have to cut the wire in different places to find the problem then so be it. Just solder it back together when your done. btw it doesn't seem a stuck relay would cause a fuse to blow, it has to be a short to ground (through a bad part, another wire, or to the chassis.)

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If you tried EVERYTHING suggested.....then you bypassed the affected circuit with a jumper wire......from the MAF to the ECM!!!

didn't you??? huh?

Then....... How did it blow the fuse...if the circuit wasn't live??

Because it's a short in the wiring. NOT THE COMPUTER!

You said you've got the schematics. USE THEM.

It's a simple plumbing thing. Find the break in the line and put in a new piece of pipe.

~:~ MarshMonster ~wonders what kind of schematics you're using~

That fuse feeds three items. EGR valve, Evaporation canister activation valve (Or some long name like that!), & the MAF. I'm going to go on the idea I missed something. When I cut the wires to these units I could make everything work with a hot wire tool like you recommended earlier. so I'm sure it's not the units themselves. Going over the schematics again last night I am leaning towards the thought that I missed something. I pulled all the wires back to their junction and found nothing. But when going over it in my head last night, (Which hasn't been working so well since we've been on long shifts at work. Which only leaves flashlight power to see what I'm working on by the time I get home! No garage yet.) The only place I haven't looked is under the fuse block. That were all the wires come in together. I'll try pulling that out next to see if the short is under there. I really am appreciating my old 78 Chevy truck. When it had issues you could just look for smoke. And there wasn't 50 wires, hoses, and stuff you had to get past to see anything. Thanks again for all the training and patience I'm getting from you folks.

======= ======= Dave, ~~Random Thought~~ You said the fuse blows when you first start driving the truck. You said the truck would sit and idle all day long without it blowing. ~end random thunk~ .

Would you run a test for me?

Unlplug the case connector on the transmission that goes to the solenoids.

Then go for a test drive and let me know if the fuse still went out on you.

We're hoping for a short in the wiring harness going down the back of the engine block, on one of the shift solenoid circuits.

~:~ Marsh ~:~

I'll give that a shot Saturday. No time to try it this week. OT at work is leaving me dead at night. Never thought to check down there!

======= ======= Dave, my schematic is showing that the fuse also feeds all the O2 circuits.

The short may be in the harness going down the backside of the engine, or one of the individual leads going to one of the O2 sensors.

Question....... Has ANY work been done to this truck within the last month or so leading up to this problem.

Any whoooo...

check the wiring to the O2's.

let us know....

~:~ Marsh ~:~

MM, Got underneath it yesterday. Thought I had it. Truck had a B&M electronic shift kit. Kind with the switch on the dash. Toook it out. Seemed to be fine. Drove it Sunday. No problem. Got it in to work this morning. All the way to the off ramp again. And on comes the light half way through the curve.

After installing the HP cam the garage that did the work said the converters were plugged. (Said that was why the computer wouldn't find the cam!) So they punched them out. (Thankfully there is no AIMS check in the county I live in.) Of course that made no difference. That was why the second cam went in. This one I did myself. I'll check the O2 sensors tonight. (If it's not pouring to bad. Dirt driveways are hell in the rain!) Makes sense that the short is underneath the truck somewhere. Especially since I have to roll in the mud to find it. Grounds already to soft to even think of trying to get it out to the barn!

Will let you know what I find!

oh, someone messed with the exhaust huh? I'll bet one of your O2 wires is cooked to the exhaust pipe.

Well guys - I'm at a confused state even more so. Got under the truck last night. Nothing obvious. Put a fuse in and fired it up. Shook every wiring harness, Tapped on every sensor, Even tapped on the computer and sensors. Nothing. went to put it back in the house driveway. Put it in reverse. POP!

In looking at the book, (Thanks to your help in investigating the wiring schematics) I found that fuse powers a lot of stuff. An Ignition A switch, The sensors mentioned earlier, O2 sensors, and more than I can remember this morning. I'm almost to the point of unplugging the EGR, MAF and The canister control unit. Stick a paper clip in there and see what smokes! And hope I can spot it before it fries something else. Admittedly if I could afford to take it in to my favorite dealer and just say "Fix it" I'd probably do it. Even though I hate to admit defeat. I keep thinking I'm overlooking something. And I hate coffing up $75 hr or something I "Overlooked!". Keep coming with the suggestions please!

Well guys, It looks to be one of the 02 sensors. I unplugged the back two. (Ones the garage messed with when they gutted the converters. So far no popped fuse. Will rehook them one at a time to figure out which one. Got a 50/50 shot! Noticed oone of them is odd colored. Guessing it was heated up to remove it. That is my first guess on which one is bad! Will keep you updated and thanks again for helping me walk through this issue!

cool!

Well it definitely looks like it's the rear sensor. Leave it unhooked and no fuse pop. Just an 0160 code about no info from the sensor. Now it's just a matter of getting the $80 up for the sensor.

On a side not. Would you know the wiring hookup for the overhead console with homelink on it? There are only 3 wires. White, Orange, and Black. The white wires look like they go to both the map lights, But I can't tell were the orange and black go. My guess is the basic stuff. Orange is power, Black is ground. White is?? Looked in my book and it's no help. The console is from a 99 Suburban. My book is for the 96 and apparently they didn't offer the homelink in that one! Schematic shows the lights but nothing about the homelink.

Thanks as always!