Mechanics

HOW FAR BACK SHOULD I GO TO FIND AN ELECTRICAL SHORT ?

1999 GMC Sonoma • 15,300 miles

I left pin prick holes on the electrical lines of my ICM and coil untaped after a recent car repairTRUCK RAN GREAT.I went back in to tape up, once done I tried to start the engine, it would not start. Cranks, but doesnt start. I checked the ICM for voltage and got none. None at the coil connector as well, but expected that. I also do not have it at the alternator, nor the CPS(CKS) but DO at the TPS. Ive checked a good 20 inches or so down the line testing power (pink) wire from ICM for voltage, HAVE NONE. I DO HAVE CONTINUITY IN LINE TO CONNECTOR THOUGH. None of the fuses are blown, what should I check next?
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Stolen75
May 14, 2012.




Also, I have NO spark at plugs, distributor, and coil.

Tiny
Stolen75
May 14, 2012.
Check and test ICM 1 fuse 15amp in underhood fuse block

Tiny
Rasmataz
May 14, 2012.
I've looked to see if it is blown, it is not. I have checked fuse for continuity (put multimeter to ohms, put leads on either fuse end, have continuity).

Mine does not have an ICM 15amp fuse. But it does have a ECM 15amp fuse. Which is blown !
Truck started right up !
Off to tape wires up PROPERLY and IDIVIDUALLY then send my firstborn to you via fedex : )

Tiny
Stolen75
May 14, 2012.
Wow. The first thing I told my students is if I find a single cut or hole in any wire to take a reading, they will stop and fix it. If I find a second one, they fail the course and can come back next year to retake it. If an employee of mine did that on the job, they might get one verbal and written warning. The second time they would be asked to find work somewhere else. I don't need people putting future problems in my customers' cars.

First of all, electrical tape is worse than leaving the holes exposed. It will unravel into a gooey mess. You need to either remove a terminal from a connector so you can slide on pieces of heat-shrink tubing, or you can use silicone gasket sealer to make a little ball of sealer around each hole. They make heat-shrink tubing with hot-melt glue inside to do a better job of sealing the holes. That's all we use under the hood or under a pickup truck box where rain water can splash onto them. With tape or with leaving the holes exposed, you are going to be chasing problems forever due to corrosion.

The only acceptable test points are at the connectors. A stretched-out paper clip makes a nice tool to slide alongside the wire where it goes through the rubber seal. That provides plenty of points to measure continuity and voltage.

Second, it sounds like you think the location of a short to ground can be found by measuring at various places along a wire. In fact, if there's a short anywhere, you will measure that short at every place along that wire, before or after the short. You can see where water is leaking from a pipe in your house, but there will be no pressure anywhere along that pipe, before or after the leak. An open circuit in a wire is a different story, but you can usually find those with a visual inspection once it has been narrowed down to a specific section of wire.

Once my students determined the cause of a prepared problem was due to a grounded or open wire, their first response to "what is the proper repair" was often "run a new wire". At that point I explained that is absolutely not correct. They don't know why that wire has a problem. It could have been rubbing on a sharp metal bracket or fallen down onto hot exhaust parts. How long before the next wire in the harness suffers the same fate? By locating the exact cause, they would very likely prevent a different future problem. The proper repair is to find the break or short and fix it. By unplugging connectors, then measuring for shorts to ground or open circuits, you only have short sections of wire to deal with, so narrowing down the location isn't that involved. It's the intermittent problems that don't act up all the time that are more involved, but we have tricks for finding those too.

There were a couple of exceptions where it was permissible to replace an entire wire. One was when it had become stiff from being overheated from excessive current. The insulation would be melted and deformed too. The other was when the entire length was too corroded to solder to. That happened regularly after someone spliced wires and tried to seal them with electrical tape. Trailer harnesses are good examples of that. You will never find electrical tape on an original harness from the factory. The plastic wrap that looks like tape is not sticky. It is only there to hold the wires together and neaten them up. Splices are sealed with what looks like friction tape or heat-shrink tubing, and exposed copper where the wires are crimped to terminals in connectors are protected by rubber Weather-Pack seals to keep moisture out.

Obviously it is more cost-effective and reliable to replace an entire wiring harness when one is damaged in a crash, but when I read that a mechanic is going to replace one to solve a problem he can't find, I know he doesn't understand how to diagnose them, or it has already suffered from someone poking holes.

Once a mechanic touches a car, they get blamed for everything that goes wrong with it for months and sometimes years later. For that reason, many of them have learned that when they find wires butchered by do-it-yourselfers, they will refuse to work on the vehicles unless the customers allow them to properly repair the wiring first to reduce the chance of future problems. Repairing those wires may not solve the problem but it will reduce the number of "ever since" complaints. "Ever since you changed my oil, my power antenna doesn't work; what you gonna do about it?" "Ever since you aligned my car, the engine overheats". Cars today are complicated enough and since the insane engineers have decided to hang multiple computers onto circuits that don't need them, piercing and cutting wires adds a whole new level of headaches and potential problems. If there are a lot of holes, this might be the third time it is better to replace an entire wire. Forget the electrical tape.
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Caradiodoc
May 14, 2012.
WoW! Doc it reminds me when I was going thru the new school back in the early 80's in electronics/electrical theory-Good Job

Tiny
Rasmataz
May 14, 2012.
Dam carway to break it down good work.

Cadieman
May 14, 2012.
I RETAPED IT. THEN PROMPTLY REFUSED TO WORK ON ANY OF MY OWN VEHICLES AGAIN. REGARDLESS TO SAY, I STORMED OUT ON MYSELF : )
SERIOUSLY, THANKS GUYS FOR THE HELP AND INFO (COULDA SWORN I CHECKED THAT EXACT FUSE BUT. OBVIOUSLY DIDN; T : )
MY DAD (WHO ELECTRICAL AND DUCT TAPES EVERYTHING) MENTIONED SHRINKWRAPPING THEM TOO, GONNA DO IT TO CLEAR MY MIND OF EVENTUAL FUTURE TROUBLE, THANKS DOC & RASMATAZ !

Tiny
Stolen75
May 14, 2012.
I should have mentioned too that my intent was not to sound condescending. I'm picking on the procedure, not the person. Unfortunately most of us learn by trying and making mistakes, but I have to stick my nose into someone else's conversation when I know I can help avoid future problems. I've run into too many "blowed-up" aftermarket radios that had grounded speaker wires from tape that unraveled on a hot summer day. It's easier to avoid problems than it is to fix 'em.

Caradiodoc
May 14, 2012.
Good for all keep a eye on that fuse. Something blew that fuse

Cadieman
May 14, 2012.
WILL DO, PRETTY SURE IT WAS THE FOUR WIRES WITH SEVERAL PIN PRICK HOLES THAT I TAPED TOGETHER INSTEAD OF INDIVIDUALLY OR SILICONED THE EXACT HOLE, BASICALLY WHEN I UNDID MY TAPE JOB, I COULD SEE WHERE THE HOLES I MADE WOULD LINE UP IN SYNCH WITH ONE ANOTHER ALL COZY IN MY TAPE JOB AND THUS CAUSE A SHORT (?) GROUND (?) BLEW THE FUSE.
DOC, U DEED SOUND A TAD CONDESCENDING. IT WORE ON ME. BUT ACTUALLY THE ONLY THING THAT MADE ME WANT TO DO IT RIGHT : ) I WAS IN GARAGE WITH YOUR WORDS RUNNIN THREW MY HEAD AND COULDN'T GET THE IDEA OF ME PICKING UP MY SON WHEN ITS HIS TRUCK AND FINDING WIRES WITH OLD TAPE ON THEM STUCK/FRIED TOGETHER ON THE SIDE OF THE ROAD (LOL)
THANKS GUYS !

Tiny
Stolen75
May 14, 2012.

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