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Electrical Advice

3K views 25 replies 8 participants last post by  advanced design 
#1 ·
OK, this needs said and I didn't want to single anyone out on a particular thread. There is a wealth of knowledge right here at your fingertips but some of you guys just won't listen.
If you have an electrical problem do the diagnostics FIRST. Quit trying to guess or have someone give you some kind of pat answer. If you aren't willing to buy a test light and digital volt/ohm meter and learn how to use them, then pay someone else to fix it. You CAN NOT do electrical repairs with out them. And get a wiring diagram for your car.
I see thread after thread of guys who just keep asking could it be this or that but never do the tests prescribed. They just want someone to tell them what part to swap out.
You can't just make guesses and throw parts at a car to fix it.
It isn't rocket science, it is just basic stuff.
You don't know how lucky you are to have guys like Doc, I had to learn all this stuff the hard way long before there was computers and internet.
If you don't understand, don't be afraid to ask for more basic instructions
Maybe there should be a sticky with electrical 101 so the basics don't have to be explained over and over for the beginners.
 
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#4 ·
Maybe, you will have to become our new resident electrical expert willow...........................seems that docvette has stopped posting for the last month or so.

I sure as heck don't know much more than just the basics........................
 
#5 ·
willowbilly3 said:
Was that too harsh? I have seen some real knowledgable people loose interest in helping and kind of drift away because of this and I would hate to see it happen here.
Naw, just busting your chops. In fact this thread could fit in any of the tech forums. The way I usually approach these lazy posts is do a search on the topic and cut and paste a half dozen or so links to old threads with no narration. Hopefully this will clue the writer and novice readers to get off their can and do a little of the leg work themselves.
 
#6 ·
I too spent years learning (still learning too) and am happy to share the hard gained knowledge with others, especially when they are really covering the basics / researching what is available. Otherwise I quickly loose interest if I feel I am being used.

Willowbilly has a good idea regarding electrical basics, - volts, amps, ohms, voltage drop for ground credibility, the difference between a short and open, proper checking of each of the measurables and what they mean are some thoughts for subjects.
 
#8 ·
I realize it is easy for people with knowledge to talk over someone's head with terms. Maybe we need a basic electrical tutorial we can send people to first so they can familiarize themselves with terms and basics. Maybe a brief overview of ohms law. And even some of the more experienced guys could gain from it. I don't know one mechanic out of a hundred that knows how to do a voltage drop test.
My problem is relating sometimes. And even though I love electrical work there is a lot I don't know either and in my shop the only books I used on regularly were my Mitchels wiring diagrams and component locators
 
#9 ·
Willow

Excellent idea about the basics. A great place to start and might even include links to reference sources? Just a thought. Now to get someone to write and stick it.

I've fixed many difficult problems by doing a voltage drop test - you really determine if a ground circuit is really grounding. While it is mostly applicable on computer module circuits it also shows quickly if an engine ground (or any ground) isn't grounding properly. The ground voltage drop test is how we teach technicians to verify a ground circuit.
 
#12 ·
You might try your college book store. I have found some good related books there. The best one I ever had was a companion book from a clinic that Interstate Battertys put on. It was full of good stuff and easy to understand. I gave all my reference material to a friend who was studing for ASE exams.
 
#14 ·
This is a little off the topic but related to resource material. When I was studying for certification as an emissions technician the best book I ever got my hands on was a companion book from an old Sun scope. Too bad the industry got away from the true ocillascopes, they were one of the best diagnostic tools ever. When you can find one they are cheap or free and if you have room to keep one they are great for pre-computerized cars. Of course they just give data, you still have to think to analyze it yourself.
 
#15 ·
Good point about the oscilliscopes being cheap. I bought an old Allen 'scope for $25 at an auction a few years ago. The 'scope still works and it came with a timing light, vacuum gauge. Very inexpensive diagnostic equipment and it looks kinda cool in my shop.

The Fluke oscilliscope proved invaluable to me on the primary ignition side (cam and crank sensors) but I never used it much on the secondary side. Technicians overall have gotten away from using a 'scope and rely on the scanners.

My old college textbooks are very good for basic electrical. Good suggestion.
 
#16 · (Edited)
One thing am oscilloscope will do is show spikes. Most of the led screen scopes don't do that accurately. I also used to keep an old analog volt/ohm meter for just that purpose as you can detect a spike on one that might go un noticed on a digital.
My old Sun scope was one of the highend ones. I never used the 2 gas because I had a stand alone Allen 4 gas but it had the dialback timing light and the cylinder kill/balance function so you could easily isolate Any cylinders that weren't making as much power as the rest.
I had a poor running 73 Chevy Monte Carlo come in once. It idled fine and had good compression and what looked like good spark but ran rough and seemed to break down under load. The kid had put on all new plug wires, points condenser and even a new coil. The scope showed the problem right away. All the spikes were upside down. Anyone care to guess why?
 
#19 ·
So here is another one for you.

Back in the 90's a new Buick Roadmaster in one of the shops was running poorly. Tech had replaced multiple electronic components. They had an old Sun 'scope so we hooked it up to the distributor. The raster pattern showed initial firings from top to bottom that made a bit of an S shape.

Thoughts on what the problem was?
 
#22 · (Edited)
Man, that's a tough one. I'm leaning towards a voltage/ground problem(i can see a capacitor doing that if the car has two coil packs but the odds of two capacitors doing that at the same time are slim to none so it must be a low voltage/bad ground preventing quick saturation of the condensors?)but I'd like to see what the other answers are.

one coil pack on that car. i'm clueless.
 
#23 ·
I think its pretty cool hearing about all the older Sun-Oscilliscope technology, between Raster and Parade patterns, to spark and firing lines, and dwell time periods. Us in the younger generation (I'm 20) have it so lucky compared you old-schoolers. We grew up on Snap-On Modis which is justy basically a ritzy scan tool with a ritzy O-Scope...The diagnostics is starting to wave bye-bye in this business...

Nice to meet everyone!
 
#24 ·
Hey NXS,

Very good thoughts regarding the problem with the Roadmaster but unfortunately incorrect. In fact I had to pull out one of my old college texts on oscilliscope patterns and the text advised a bent distributor shaft would cause that problem. Replaced the shaft and the car was happy.

Welcome Matto,

The scanners are a good diagnostic tool and we couldn't be without them on the new products but you still have to interpret what it is telling you. If you have an SES light, a missfire code and see missfires counting up on a cylinder you still don't know if it is plug, coil, wire, injector, injector wiring, base engine problem, or ecm. Then the diagnosis really begins though I see a lot of guessing.
 
#25 ·
My 96 F-150 ran out of gas at as I backed it away from the alignment shop. I switched tanks and restarted it to the greetings of a check engine light. You guessed it, random misfire code. Weird thing is that it's a hard code, I would think it should be a soft code and the light would go out if the misfire didn't reoccur
 
#26 ·
Don't remember about the misfire code light staying - would have to check the parameters but my guess is after a number of key cycles without reoccurring the light would go out. Maybe not as emissions related.

Any case we've gotten off the topic you originally started. Some basic electrical information for reference / sticky. How do we get that done?
 
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