To DIY'ers-how not to wire things

[railgun]

Sorry for the long winded post...

When you think that you did the most awesome wiring job, regardless of what it is, you probably didn't, or missed something that's way too obvious.

I had wired in an FJO injector driver box about two years ago out of necessity as well as what I had read on various forums indicating their benefit. I did a somewhat hack wiring job at the time in that most of my wire lengths were way too long and not exactly neat. Most of my connections were just crimped and just kind of hanging around the box itself, which was mounted where the ABS unit sat.

Fast forward to this early spring and I had rewired my engine harness including the rewire of the FJO to better integrate it into the main harness. I soldered everything, cut to the proper length, covered every solder joint with heat shrink, then wrapped with some high temp vinyl tape, then some self vulcanizing tape. Everything was perfect.

Fast forward again to last weekend when I'm sitting at a stop light not 10 miles from my house on the way to Indianapolis when I start 1-rotoring it. WTF? So we pull into a Speedway gas station on the corner at which we were sitting. Spark, and make shift compression check are good. So in the middle of said gas station, we pull everything out. I can't pull my primary injector clips due to my installation, so we pull the fuel rail. Boiling fuel on top of a motor isn't something I recommend many people to mark off as something they've accomplished, but out of necessity it was pulled.

Long story short, the front primary injector wasn't firing. The injector was good by giving it some power directly, so either the FJO unit was toast or somehow the PFC.

Initial wiring testing showed that the FJO was suspect.

A tow home and further testing the following week showed that I in fact had a short between the ECU and the FJO. While the heat shrink was great and all, due to it's placement (proximity to the exhaust and the fact that they were all bunched together at the same point), as some know, the heat softened the tubing up enough that the solder points (admittedly not the cleanest) started to poke through and the front primary and the 12v touched.

Didn't take much...





Needless to say that I got extremely lucky that it was the primary. Had it been a secondary and I didn't know and I romped on it...bye bye motor.

So another rewire, an extra helping of tape around the heat shrink and a relocation of the unit away from the exhaust and were NOT back in business. That short, and running the motor long enough after it happened, caused the PFC's front primary channel to fry. But, I found a somewhat unscientific method of testing the injector channels.

Just behind the connector block and those four pins, there are four resistors and four capacitors along the edge of the PCB. One of those cap solder points and the ECU pin will show a resistance of about 440 ohms. The front primary gave about 13k+ ohms. I'd call that a failure. That and the fact that the car woudn't start.

So the moral of the story? When you wire something like that up, pay attention to where the installation is. Offset your connection points, whether crimped or soldered. And ensure that it's secure; that heat and vibration won't cause that connection to fail. Common sense? Sure. But if you'd seen the original wiring job, I think that you'd agree that it was a really good job. It's those little things that you don't realize that'll get ya.

[Nopis1O]

ha way to scare me. im finishing up the wireing on a birds nest right now.

[speedjunkie]

Damn, this scares the shit outta me haha. From what it sounds like mine is currently set up pretty similar to the way you had yours when you first installed it, and at some point I was planning on redoing it to make it clean, along with soldering with heat shrink and all that. Thanks for the heads up! Mine unit is over by the ABS, but my connections are all over the engine, close to the injectors, and all that is wrapped up in heat shielding. Hopefully that helps. Now I'm freaked haha.

[theorie]

ouch! yeah you really gotta make sure you use high quality shrink...and avoiding exhaust definitely helps. lol

[Brent]

Glad nothing too bad happened. Very informative post.

[Garfinkles Motor Works]

I always double the layers of heat shrink tubes .Some times using the same size if the wire is small or I use two different sizes one over the other .Never leave a bump in the solder joint,reheat the bump or press it down with pliers .

[88turboii]

yeah i dont trust heat shrink alone anymore, usually follow it up with a layer of electrical tape also

[railgun]

Originally Posted by Garfinkles Motor Works

Never leave a bump in the solder joint,reheat the bump or press it down with pliers .

Heh...believe me. Lesson definitely learned.

[jkstill]

Another post that makes the assumption that soldering is better than crimping.

It ain't so.

High quality crimps make a very good connection.

Solder connections have a tendency to break in high vibration environments.

In the pics in this thread, the soldering was not done properly if is sharp enough to poke through the heat shrink.

The wire needs to be heated with the soldering iron, and the solder melted on by touching it to the wire, not by touching it to the solder tip.

Want the best of both worlds? Use some cheap bare crimps, and flow a little solder into it. You can get these at radio shack, and it makes it easier to make a good solder connection.

[RIZZXX7]

I follow mine with tape also, this type of thing happened to my mr2 and I kept on blowing fuses, shit drove me nuts

[Garfinkles Motor Works]

We know that the wire is workharded after solder but I have had less trouble with soilder joints than crimped .My customers get the best I can offer and I have been selling them my time and knowledge for 47 years .I solder the bare connectors as well but I get ones that are better than the one from Radio Shack .the R S ones are thinner gage metal .

[railgun]

Originally Posted by jkstill

Another post that makes the assumption that soldering is better than crimping.

It ain't so.

Nowhere did I assume that crimping was substandard to soldering. And those solderpoints weren't sharp per se, but rather not exactly straight and due to how they were bundled, and as tight as they were...you get the idea. And I know how to solder. The method you described is exactly what I did.

[jkstill]

^ sorry for the assumptions then.

Seen too many bad solder joints.

Even made a few myself.

[joff]

Originally Posted by jkstill

^ sorry for the assumptions then.

Seen too many bad solder joints.

Even made a few myself.

Solder joints are the not the problem. Its undeveloped skills at soldering.

If solder was the wrong way to do things, we'd all have a problem as the thousands of internal connections inside an ECU, sensor, etc are all soldered and not crimped.

Every solder joint I've ever seen fail has been due either to a cold solder joint that someone experienced would identify right away as botched from the start, or long term corrosion from improper cleaning of flux residue. Comparing soldering to crimp connections is like comparing pop-rivets to a quality TIG weld.

I found the best thing for an amateur solderer is to introduce them to standalone liquid rosin flux. Flux core solder is nice, but you must work quick before the flux burns off which is not a skill you will have as a novice. With the liquid flux, you can fix a cold solder joint by just dripping some flux and reapplying heat.

[joff]

Originally Posted by jkstill

Want the best of both worlds? Use some cheap bare crimps, and flow a little solder into it. You can get these at radio shack, and it makes it easier to make a good solder connection.

Actually, contrary to common sense, this is not the best of both worlds. Its identical to soldering only and has none of the benefits of the crimp. The only reason to favor a crimp connection is when temps are over 400F (solder melts) or when the wire is under tension/stress.

The copper/solder alloy is more brittle than the regular copper and doesn't bend much before it will fracture. Many non-engineers will fixate and overreact to this fact but the truth is it usually doesn't matter as none of the wires in our wiring harness are under significant stress. Vibration alone does not matter as the flexible wire before and after the joint flex before the solder/copper alloy flexes -- it needs to be high vibration and under tension in such a way that the joint "feels" like its being bent. For instance, voice coils in speakers are soldered and they are under extreme vibration -- BUT -- there is slack in the wire so the solder joint is not effected and there is no stress to the copper/solder.

When you crimp + solder, your crimped connection now contains the brittle solder/copper alloy. All you did was waste time and a perfectly good crimp on a soldered joint and you didn't even save any time.