You are here:

Automotive/TBI Fuel injection wiring harness

Advertisement

Expert: - 3/25/2011


Question
Hi Ernie,

Been thinking about this for a few days and wondered if you could shed some light on this conundrum for me.

I have a 1991 GMC Sonoma with a 2.8 and TBI. My buddy gave it to me as he upgraded and would not get much trade in value for it.
Anyway, it appears the diaphram in the air cleaner has been stuck open and it has melted the injector harness to the point of there being bare wire exposed.

My question is this: If I obtain another harness from the wrecker, and cut the old one out just behind the throttle body,  would a good splice with soldered connections and heat shrink, change the impedance of the wire in respect to the ecm picking up abnormal signals in voltage and amperage due to soldered conections in the circuit?

Would like to do this, but if you think it may be troublesome, I can always tape and loom the wires and not risk a bunch of ECM nightmares ;)

thank you Ernie,
I anxiously await your reply,
Todd

Answer
First, allow me to apologise for not getting back to you a week prior to this!!!  In fact, I DID produce a reply, and was only a closing line away from sending it, when we had a power issue here in our power lab, and this non-UPS equipped PC went off-line, removing even the unsaved back-up of the <cntl-c> I routinely do as a due-diligence way to stay ahead of the unexpected.  At that point, I was running late as well, so decided to get back to this later.

The assignments and midterm exam I was prepping for this week took all of time over the weekend and into the mid week, so I am getting back to this only now!  Let's try again:

First, I would say that harness impedance or resistance would be an issue ONLY if the harness itself was intended to be and INTEGRAL PART of a low-impedance sensor circuit, ie: a current-sensing (by way of voltage drop over a specific length of wire of specified wire gauge) or maybe one leg of a Wheatstone bridge.  In cases such as those, the characteristics of the connecting wire itself IS important, and must be accommodated in whatever repair is being undertaken.

Having said that, my instinct is that this is not the case here.  To mangle the purported words-of-wisdom by the late Sigmund Freud: "Sometimes a Wire is only a wire!" (of course, he was talking about cigars .. etc!)   Due diligence would dictate that one should check into the literature - manuals, if they are available, to see if there is anything one does NEED to know.

Your description of the soldering/finishing process you propose to follow suggests that you are versed in those techniques, and so I will offer nothing further there except to say that the only "somewhat tricky" task you might encounter would be if any of the leads are shielded, via either braid or foil.  The shielding itself would have to be repaired so as to maintain integrity against electromagnetic interference and, before this is done, the core conductor(s) WITHIN that shield must be repaired so as to be as least bulky as possible, as well as electrically sound ... have "been dere and done dat" and it definitely is a FUN job!

By now, I do hope that you already have your repair in place anyway.  If not, then I hope that my thoughts help.

Again, sorry not to get back to you much earlier.  The middle of the term in  electrical engineering technology courses offers even less spare time (not to mention sleep time) than does the rest of the term!  Of course, it really IS fun, or I wouldn't have been doing it for years.

Cheers and regards ... EGK

Automotive

All Answers

Answers by Expert:

Ask Experts

Volunteer

Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

©2012 About.com, a part of The New York Times Company. All rights reserved.