Automotive Wire Splicing

Wiring splice cure for a mystery misfire malady

Sometimes you'll find a certain make and year of vehicle with a common problem that warrants a specific article, which covers both the cause and proper fix. In this case, we'll focus on a potentially baffling drivability symptom on the Hi-Lux pickup and 4Runner dating back to the mid-'80s. This malfunction typically appears on higher mileage, off-roaded (in the wet) and/or frequently "steam-cleaned" examples of these otherwise fine machines.

Old Faithfuls

Although aging and now considered vintage (since its replacement by the Tacoma model in the early/mid '90s), the Toyota Hi-Lux Pickup is still considered a viable light-duty workhorse. Its durable design and simple construction, along with low cost maintenance ease, make it an attractive alternative to costly, ungainly, fuel guzzling modern haulers. Many a parent has also appreciated these virtues when considering purchase of a "first drive" for their aspiring offspring. (Read that: "It stands up to the kind of abuse that inexperience dishes out.")

By the mid-'80s, the Hi-Lux (most folks just called it "the Pickup", since their were no other such offerings in the Toyota lineup until the T-100 and Tacoma) could be purchased with the electronic fuel-injected version of the OHC 2.4-liter 4-cylinder engine. The 4Runners of that period came with the same engine as standard equipment. (While it's true that Toyota also sold passenger car models with this engine/management combo, they don't seem to experience the problem about to be described, due to a slightly different design.)

If you have one of the Toyota trucks or SUVs mentioned above, and it experiences an intermittent or steady, single or multiple cylinder misfire, mostly while under acceleration that is definitely NOT caused by any other mechanical or ignition system malfunction, then read on. Relief is in sight.

Wiring Sub-Harness

The problem lies in the fuel injection wiring sub-harness as it runs from the upper portion of the right front inner fender to the intake plenum, just below the throttle body. The harness, about the size of a large human thumb and covered by common plastic corrugation and electrical tape, heads downward from the fender, looping upward to its anchor point at the intake plenum.

Water can enter further up the harness (often on the fender side), travel down the harness to the bottom of the "loop," and just hang out there, since the corrugation and tape seem to do an excellent job of preventing its drainage at that point.

This wouldn't be so bad if the wiring getting soaked was completely and positively insulated, so corrosion couldn't be induced. Unfortunately, this is not the case. There are two splices for the fuel injector grounding circuit located in this area. These consist of four ground wires (one from each injector) pairing up to two grounding wires leading to the engine management computer. The computer grounds internally, completing the circuit, firing off the injectors in banks of two. Unless, of course, the splices get corroded and cause poor contact, thus causing an open circuit, which prevents the injector from being grounded, and consequently not functioning.


It's fairly easy to check for this condition. While the engine is idling, and the vehicle is secured on a flat surface-in Park or Neutral (M/T equipped) with the parking brake securely engaged-safely grab the harness in the area in question and give it a twist or two. If you can consistently induce a misfire by doing this, then you have pinpointed the problem described above.

Repairing the problem will not be as easily accomplished, and the better the quality of repair, the more time it will take. On the brighter side, it sure will be cheaper than buying an entirely new harness (which may still be available at this writing, if you don't mind the significant extra expense).

Repair Process

You'll first need to remove the tape and pull back or remove the corrugation in order to access the spliced wires. Having access to a wiring schematic for the specific year and model is a really good idea, as there are other unrelated splices in the same area. If you don't have access to one, you can pull the tape off of all the individual splices, checking for the damaged ones. The corrosion will be obvious and, in many cases, what's left of the actual splice will disintegrate during the removal of the tape (you may wonder how the injectors managed to work at all).

The photo above clearly shows the exact condition just described. The white wire with red tracer at the bottom of the photo had once been bonded to the two disconnected and severely corroded wires in the middle. You will notice that the other trio of exposed wires just to the left, while still joined, is showing moderate signs of corrosion. They will need to be repaired also.

Once you've gotten over your state of wonderment, take the appropriate wire-stripping tool and begin to remove insulation from the existing wiring. Work on one set of three wires at a time, or you may get confused as to where they all go later. When you finally find un-corroded wire, you will probably notice that you'll have to patch in a small section of wire to offset the length of wire lost to corrosion.

Although insulated crimp connectors can work okay, using bare crimp connectors (with fluxed solder, to really go deluxe on your Hi-Lux-sorry!) and heat-shrink tubing insulation is the best way to go. If you have no experience with this repair technique, you could get a book and practice on some dummy wiring, or find a willing friend who has well-developed skills in this area.

Once that is done, reassemble the corrugation and renew the tape on the harness, leaving a small break in the corrugation and tape at the geographical bottom of the harness loop, so future floodwaters will have a place to drain out.

Start the engine and perform the previously outlined twist and wiggle test. If there is no adverse effect on the way the engine runs now, you have successfully restored the connections by administering the "splice of life"!

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