This column completes ourcoverage of Nissan electricalproblems we started last month.We’ll begin with a warning aboutthe ground gremlins that canplague the Japanese maker’s mass

airflow (MAF) sensors.First of all, be aware that bad airflow sensor

grounds have fooled more than one goodtechnician. The single most common symptomis intermittent stalling with the engine fullywarm and idling. The driver will tell you thishappens very sporadically and that, if it does,the engine usually restarts readily. Occasionally,the customer may also notice a hesitationduring acceleration. When you check thevehicle, typically no trouble codes will be setand you won’t find anything obviously wrong.

Worse yet, if the ECU finally does set a code, itwill confuse you with a Code 45 (leaking injectors).Meanwhile, the vehicle has frustrated you so muchyou don’t notice that this California-specific code isappearing on a 49-state vehicle! A bad airflowsensor ground can spur a chain of events thatultimately triggers this erroneous Code 45.

Remember that although a bad ground canafflict any Nissan airflow sensor, it seems to be

most prevalent on the six-terminal unit Nissanused until the early 1990s. When you encounterthe symptoms we’ve described, it’s smart tocheck the airflow sensor ground early in yourdiagnosis. To do this, backprobe the sensor’sground terminal with one lead of your DVOMand ground the other lead securely to theengine, then start the engine. If the voltage dropexceeds 9 to 10 millivolts (.009 to .010 volt),repair the ground and retest.

Last month we mentioned that Kent-MooreTool Kit J-38751 usually has the terminals youneed to repair a Nissan or Infiniti sensor oractuator. Some techs remove the old groundterminal from the sensor harness connector androute a separate ground wire directly to theengine. Then they crimp the proper spadeterminal onto one end of a wire and an eyeletonto the other end. The spade is then pluggedonto the airflow sensor, the eyelet bolted to aclean spot on the engine.

Another approach is to see if the harnessterminal is making a good witness mark on thesensor terminal. If it is, some techs opt to“piggyback” another wire onto the existing sensorground wire. Then they ground this supplementalwire directly to the engine. If you use this

Dan concludes his series on Nissan driveability issues

by looking at the electrical problems that can afflict

the Japanese maker’s MAF sensors and TBI injectors.

DanMarinucci

Foreign Service

20 February 1999

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approach, be sure to solder the splicesecurely and seal it against the elements.Regardless of which method you use,always repeat the voltage drop test to besure your repair works.

Truck TBI TroublesOrdinarily sturdy Nissan trucksequipped with throttle-body injection(TBI) may have wiring problems thatcause intermittent injector failure. Thisone could drive you nuts! For one thing,the wiring failure may not occur longenough to set a trouble code. Foranother, no TBI truck ECU provides aninjector circuit failure code. So lookbefore you leap or you may replace somevery expensive injectors needlessly!

Note that earlier four-banger TBItrucks have two injectors, later modelshave one. All V6 TBI trucks have twoinjectors.

The first potential problem is frayedinjector wiring inside the rubber protectorsleeve we’re pointing to in photo 1 onpage 20. See if flexing or shaking the wiresnear this sleeve makes the engine misfireor stall—not to mention disturb theinjector pattern on your scope. If it does,you can just replace the injectors or tryreplacing or repairing the wiring.

Forewarned is forearmed: SomeNissan truck TBI injectors cost morethan $200; others cost nearly 300 bucks!If you do replace the injectors,remember that the new ones come withterminals you must attach yourself. Todo this, slide the new injectors’ wiresthrough the harness connector and thencrimp the enclosed terminals onto thewires. Crimp the new terminals carefullyor you may put another intermittentproblem right back into the vehicle!

You can also try splicing in a new lengthof wire in place of the frayed stuff, butyour splice job must be compact enough

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to fit under the domed aluminum partthat covers the injectors. Jeff Miesen ofKeith’s Auto Service in Portland, Oregon,told us it’s simpler and more reliable tojust replace the entire length of frayedinjector wire. To do this, he peels back theboots shown in photo 2 on page 20,revealing the soldered connections atopthe injectors. Then he uses a 60-watt,pencil-point soldering iron to unsolder theOE wires from the injectors.

The soldered terminals aren’tavailable from Nissan, but the terminalson the other end of the injector harnessare. So, Miesen attaches new wiresdirectly to the injectors. First, he stripsthe end of the new wire and carefullyshapes the bare copper into a littlehook. Then he “tins” the little hook withsolder and slips the hook around one ofthe injector pins shown in photo 3.Using the pencil-point iron, he quicklyflows the solder onto the injector pin.Miesen repeats this procedure on theother injector pin and routes the newwires into the injector harnessconnector to complete the job.

What if shaking the injector wires nearthe rubber sleeve has no effect on theengine or your scope pattern? In thesecases, a loosened OE splice in the powerfeed to the injectors may be the rootcause of the truck’s intermittent injectorfailure. Patiently unwrap the harness onthe top right side of the enginecontaining the injector power wires untilyou find the spliced connection shown inphoto 4. If an imperfect crimp here hasloosened up with age, the resultingexcessive resistance could causeintermittent injector shutdown.

Recrimp the little metal band at thisconnection, flow some solder into theconnection and carefully seal it withtape again. Rewrap the harness, andthe truck should be ready to roll.

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