Fuel Injection wiring problems

[James H. Lynn]

I have a 97-Explorer-5.0L. I replaced the #6 injector 3 times. I still receive the P0306 code on my scan tool. I have check all electrical aspects-short finder, ohm test, volt test, continuity check, replaced intake and upper intake gaskets, checked plug wires, vacuum leaks and still everthing checks out per specifications. I cleared all codes several times and after about 20 minutes warm-up time, the light comes back on. I checked for a possible broken wire and still I keep getting the P0306 code. I changed the #7 injector with #6 and vise versa-still no change.
If you have any information reguarding this problem would be very deeply appreceiated.

Thank You,

Jim Lynn

 

[Alec]

I don't know how specifically the injectors are wired in your truck; but usually an injector gets a constant power feed and is ground side switched directly by the computer. If the wiring is ok, then the fault would be the controller.

If you can, use a logic probe. Wire up direct battery voltage and ground. Then with the probe, the hot side of the injector should have a constant red lamp, and the ground side should have alternating red and green lamps in addition to a flashing yellow lamp. This is IMO the best way to non-specifically test an injector circuit.

 

[James H. Lynn]

Fuel Injection wiring problem

Thanks for the response.
I just rechecked everything, coil packs, noid light tester, ohms, volts, no nicks, breaks or cuts in wiring harness. Checked direct ground for leakage from injector. 0.00 was noted on the ohm meter when tested to the (-) side. Positive side shows 4.56 on ohm meter.
Used a short finder meter. No shorts noted or the needle did not detect one.
Everything is stock. Can't afford mods yet.
I really don't know what else to do. I don't have the scan tools the shops have. Just a standard scan tool. I don't have that specific probe you spoke about either.
Could the PCM be baaaddddd????

Thanks,

Jim

 

[Opera House]

Not sure if this is different for the V8, but P0306 indicates just a missfire on six and that could be anything.

"Checked direct ground for leakage from injector. 0.00 was noted on the ohm meter when tested to the (-) side. Positive side shows 4.56 on ohm meter." In the V6, the injectors are fired in banks of three. The V8 fires each injector individually. A low resistance reading on the minus side indicates a shorted output device in the computer or in the wiring.

I would compare that reading with another injector first. If it does look shorted, remove the connector from the computer and test again. Goes away, a bad computer. Knew someone with a shorted output driving the IAC wide open. Removing the computer connector and reconnecting fixed it. Must have been a little piece of wire shorting it out. Worth a try.

 

[Alec]

BTW, a simple logic probe is $12 at RadioShack.

 

[Opera House]

Sounds like he has a fantastic meter now! "Positive side shows 4.56 on ohm meter." Question is, 4.56 what. It takes some fancy equipment in a lab to measure two decimal points of resistance. "0.00 was noted on the ohm meter when tested to the (-) side." A resistance that you are unable to read with certainty under 1/2 ohm. Maybe he is looking at volts, in which case the 12V buss has lost a lot. At least comparing one injector to another might indicate something.

 

[V8BoatBuilder]

As Opera House said, the P0306 is a misfire code, not an injector failure code. After putting so much time into the fuel system, I would look into the ignition system. Possibly bad plug, wire, coil pack?

If you can get an OBD-II scan tool that reads ford enhanced data, you can monitor all eight injectors in real time for a "yes/no" fault detected code. You can also get realtime misfire counts for all eight cylinders. They're not expensive at all, PC based ones are as low as $100.

I would also do a compression test, (gauges availible at Autozone for $40) or Even better, a leakdown test. You might have a problem giving you low compression on #6, causing the cylinder to misfire.

I just had to do a valve job/head gaskets/ignition on my 97 V8 to cure what started out as a misfire problem. Small, subtle problems on multiple systems added up to a large one. Hopefully your problem is simpler. http://www.explorerforum.com/forums/showthread.php?t=108712