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Odd issue with rough idle

Ecomike

NAXJA# 2091
NAXJA Member
Location
MilkyWay Galaxy
This is a general rough idle, fuel injector question!

I am working on my son's 1996 Ford Taurus again. I did a bunch of repairs, (new plugs, proper gap, new O2 sensor, 3 years ago new heads.....) and It has a rough idle. But OBD-II seems to be happy.

If I pull the connection to fuel injector #4, the idle smooths out, but it throws a lean code on the OBD-II.

Seems very odd that it would smooth out by disconnecting the injector signal to a fuel injector.

Does this make any sense to any any one else? If disconnecting it did nothing, I would understand that, and would tell me that injector or cylinder had a problem (spark, valve, fuel injector....). Disconnecting the other fuel injectors makes the rough idle a lot worse!

The rough idle is the only remaining symptom, problem I know of so far having to with the engine.
 
Well I just got a P0402 code, excess exhaust gas flow (meaning EGR), and that can cause a rough idle, but it does not answer my question about the fuel injector?
 
purely hypothetical, but could the injector be malfunctioning (i.e. flowing too much fuel) when plugged in? Then it would be contributing to rough idle only when plugged in. An injector appears to be fairly inexpensive if you wish to rule it out. http://www.autozone.com/autozone/pa...lterByKeyWord=fuel+injector&fromString=search
EGR will contribute to rough idle if it is returning excessive amounts of exhaust gas back to your intake, but if it can be located and disconnected temporarily it could be ruled out as well. Injectors should make a steady ticking sound that increases and decreases proportionately with the engine rpm (listen using an automotive stethoscope 9.99 at autozone or similar parts store), the mass airflow sensor often contributes to rough idle and sometimes the engine performs better when this sensor is disconnected while idling. I dont know if this helps but its some starting points, happy hunting.
 
Got me stumped, the only time I can remember anything vaguely similar was when I crossed two plug cables. My guess is I crossed the magic two, any other combination and the idle was rough, the configuration I had ran smooth with one plug cable disconnected. And ran rough with it connected. It was a real head scratcher for awhile.

I double checked my firing order and sorted out my crossed plug cables and all was right again. It may be possible to do the same by crossing two injector plugs. May also be a crossfire, usually happens inside a dirty distributor cap. Sometimes across two plug cables when one has excessive resistance.

Sometime when I hit a wall I start over with the basics, more often than you think it turns out to be something simple.
 
I checked the plug wires on that side, they are correct.

It is easy to crisscross the jeep wires!:eek:
 
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