Rough idle, Bad injector?

[hammerfore]

My 97 explorer has a rough idle. It is showing codes for a random misfire in cylinders 1 and 6. It has new plugs wires and coilpack. I have good spark. A compression test showed a little low (90 lbs) in #5 . I then tested the injectors, using the ohm test, and they all test ok. A little research on the web tells me that the ohm test is not a very good indicator of a failed injector. Any suggestions where to go from here now that I have it all apart?

 

[imp]

My 97 explorer has a rough idle. It is showing codes for a random misfire in cylinders 1 and 6. It has new plugs wires and coilpack. I have good spark. A compression test showed a little low (90 lbs) in #5 . I then tested the injectors, using the ohm test, and they all test ok. A little research on the web tells me that the ohm test is not a very good indicator of a failed injector. Any suggestions where to go from here now that I have it all apart?

Look at what injectors do, and consider what can go wrong with them, mechanically, but no electrical issue, and what such wrong things might cause.

An injector can leak. They have fuel pressure available behind their little pintles (valves) all the time. A leak, though, usually will affect mixture towards too rich, this condition being "caught" when the 02 sensors can no longer properly "trim" the fuel/air ratio. That causes an 02 code, not misfire code, I think.

An injector can get stuck. Then, it won't open at all, or not enough. No fuel, or too little, maybe equals misfire code? But why on 2 cylinders at the same time? In my experience, a stuck injector is a RARE occurrence. 2 of them simultaneously, no way. But, a faulty connection, electrical, WILL shut down an injector, resulting in no fuel to that cylinder. Depending on the level of PCM ability, and here I'm not too certain, but the PCM "knows" when an injector is not drawing current to operate it, and will throw a DTC.

I would check carefully, the connectors atop those two injectors, get a voltmeter across each set of leads of each injector, engine running, and see whether the signal is coming through. If none, possibly a broken, or otherwise damaged wire is present upstream somewhere. If you do this at the PCM, you will be not seeing the conductors ability between there and the injector's connector.

Alternately, you could yank out those 2 injectors and replace them. Academically, if this is a high-mileage set of injectors, after ripping things apart, I'd replace them all. However if the problem lies outside of the injectors themselves, the misfire will still be present. imp

 

[hammerfore]

thankyou for your quick reply. With the upperintake off I cannot do the electrical test you suggested. If I do this check just cranking the engine will I get the test results I am looking for . The rough running seems to be only at idle. Indeed when first started , that is when it is cold, the engine runs much smoother. The rough running only appears after it warms up. This allong with the random misfire codes leads me to believe the injectors may be partialy blocked. Am I on the right track, and if so are the fuel injector cleaner devices built on youtube wourth a try?

 

[imp]

thankyou for your quick reply. With the upperintake off I cannot do the electrical test you suggested. If I do this check just cranking the engine will I get the test results I am looking for . The rough running seems to be only at idle. Indeed when first started , that is when it is cold, the engine runs much smoother. The rough running only appears after it warms up. This allong with the random misfire codes leads me to believe the injectors may be partialy blocked. Am I on the right track, and if so are the fuel injector cleaner devices built on youtube wourth a try?

This I cannot comment on knowledgeably, sorry. The testing for signal to the injectors may be done at the point where the upper engine wiring harness exits forth from under the manifold, probable at the back. Opening the harness to access individual electrical conductors is necessary, as is also a wiring schematic specific to the vehicle and engine, to identify wires feeding suspect injectors. So, this becomes rather academic. As I said, replacing the injectors, if even just the two, may be a reasonable gamble.

Yes, cranking the engine using the ignition switch, as normally done, will certainly send signal pulses to the injectors. However, with the manifold removed, The cylinders will still fire, and the engine attempt to run, though it will lack inputs from several sensors, the important ones being Throttle Position Sensor, and Mass Air Sensor. If you go ahead and attempt this, I would recommend doing it with all the spark plug wires removed. This could be accomplished at the ignition coil. Or, the low voltage connector at the coil could be removed (this might be easier). imp

 

[hammerfore]

So I cleaned the injectors and put it all back together. I changed the injectors positions to see If the fault followed them. It didnt. I still have a random misfire in #6 . The misfire in #1 has gone. I now have a code for a vacumme leak I havent had a chance to find the leak yet. While putting it back together the #6 wire seemed to not seat on the coil properly. I will check this out and see if it solves my problem.