QuestionQUESTION: Hi,
A couple days ago, my 1998 Chrysler Cirrus (2.5 V6) check engine light came on, accompanied by rough running, thick, white, exhaust (that smelled like fuel), and very excessive fuel consumption. After checking the code, I got P0204 and P0304. Conveniently enough, I was planning on changing the injectors the next day. I went ahead, thinking that injector 4 had failed and that the replacement would solve the problem. Upon replacing the injectors, and restarting the car, the problem and P0204 were still there. I checked the resistance of the injector (14.7 ohms, ok) and the continuity between the wire harness connectors for injector 4 (there was continuity). Checking both injectors 2 and 6 showed no continuity between their respective connector wires. Checking the voltage when the car was running, the connector for injector 4 was showing a constant 14 volts. I started tracing the path of the wires (dk green/orange and lt blue/brown) coming from injector 4 with the help of my Haynes manual, which led me to the PCM. After unplugging the PCM connector, and checking continuity between the wires at the wire harness connector for injector 4, there was none. Plugging the PCM connector back in, there was continuity between the wires at the wire harness connector for injector 4. I assume that there should be no continuity between the wires at the connector, and am thinking that there is a faulty connection in the PCM that is causing the wires to short, resulting in the injector staying open and dumping fuel into the cylinder. I wanted to confirm my suspicions with you, and see if there were any fixes besides replacing the PCM.
ANSWER: Hi Aleks,
When you say 'continuity' and "between the wires" without referencing exactly which wires and at what point you are measuring it can be a bit ambiguous. It is not complicated:
The dark green/orange wire (from pin 6 of the pcm) should show 12-14v, as you found, when the engine is running.
And the injector should measure about 10-15 ohms across it when disconnected from its plug.
The control wire is light blue/brown and runs from pin 1 of the injector plug to 16 at the pcm. It should show continuity between those pins when the plugs are disconnected at both ends of the wire. And it should show no continuity to ground when similarly disconnected at both ends. If you then put the plug back in the pcm and measure the resistance of the control wire to ground it should be more than 5 ohms and if not the pcm is bad. You can verify with any other of the 5 injectors that they don't behave as does #4 in these regards. All the latter control wire measurements are made with the ignition off.
When the key is 'on' and the engine is running the voltage on the control wire will oscillate between 0 and 14v, pulsing everytime the engine rotates through 2 revolutions but your meter will probably not resolve that pulsing unless you compare the average reading on that driver wire with that on any other of the injectors (showing a slight difference in the average voltage). For the injector to leak fuel continuously the control wire either has to be shorted to ground, or the pcm at pin 16 has to be shorted to ground instead of pulsing. If the wire is not shorted to ground, then you pretty much have to conclude that the pcm is bad.
Roland
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PPS You mentioned thick WHITE smoke and a smell of fuel. When an injector is staying open I would expect the smell of fuel but I would alsoi expect the smoke to be black in color. Heavy white smoke that smells of anti-freeze is a sign of a head gasket leak. I don't know however why the injector driver fault code would be caused by a head gasket leak. So that is anomalous. But keep it in mind that if the driver circuit seems correct, and the smoke is heavy white, that you could have a head gasket leak.
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QUESTION: With the plug attached to the PCM, and measuring the resistance of the control wire (lt blue/brown) while connected to ground, it read 20 ohms. I checked the resistance of the control wires connected to ground for injectors 2 and 6 as a comparison, and they both read approximately 35 mega ohms each. Disconnecting the plug from the PCM, and measuring the resistance between pin 16 and ground gave 20 ohms. All the measurements were taken while the car was off. If this is indicating that the PCM is bad, is it as easy as swapping for another one, or is there more work involved? Thank you for taking the time to get back to me so quickly before.
AnswerHi Aleks,
It certainly would appear that the driver for that injector is not working properly. In '98 there is probably nothing that would be required to program a replacement PCM to get you going. The VIN and mileage of your vehicle should be updated into the replacement PCM or there may be a trouble code set in its memory but that should not impair its function. That unfortunately needs a DRB III unit to accomplish at a dealer. But focus on getting the PCM from the same year/model/body style/engine/transmission so that any pre-progammed paratmeters are identical.
Roland
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