QuestionQUESTION: Hi Roland, The PCM on my car shorted out and left me on the side of the road.Got the car home, replaced the PCM with a junkyard part. The car started, ran pretty smooth but wouldn't shut off.Took the PCM out, replaced it with a remanufactured one. Car won't start, I have spark and gas up to the carb. Code reader gives me a code 27. engine is a TBI 2.5 liter. All connections at PCM seem good. I don't know what else to do. Can you help? thank you in advance Fern Tremblay
ANSWER: Hi Fern,
The 27 code says that the circuit which turns the injector on and off doesn't look right to the PCM.
The junkyard PCM wouldn't shut off?? That sounds to me like an issue with ignition switch or the autoshutdown relay being stuck 'on'.
As for the third PCM, remanufactured, I would wonder if it is working properly. Try the junkyard one again, and see whether it truly won't shut off.
By the way there are two modules for this engine: a power module and a logic module. The first is in the engine compartment, the second is in the cabin. Which one was replaced and what evidence was there that it 'shorted out'?
Roland
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QUESTION: Hi Roland, thank you for your timely answer. The pcm is located in a plastic housing in the air stream to the carb. The housing was melted and smelt burnt. The junkyard part is no longer available. Should I return the remanufactured part and try another one? It has a twelve month warranty. I am not equipped to test it in any way. Thanks Fern
AnswerHi Fern,
If you have fuel pressure and spark, but a code 27, then there is a chance the the throttle body fuel injector itself has gone bad. Have a helper crank over the engine after you have removed the lid from the air cleaner housing. While cranking it over notice whether there is or is not a fine symmetric spray of fluid falling on the surface of the butterfly valve that is injected from above it. Use a flashlight and look closely for the spray and when the helper stop cranking also watch then for any frank drips of gasoline. If there is none then either the injector has 'opened up its circuit' or the circuit and wiring from the logic computer to it is somehow impaired. An injector costs about $150 so you would do well to remove its plug and test it for continuity between the two contacts at the socket. It should show continuity (a resistance reading of about 1 ohm). If it shows a higher or infinite resistance then I would believe you need a new injector. If it shows continuity then we need to check the wires from the plug to the logic module with an ohmmeter. So take a look for the spray pattern and let me know. You did verify that you do have spark as well as fuel pump action (humm for a second when you turn the key to the run position), correct?
The injectors do burn/leak so if you haven't ever had to change yours it is probably about time.
It might be worth getting a modest digital volt-ohm meter.
The power module is the part that burned up, evidentally. However, the fuel injector is actually controlled by the logic module in the cabin. So it may just be that the power module and the injector failed concurrently or by chance. I can tell you the steps to replace the injector if you opt for that route.
Roland
