Nissan Repair Questions? Ask a Mechanic for Answers ASAP
did you check for power at the red wire and ground at the block wire at the coils
I just read the long story and at a glance it would look correct as to the new PCM having gone bad. When you have a spark like you had at the battery due to a poor connection there is always the risk of damaging the PCM.
Let me look at this thoroughly and get back to you here in a bit with a diagnostic process.
The communication with the scanner is the one we need to address first.
Here is what I would like you to do first. Check the ground wires that hook to the intake manifold. These will break and it is possible that you may be getting a reading with a volt meter and yet not have a strong enough ground to boot up the ecm. Pull on them and make sure that they are good and strong.
The next thing is to check fuse #19 in the underdash fuse box which is the power for the scanner.
If both of these are good then we will move on.
Please let me know your results.
Ok, I'll check back a little later
OK, I will look for your response Sunday
Sorry about the delay, here are the tests that need to be done. I have a sinking feeling that the replacement ecm may be damaged but we must do these tests.
Due to the fact that the ECM is clearly not working even enough to get communication so the tach will not work until we resolve the root problem.
The way that we need to test grounds is by using what we call a "live circuit resitance test". Put one terminal of your volt meter to the ground that you want to check (with everything hooked up, put the other lead of the volt meter to the battery negative terminal and then crank the engine. If you get more than .05 volts then you will need to either find and fix that ground or add ground to that wire. You can do a positive voltage supply test in the same fashion by putting one lead of the volt meter to the supply wire and the other to the battery positive post. On some of those you may see up to .5 volts and still be ok.
I am quite certain that you will find one of the grounds that breaks down under the load of the pcm attempting to boot up and you will probably find a reading of 2 volts or higher at one or more grounds. It will be simpler to just piggy back some wires that you then bolt down firmly to a good ground.
Let me know what the results are of this test. Any typical tests that you have done are not reliable because if a ground wire is hanging on by one thread of copper somewhere it will measure like it is ground but it will not be able to carry the necessary load.
Excellent. Unfortunately it all leads to "bad ecm" which you say you have replaced with others. The fact that it is getting hot is why I suspect that there is still a ground or power problem that could take out another ecm.
#20 is not a power input. The instructions say that that is the ground output to the ecm relay. So with key on there should be a solid ground there. You can do what it says next and just ground that white/black wire and see if the ecm powers up but I suspect it won't.
The next thing they want checked is the reference voltage. #65 at the ecm should read 5 volts with the key on, check that and let me know what you have there.
You don't mention grounding terminal 20....have you done that step and checking to see if you can then communicate with the ecm?
This thread is now so long that I need you to understand that I cannot remember or look through everything we have already "checked". So humor me and recheck some things if you already have checked them.
Here is a "no communication" concern to check out: