I have some sort of electrical issue that has taken up residence beneeth my hood, and I want it gone! Can anyone offer suggestions as to a possible cause?
Here is the background... It started gradually running richer and richer at startup (cold), and got to the point where I parked it because it was so pig rich It would barely stay running. I thought it was the MAP sensor (because it through on the "check engine light" once and that was what it pointed the finger at. So I replaced it. It started and idled great after that but ran like $hit everywhere else in the RPM band? It is still running poorly throughout the rpm band but will idle ok if you don't touch the throttle. I have since put the old MAP sensor back on, as it seems to make no difference now which one is on there. It runs the same, and the voltage signal output back to the PCM is identical, with either one. (which tells me it was never bad to start with) :banghead:
Things I have done: (besides pull out my hair) :nod:
1. I checked the 5V source coming from the PCM to the MAP and it was right on 5V. The output signal that the MAP sensor sends back to the PCM is messed up though. It is soposed to vary from .5V (idle) to 4.49V (WOT). It will drop no lower than about 2V? I don't know why, but I do know that explains the rich condition! I even went so far as to test the MAP when I had it off. By attaching a small length of vacuum line to it and sucking on it (creating a vacuum) while supplying a 5V source to it's input, I could get it to drop to .5V on it's output voltage. So it would seem the only reason for it not to drop to .5V on the vehicle is insufficeint manifold vacuum. (ie...a vacuum leak) But I cannot locate one, and my vacuum gage, at idle, reads 19?
2. I checked the TP sensor and it is also getting it's 5V supply from the PCM. It is functioning like it should on it's voltage signal back to the PCM varies from .7V (idle) to around 4.5V (WOT).
3. I have checked for vacuum leaks and came up empty handed, as I thought a vacuum leak could cause the high MAP voltage signal.
The idle air control circut I sopose could be a culprit, but I have no way to check it (need a DRB scan tool) and I don't see how that would effect the MAP voltage. I don't know if, when they fail, it produces the symptoms above? I am, what I would consider to be, a fairly smart guy when it comes to working on vehicles, but I am just about out of ideas. Other than spending money (like I did on the MAP sensor) replacing sensors that probably aren't bad, one at a time! This however seems to be more of a simple problem causing the MAP and perhaps other sensors not to function right, rather than a sensor failure problem. :confused: :confused: :confused:
Thoughts?
(I am continuing to search for a vacuum leak)
