Interesting this thread was revived and a few members requested MAP data.

I had my car act up on the way to the hotel tonight, and it had the typical MAP symptom of intermittent bucking/hesitation/rough idle etc. So when I got to the hotel I opened the hood, got my trusty channel-locks, and whacked the MAP sensor 2-3 times. The engine nearly stalled with the first whack, but recovered and idled better, though not perfect.

I just happened to have my OBD cable so I connected it up and logged the following :


I don't know if this is normal or not. It looks like the MAP readings are pretty erratic, and what confuses me is that MAP runs about 9-10 at idle (closed throttle) but DROPS when the throttle is opened and RPM increases (throttle is yellow, you can see where I brought the rpm's up). I would have thought MAP would increase with any throttle opening?

Am I missing something?

EDIT - I just re-read this thread and find it interesting that:
1. I replaced my origninal MAP sensor at about 25k, fixed my hesitation problem.
2. I installed a Comptech SC at 67k (oiled air filter)
3. I now have 120k, and 3 days ago did a track day. No visible smoking in turns, but maybe the oil contamination idea has some merit since I had a MAP problem so soon after a track day?

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Just a thought - if you always get a misfire code on #1, maybe there's a problem with #1's ignition system. And maybe that's what is frying the ECM's.

Have they swapped coil packs around? Might be interesting to move them all (1-2, 2-3, 3-4, 4-1) before it breaks again and see if it is still #1 that causes the problem.

 

MAP in inHg will drop when the throttle plate is opened, as the Vacuum in the manifold decreases.

With the throttle closed, engine vacuum is high, because the engine is only drawing air through the IAC port. when you increase the amount of air with the throttle, the pressure increases towards atmostsperic. At WOT on a NA car it should be very close to the BARO sensor's output.

Whenever the MAP V's go over the BARO V's, the PCM can go into bug out mode.
The bad MAP sensors that I have seen do this.

 

[QUOTE=Slows2k,Jul 12 2004, 09:59 PM]MAP in inHg will drop when the throttle plate is opened, as the pressure in the manifold decreases.

With the throttle closed, engine vacuum is high, because the engine is only drawing air through the IAC port.

 

I've edited my previous post.

"Pressure drops" was meant relative to the Vacuum reading of 20inhg.

If you are watching a Vacuum gauge, when you open the throttle the vacuum reading drops. This is source of my error.

 

I'd be curious what the IAC duty cycle was. The IAC would be another varible for the MAP reading when the throttle is closed.

 

Is IAC available through OBD? I can't seem to find it in my "Car Code" software.

 

IAC is supported on most of the scan tools I've seen. Usually displayed in duty cycle.

 

hmm.... i havnt had any problems since a couple days ago... strangely enough. Keep up the research you guys... im curious as to what this gremlin is so all of us can not worry about it anymore.

 

what would be a good way to describe this to honda, because they think i have a bent valve due to my hesitation. They say they think this because my map sensor is reading a 1.29 voltage opposed to a .95. I just hop ethe map is all it is