Godless Commie

iTrader: (2)

Cliffs first:
Would the MAP sensor built in the MS2E act funny on its way out, or would it just die?
Mine acted VERY strange for a day.

Details:

I had to make some minor adjustments to my VE table (bottom left cells, "idle zone") to pass my emissions test yesterday. All went fine.
I also made a couple simple changes to idle speed. Nothing big.

After the test, I got on the very congested freeway. I am still breaking the engine in after a rebuild, so I am taking it rather easy on the engine. (About 850 miles so far)
There was an opening I could not miss to merge in, so I got on the gas and accelerated with about 10 psi boost for a few seconds.
I heard a muffled "plof" as I accelerated. Traffic was intense, so I was paying attention to my driving rather than the gauges.

Later on, I felt he car was sluggish, idle went waaaay down, and AFR gauge read 10.
Vacuum / boost gauge was perfect.
I tried coasting at 2000+ rpm, and realized there was no fuel cut anymore. That's when I realized there must be a MAP problem.
3-4K revs with moderate throttle would produce around 12-13 AFR. Weird.

I armed myself with my latest good tune (from about 2 weeks ago) and hooked the laptop.
Loaded last known good tune, started the engine..
60 kpa load at idle... No wonder fuel cut does not work. (Needs below 40 kpa)

I then disconnected the vac hose that leads to all three MAP sensors - one for the vac/boost gauge, one in the MS2E and one inside the water injection controller.
I thought there might be a physical problem with the vac lines.
Not having a mityvac, I blew into the hose I disconnected from the rear of the intake manifold. Almost no resistance. Sucked on it, same result. I tried that half a dozen times, pretty hard, and I was convinced something had popped/burst/come loose.

Then, I had to something entirely unrelated for about an hour.
Came back to the same hose after I was done with that, and blew on the hose again.. Resistance. As in, deadhead. No leak.
I hooked the hose back up, started the engine, all perfect. Weird, in a different way.
Test drove with very high vacuum on decel and up to 12 psi boost for half an hour, still perfect.

So I buttoned everything up, and drove around. No problems.

The question is, I know these MAP sensors do not have diaphragms in them. They don't magically seal themselves if they leak.
Has anyone had a problem like this?
@Reverant

Wouldn't these type of sensors just die, or would they act erratically like this?
I am baffled.

Reverant

iTrader: (10)

That would be a hose issue - the MAP doesn't have a diaphragm like you said (just a flexible board that changes how much it flexes based on vacuum/pressure, and that flexing changes the board's resistance) and once they go, they are done.

Godless Commie

iTrader: (2)

Thank you.
I guess I need to check all hoses and hard lines for leaks once again.

Godless Commie

iTrader: (2)

Interesting development:

It happened again today, with somewhat different symptoms. This time idle AFR was 11, and cruise was 12.5
I was able to get fuel cut off on decel.

On a whim, I turned the engine off when traffic stopped, and waited for a few seconds with the key on before cranking the engine.
Engine started with perfect AFR, and everything was normal.
I tried several restarts, and all's OK.

One bothersome detail:
If I start the engine with laptop hooked up (tunerstudio running) I see a "MAP sampling error" warning maybe 7-8 times out of 10 starts.

Also, come to think of it, if I had a hose problem, it would affect the rest of the MAP sensors on the same vacuum line.
(Please see first post above for explanation of MAP sensors)

I guess I will have to start logging till it happens again.