MS2E erratic MAP sensor adventure
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. |
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.
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Thank you.
I guess I need to check all hoses and hard lines for leaks once again. |
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. |
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