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Old 02-10-2011, 09:08 PM   #1
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Default Bad MAP sensor? Reads 100kpa on overrun.

I've been chasing a problem that started after my car sat for about a month. It sat through rainy days and then well below freezing days/nights and i'm wondering if some moisture froze in the MAP sensor and fuxored it.

Then again, it seems to be RPM dependent. When I let off the gas at 4krpm + it does this weird overrun thing where the map reads 100kpa and my LC1 reads full rich. Overrun works fine below 4k.

Also, above 4k at part throttle the car runs extremely lean. It doesn't matter how much fuel I add in those cells it still leans waaaaay out.

So far I replaced my FPR thinking that might be the problem, no change. Swapped CAS thinking that would do it, still no different. Checked my coils for looseness and they're fine. Reburnt firmware and MSQ, checked all my settings (barometric correction is off), triple checked base timing, etc. Checked all my grounds. All the ground pins on the DB37 run straight to the lug on the intake mani. Been fine like this for a really long while. I'm really not sure where to go from here.

Here is a datalog of the problem.
Attached Files
File Type: msl 2011-02-10_16.33.30.msl (72.7 KB, 70 views)
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Old 02-10-2011, 10:05 PM   #2
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What kinda vacuum line are you running? Could be sucking shut if you aren't running vehicle rated vac. line.
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Old 02-11-2011, 02:28 AM   #3
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What kinda vacuum line are you running? Could be sucking shut if you aren't running vehicle rated vac. line.
Oh snap I hadn't thought of that. I'll investigate that possibility. That doesn't explain the weird lean condition at part throttle above 4k but that could be unrelated.

The weirdest part is that under overrun, when it reads 100kpa, its going full rich (8.5:1) which I've never seen before. The LC1 is only setup to go from 10 to 20 so I suppose I should try the reflashing to an older firmware and see what happens.
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Old 02-11-2011, 09:41 AM   #4
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those map sensors will go bad if the condensation in the lines freeze up the sensor. I've had to replace a few before on other's units, I think Curly's failed last year for the same reason.

you're supposed to try to make it so the sensor always points down, I couldn't make that a reality so I have a large loop in my map line just before the MS unit.

if you need a new 2.5bar map sensor I can send you one.
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Old 02-11-2011, 01:42 PM   #5
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those map sensors will go bad if the condensation in the lines freeze up the sensor. I've had to replace a few before on other's units, I think Curly's failed last year for the same reason.

you're supposed to try to make it so the sensor always points down, I couldn't make that a reality so I have a large loop in my map line just before the MS unit.

if you need a new 2.5bar map sensor I can send you one.

I think you're thinkiing of cueball's and yes I remember his thread about that last year. I hadn't thought about putting it with the map facing down.

I'm going to investigate the possibility of a pinching hose first then i'll let you know on the sensor if I need it. It's still suspect.
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Old 02-11-2011, 01:57 PM   #6
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well... power the MS and connect to a laptop.

then run a new dedicated vacuum line to MS, then suck, you should be able to pull over 18kPa if you keep pulling in air.
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Old 02-11-2011, 05:58 PM   #7
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Quote:
Originally Posted by Braineack View Post
well... power the MS and connect to a laptop.

then run a new dedicated vacuum line to MS, then suck, you should be able to pull over 18kPa if you keep pulling in air.
Oh ya, i'm going to suck it. Then i'm going to blow it too.
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Old 02-11-2011, 06:42 PM   #8
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should be able to squeeze out 2psi.
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Old 02-13-2011, 10:53 PM   #9
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I can't get a map reading over 74 kpa blowing as hard as I can into the line from the engine side. While driving I don't see over 65-66kpa anymore. Car runs fine and I am watching the wideband to make sure it doesnt lean out. Anyone got a link on a diy for replacing the map sensor? It's a 9495pnp. I am also naturally aspirated
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Old 02-14-2011, 09:28 AM   #10
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you have it calibrated locally incorrectly. 100kPa is atmospheric. You are seeing less than 74kPa without pressure, then you live on the moon.
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Old 02-14-2011, 04:26 PM   #11
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Quote:
Originally Posted by Braineack View Post
you have it calibrated locally incorrectly. 100kPa is atmospheric. You are seeing less than 74kPa without pressure, then you live on the moon.
Theres is no need for live on the moon to see less than 74 kpa. In fact my map sensor reads ~70kpa when i go to Sierra Nevada (has the highest tarmac road in Europe)
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Old 02-14-2011, 05:21 PM   #12
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There's nothing wrong with your MAP sensor or your lines.


Have a look at the kpafactor4250.inc file on your laptop, and I think you'll see why this is happening.
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Old 02-14-2011, 05:26 PM   #13
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The problem is when I did the Ts update somehow it swapped map sensor in the project properties. Fixed with a click of the mouse
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Old 02-15-2011, 03:19 PM   #14
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I should mention that I tested the map sensor by way of mouth. It seemed to be working fine. I swapped ECUs and i'm still having weird *** problems (like tach jumping around?) so I'm just going to keep hunting for the issue.
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Old 08-21-2011, 03:13 PM   #15
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Default map sensor issue on my 99 miata

I have just recently bought a 99 miata and the check engine light has been on since the purchase. I have already taken my car to an advance auto shop and they plugged their computer in and told the check engine light was a result of my map sensor. the car seems to run perfectly fine so i can be pretty sure the problem isn't to serious. Now, my knowledge on this very limited so im not really sure wat to do about this problem exactly and was hoping some one could help me out.. PLEASE!

Last edited by NateA99; 08-21-2011 at 03:25 PM.
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