FlatFourFun

Is it correct that the map sensor on the drivers side strut turret of a MY97, is the sensor that tells the ecu the current boost pressure? If so, is there any way to test this is reading correct, other than hooking up a select monitor?

PlaneSailing

would normally throw up a CEL light if the MAP sensor wasn't showing the ECU what it 'thinks' it should be seeing (try starting your car with one of the hoses disconnected and you'll see she the CEL illuminates.
If you think you have boost control problems your best bet is to connect a boost gauge and see what boost you are getting at your inlet manifold as ignition and fuel problems can feel like boost issues.
Don't forget to re-set your ECU if you try my test above otherwise you'll be in limp home mode and only boost to 0.5bar anyway!!!
You can clean the MAP sensor with carb cleaner (then dry it out with an air gun), then re-set your ECU.
What problems are you having that you think may be MAP related??

FlatFourFun

the car is a type R V4, which i'm told should run 17psi. It is completely standard and the most it will run is 14.5 (autometer boost gauge). Just before i bought it, the car was in the subaru dealer in Ayr, and they reported 17 psi. I'm thinking that they got this figure from the select monitor tool, which I believe gets its reading from the ecu via the MAP sensor. What I wondered was, at 14.5 psi in the inlet manifold, could the MAP be signalling 17 to the ecu, thus opening the wastegate?
I cleaned the boost solenoid, and switching valve then reset ecu (didnt do MAP sensor). This allowed nearly 15, then as the miles piled on, droped to about 13.5 - 14.

FlatFourFun

bttt

nice guy

maybe 17psi before the intercooler ?

FlatFourFun

I tried putting the boost gauge on the pressure outlet of the turbo, but the reading is wildly unstable so couldnt actually check the pressure. I disconnected the wastegate pipe and tentativly tested the car like that, without any problem, the gauge flicked round to 20 psi, so I backed off and reconnected the pipe. This makes me think that the turbo can produce the pressure, but the ecu is holding it back. On a select monitor, it showed no problems, also 0 knock correction, which I believe means the fuel octane is adequate. So i wonder, does the ecu think it is actually getting 17psi signalled from the MAP sensor? Are the MAPs the same on uk's and imports on a 97?

nice guy

I would'nt normally say this (because i am myself a stickler for HAVING to find the cause of the problem), BUT..... In past experience, by the time you have gone down the route of, change MAP, change ECU, strip this, clean that, pull out every hair on you're head.....only for someone to end up saying....I have a 97 v4 an that runs at 14.5 aswell, anyway i digress......

If you want 17.5 fit a boost controller, have whatever boost you desire, save yourself £££ and keep you're blood pressure nice an low.

Only a suggestion mate, cos i'm still not convinced it should be running more than 14.5 anyway, but thinking of the cost by the time you do find, or if you find a problem, compared to the cost of a controlller that can give you so much more scope anyway......

Unless you have other probs, inconsistant boost or something, is the main problem lower boost than you expect, or is there more to it? If not...Boost controller .

FlatFourFun

I'm afraid I'm one of these "has to be right types". I'm not particularly concerned about the actual boost level, I'm more concerned that I get it to the correct level. It worries me that if it is down, then why? I suppose if its down 3 psi, maybe it will prolong engine/turbo life (its already done 79 thousand miles on original engine), but it would be nice to know its running as it should without resorting to altered hardware. The trickiest part seems to be finding manufacturer type data on imports

Delboy2

There are other ways of testing the map sensor accurately providing you have the correct equipment - I wanted to correlate pressure/voltage outputs from my Pre-96 Map sensor against a MY00 Map sensor which iirc are the same as the MY97. You need to use a calibrated pressure source and a DVM and of course the Map Sensor pinouts.The outputs are reasonably linear as expected (MY96 ranged to 17.2psig (4.92v) the MY00 Map Sensor ranged to 24.2psig(4.72v)
You will see a lower pressure on the inlet manifold side in comparison to the compressor outlet due to pressure drop across the intercooler core - the differences you are seeing could easily be innaccuracies in the pressure guage and the select tool you are using - my gauge was at least 1-2psig over reading before it was calibrated

Cheers