legacycentral bbs

alright so i have a problem. when ever i reach 0 psi of boost the car will cut out and will not accelarate i fixed most of the boost leaks and i can not figure out what is wrong. i would be thankful for any help.
Jason

Sounds like the ECU's reaction to a bad (or otherwise disconnected) MAP sensor.

Freestyle's probably right... had a similar problem when i installed my pneumatic fcd... turns out the hose running to the map sensor, even though it looked good was just a tad too loose (had to really work it, to get it off during the fcd setup)... replaced it with a tighter hose and it fixed my problem.

good luck.

I had the same problem. Every time I got positive boost it would cut fuel. This happened a lot after I went with a MBC. I changed the dropping resistor and the problem went away or at least hasn't happened again. I would also get a CEL at the same time the problem would occur. Seemed to happen more on cold mornings.

ok i get what you guys are trying to tell me but ive looked everywhere for this map senser and by everywhere i mean the search button on the top, i went to subaru and he did not have any idea that the ss even had one and i also looked in the full set of fsm manuls i have and there wasent even a mention of a map senser so i think you guys are talking about either one of the two thing s i have circled in yellow on the fallowing electoinics map.so look and let me know. thanks for all your help.

They're referring to the pressure sensor in that picture.

Yeah - MAP sensor = Manifold Absolute Pressure sensor. Sorry to toss acronyms, I'm very used to using that particular one.

Could be an electrical failure (power or ground situation, or faulty / discombobulated sensor) or a pressure line situation (leak in one of the hoses going to the pressure sensor). The ECU will prevent you from boosting if it does not read any pressure (and too much airflow, maybe?)

Subarus (at least, as far as I know) don't base their fuel injection on the MAP sensor reading like GMs do... we have MAF (Mass AirFlow) sensors that meter the incoming volume of air and look up how much fuel to inject. The Subaru MAP sensor is only used to determine if your turbo overboosts (boost control / wastegate hose blown off) and if so you get fuel cut to protect the car. That's why it doesn't let you boost unless it sees that it's measuring that boost first. An FCD completely bypasses this safety feature and at the same time satisfies the computer that the sensor is working correctly, thereby making your MAP sensor useless but still required for operation.

Hope my ramblings make sense and help you out. If you need a new MAP sensor, ask BlackBart he's got tons of good spare Legacy parts and he's the man.

in my particular instance, the hose i'm referring to is the one between the right side of the pressure exchange solenoid and the "t" coming from the block.

my fcd (pressure release valve) was installed between the two, so that my pressure reading never exceeds the 13psi needed to trip the fuel cut.

the hose that slipped over the nipple on the pressure exchange solenoid fit, but was not tight.

literally cut the hose shorter for a less streched section or replaced it altogether... can't remember which but it solved the problems immediately.

Sounds like the first problem I had with my '93. It turned out to be a bad auxillary purge control thingey. After tearing it apart I found that the rubber diaphragm was unseated. I rigged it back together and the problem went away. That was my first real taste of boost and I was addicted with the first hit. Anyways, my friend that sold me the car (broken) said that he blew into/sucked a vacuum line to get some reaction with the boost guage he installed. I think that's what caused the diaphragm to come undone.

Also, is it throwing a check engine light? If so, search for the procedure to check the codes. It would be good to check the history anyways.


I hope this helps.

Definately flash the codes, it's easy to do and will give you a damn good idea of what's wrong.

finnaly figured out the problem. the wire running to the ecu from the map was almost disconnected in one spot it was almost like someone tried to cut it.