legacycentral bbs

I'm new to the Subaru thing. I picked up a EJ22T for a little project of mine over the summer and I trying to figure everthing I still need to get it running. I was just reading about the MAP over in the turbo thread. I didn't realize that the legacy motor had both MAF and MAP, since mine only came with the MAF. Does the ecu use MAF for fuel, and MAP for ignition like Chevys?...if not, I'm cunfused why it needs both. Since the MAP cuts fuel after 14 psi, is this only a 1 bar MAP?...if this is true is this the same part from the N/A? Thanks for any help.

~Josh

Personally I don't think I care for your name (not that it should matter to you what I think ), but hey I'm one of those guys that doesn't like an engine from one car maker going into another.

Anyway, I believe the MAP only measures intake manifold pressure, aka boost. So an NA car woudln't need one. It uses the MAF just like an NA car. What all came with your engine? If you can't get the map from the seller you can always throw a similar system together. vrg3 did a write up on how to use chrysler parts: http://www.graphics.cornell.edu/~v/chrysler_map/

I can understand you not likeing the engine swap, but you can't argue with me wanting a better engine for my beetle (aircooled + carbs = serious suckness). I thought that I had everything that is bolted to the engine (nothing that was connected to the firewall or the sides), the entire wiring harness and the stock ecu. Although it turns out I don't have the coolant tank on the intake manifold either.

I know that a MAP is for manifold pressure, not just for boosted cars though (my celica runs on MAP). And there are plenty of turbo cars out there that run strictly of MAF (such as any DSM). What I want to know is what does each control. It makes sense if the MAF controls fuel and MAP controls ignition, but it just doesn't seem nesecary. I'm really more concerned with knowing if the MAP is a 1 bar map sensor, and if this is the same one that is in the N/A model (since they are all over the place in junk yards).

~Josh

didn't look a the link before I posted.....thanks, that was very helpfull. vrg3, you are definatly the most usefull person ever!!!

~Josh

hmm, I think we're not communicating very well.

I didn't mean no NA cars have MAP's I was just saying about the 1st gen legacy's. I believe the MAP is really only used to control boost, but someone else more knowledgable would be able to verify that. It measures how much boost there is an then sends the info to the ecu which does calcs on that and other schtuff and sends info to the boost controller to limit boost. So an NA car wouldn't need one. The MAF doesn't contorl fuel, the ECU does. The MAP doesn't control ignition, the ECU does. Someone correct me if I'm wrong but all the MAF does is measure the amount of air coming in and send the info to the ECU.

Ok I think I understand. If the maps in the ecu are run off MAP or MAF or both I don't know. But some of the maps for fuel might only look at the MAF signal to determine the injector pulse. Or that at 5psi it pulls 5deg and at 8psi it pulls 10deg.

Thats a good Q. vgr3 might know, and I would like to find out.

Oh and I don't care what engine you put where as long as it's not a SBC

Thawa,
I guess I didn't read you post correctly, and yes I know that the MAP or MAF isn't dirrectly controlling fuel or spark. It is just one of the variables (TPS, RPM, etc.) that the ecu uses to control both fuel and igniton timing. If the MAP is only used to control boost, then why can't you just take it out of the system when using a manual boost controller?

As was stated earlier, the ecu uses the MAP sensor to measure the amount of pressure in the manifold (aside - the reason why you probably didn't get it with your engine is because it's attached to the passenger strut tower so it's not on the recycled engine). The MAF sensor is used by the ecu to measure the amount of air entering the engine.

Now, taking those two inputs, and monitoring load (with the throttle position sensor), the ecu extrapolates a best fit fuel map from its memory. The reason why you need all sensors functioning is because the ecu needs inputs from ALL THREE of these sensors in order to determine the proper fuel map. If one or more of those inputs (as well as the o2 sensor when the car is in closed loop mode, possibly in open loop, but I'm not sure) is taken out of the system, the ecu won't have the required inputs and will throw a code, since it won't be able to properly address fuel and timing. Once a code is thrown, the ecu will run a "limp mode," which is a map with severely retarded timing and ultra rich fuel mixtures, just to be safe.

Of course, you could go standalone ecu, if you don't want to install the MAP sensor. No need to deal with OBD regulations if this engine is going into a 60-70s beetle.

Thanks for the info. That is inteseting that it uses both MAP and MAF for fuel, all cars that I have delt with in the past uses one or the other. I do plan on going with a stand alone in the future (along with bigger turbo, intercooler, injectors, etc.), but I don't have the money for that right now. I guess that I didn't make it clear from the start that I do understand how the ecu uses MAP (load based) and/or MAF (air flow) to determine fuel (which map) and how much timing to add. I have been around a descent amount of aftermarket tuned cars, there are a couple of turbo hondas and a couple of very not stock dsms sitting in my driveway. I was asking a more legacy specific question... sorry for the confusion.

~Josh

Volksabu wrote:Thanks for the info. That is inteseting that it uses both MAP and MAF for fuel, all cars that I have delt with in the past uses one or the other.

My guess is that subaru uses a MAF sensor to get by the more stringent emissions laws (even back in the day). LEV status or something like that. Typically, MAFs have more precise measurement of airflow into an engine compared to MAP sensors.

Since the car is turboed, the ecu needs some way of measuring the amount of boost that's being produced so there is an incorporated MAP sensor as well.

BTW, do you know of any stock turbo cars that just use a MAF sensor? You mentioned DSMs, however, there are still fuel cut defencer applications for DSMs, which would automatically point to a MAP sensor being used.

The reason I ask is that I can see no way to be able to use strictly a MAF sensor on a turbo car. How would the ecu know how much boost is entering the engine?

BTW, do you know of any stock turbo cars that just use a MAF sensor? You mentioned DSMs, however, there are still fuel cut defencer applications for DSMs, which would automatically point to a MAP sensor being used.

Stock DSM definatly do not have a MAP. The overboost protection is contorled by a set air flow/rpm ratio. Although this obviously isn't the most acurate way...which is why the dsms in my driveway have maps in them (not for overboost, just for better monitering what the engine is doing). Other than that, most turbo cars that I am familar with run striclty a MAP.

~Josh

Fueling is primarily computed using the MAF signal, as are load computations that are used for ignition control.

The pressure sensor is used for closed-loop boost control and for overboost detection. It may or may not also be used to measure boost for fuel enrichments and/or timing retard. It's also used to measure barometric pressure, since turbo ECUs don't have pressure sensors built into them.

Plenty of factory turbo cars use airflow meters. Off the top of my head, I think the list includes 300ZXes, Supras, MX-6es, T-birds, Celicas, and the aforementioned DSMs. Some also use pressure sensors and some don't.

FCDs for DSMs clamp the airflow signal. When using one you have to figure out another way to fuel correctly, just as when clamping the MAP signal with a speed density system.

I believe 80s Subaru turbos also implemented airflow-based fuel cut as a form of overboost protection.

Josh, the stock sensor needs to detect boost so it has to have a range greater than 1 bar. It's roughly a 2-bar sensor. Your best bet is probably to get a Chrysler setup and adapt it as described in my page that THAWA linked to.

Here is one for you. '97 outback sport wagon (impreza based) with the n/a 2.2 has a map with a baramotric sensor. I was looking at a friends over break and it looks the same as the legacy turbo one. Is this really the same part?

~Josh

No. It's different. The NA pressure sensor is roughly a 1.5-bar sensor; it reads up to about 6 psi of boost.

If you actually look at the pressure sensor (under the pressure exchange solenoid) you'll see that the NA and turbo ones look completely different. The turbo one is much larger.

The pressure exchange solenoid isn't exactly the same but is almost the same, and is interchangeable.

I realize this is probably a stupid question, but what exactly does the The pressure exchange solenoid do? Also, my motor is a '93 and does not have the barametric pressure sensor ecu pinout, does this mean there is a sensor in the ecu? Thanks for all the help.

~Josh

OK, I think I figured it out....please correct me if I'm wrong. The Subaru pressure exchange solenoid does the same thing that the Baro-Read solenoid on the chrysler MAP does. Basically all it does is switch between which pressure the MAP sensor is reading (MAP or Barometric). This still leaves me wonding what the barometric sensor ecu pinout that my ecu does not have does?

~Josh