Myxalplyx Posted December 11, 2004 Share Posted December 11, 2004 I was reading information on fuel cut and there doesn't seem to be any clear cut answers on how to eliminate it. Some people have suggested an SAFC, others a device built by someone to electronically fool the ECU. So, tonight I've been reading posts from back in the day to see that even with my VERY limited mechanical know-how, I could think of something. I don't want to have this problem when I crank up the boost. Then I saw this posted up in a past thread by 'All Talk. It's from this thread: http://www.ultimatesubaru.org/forum/showthread.php?t=14610&highlight=fuel Apparently, it's not a maf based signal. It's just a signal from a positive pressure switch. I'm by far no mechanic and I'm at work like I am always posting this suggestion so I can't look in my engine bay but here it goes.... Since this pressure switch works by positive pressure coming from the intake manifold, a simple solution to this mess would seem to be to install a manual boost controller between the intake manifold and the pressure switch itself. Set the manual boost controller at a psi that is a psi or two less than where the fuel cut psi would take place. This way the pressure sensor would see positive boost when the turbo is supercharging but it would never see a psi over what the manual boost controller is set at thereby eliminating boost cut. Does this make sense? If it's a stupid idea, I'm sorry. I don't have much if any experience with these cars and how they work. Quote Link to comment Share on other sites More sharing options...
Vanislru Posted December 11, 2004 Share Posted December 11, 2004 An easier solution is to unplug the connector. This works good for pre 87 cars, I boost at 14 psi, and higher on climbs 16-18, no prob.. On the hotwire cars this isn't effective for stopping fuel cut and I can't remember why [ i have all 86's]. Quote Link to comment Share on other sites More sharing options...
bushbasher Posted December 11, 2004 Share Posted December 11, 2004 On flapper door style cars (85-86 I think) its a pressure switch, on later cars the MAF signal is used to determine boost. Those are the cars that we havent figured out yet, because to trick the MAF would also trick the computer to give less fuel than the motor needs. Quote Link to comment Share on other sites More sharing options...
Subarutex Posted December 11, 2004 Share Posted December 11, 2004 On my left front strut, i have 3 things. Pressure switch: For the turbo light Wastegate solenoid: Controls wastegate? Dropping resistor: Which is connected to the 4 fuel injectors, and to the ecu. Theory: COuld it be, that this passage was accidently left unaltered from the 85-86 mpfi systems? Quote Link to comment Share on other sites More sharing options...
Myxalplyx Posted December 11, 2004 Author Share Posted December 11, 2004 On flapper door style cars (85-86 I think) its a pressure switch, on later cars the MAF signal is used to determine boost. Those are the cars that we havent figured out yet, because to trick the MAF would also trick the computer to give less fuel than the motor needs.Wait a minute guys. In that link I posted where that pic came from, All Talk said this, I was reading through the ’89 FSM (is it normal to use a FSM for pleasure reading?) and found this bit of info (see pic). Looks like the fuel cut is suppose to come in at 9psi and if we determine the switches normal position (closed or open) we should be able to bypass it and defeat the cutoff. Or maybe we could find a way to adjust/replace it to work at a higher pressure. My RX is not ready for extra boost so I cant test it yet but looks promising. Maybe use it for fuel enrichment or water injection. Gary That's why I posted what I did. It was found in an '89 FSM so it would apply to a 1989 vehicle (at least that year). I know I'm missing somthing but what? Quote Link to comment Share on other sites More sharing options...
WJM Posted December 11, 2004 Share Posted December 11, 2004 I remember my 87 strut tower...looks like suby tex's. That first switch as described is still the turbo indicator in the dash...its still there. There is a solienoid there too now, and it control boost more directly. There is also a block there, that when unplugged, the fuel injectors dont work. That must be the resitor block. 85-86 cars dont have those last two....BUT they have that second switch as decribed by the FSM excerpt. Im going outside really quick like... Ok, back... There is indeed ONE pres switch there...upon unplugging it, turbo indicator light no fuction...boost cut still there. on 85/86...boost lite work, fuel cut gone. Hmmmmmmmm........i wonder why that is in an 89 where fuel cut is supposidly built in.... This GOOD thread! Quote Link to comment Share on other sites More sharing options...
Myxalplyx Posted December 11, 2004 Author Share Posted December 11, 2004 There is also a block there, that when unplugged, the fuel injectors dont work. That must be the resitor block. 85-86 cars dont have those last two....BUT they have that second switch as decribed by the FSM excerpt. That block you speak of, does it have a vacuum hose or something going to it so that it can monitor boost pressure? If so, do you think my idea could work? I can't check or do anything as I have 7.5hrs more to go before I get off of work. Quote Link to comment Share on other sites More sharing options...
WJM Posted December 11, 2004 Share Posted December 11, 2004 That block you speak of, does it have a vacuum hose or something going to it so that it can monitor boost pressure? If so, do you think my idea could work? I can't check or do anything as I have 7.5hrs more to go before I get off of work. No vac lines. Just a large elec. connector. Quote Link to comment Share on other sites More sharing options...
Myxalplyx Posted December 11, 2004 Author Share Posted December 11, 2004 No vac lines. Just a large elec. connector. Oh no! I PM'd 'All Talk' to clarify his post in that what he saw was in fact information from a 1989 FSM. I have an '88 FSM and I can look in it as well to check if the same info applies. I don't want fuel cut. Quote Link to comment Share on other sites More sharing options...
Vanislru Posted December 11, 2004 Share Posted December 11, 2004 On my left front strut, i have 3 things. Pressure switch: For the turbo light Wastegate solenoid: Controls wastegate? Dropping resistor: Which is connected to the 4 fuel injectors, and to the ecu. Theory: COuld it be, that this passage was accidently left unaltered from the 85-86 mpfi systems? The wastegate is actuated by pressure from the hose that plugs into the turbo housing. The turbo is not controlled by anything on the car it is a stand alone unit. The actuator is mechanical just a diaphram nothing else. So the second pressure switch you are talking about is the safegard for overboost conditions, it sends the signal to the ecu under high boost cond. This is the one you disconnect to end fuel cut probs, if you have an 86 or older. As Bushbasher already said the problem on 87 & up cars is the ecu recieves overboost info from the pressure switch by the strut and the hotwire maf, the hotwire maf senses the amount of air and if it passes a certain amount the the ecu sees that as overboost. This is why fuel cut defenders exist. As far as what the service manual says well... if it were that simple there wouldn't be hundreds of posts regarding this issue on 87 and younger turbo subes. I think if you look at the 85-92 manuals they all say that, mine does. There is nothing that has been overlooked, guys have overcome the hotwire maf issue but it's still a hassle, that's why I have all 86 turbo's they have all the new gen goodies but the flapper maf. OK I'm done. In the time it took me to write this there was 4 posts!!!!!!!!! NICE Quote Link to comment Share on other sites More sharing options...
WJM Posted December 11, 2004 Share Posted December 11, 2004 I dont want fuel cut either. I wish subaru had left the external switch....maybe its still somewhere on the car....but its certinly NOT in an obvious place like the 85-86'ers were. Quote Link to comment Share on other sites More sharing options...
WJM Posted December 11, 2004 Share Posted December 11, 2004 The wastegate is actuated by pressure from the hose that plugs into the turbo housing. The turbo is not controlled by anything on the car it is a stand alone unit. The actuator is mechanical just a diaphram nothing else. So the second pressure switch you are talking about is the safegard for overboost conditions, it sends the signal to the ecu under high boost cond. This is the one you disconnect to end fuel cut probs, if you have an 86 or older. As Bushbasher already said the problem on 87 & up cars is the ecu recieves overboost info from the pressure switch by the strut and the hotwire maf, the hotwire maf senses the amount of air and if it passes a certain amount the the ecu sees that as overboost. This is why fuel cut defenders exist. As far as what the service manual says well... if it were that simple there wouldn't be hundreds of posts regarding this issue on 87 and younger turbo subes. I think if you look at the 85-92 manuals they all say that, mine does. There is nothing that has been overlooked, guys have overcome the hotwire maf issue but it's still a hassle, that's why I have all 86 turbo's they have all the new gen goodies but the flapper maf. OK I'm done. Well said. I dont think the sensor/switch that is there on the 87+ has anything to do with ECU stuff...its just a light switch. There's got to be a simple/easy/not too difficult way around fuel cut. Quote Link to comment Share on other sites More sharing options...
JWX Posted December 11, 2004 Share Posted December 11, 2004 well considering some cars have it and some don't I think it might be ECU related. maybe they used a different one in some cars? Quote Link to comment Share on other sites More sharing options...
WJM Posted December 11, 2004 Share Posted December 11, 2004 in the case of the 89...i think it was the fact I never had it high enough for it to really fuel cut. the 87 right now, will run 11 psi for a LONG time...I still get the 5 sec gremlin, but it only did the REAL cut once....out of like 15 pulls. The 89 never seen more than about 12...and that was all boost creep. The 88....I dont think steven ever held a gear long enough to hit the cut when it was at 17 psi....BUT, on the dyno run...which was about 4 mins at WOT in 4th gear at 12 PSI...IT NEVER MISSED A BEAT. Quote Link to comment Share on other sites More sharing options...
archemitis Posted December 11, 2004 Share Posted December 11, 2004 ok, what about this, you guys are runing stock fuel pumps right. what does an na efi system run, about 40 psi? i have no idea, but im guessing, if your runing around 30-40, then you add 14 lbs of boost, what if your just maxin out your stock fuel pump, and not hitting fuel cut? the pumps dont put out much more than 45 lbs afaik. Quote Link to comment Share on other sites More sharing options...
Vanislru Posted December 11, 2004 Share Posted December 11, 2004 ok, what about this, you guys are runing stock fuel pumps right. what does an na efi system run, about 40 psi? i have no idea, but im guessing, if your runing around 30-40, then you add 14 lbs of boost, what if your just maxin out your stock fuel pump, and not hitting fuel cut? the pumps dont put out much more than 45 lbs afaik. Nope, fuel pump puts out 80 -95 psi i believe, the fpr sends fuel back to the tank at 45 psi or something like that. What I'm saying is the fuel pump isn't the weak link, the fpr determines the pressure and is downstream of the injectors, so if you use a higher rate fpr you get more pressure to the injectors but a lack of pressure is definately not related to the fuel cut. Could you not use an 86 computer and flapper maf, from what i've seen the connectors for the computer are all the same? Quote Link to comment Share on other sites More sharing options...
Myxalplyx Posted December 11, 2004 Author Share Posted December 11, 2004 Ok, here are a few pictures I took of what I think you guys are talking about. If it is what you guys/gals are talking about, then it'll help some of us 'EA82-T for Dummies' folks feel a little more knowledgable. These are picturs of the driver's side strut tower. I'm thinking that the pieces with the vacuum hoses going to it are the pressure switches. If I'm correct, then one if for the turbo light on the dash while the other is for fuel cut like the picture at the beginning of the post states. If these are the right pieces, which one is for the turbo light and which is for the fuel cut (refer to them as the one with one red dot and the one with two red dots). The 2nd picture shows two wire-like pieces that extend outward from the pressure switches as white wires. Since these look like vacuum lines (I didn't trace because I have to leave for work RIGHT after I post this), then all I was suggesting is placing a manual boost controller in between the one that triggers the pressure switch for fuel cut and wherever it goes into the intake manifold. I do understand now that the ECU receives information from both the pressure switch AND the Maf sensor. I'll be taking my FSMs to work tonight because it should state this inside somewhere. ??? I could be looking at the wrong pieces altogether. Thoughts? BTW: These pics are from a 1988 RX Turbo (Manual tranny, FTWD). Quote Link to comment Share on other sites More sharing options...
calebz Posted December 11, 2004 Share Posted December 11, 2004 First -Vanislru The turbo fuel pump is 61-72psi The FPR is a 1:1 Rising rate that begins at ~36psi Second - Kevin.. Sorry bud, those pics are of your Diff Lock Vacuum solenoids The pressure switches and such being discussed are on the passenger side inner fender well in front of the strut tower Quote Link to comment Share on other sites More sharing options...
WJM Posted December 12, 2004 Share Posted December 12, 2004 yeah kevin, those are the diff lock/4wd engage dohickys....the things we are discussing are 'behind' the air box on the strut tower. Quote Link to comment Share on other sites More sharing options...
Myxalplyx Posted December 12, 2004 Author Share Posted December 12, 2004 yeah kevin, those are the diff lock/4wd engage dohickys....the things we are discussing are 'behind' the air box on the strut tower. So this is the thingamajigga dohicky that you are speaking about...? Quote Link to comment Share on other sites More sharing options...
JWX Posted December 12, 2004 Share Posted December 12, 2004 yes those would be them BTW does your RX have air susp.? Quote Link to comment Share on other sites More sharing options...
Myxalplyx Posted December 12, 2004 Author Share Posted December 12, 2004 yes those would be them BTW does your RX have air susp.? I think it may have had it at one time but no longer. It doesn't raise and lower like my XT6. I think the rubber shock tower caps were just left on. I didn't notice the air compressor come on if it is still installed. Quote Link to comment Share on other sites More sharing options...
WJM Posted December 12, 2004 Share Posted December 12, 2004 Ok, the blue one is the dash turbo light switch. Green=injector 'dropping resistor' block thingy. Unplug that and the injectors dont work. Red=WHAT IS THAT???? Cruise control unit? Quote Link to comment Share on other sites More sharing options...
DrKrazy Posted December 12, 2004 Share Posted December 12, 2004 Yep Red=Cruise control vacuum unit What are the vacuum lines that are running under the turbo light unit going to though? In other words what else is right under it? (wondered what that was while trying to figure my vacuum mess out) Quote Link to comment Share on other sites More sharing options...
WJM Posted December 13, 2004 Share Posted December 13, 2004 under that mess, the item in question is what appears to be a boost control solenoid. It hooks up in between the compresor housing, and wastegate...and there is a 3rd line going elsewhere....and there is wires going to it. I've still not fully figured out tis fuction. Quote Link to comment Share on other sites More sharing options...
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