Fuel Cut Solution

[oddcomp]

my 87 had the boost solenoid that the ecu conrols lets teh turbo hit a higher psi when you stomp it

but only briefly pretty much like a emergency thing in theory so if you gota move and get out of someone's way then you stomp it get higher boost for a few seonds or so than the ecu would normally allow

at least thats how those work on other cars

 

that same boost solenoid would work with the boost controll off the ms box if anyone is wondering...

prolly work witha apc box as well like i have

 

the second unit <not shown in the pictures tere.

thats on my 87 is a vacum pump setup

to supply vacum to things like heater controls and cruise control

alot of turbo cars have them

[All_talk]

Hey guys

 

Sorry for the late response, I don’t get to the computer much on the weekends. That paragraph I posted was copied from a PDF version of the ’89 FSM I found online. As others have suggested, I now believe it to be incorrect and I have never found a second pressure switch on my ’87.

 

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.

I too would like a better understanding of the “boost control solenoid”, Here’s what the ’89 FSM has to say (same one with the bad info on the pressure switch :-\ ), apparently it has something to do with altitude compensation…

 

 

Gary

[Myxalplyx]

There are just SO many vacuum hoses under the hood of this car that it can frustrate the average Joe (me) in understanding what is what. I look at my Impreza and XT6 and they seem like they are worlds apart than this RX turbo as far as vacuum hoses go. They are much simpler.

 

Thanks 'All Talk' for posting and clarifying the info from the FSM. To know that the FSM is giving bad info is scary. Now I'll be doubting everything I read from it.

[WJM]

alot of those vac lines are useless...,just to let you know...

[iluvdrt]

Is there a way to bypass the maf entirely, by putting a wire in the connector to feed the pos side to the ground? I know in some older hot wire saabs you can do this. It just gives it a generic signal. But the it might not let your fuel get metered right.

 

What about creating a restrictor plate to limit the amount of air the hot wire sees? Like a small damn to bypass the wire a little bit?

 

I hope someone figures it out, as I am sick of my fuel cut, it is very violent sometimes and has on many occasions almost caused to me wreck.

[Do It Sidewayz]

The "Boost Control Solenoid" works to adjust boost pressure to to a number of factors. Basically, it restricts (shuts off) the boost pressure from reaching the Wastegate accuator. When the computer senses it has had enough boost it will open, and allow the wastegate to open. When it doesn't have enough boost it will remain closed.

 

The 85-86 cars did not have any kind of Boost Control, except the wastegate, If you look they only had like a 2 inch vaccum hose coming from the compressor outlet to the wastegate accuator. The wategate accuator will actually open at about 9 PSI, you loose a pound or so getting to the intake runners and then you have 7-8 PSI. These cars had the "Overboost switch" because the computer had no boost control, When the overboost switch sensed 10 PSI the Computer assumes that the Wastegate was stuck closed, so it would cut the fuel. On these cars. just unplug the overboost switch.

 

On the 87 and up cars, they added a boost control element into the computer. Really.. the computer has almost no idea how many PSI it is really making, it just monitors airflow. So..you will find on these cars when it's really cold or really hot you will pull different amounts of boost AND the fuel cut will be in a different spot. The Computer senses the "overboost" situation through the MAF, as it believes that for "X" amount of airflow the engine will be making "X" (about 10 Lbs). The reason the computer needs to see this "overboost" situation for more than 5 seconds is because FIRST the computer will open the wastegate solenoid, in a hope to open the wastegate, In STOCK cases this will work fine. However when you start experienceing boost creep (with free flowing exhaust), and you have installed an aftermarket Boost Controller, the Factory boost solenoid doesn't do much at all, especially with boost creep, as the wastegate can be fully open, but not have any effect. The MAF is the heart of the 87+ cars. If you have a boost gauge on an 87+ car you will actually watch the boost come up over "fuel cut level" and come back down. Even a stock car will go up to "fuel cut level" then back off the boost.

 

We have two or three 87+ race cars. All of them will pull WELL over 12 PSI, with no Fuel Cut defender. We only run an MBC, and we set one car to 13-14 PSI, it will run all day long. Another car we set to 15-16 PSI and it will run all day long with no fuel cut, once we cranked it up to 22 PSI and still no fuel cut.

[bushbasher]

Is there a way to bypass the maf entirely, by putting a wire in the connector to feed the pos side to the ground? I know in some older hot wire saabs you can do this. It just gives it a generic signal. But the it might not let your fuel get metered right.

 

What about creating a restrictor plate to limit the amount of air the hot wire sees? Like a small damn to bypass the wire a little bit?

 

I hope someone figures it out, as I am sick of my fuel cut, it is very violent sometimes and has on many occasions almost caused to me wreck.

The problem is, any attempt to give the MAF a lower signal will result in a lean condition because the MAF is a primary control for the fuel injection.

 

One idea is to create a circuit in line with the maf that cuts the signal just below the fuel cut level, and run a secondary injector setup like an spfi injector, activated and perhaps even regulated by the same circuit. That way, even though the computer is going to give less fuel, the secondary system will start pumping to keep up with the engines real needs.

 

Or just convert to MS.

 

I'm no ea82t expert but one can get pretty far with a basic understanding of the system and a little bit of logic.

[bushbasher]

The problem is, any attempt to give the MAF a lower signal will result in a lean condition because the MAF is a primary control for the fuel injection.

 

One idea is to create a circuit in line with the maf that cuts the signal just below the fuel cut level, and run a secondary injector setup like an spfi injector, activated and perhaps even regulated by the same circuit. That way, even though the computer is going to give less fuel, the secondary system will start pumping to keep up with the engines real needs.

 

Or just convert to MS.

 

I'm no ea82t expert but one can get pretty far with a basic understanding of the system and a little bit of logic.

OH OH OH has anybody looked around to see if ea82 ecus are programmable at all? Maybe somebody with dealer connections can get ahold of the old diagnostics computers and see what can be done.

[Do It Sidewayz]

Ofcourse the old computers can be reprogrammed.

 

They use an Eprom.

 

In a nutshell. you need an eprom reader/writer. You need to take apart the ECU, de-install the Eprom, then install an eprom socket. Then when you want to program the eprom you take it out of the ECU and plug it into your reader/writer. Then you have at it.

 

Almost any "tuner" who has been around for a while will have all the crap to do this burried in dust.

 

it is where the term "chipping" an ECU came from. They can adjust the fuel maps, lift Fuel Cuts, just about everything. There isn't as much adjustability as the new OBDII computer, because the ECU simply does not monitor as many sensors. But there is still lots of room to play.

 

You can buy all the crap to do it yourself also. It's not that grossly expensive. It's the same stuff used for programming Satelite Dish recievers and cards. You just need a different program to interface with the ECU.

[Myxalplyx]

The reason the computer needs to see this "overboost" situation for more than 5 seconds is because FIRST the computer will open the wastegate solenoid, in a hope to open the wastegate, In STOCK cases this will work fine. However when you start experienceing boost creep (with free flowing exhaust), and you have installed an aftermarket Boost Controller, the Factory boost solenoid doesn't do much at all, especially with boost creep, as the wastegate can be fully open, but not have any effect. The MAF is the heart of the 87+ cars. If you have a boost gauge on an 87+ car you will actually watch the boost come up over "fuel cut level" and come back down. Even a stock car will go up to "fuel cut level" then back off the boost.

I have noticed this and freaked out. I basically was holding on waiting for the hand of gawd to come down on my car once the injectors turned off. It never happened. Boost would go up to around 10psi or so after sudden application of the gas pedal. It didn't do this all the time, only during certain situations. Even still, if the maf sensor controls fuel cut by the amount of air that it sees coming through it, why is it that some people like you can run higher boost levels without issue? Or is this just the big mystery that most people have solved yet.

 

I personally would like to have an EGT gauge before turning up the boost. This whole discussion is very interesting (as it has been in the past). Good info!

[Do It Sidewayz]

It's all about air density.

 

When it's 30 below, or 30 above, there is a great difference in the amount of air needed to make "x" amount of boost. The same amount of air at 30 below might make 30 PSI, but at 30 above make 20 PSI.

[WJM]

that and subies are just all different...yet the same.

[Myxalplyx]

that and subies are just all different...yet the same.

--*Weird music plays in background after the quote*--

Thanks Will!

 

<-----Sees wise old man sitting on a rock embedded with 5 stars that only lights when the sun hits it through some boulder cracks, at 5:55p.m.

 

*Ok...back to topic*

[iluvdrt]

Ofcourse the old computers can be reprogrammed.

 

They use an Eprom.

 

In a nutshell. you need an eprom reader/writer. You need to take apart the ECU, de-install the Eprom, then install an eprom socket. Then when you want to program the eprom you take it out of the ECU and plug it into your reader/writer. Then you have at it.

 

Almost any "tuner" who has been around for a while will have all the crap to do this burried in dust.

 

it is where the term "chipping" an ECU came from. They can adjust the fuel maps, lift Fuel Cuts, just about everything. There isn't as much adjustability as the new OBDII computer, because the ECU simply does not monitor as many sensors. But there is still lots of room to play.

 

You can buy all the crap to do it yourself also. It's not that grossly expensive. It's the same stuff used for programming Satelite Dish recievers and cards. You just need a different program to interface with the ECU.

So you could actually reprogram the ecu not to cut fuel. That sounds like the only option for us 87+ guys. Now that would be some money involved for those of us whgo dont know how to reprogram.

[WJM]

i want to program, but not take chips out....IE take ecu out, plug up to stock ports and reprogram.

[JWX]

how much would the "reflash" cost? that might hold some people(me) over till they(I) can get the megasqurt&EDIS.

[Myxalplyx]

Hey Guys,

 

I had PM'd Michael of ECUTune to do a reflash for us back in August sometime. This was before I had an RX turbo (I had XT6s then...and now) but he game me an interesting reply.

BTW: For those of you not familiar with Michael of ECUtune, he's the one that has the chip out for the SVX that everyone is raving over......chips programmed for 87 octane, normal high octane and for nitrous use. Those guys over at SVX network loves the low end torque the chip gives their SVX. Also, there's a Stage 3 chip that's for use with the supercharger he's almost finished making for the SVX. Ok, here is the PM I sent Michael and his reply.

 

 

 

"We have the hardware to do any obdI subaru. If you set up a group buy with enough people for whatever model it is you want then we will do it.

 

Michael

 

 

 

quote:

 

 

 

 

 

Myxalplyx wrote on 08-28-2004 05:16 PM:

Do you plan on making chips for other Subaru models like the Impreza in the future? The N/A 2.5RS folks are dying for an aftermarket ECU to put on their cars. I have a 2.2ltr Imprez (N/A) and two XT6s. I spoke to you previously about making them for the XT6 and I'd be the first purchaser. Unfortunately, you'd need an XT6 where you are at for testing purposes and I'm just too far from you.

 

There's a LOT of money to be made, especially if you can tap into the N/A impreza market.

 

 

 

 

Michael

94 SVX LSI, Ebony Pearl profile

94 SVX LSI, Ebony Pearl from back

"

 

 

So there you have it.

 

[WJM]

man......lets get him to do the 87+ turbo stuff.

[JWX]

I agree

[Subarutex]

A reflash would be a sweet deal. Cost is a big thing though. Find out how much coin it will take.

[JWX]

I agree

[WJM]

I agree

I agree

 

I say something....and...._______

[JWX]

what? I can't agree to something till I know what it is.

and I asked about price up there and said we should see about getting a reflash. so ya I agree

[WJM]

so ya I agree

 

THATS IT!!!!!!!!!!!!!

[Myxalplyx]

I'm awaiting a response about the ECUTune reflash and will post in a new thread.

 

Meanwhile, I have one question about the fuel cut problem. I noticed alot of people say it's monitored by the ECU via the airflow sensor and that a certain voltage (5v or more for instance) is what triggers the cut. A countdown of sorts happen and if air flow is still creating a post 5V reading to the ECU from the air flow sensor, then the fuel cut occurs.

 

Is there any documentation anywhere that this is what takes place on 87+ turbo'd Subarus? I mean, where does it say the airflow sensor is what sends and voltage to the ECU to trigger a fuel cut situation? I just want to be able to read further on this. Thanks!