Hi,

recently I wrote to Hush (hush777) asking to swap from MPFi to carb and he gently answer me this:

Edwin, I think that you would be better off fixing the problems with the MPFI then to go to the carb.

The reasons why are.

1. The Intake manifold for the carb (or SPFI) is different from the MPFI and will not bolt on to the MPFI heads.

2. Fuel mileage would be worse with a carb (both systems running correctly).

 

If you would still like to do the swap, try to find a donor car (parts car) for cheap and swap the whole engine in to you car. Also change the distributor and the fuel pump and filter.

 

Thing to look at with your car as to why the poor fuel economy and other problems would be first the oxygen sensor.

The new car I got for my old lady was a turbo MPFI system and after rebuilding the engine it got a whopping 100 miles on a tank. Changed the oxygen sensor and it is getting around 325-375 on a tank. (Less right now because of the temperatures here)(Warm up takes a lot longer when it is below 0).

Also do a regular tune up.

Distributor cap and rotor and spark plugs, maybe even a new set of wires.

Also air and fuel filters.

 

Now Im on big trouble because some mechanics says that they can do that (the swap without head mods) and they (I think) doest know this issue. Now my problem is locally doesnt know this subaru injection system but I want to keep using my subaru. The sympoms of the problems are:

1. Black smoke

2. No oxygen sensor system (I inspect all exhaust and I didt see it, or a hole, etc.)

3. The spark plugs black (I have to replece every 20 days)

4. Poor gas mileage

 

Is there a troubleshooting guide for the MPFI for my subaru 87 on the board?

 

Thanks for any advice...

 

Edwin

I would agree with Hush777 that it would be better to stay with the MPFI. Regarding the mechanic that said that he could do it, I believe that he was just going to replace the throttle body with a carburetor, rather than removing the entire intake system and replacing it with a carbureted system.

 

The oxygen sensor is needed for the MPFI to operate properly; it is possible that the previous owner replaced the front portion of the exhaust system with a part from a vehicle that did not use an oxygen sensor.

 

The oxygen sensor should be mounted where the two pipes from the engine exhaust ports join beneath the engine, very near to the right side (as viewed from the driver's seat) axle's inner joint (rubber boot).

Have you checked the ECU for any code errors? I would think there would be some. One possibility is the coolant temperature sensor may have gone bad and is causing the engine to run rich.

Thank you, do you have a photo to see where is the oxygen sensor?,

 

 

Edwin

 

 

I would agree with Hush777 that it would be better to stay with the MPFI. Regarding the mechanic that said that he could do it, I believe that he was just going to replace the throttle body with a carburetor, rather than removing the entire intake system and replacing it with a carbureted system.

 

The oxygen sensor is needed for the MPFI to operate properly; it is possible that the previous owner replaced the front portion of the exhaust system with a part from a vehicle that did not use an oxygen sensor.

 

The oxygen sensor should be mounted where the two pipes from the engine exhaust ports join beneath the engine, very near to the right side (as viewed from the driver's seat) axle's inner joint (rubber boot).

 

The oxygen sensor is needed for the MPFI to operate properly; it is possible that the previous owner replaced the front portion of the exhaust system with a part from a vehicle that did not use an oxygen sensor.

 

The oxygen sensor should be mounted where the two pipes from the engine exhaust ports join beneath the engine, very near to the right side (as viewed from the driver's seat) axle's inner joint (rubber boot).

 

I belive some non US spec subarus did not use an O2 sensor. I think this might be the case here.

 

I also have an idea where to look for your problem. check The coolant temp sensor (as Cougar sugested) and the connector/wiring to it. I just posted a thred about the importance of the Coolant sensor and its conncetion. a corroded connection can cause the computer to think its cold all the time and dump too much fuel.

 

some other basics would be to check fuel pressure, check the mass air flow sensor, Throttle position sensor.

 

and no dont convert to carbs. find a better mechanic that understands your car.

Thanks, how can I see the code errors of the ECU?,

 

Edwin

 

 

Have you checked the ECU for any code errors? I would think there would be some. One possibility is the coolant temperature sensor may have gone bad and is causing the engine to run rich.

Through the OBDII port.usually is a little black connector looking thing.May have a cap over it.Need to have a code reader though.See if you could take it to a shop and have them scan it for you.Some may do it for free.

The codes are checked by viewing the LED that is seen through a hole in one end of the ECU. The ECU is a box that is mounted above the drivers feet. It will have several connectors going to it probably. The panel under the dash has to be removed to access it. The codes are flashed out by using long pluses as units of 10 and short pulses are single units. Two long flashes followed by three short would be code 23. More than one code can be flashed also.

 

My '88 manual shows the O2 sensor connector my be near the transmission area on the passenger side. For a manual transmission it shows a harness that has three connectors at the end. One of them ties to the sensor.

 

This system is OBD 1, not 2.

 

 

Thanks, how can I see the code errors of the ECU?,

 

Edwin