ECU for a 7afe in a 5sfe 1996 manual celica Options

[thebestofall007]

Hello all, I found a surprise in my 1996 Celica: It has an ECU for a 7afe manual transmission engine, however, mine is a 5sfe manual. The engine runs well, but gas mileage is not as good as it is supposed to despite replacing the cap, rotor, plugs, wires, and I get a P0141 code despite replacing the O2 sensor with an OEM Denso and checking the wiring connection between the sensor and the computer. The cables don't appear to be all spliced up, either.

Why would someone do this, and what would I have to do to replace it with the original (if this would fix the gas mileage and sensor issues)?

This post has been edited by thebestofall007: Oct 21, 2016 - 5:00 PM

[mkernz22]

You'd just have to unplug the old one, take it out, and put the new one in.

[thebestofall007]

You'd just have to unplug the old one, take it out, and put the new one in.

Oh good, that's a relief, no having to change sensors or the like.

[Bitter]

I'm shocked a 7A ECU would run a 5S at all let alone well enough to drive.

[VavAlephVav]

Yeah, I'm surprised it works I'd guess it has all the same signals it's just going to be sending the wrong amount of fuel n such. As to why they did it, obviously because that's just what they could find and it worked. If you had to buy one of those things from Toyota back in the day it would have cost you a **** load of money. You can buy refurbished ones on Rockauto.com for $250 or if you get lucky you might find one at a salvage yard. I'd check for part-out threads too.

[thebestofall007]

I'm shocked a 7A ECU would run a 5S at all let alone well enough to drive.

Yeah, me too. I am wondering if this is a modded ecu, perhaps. This ecu mismatch could be causing my check engine light obviously, despite changing the o2 sensor to a new oem denso. What's weird is this is now the ONLY check engine light I have, but it's like an itch I can't scratch and I can't get rid of it.

[thebestofall007]

Yeah, I'm surprised it works I'd guess it has all the same signals it's just going to be sending the wrong amount of fuel n such. As to why they did it, obviously because that's just what they could find and it worked. If you had to buy one of those things from Toyota back in the day it would have cost you a **** load of money. You can buy refurbished ones on Rockauto.com for $250 or if you get lucky you might find one at a salvage yard. I'd check for part-out threads too.

The salvage yard looks to be my option. I have a pull n save lot close to where I live that might have one where I can get it for about $40.

[slavie]

If I were you, I'd check the pinouts of 5S and 7A ECUs to make sure they match before you plug in a 5S ECU. Whomever did this in the first place might have re-pinned the ECU connectors to match the 7A ECU pinout, and if you don't pin it back you may have further issues.

Of, you may try to get the 7A O2 sensor, until you find the correct ECU at least.

The ECU really doesn't do as much "engine control" if you boil it down - it's just injectors and ignition, really. Most of the other crap is emissions, various sensors, AC, and so on. Given how conservatively Toyota ECUs are tuned, it's not too much of a surprise that it does run. Really cool nonetheless.

Yeah, I'm surprised it works I'd guess it has all the same signals it's just going to be sending the wrong amount of fuel n such. As to why they did it, obviously because that's just what they could find and it worked. If you had to buy one of those things from Toyota back in the day it would have cost you a **** load of money. You can buy refurbished ones on Rockauto.com for $250 or if you get lucky you might find one at a salvage yard. I'd check for part-out threads too.

Not necessarily - 5SFE would have bigger injectors to match it's increased displacement, so the amount of fuel may actually be correct, or close enough that the ECU may correct it with fuel trims - LTFT can add or subtract up to 20% before triggering CEL

This post has been edited by slavie: Oct 22, 2016 - 7:48 PM

[thebestofall007]

I did some looking at the wiring schematics of one out of 7afe m/t, 7afe a/t, and the 5sfe m/t I have, and the 5sfe m/t and 7afe a/t ECUs appear to have similar wiring diagrams, but the 7afe m/t has a different plug layout compared to my 5sfe. Something is telling me that someone got into this ECU or refurbished it at some time and mismatched the cover or something. I found some numbers written on it as well.

[Bitter]

I was going to mention that the connectors may not be the same but I didn't feel like putting in the effort to confirm it.

You're sure it's a 5S under the hood right? Weird things happen....

[thebestofall007]

I was going to mention that the connectors may not be the same but I didn't feel like putting in the effort to confirm it.

You're sure it's a 5S under the hood right? Weird things happen....

The previous owner had the original 5sfe throw a connecting rod when I first got the vehicle and I had to replace it with another 5sfe. I did not know about the mismatch with the numbers on the ECU at that time.

[mkernz22]

I agree, get us some pictures so we know what we're working with

[thebestofall007]

I agree, get us some pictures so we know what we're working with

You asked, and here they are (Sorry I had to use imgur):

The engine:

http://imgur.com/a/t7Bv5

The ECU from the top (I did a search on the ECU's black numbers, and it came out of a '97. Does anyone recognize the numbers written in blue?):

http://imgur.com/MqoLsrh

The bottom of the ECU (Does anyone recognize the yellow numbers?):

http://imgur.com/6OMr2xL

The guts from the top (does anyone recognize if the internals are original?):

http://imgur.com/a/DNRDs

The guts from the bottom (does anyone recognize if the internals are original?):

http://imgur.com/eOtTTBG

And the plug:

http://imgur.com/WVU2THA

This post has been edited by thebestofall007: Oct 26, 2016 - 8:39 AM

[thebestofall007]

If I were you, I'd check the pinouts of 5S and 7A ECUs to make sure they match before you plug in a 5S ECU. Whomever did this in the first place might have re-pinned the ECU connectors to match the 7A ECU pinout, and if you don't pin it back you may have further issues.

I found some pinout PDFs from shop manuals that might help in this:

5SFE

7AFE

I also want to get the plugs off the donor's wiring harness when I go to the wrecking yard to get the ECU to compare to mine so I can see if the previous owner did re-pin my plugs and re-pin them back if necessary.

This post has been edited by thebestofall007: Oct 26, 2016 - 8:52 AM

[slavie]

If it's a 97, you can hook it up to your laptop via an OBD dongle and get the info on what engine the computer is for. Not all software will show you this, but Toyota's TVIS will (though this one requires a special cable...)

Also, check ECU's on eBay - some sellers post pics of them opened up.

[thebestofall007]

If it's a 97, you can hook it up to your laptop via an OBD dongle and get the info on what engine the computer is for. Not all software will show you this, but Toyota's TVIS will (though this one requires a special cable...)

Also, check ECU's on eBay - some sellers post pics of them opened up.

I'm not sure if mine has the TVIS, but it would be nice to see in real time what my sensors and whatnot are all doing, that way I can not only have info on the engine it's made for, but also if the ecu is defective or not.

This post has been edited by thebestofall007: Oct 28, 2016 - 7:41 AM

[VavAlephVav]

You can get the USB to ODBII cable on ebay pretty cheap. And the Toyota TVIS software is on the bittorent network but using bittorent has suddenly become dangerous.

[thebestofall007]

I just noticed something regarding the P0141 code I get that may point to my need for another ECU. I got the OBD dongle and used it with scantool and the code is saying that it is related to an O2 sensor heater malfunction, but the O2 sensors in my car DON'T HAVE A HEATER. They are the 2 wire type, and not the 4 wire that has one, so I have a suspicion that the computer expects them to be there, and they aren't, and that's why the code is being thrown despite getting the Denso sensor.

[Bitter]

That's quite possible. You'd need to check at the ECM to see if those cavities in the connector have terminals and wires or not, my guess would be those are empty cavities. You could squash the code by just jamming a resistor in there of the correct value for an O2 sensor heater But you should still get the correct computer!

[thebestofall007]

That's quite possible. You'd need to check at the ECM to see if those cavities in the connector have terminals and wires or not, my guess would be those are empty cavities. You could squash the code by just jamming a resistor in there of the correct value for an O2 sensor heater But you should still get the correct computer!

Oh, and I also noticed that in the fuel trims, the computer has to move the fuel mixture up by around 7.5 percent. The engine stumbles at times, especially at idle, despite changing out the cap, rotor, plugs, wires, and thermostat after changing the coolant. I think this is all the more reason to get the computer when I get my check.