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Discussion Starter · #1 ·
2001 MR2 Spyder originally had 1zz with 5speed MT - I had previously taken the 1zz apart to drill out bigger oil return passages and hone the cylinders about 10 years ago. That reduced oil consumption but apparently didnt completely solve it. Last year my 1zz motor through a rod through the oil pan so I figured I would do a 2zz swap- should be simple and straight forward. Wrong - it has been an absolute nightmare to fix 1 minor issue. MREL will never send power to activate the relay which sends power to the ECU

Does anyone understand what exactly tells the ECU to send power through MREL? I have been working on an insurmountable, unsolvable electrical problem for almost 8 months now.

I started with a used celica 2zz that I replaced the timing chain, replaced head gasket and studs, replaced all the sensors with new ones, port matched the intake and exhaust gaskets, polished the cylinder head both intake and exhaust and did all the normal top end rebuild stuff. I also replaced the 5 speed with a 6 speed transmission. No problem - everything went as it should. Motor and trans went in without any issues.

I have an Apexi stand alone ECU and and a US Celica 2zz ECU. I started with the OEM ECU so I could use the OBD code reader. The reader cannot communicate with the ECU unless I jumper the EFI main relay. Both the Apexi and OEM behave the same. With OBD reader and stock ECU and EFI relay jumpered it will power up the ECU but the car will not start. With the Apexi and hand held Apexi controller it is the same. With the EFI relay jumpered it knows the ECU is there and it says no errors but the car will not start for both ECUs.

I thought I must have somehow f**cked up rewiring the harness for the 2zz. I bought a used engine bay harness and interior floor harness so I got all 4 ECU connectors set back to stock MR2 and then bought a monkeywrench swap harness so that I would be certain all the connectors are set to correct locations for the 2zz. I checked both harness for any broken wires and soldered in a few new sensor connectors that looked sketchy. With the 2 harness you also get the engine bay fuse box and engine bay relay box. I bench tested all the relays in all the fuse boxes and used one of the little tools that lights up when testing fuses.

Again I have the exact same issue - MREL will not turn on unless jumpered.

I have replaced every single relay and fuse in all fuse and relay boxes with new ones even though none were blown and all the relays tested good.
I have replaced the engine switch
I have cleaned and sanded all the harness ground points and tested for continuity at every single ground point listed in the service manual
I had gotten a temporary subscription to TIS and have downloaded all the documents for both the MR2 and celica and have gone over the diagrams hundreds of times. I have taken apart both of my old harness and put them back to MR2 stock configuration then checked every wire for continuity and rewrapped the harnesses in nice new harness protectors from ebay. Unfortunately it behaves exactly the same as with the other harnesses.

I pulled the dashboard (not easy on the MR2) so I could make sure that there were no breaks in the wires from the ignition switch to the fuse panel near the driver left leg. No wires are broken and every connector was connected.


Again I still have the same problem.

All of the following grounds have been verified at the ECU testing for continuity with the frame. As I said earlier every single ground has been cleaned and sanded also;

d31
d21
c17
c18
a7
b12

a1 12.5
a8 0 switch off 12.5 switch on
a16 0 switch off 0 switch on (if EFI relay jumpered then 12.5)
b21 0 switch off 0 switch on (this is what is supposed to tell EFI relay to turn on)


This f**king car is making me question my sanity. It should not be this hard to make a motor run. I have pulled and reinstalled both the AB harness and the CD harness at least a dozen times. I have tried different combinations of the "new" harness for AB and the old one for CD and vice versa. I have cleaned all the harness connectors with electrical cleaner and checked and rechecked the grounds probably a hundred times. I always have the same issue. No power to MREL.


All my lights, accessories, windows, everything works but it will not start even with EFI main relay jumpered. Both the Apexi handheld and the OEM ECU with code reader say no problems found when EFI relay jumpered. It seems like signal that tells the ECU - hey I want to start this thing isnt working. The car turns over and I can hear the fuel pump turn on and have gas on the spark plugs after trying to start it.


I may have to junk this simply because I cant figure out what tells MREL to turn on.
Car Wheel Land vehicle Vehicle Tire
 

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I can’t tell if you have or not.
We spent 2 days chasing a no ignition after an engine swap.
We checked and re-checked everything we did, then swapped roles checking each other’s work.
Then we removed all the wiring to engine install stage and put it back in.

At that point we found the plug pack into the bottom of the main fuse box was clicked in secure but it has a hard SNAP into spot. So something that felt correct and fitted was not quite there.

the hard two handed SNAP in and reassemble was the culprit.

back together, everything talked and started first kick.

something just dumb is the worst to chase.

Your Experience May Vary.
 

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Electromagnetic Wave :-h
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Check ECU pin G-24 ('03-'05) IGF for +12V with IGN switch ON. A8 IGSW on '00-'02.

MREL should go to +12V when the IGN switch is ON or cranking.
 

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Discussion Starter · #4 ·
Check ECU pin G-24 IGF for +12V with IGN switch ON.

MREL should go to +12V when the IGN switch is ON or cranking.
I think you must mean D25 Ignition misfire (labeled IGF in my diagrams). My CPU has A, B, C and D connectors (2001 Celica GTS 2ZZ. Thanks I will check that. You are absolutely correct that MREL should go to 12 V when switch turns to on or start. Thats the issue - why is that not happening. B21 is the connector for MREL for my CPU and that definitely should turn on with 12 v when switch is in start or on. . Maybe if IGF doesnt get 12V when switch is in ON or START that is preventing it from firing. I will check that.
 

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Discussion Starter · #5 ·
I can’t tell if you have or not.
We spent 2 days chasing a no ignition after an engine swap.
We checked and re-checked everything we did, then swapped roles checking each other’s work.
Then we removed all the wiring to engine install stage and put it back in.

At that point we found the plug pack into the bottom of the main fuse box was clicked in secure but it has a hard SNAP into spot. So something that felt correct and fitted was not quite there.

the hard two handed SNAP in and reassemble was the culprit.

back together, everything talked and started first kick.

something just dumb is the worst to chase.

Your Experience May Vary.
I was hoping that by taking everything apart and reassembling I would find something similar. I also checked for any bent pins in all the connectors. I have taken everything apart and put it all together again many many times with always same result. Maybe its something like that but for the life of me I cant find it
 

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Electromagnetic Wave :-h
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I think you must mean D25
My bad. I was using an '05 schematic. No, not D25. A8 IGSW should be the one that is +12V when ignition is on or cranking for '00-'02.

You are absolutely correct that MREL should go to 12 V when switch turns to on or start.
Nope. I was incorrect there too. MREL on '00-'02 sinks to GND to engage the EFI relay. IGSW engages the IG2 relay (that supplies +12V to the EFI relay) and provides switched +12V to the ECM. EDIT: WRONG!
 

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Discussion Starter · #7 ·
My bad. I was using an '05 schematic. No, not D25. A8 IGSW should be the one that is +12V when ignition is on or cranking for '00-'02.

Nope. I was incorrect there too. MREL on '00-'02 sinks to GND to engage the EFI relay. IGSW engages the IG2 relay (that supplies +12V to the EFI relay) and provides switched +12V to the ECM.
It should be ground? Ok let me test that.

I am starting to wonder if I have somehow managed to fry both of the ECUs I have. I am going to purchase a 2000 Celica GTS AT ECU just for testing (much cheaper than MT ECU). I think it would be able to start the motor but will throw lots of transmission codes.
 

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Electromagnetic Wave :-h
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It pulls to GND, probably through a transistor switch in the ECM. EDIT: WRONG! DO NOT GROUND MREL!

My apologies about earlier. I just grabbed the '05 schematic, ignoring the significant differences to the earlier years. I usually use the '02 one... except this time. 😆

You'll find the schematics & ECM pinouts in the Electrical sub-forum.

Yeah, you don't want to apply straight +12V to MREL on an '02 (it has to be current limited by the EFI relay). It will fry the transistor. EDIT: WRONG!

Off the top of my head, you need: BATT, +B, IGSW, & GND to the ECM.
 

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Electromagnetic Wave :-h
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Damnit.... NO!

I looked again at the '02 schematic & MREL does go positive to activate the EFI relay. 😡

I'd focus on checking +12V on A8 IGSW.
 

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Discussion Starter · #10 ·
Thank you everyone - it was my ECU.I bought a cheap AT Celica ECU and put it in. I should have started out this way instead of frying a new Apexi ECU and a Toyota MT ECU. Whatever I did wrong initially did the same thing to both ECUs. They both failed the same way. Anyone know of a place that does repair of Apexi ECU?
 
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