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Discussion Starter · #1 ·
Hi all, Larry here
I’m based in Dublin ireland and new to the site

I’m having a head scratcher of a problem, I completed an full engine rebuild and ever since the car refused to idle , I could get it to start randomly , but would get several pops and bangs from it fuel pump would shut off and it would die . So I’ve changed ptu, coils, leads , all injectors are 360 type , even had my stock ecu fully tested and no fault was found . So one day I decided to try my spare non turbo ecu in the car( I’d tried everything else at this point so I thought what the hell). And boom fired right up and ticks over fine , I obviously can’t Rev the car as it’ the wrong Ecu , fuel ratio etc however it proved at least the engine rebuild was done correctly .

Has anyone any suggestions as to why the car will fire up and tick over on a non turbo ecu but misfires on a fully tested TT ecu …. I’m 18months on and off trying to fix this so truly about to loose my mind

regards Larry
 

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If you suspect it's shutting off because the fuel pump shuts off, I'd want to confirm that... Not sure if the GTO test connectors are in the same location behind the right side strut tower, but I would assume so. Get a test lamp on the black connector and see if the power is going away.

If so, I would immediately suspect the 2 speed fuel pump wiring. Start it with the airflow sensor unplugged, (it will be in limp mode running off of crude calculated numbers) and see if the pump continues to run.

There's really no wire diagrams out there for the GTO that aren't in Japanese, but you can use the USDM versions and get pretty close. Many of the systems are the same. The fuel pump #2 relay and resistor that control the pump speed are under the engine compartment fuse/relay box.
 

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a fully tested TT ecu …

regards Larry
Hi Larry.

How exactly was the ECU tested? Most general ECU repairers can't really fully test ECUs, often they just visually inspect them.

The easiest way to really find out is to fit your TT ECU to another car and see what happens, just so you can be sure that's not your problem, before you continue your wild goose chase.
 

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Discussion Starter · #4 ·
Hi Larry.

How exactly was the ECU tested? Most general ECU repairers can't really fully test ECUs, often they just visually inspect them.

The easiest way to really find out is to fit your TT ECU to another car and see what happens, just so you can be sure that's not your problem, before you continue your wild goose chase.
we’ll I used a company called the ECU doctor in the Uk , they have been teasing and repairing Gto/3000gt for many years but as far as testing goes I’ve no idea what the actually do

i am hoping to plug into another cart this weekend so I’ll let you know
 

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Discussion Starter · #5 ·
If you suspect it's shutting off because the fuel pump shuts off, I'd want to confirm that... Not sure if the GTO test connectors are in the same location behind the right side strut tower, but I would assume so. Get a test lamp on the black connector and see if the power is going away.

If so, I would immediately suspect the 2 speed fuel pump wiring. Start it with the airflow sensor unplugged, (it will be in limp mode running off of crude calculated numbers) and see if the pump continues to run.

There's really no wire diagrams out there for the GTO that aren't in Japanese, but you can use the USDM versions and get pretty close. Many of the systems are the same. The fuel pump #2 relay and resistor that control the pump speed are under the engine compartment fuse/relay box.
im fairly sure the fuelpump is ok amd the car ticks over fine on the non - turbo ecu
 

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im fairly sure the fuelpump is ok amd the car ticks over fine on the non - turbo ecu
I'm pretty sure from what you posted that the pump is fine, and I believe you that it starts with the N/A ECU... Not sure how any of that is a reason do discount what I said.

I'm not in any way saying the first thing I would test is in fact the problem, but are we going to test stuff? or just look into a crystal ball and hope for answers..? I could check that car out armed with a $5 hardware store test lamp and a wire diagram, and tell you why that car won't start in 15 minutes... Unfortunately I'm many thousands of miles away, and would need a little cooperation.
 

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Discussion Starter · #7 ·
Sorry for the delay in getting back to you I’m open to all suggestions this is what I know and have tested so far
  • Plugged in a non turbo ecu , car starts and ticks over
  • plugged my tt ecu won’t start
  • plugged my tt Ecu into a friends Gto and his car runs and drives fine
-have swapped the throttle body
  • have swapped the injectors
  • have swapped ptu
 

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Discussion Starter · #8 ·
If you suspect it's shutting off because the fuel pump shuts off, I'd want to confirm that... Not sure if the GTO test connectors are in the same location behind the right side strut tower, but I would assume so. Get a test lamp on the black connector and see if the power is going away.

If so, I would immediately suspect the 2 speed fuel pump wiring. Start it with the airflow sensor unplugged, (it will be in limp mode running off of crude calculated numbers) and see if the pump continues to run.

There's really no wire diagrams out there for the GTO that aren't in Japanese, but you can use the USDM versions and get pretty close. Many of the systems are the same. The fuel pump #2 relay and resistor that control the pump speed are under the engine compartment fuse/relay box.
yes the jap/uk versions of the 3000gt have the black connector from the fuel pump
with the mag unplugged and test light connected to the black connector I have voltage to the pump continually while cranking and only drops off when I release the key
 

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Discussion Starter · #9 ·
Hi Larry.

How exactly was the ECU tested? Most general ECU repairers can't really fully test ECUs, often they just visually inspect them.

The easiest way to really find out is to fit your TT ECU to another car and see what happens, just so you can be sure that's not your problem, before you continue your wild goose chase.
plugged it into another gto and runs perfect
 

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yes the jap/uk versions of the 3000gt have the black connector from the fuel pump
with the mag unplugged and test light connected to the black connector I have voltage to the pump continually while cranking and only drops off when I release the key
You need to check it when the engine starts... We need to qualify if the engine is shutting off because the power to the fuel pump is going away.
 

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Discussion Starter · #11 ·
You need to check it when the engine starts... We need to qualify if the engine is shutting off because the power to the fuel pump is going away.
Thanks for getting back to me… the engine will not start at all with TT ecu . It will only turn over
With the non turbo ecu it will start and run and the power stays on the pump continually until I switch it off
 

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If so, I would immediately suspect the 2 speed fuel pump wiring. .....................................The fuel pump #2 relay and resistor that control the pump speed are under the engine compartment fuse/relay box.
  • Plugged in a non turbo ecu , car starts and ticks over
  • plugged my tt ecu won’t start
  • plugged my tt Ecu into a friends Gto and his car runs and drives fine
@RealMcCoy is probable right on the mark here, about problem with either the fuel pump #2 relay, resistor or wiring. I suspect it’s most likely the relay problem only passing voltage in the non activated (high speed) state.

Using @Larryc1980 above symptom descriptions I try to explain why that makes sense to me.
Starts & runs with NA ECU – Pin 21 of TT ECU activates 2 speed relay, that pin is not used by NA ECU, so it would leave 2 speed relay in non activated high speed state allowing pump to continued to run.
Won’t start with TT ECU – Pin 21 shifting relay to activated (low speed) state when first ignition signal is received, stopping pump when key is released from start position and not allowing engine to run.
Friends car works with TT ECU – Friends car has a proper working 2 speed pump relay system.

Disclaimer: My assumptions and $2 might get you a medium coffee at 7-Eleven. :p
 

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Discussion Starter · #13 ·
@RealMcCoy is probable right on the mark here, about problem with either the fuel pump #2 relay, resistor or wiring. I suspect it’s most likely the relay problem only passing voltage in the non activated (high speed) state.

Using @Larryc1980 above symptom descriptions I try to explain why that makes sense to me.
Starts & runs with NA ECU – Pin 21 of TT ECU activates 2 speed relay, that pin is not used by NA ECU, so it would leave 2 speed relay in non activated high speed state allowing pump to continued to run.
Won’t start with TT ECU – Pin 21 shifting relay to activated (low speed) state when first ignition signal is received, stopping pump when key is released from start position and not allowing engine to run.
Friends car works with TT ECU – Friends car has a proper working 2 speed pump relay system.

Disclaimer: My assumptions and $2 might get you a medium coffee at 7-Eleven. :p
@RealMcCoy is probable right on the mark here, about problem with either the fuel pump #2 relay, resistor or wiring. I suspect it’s most likely the relay problem only passing voltage in the non activated (high speed) state.

Using @Larryc1980 above symptom descriptions I try to explain why that makes sense to me.
Starts & runs with NA ECU – Pin 21 of TT ECU activates 2 speed relay, that pin is not used by NA ECU, so it would leave 2 speed relay in non activated high speed state allowing pump to continued to run.
Won’t start with TT ECU – Pin 21 shifting relay to activated (low speed) state when first ignition signal is received, stopping pump when key is released from start position and not allowing engine to run.
Friends car works with TT ECU – Friends car has a proper working 2 speed pump relay system.

Disclaimer: My assumptions and $2 might get you a medium coffee at 7-Eleven. :p
Thanks , that does make sense, i pull up the pump relay under the fuse box this morning , is there a pin out diagram that will show me pin 21 on the ecu I’d like to double check the pin itself and if I have voltage comming out of it
 

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Thanks , that does make sense, i pull up the pump relay under the fuse box this morning , is there a pin out diagram that will show me pin 21 on the ecu I’d like to double check the pin itself and if I have voltage comming out of it
I’m assuming a Mark 1 is a 1st gen 91-93, if correct below is pin out for 91-93 and even for some 94-95. But ECU doesn’t supply power from that pin, it uses it to complete the ground activating pump speed relay coil (closing the relay). You could read battery voltage (~12v) at that pin when starter is first activated, but as soon as ECU grounds that pin voltage will fall to much lower voltage.


Easy way to know if there’s a problem with pump speed relay, wiring or resistor circuit, is to supply battery positive voltage straight to the black pump test connector and then try to start engine. If it starts and runs then you’ll know for sure pump speed circuit is the problem, because with black test connector jumped to battery + the pump speed circuit is completely bypassed and pump will run forever until you remove that jumper wire.

If you confirm a problem with pump speed circuit and decide to bypass it (some have), below is link about how to do that by simply removing relay and adding short jumper there which still allows ECU to control when pump starts and stops from MFI relay. Which is the way I recommend it being done, instead of a switched hot wire to pump that totally removes ECU control of on and off. There’s also a schematic print in that link showing the pump speed relay/resistor circuit, in that print the wire leaving #1 pin of pump relay (going downward) that is the wire to pin 21 of ECU, indicated by TO ECM in print.
 

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Discussion Starter · #15 ·
I’m assuming a Mark 1 is a 1st gen 91-93, if correct below is pin out for 91-93 and even for some 94-95. But ECU doesn’t supply power from that pin, it uses it to complete the ground activating pump speed relay coil (closing the relay). You could read battery voltage (~12v) at that pin when starter is first activated, but as soon as ECU grounds that pin voltage will fall to much lower voltage.
View attachment 303450

Easy way to know if there’s a problem with pump speed relay, wiring or resistor circuit, is to supply battery positive voltage straight to the black pump test connector and then try to start engine. If it starts and runs then you’ll know for sure pump speed circuit is the problem, because with black test connector jumped to battery + the pump speed circuit is completely bypassed and pump will run forever until you remove that jumper wire.

If you confirm a problem with pump speed circuit and decide to bypass it (some have), below is link about how to do that by simply removing relay and adding short jumper there which still allows ECU to control when pump starts and stops from MFI relay. Which is the way I recommend it being done, instead of a switched hot wire to pump that totally removes ECU control of on and off. There’s also a schematic print in that link showing the pump speed relay/resistor circuit, in that print the wire leaving #1 pin of pump relay (going downward) that is the wire to pin 21 of ECU, indicated by TO ECM in print.
I have already tried the “black plug” bypass and still the car won’t start on the correct ecu
 

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I have already tried the “black plug” bypass and still the car won’t start on the correct ecu
In that case if you heard pump running with power to “black plug” and still had no start then your problem is not with fuel pump control. Which is exactly why @RealMcCoy indicated testing things and not just assuming.
 

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Discussion Starter · #17 ·
In that case if you heard pump running with power to “black plug” and still had no start then your problem is not with fuel pump control. Which is exactly why @RealMcCoy indicated testing things and not just assuming.
Thanks to everyone giving there advice is very much appreciated. Please keep options and opinions comming as I’m desperate to get this car back on the road
 

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Thanks to everyone giving there advice is very much appreciated. Please keep options and opinions comming as I’m desperate to get this car back on the road
You might do the below input/output test at ECU connector, to see if something isn’t correct with your car, that we could possibly determine might not have same affect on a NA engine than it does on a TT engine and might not exist in friends GTO for some reason.

SV stands for standard valve of battery voltage and without engine running the pin 8 (idling test) can be done while cranking engine. Be sure to use second left column for DOHC ECU pins and not first column for SOHC pins.


Edit: And by the way What year is your car and your friends car?
 

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Discussion Starter · #20 ·
You might do the below input/output test at ECU connector, to see if something isn’t correct with your car, that we could possibly determine might not have same affect on a NA engine than it does on a TT engine and might not exist in friends GTO for some reason.

SV stands for standard valve of battery voltage and without engine running the pin 8 (idling test) can be done while cranking engine. Be sure to use second left column for DOHC ECU pins and not first column for SOHC pins.


Edit: And by the way What year is your car and your friends car?
Thanks man I’ll try this asap
Silly question, but what does it do if you try to start it with the MAF disconnected?
Hi “box”
No difference
 
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