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Discussion Starter #1
I have a 1994 3000gt sl I just got a few weeks ago as far as I can tell it is stock.

I been repairing everthing on it to get it to start up the problem I'm having is no spark/fuel pump I know the Mfi relay controls them I ran all the test on it to what the book says it should be good next step went to the ecu found out not geting power on pins 12&25 which are the main power started running test to figure why not checked all fuses and wire for breaks with volt meter sat down done some research found out with ignition switch in on power should be going to pin 62 to ecu checked it have 12 volts with the research I found it says the ecu should send ground to pin 108 which is the mfi relay then the mfi send power to pins 12&25 which I can not get to happen so went to do some more test unplugged fuel pump to see if power was getting there at all answer no went back to mfi started testing again after done and it checked out to wait I think is good went back to fuel pump plug to check again know I had power with test light put volt meter on it had 12v to it was like ok I'll go try spark now and had it turn over had none went back to fuel pump plug no power then back to ecu pins 12&25 no power ?????????? Then started more test found out if I put a ground to pin 108 on ecu with my test light you will hear relay click then have power to pins 12&25 and fuel pump plug but after trying to start it to check for spark I would lose it all again trying to find out is there a way to test my ecu to find out if it is not working I took it out checked it for bad spots from what I read is common of them is there anymore test I can do our any help would be very appreciated oh I forgot to say the ecu is the 3 plug unit a n/a dohc
 

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93 NA ATX 3000gt DOHC
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Put a temporary ground wire from pin 108 to ground and test for spark while cranking. If power stays at pins 12 & 25 as long as temp ground is in place, that would indicated ECU has an internal problem (transistor probably). DO NOT leave temporary wire connected, as it will hold power side of MFI energized even with key turned off.

The fuel pump will only get power when starter circuit is energized closing pump side of MFI and will lose power after short period if ECU doesn’t receive run signal.
 

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Couple things
I have a 1994 3000gt sl I just got a few weeks ago as far as I can tell it is stock.

I been repairing everthing on it to get it to start up the problem I'm having is no spark/fuel pump I know the Mfi relay controls them I ran all the test on it to what the book says it should be good next step went to the ecu found out not geting power on pins 12&25 which are the main power started running test to figure why not checked all fuses and wire for breaks with volt meter sat down done some research found out with ignition switch in on power should be going to pin 62 to ecu checked it have 12 volts with the research I found it says the ecu should send ground to pin 108 which is the mfi relay then the mfi send power to pins 12&25 which I can not get to happen so went to do some more test unplugged fuel pump to see if power was getting there at all answer no went back to mfi started testing again after done and it checked out to wait I think is good went back to fuel pump plug to check again know I had power with test light put volt meter on it had 12v to it was like ok I'll go try spark now and had it turn over had none went back to fuel pump plug no power then back to ecu pins 12&25 no power ?????????? Then started more test found out if I put a ground to pin 108 on ecu with my test light you will hear relay click then have power to pins 12&25 and fuel pump plug but after trying to start it to check for spark I would lose it all again trying to find out is there a way to test my ecu to find out if it is not working I took it out checked it for bad spots from what I read is common of them is there anymore test I can do our any help would be very appreciated oh I forgot to say the ecu is the 3 plug unit a n/a dohc
Couple things here don't make any sense... Primarily, even though they are in the same housing, electrical control and fuel pump control are two completely different systems. There are two completely different relays in that housing. grounding pin 108 turns on the engine controls, grounding pin 8 turns on the fuel pump. The ECU never turns on the fuel pump unless the engine is cranking or running. How you could be getting power at the fuel pump by energizing 108 makes no sense...

Does your CEL bulb check when you turn on the key? Do you have battery power at pin 60? Do you have key-on ignition power at pin 62?

Don't forget to check all your grounds too... I like to load them down with an old headlamp to make sure they don't crap out under load.
 

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Discussion Starter #5 (Edited)
I was assuming it was because the ecu was not geting power to 12&25 then when that happen it was sending power where it should like the fuel pump and other places

Update fix a ground found out it was arcing off the driver side top motor mount did notice that tell it got dark lol now when I turn the key to on you hear the mfi relay click then you go to fuel pump plug has power to it have coils have power to them but no spark I dont know if this helps anymore as info but my rpm gauge does not move when you try to crank it.
The check engine light stays on also
 

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Turn the key to the on position without cranking

Does the check engine light come on?

If no = bad ECU
 

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I was assuming it was because the ecu was not geting power to 12&25 then when that happen it was sending power where it should like the fuel pump and other places

Update fix a ground found out it was arcing off the driver side top motor mount did notice that tell it got dark lol now when I turn the key to on you hear the mfi relay click then you go to fuel pump plug has power to it have coils have power to them but no spark I dont know if this helps anymore as info but my rpm gauge does not move when you try to crank it.
The check engine light stays on also
Again... Something very strange is going on if it's powering up the fuel pump... I'd want to find out where that power is coming from, and why.

The CEL should bulb check and go back off. If it's staying on it probably has codes. I'd check for that as well.
 

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I was assuming it was because the ecu was not geting power to 12&25 then when that happen it was sending power where it should like the fuel pump and other places......
No…. As RealMcCoy indicated pump should not get power until ECU pin 8 gets grounded, which has nothing to do with power delivery side of MFI closing when key turned to ON. Like he said twice if pump starts by simply turning key to ON, there’s either a problem or somebody hot wired pump maybe.

Since you now have MFI power delivery side closing and staying closed :unsure:when cranking, there’s a few test that can narrow down spark issue. An analog (needle) meter is needed, do you have one? I’m thinking concentrate on one issue at a time instead both spark and pump starting wrong at same time, might stumble on correction for both with some luck.
 

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Discussion Starter #10
As of today I been working on find out why no spark an not really worried about fuel pump today I just unplugged it for now as for codes going to try the paperclip trick just dont under stand how to read the blinks the analog meter I dont have one trying to hunt down one for doing more testing

As of right now the coils are getting power but no spark when testing with test light show all are at least getting some power just no spark fixed the main ground put it back on transmission housing it was on crossmember so that was wrong and last night seen it arcing on driver top motor mount ( under it ) you could see it when trying to start stopped when I changed the main ground to transmission housing
But didn't change anything else
No rpm gauge movement when trying to start and coils seem to get some power to them but not sparking any of the testers
 

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Again... Something very strange is going on if it's powering up the fuel pump... I'd want to find out where that power is coming from, and why.

The CEL should bulb check and go back off. If it's staying on it probably has codes. I'd check for that as well.

If you put the key to “on” position without starting the engine, the check engine light will stay on. If y0u never see the check engine light come on, there is a problem w/ the ECU.

How ever, if you start the car, the check engine light should go out after a few seconds
 

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Discussion Starter #12
Ok so the ecu should be working at less by the light being on the dash "it not a 100% say it is working but should be doing something "
Is there a test I can do on the ptu to see if it is working
 

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As of today I been working on find out why no spark an not really worried about fuel pump today I just unplugged it for now as for codes going to try the paperclip trick just dont under stand how to read the blinks the analog meter I dont have one trying to hunt down one for doing more testing
You have a 94... You don't need a meter to check codes. You ground pin 1 of the DLC, and the CEL blinks the codes at you.

What are you using for service info? Do you have copies of the FSM?
 

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Discussion Starter #14
You have a 94... You don't need a meter to check codes. You ground pin 1 of the DLC, and the CEL blinks the codes at you.

What are you using for service info? Do you have copies of the FSM?
No copies of fsm been getting the info off line from 3si.org and 3swiki.com and other sites been reading found manual diagram of what to test and pin lay outs
Got a find a manual to buy
 

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.......as for codes going to try the paperclip trick just dont under stand how to read the blinks the analog meter I dont have one trying to hunt down one for doing more testing
You can pickup cheap analog meter (~ $15) at any auto parts or even Walmart, you don’t need an expensive one because you’re just going to be watching needle sweeps.

No rpm gauge movement when trying to start and coils seem to get some power to them but not sparking any of the testers
Coils get their power from ignition switch thru #12 fuse under dash, which is not affected by MFI, ECU or PTU. But coils need to be triggered for spark to occur, that takes input from crank/cam sensors, MFI, ECU and PTU to function. That is also needed for tach to work.

Is there a test I can do on the ptu to see if it is working
PTU test part1.JPG PTU test part2.JPG

Edit: But before jumping to individual component testing, I’d suggest some test I mentioned in post #9 that you needed analog meter to do. Those test can be done from ECU pins to narrow down which direction to proceed.
 

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Discussion Starter #18
I have a update on my car
"I'm a bloody genius" and such A big DA all with the same breath the moment I got the car I been replacing parts that the other owner took off to try to fix his 1995 3000gt that he just got and the 1994 was running??? Never know why he did it. But anyway went to work on the car I was ok let me check the ptu today went to get it off the car to test it and my you a big DA moment it's not there he took it out the car so of course I will never get spark with out it so I order one an waiting for it to show up to try it again and I got to triple check to make sure nothing else is gone to
 

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......went to work on the car I was ok let me check the ptu today went to get it off the car to test it and my you a big DA moment it's not there he took it out the car so of course I will never get spark with out it so I order one....
🤣 ROFLMAO…. That’ll cause no spark for sure. But look at bright side you don’t have to test it for proper operation.;):)

Edit: On the serious side, be sure to mount it to the plate as it’s my understanding that it helps to remove heat from PTU. Hoping he at least left mounting plate. :unsure:
 

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Discussion Starter #20
Got 3 ptus 2 are used and one is new all 3 of them do the same thing when trun key to the on position rpm gauge jumps up to 3g then bounce up an down in the on position also with spark tester in its sending spark for about 30 seconds or so never trying to start it does this when you try to start I get spark but no start I'm geting fuel checked timing it lines up put new crankshaft sensor on still does this
 
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