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· Registered
150 Posts
Need some help with my 1991 GTO
Fuel tank was filthy with stale fuel and the pump not working, flushed and cleaned the tank, refitted and installed a new 524 lph pump
ran it for a hour, took it for a drive the next day, drove for about 30 kms, then blew my clutch master cylinder ( found that I'd put a hole in the piston )
turned off while thinking how i was going to get home, went to start in gear fuel pump not working,
tilt tray home, thought might've been fuel pump relay, after arrival
worked out fuse number 12 was blowing when ignition turned on reds,
Did the *** globe trick plugging in a globe into the fuse slot
unplugged fuel pump, turned on to reds each time, then mfi, fuel pump relay and when i unplugged coil the light went out
disconnected each coil pack one by one found the coil closest to the firewall triggering
ordered a new coil pack fitted today and exactly the same thing happens to the globe at fuse,
I removed the pump at one point and checked it was working okay out of tank, noticed the joining plug in tank had fuel around, there is a rubber grommet but still getting wet
Im not sure if matters,
It wasn't doing it before but with the coil pack unplugged, the MFI is repetitively clicking with the fuel pump plugged in,
disconnected the fuel pump, MFI clicks once on reds
I think maybe I'm dealing with 2 problems?
What do you think my chances are getting a new coil pack which is faulty
I might go swap coil packs around see if makes a difference
Clutch is all working now
Thank you for your help :)
First, I will assume that a globe to an Aussie is a light bulb to an American. I will also assume that you attached the bulb across the two fuse contacts and no fuse in the circuit remaining. Your assumption is that a short exists if the bulb lights when fuse 12 would normally be powered. So, no light! In this instance, this circuit, not necessarily true. Fuse 12 provides battery power to at least 5 different circuits that can be divided into three categories that get turned on only when the key is in a specific position....on/run/your"reds", start/crank....or back to run after the car starts/running and feeding a crank sensor and a cam sensor signal back to the ECU. You said the fuse blew every time the key was only turned to the on (reds) position. You were focused on the fuel pump being involved, but you changed several things each time between trials confusing matters. The fact that the fuse blew in only key on position rules out the fuel pump as a cause. Fuse 12 is powered when the key is turned to the on position feeding power to pin 62 of the ECU turning it on which activates the MFI power side sending voltage from a different fuse (ECI) to many sensors and the injectors. Key on also sends voltage to the ignition component category.....the PTU, the three ignition coils and a filtering condensor/capacitor for the ignition system. Fuse 12 also feeds two circuits that go through the fuel relay side of the MFI to power the fuel pump....but one is turned on only when the key is turned to crank position, and the second only after the car starts. So, forget the pump for now. The bulb will stay on even with no short in the ignition system(or all coils PTU and condensor disconnected) because the ECU is still powered on and connected to its expected ground. Your 1st generation ECU may be bad and shorting,but your bulb can't tell you. Unplug the two connectors to the PTU, the one connector feeding all three coils, and the connector to the condenser. Turn key to run and see if fuse 12 blows. If yes, ECU or wiring in circuits is shorted. If no, turn key off and plug in PTU only...key on. Then repeat one at a time with coil packs only, then condenser only....Don

· Registered
150 Posts
Thanks for very helpful info Steve and Don
Have tested the MFI all working as per test
still it clicks if fuel pump connected

Ecu is Adaptronic select engine management e420d basic with a M & W Ignitions type ECU3 ill attach pics,

Cannot have fuel pump plugged in without the MFI relay clicking continuously on reds, bulb flashes (wouldn't blow fuse if inserted but i don't leave on long enough to do damage,)
Tried to crank doesn't make any difference, which is strange as i thought fuel pump only powered up while cranking or running
have unplugged condenser, coils and the ignition bulb goes out on Reds when i plug in coils it lights up bright will blow fuse straight away, disconnect centre coil and it doesn't light up, so Ive now got 2 blown coils as tried the last old one which was removed and it is still shorting lights up bulb brightly
I wondering if i unplug ecu if the mfi will click with the fuel pump plugged in?

I did read about the oxygen sensor shorting out blowing the fuse, but car is low and cant access atm

View attachment 308944 View attachment 308945
Didn't expect that info. Was the car used for drag racing? That computer is completely generic and is used for many car makes/models using different sensors, ignition systems, fuel injection systems, etc.,etc. Essentially every necessary wire has to be pulled from the old harness and put in the right spot on this computer. Then it interfaces on a laptop so each component can be turned on and programed individually based on what you want it to do based on parameters and input values. So, the previous owner made choices like whether the ECU would act as the power relay MFI/ECI directly or use use the stock MFI relay and how and when. Same with the fuel control relay half of the MFI being used or not or set up to activate a higher amperage aftermarket relay for a high output pump or turn on and program generic circuits within the ECU so it becomes the fuel controller bypassing the MFI. On top of all that, the stock PTU has been replaced with an aftermarket ignition controller/igniter wired in that creates higher voltage/amperage to charge the coils and then trigger the spark to the plugs.(CDI technology). Without knowing how and where all those wires are spliced and what connectors remain, its nearly impossible to help you. I've got some ideas to explain what may be happening, but need to know:
Are the coils still the stock ones and connected to the base metal plate with their wires uncut and connected to the stock square 4 pin connector just below the plate? Do you have a digital multi-meter and know how to use it? Do you also have an analog voltmeter(old needle type)? Is the fuel pump you just installed really 524lph and what make and model is it. Do you have the specs for it ...x/lph @ x [email protected] x amps ?? Was fuse 12 a 15amp fuse? Do you have the service manual for your car? When you say "fuel pump relay", are you talking about the one inside the gold MFI box?

· Registered
150 Posts
air con controls unplugged hasn't changed
Unplugged and cleaned socket at the 5 pin fuel pump relay under air box, tested with fuel pump plugged in and mfi relay only clicked once likes its suppose to do
Have a i got 2 buggered 5 pin fuel pump relays? or is there a test i can perform, it seems like this relay is fighting with mfi relay
unplugged ecu and still same repetitive clicks from mfi and bulb lights up flashing in sync with mfi clicking as was doing..
unplugged the 2 pin resistor near the fuel pump relay and the mfi repetitive clicks but the bulb does not flash or light up? I'm not sure what that means or my next step
Need answers from you before I can go further.
1. Make/model of fuel pump and lph output.
2.What type of bulb are you using incandesant LED etc., and what wattage is it?
3.Use your voltmeter and test voltage of battery directly on battery posts.
4. You said you disconnected ECU and MFI clicked with key on. Did you disconnect all 6 connectors from the ECU ?
5. Is there any kind of anti-theft device on the car....even if its turned off or not used?
6.Make sure battery - cable is attached to engine at a bell housing bolt or starter mounting bolt.
7.Make sure two ground wires are present,clean, and tight going from battery - terminal directly to firewall attachment just below wiper motor.
8.Make sure there is a braided ground strap going from upper middle of firewall, across to plenum/accelerator cable bracket.
9. Put your hand on top of the MFI relay to be sure you feel it clicking when you hear it clicking.
10. Remove MFI from console wall and disconnect the connector. Look on back wire side of connector, inside the connector terminal 10 ports, and inside the MFI at all the pins. Look for burnt or melted wires or plastic or exposed bare copper on the wires or terminals that have been push back and not making good tight contacts on the pins.
11. In your engine pic I can't see where each spark plug wire ends up, but just seeing if each wire heads to the front or rear bank, there are mistakes. Going from the firewall to the front of the car, the order should be 1 4 2 5 3 6.

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150 Posts
It is 3 in the morning here so I gotta go to bed. But, I wanted to just give you a few super quick facts since we have opposite sleep/wake times living 12 time zones apart. When you use a light bulb as a fuse, it regulates the maximum total current/amperage that is available for every component operating on any circuit branch beyond that point that is being powered through that 15 amp fuse/now bulb..The factory fuse #12 (15amp) circuit powering its original stock pump, igniter, ECU, coils, etc., had a total current draw probably close to 10-12 amps. Your high current aftermarket replacement igniter probably raised the current draw close to the 15amp blowing point of that fuse. The new pump you just installed by itself draws 20+ amps depending on demand. The stock wiring to the MFI, the MFI fuel relay contact points inside the MFI that turn the pump on/off and pass the current on to the fuel pump, the wiring after the MFI, the pump speed control relay and its resistor pack are not capable/designed to carry that much current. So, those components quickly get hot and melt/burn when powering your new pump. That ends when something is toasted and comes into contact with any metal chassis area or a melted wire melts into a neighboring ground wire causing the fuse to blow. Using that light bulb drastically complicates everything. Your bulb is 21 watts.....watts=ampsXvolts.... so 21watts/12.36volt= 1.7amps maximum leaving the bulb to power that entire circuit now. You are expecting the amount of electricity that it takes to turn just 1 turn signal bulb on and off to power your entire fuel pump system, ECU, and your entire high voltage/high current ignition system at the same time you may still have the shorted part that blew the 15 amp fuse still in place and still shorting out. Nothing will work as expected and your ECU and your igniter will keep turning on/off rapidly making MFI click rapidly as the bulb blinks. The logic/processor chips inside the digital electronics are designed to do this for fire safety and prevent their own destruction. Normally, when the igniter turns on it charges the coils. But now it instantly shuts back down which triggers the coils to discharge a the plugs. The rapid blinking/triggering on/off coils get super heated and become toast quickly as you saw. That also creates another new short to ground regardless if the pump circuit is unplugged. Thats why you don't use light bulbs as fuses.You may have also toasted your igniter's internal thyristors,charging capacitors, or transistors by now. The MFI is likely shorted inside now also. The two internal MFI relays click on when the ECU provides a ground to activate them. The fact that the MFI relays rapidly click even when the ECU is fully disconnected and not providing any ground path to turn them on/off is a bad sign. On the 91-93 MFI relays there are 2 extra pins (10 vs 8 after 93). One of those pins goes straight to ground-pin6 and could make the MFI click when the ECU is disconnected, but only if the fuse 12 input to the fuel side MFI internal relay has already melted/shorted and remains in that state. You need to use your multi-meter and go part by part. Your pump will need to be powered by the battery through bigger gauge wiring with a 20-25 amp fuse in-line (not fuse #12) and through a 30Amp relay. If the relay and wiring you just installed isn't rated for that current, it won't last long and is dangerous. Good luck....your buying my Fosters !!!!
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