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Discussion Starter · #1 ·
Hi everyone! Heres my problem I am experiencing is my car starts and shuts down after about 5 seconds. In those 5 seconds I can rev the engine but then its just like the accelerator just stops responding completely and the car stalls. This problem first occurred when I was very low on gas, so I thought that was the problem. My friend where I was at the time had a Jerry can with some "gas" in it. I don't know if there was any water in it or even what it was actually now that i think about it but we had used it moments ago for his dirt bike which reluctantly started.. so the gas couldn't have been that bad but who knows what was in there. BUT... after 2 more tries the car started up fine and remained running so I drove straight to the nearest gas station and I put 15 liters 93 octane in the tank. I started the car again (once more it started fine) then I drove back home which was about a 50km drive. The next day I go to start car and it starts doing the same problem again: it starts fine but then stops responding to all Accelerator pedal input and just stalls out. There is nothing I can seemingly do to save it.

I just got back from the gas station (bro gave me ride) with 10L of SHELL V-Power 93-Octane petrol. Moments from now I will proceed into my garage where my car is sitting on jack stands. I am going to drain the tank. I wonder what angel is the best for the tank to drain completely. I am so glad for the drain bolt. I no like siphoning gas. I am hoping that once I swap in new gas that the problem will be solved.

If anybody can offer any advice it would be met with gratefulness :)

Thank you for reading!
 

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93 NA ATX 3000gt DOHC
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Could be water or trash in tank that mixes with fuel when car moving or when gas added stirring things up when added. But then settles to bottom of tank after sitting, causing mostly water to be drawn in on startup stalling engine or if trash it could be covering pre-strainer on pump pickup stopping fuel flow.

It will be interesting to see what you find when draining tank. Lastly with yours being a ’92, there’s always possibility of ECU problem but the likelihood of that coinciding with adding gas seems slim.
 

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Discussion Starter · #3 · (Edited)
UPDATE :p:p:D:D:p:p:D:p:cool::cool::cool::cool:(y)(y)(y)(y)

After an age here is the update:

New gas: problem not fixed. No difference

Installed new fuel filter, runs a little smoother for the few seconds it does. Engine still dies every time after a few seconds. Not fixed.

Next, I hooked up jumper wires and a multi-meter to the fuel pumps (-) Negative Post and the other was connected to the fuel pump 12V+ line. I started the car while monitoring the voltage I watched the car start up and the volts shoot right to 12v no problem, and then the volts go to zero, as I can hear the relay golden box thing attached behind the carpet on the right side of my centre console. as soon as it loses voltage, the box clicks, and the engine dies, then the box clicks again.

Next, as I see that it is losing power to the pump and that's what the problem is. not the pump itself. The pump is fine most likely. So, I run the jumper wire I have connected in line with the fuel pumps power wire out the window, my brother who is assisting me attaches a connector to it and he clamps it top the 12v + Positive post of three battery. Instantly I hear the pump kick in for the first real time ever that I have actually heard it, I started the engine and it continued to run just fine. Bingo! Problem Identified.

Now a lot of my problems are beginning to make sense.... I was constantly experiencing fuel cut and i could tell I was running lean because I wasnt burning as much gas as regularly and my boost would be horrible spikes and frequent random fuel cuts. Lots of bucking. Perhaps ive been experiencing voltage drop for whatever reason, and perhaps now it's just gotten so bad that the car wont even run for more than 2 seconds. I dont know, maybe someone could offer some wisdom.

Does anybody know what the cause of the problem is or is the one fix fixes all the Hotwire/Relay Mod??

I am so excited to have finally made some solid progress and identified one of possibly several points of failure which are causing my problem.

Would anybody be kind enough to direct me to the guide most appropriate for the problem I am facing? Thank you all!
 

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1995 Mitsubishi 3000GT SL Spyder, 1995 VR4, 1991 Stealth RT TT
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I had a similar problem where my car would start and idle fine the after 20 seconds the RPM would drop (even with accelerator pushed) then stall out. I removed IAC and it failed the voltmeter test. That can damage ECU. So check your IAC and ECU.
 

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It sounds like you have a bad MFI relay and/or ECU. The MFI relay receives a ground signal from the ECU when cranking and should energize the relay while running. So you could either have a bad relay (it happens, the original on my ‘92 died one day) or the ECU is fried and isn’t outputting the ground signal. Because the car runs with the fuel pump hot wired, my guess would be the MFI relay. I have an aftermarket (SMP brand) one that works fine if you don’t feel like paying for an OE part.

Standard Motor Products RY-402 Relay https://a.co/d/dlkdRcI


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Next, I hooked up jumper wires and a multi-meter to the fuel pumps (-) Negative Post and the other was connected to the fuel pump 12V+ line. I started the car while monitoring the voltage I watched the car start up and the volts shoot right to 12v no problem, and then the volts go to zero, as I can hear the relay golden box thing attached behind the carpet on the right side of my centre console. as soon as it loses voltage, the box clicks, and the engine dies, then the box clicks again.
Not sure if I completely understand where meter was attached (at pump connector in hatch access panel opening maybe), instead of fuel pump test connector near wiper motor under hood. But the “golden box thing” is the MFI relay which half of it controls the fuel pump on/off, which as @beegeezy pointed out is done by ECU closing/opening that half of the MFI relay by supplying/removing control coil ground.

When key turned to start position pump half of MFI closes sending power to pump (thru pump speed relay), if ECU receives a run signal from engine it will keep pump running by holding that half of MFI closed. If ECU doesn’t receive run signal in a given amount of time it will open that half of MFI stopping the pump. So you could have problem with MFI relay, ECU not maintaining ground or ECU not getting a run signal from engine.

Does anybody know what the cause of the problem is or is the one fix fixes all the Hotwire/Relay Mod??
If you mean pump speed relay bypass with this statement, that won’t cure your problem, if you’re hearing MFI relay open (click) right before voltage drops to pump and engine stops. MFI relay sends power to fuel pump speed relay which then shifts between high and low speed when ECU determines which speed is needed. So if power is being lost leaving MFI relay, pump won’t run in either low or high speed.

Would anybody be kind enough to direct me to the guide most appropriate for the problem I am facing? Thank you all!
I’d start by monitoring voltage leaving MFI relay on Black wire w/blue stripe (B-L) when starting and running to see if power drops there before engine dies, if does you’d know it’s with MFI relay or ECU control of it.
 

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Discussion Starter · #7 · (Edited)
Thank you for suggesting I do a resistance check on the IACV as well... I might preform this first. If I understand correctly its possibly to rebuild the IACV if done carefully. How realistic would rebuilding it be if when I measure it I get out of spec readings?

Not sure if I completely understand where meter was attached (at pump connector in hatch access panel opening maybe), instead of fuel pump test connector near wiper motor under hood. But the “golden box thing” is the MFI relay which half of it controls the fuel pump on/off, which as @beegeezy pointed out is done by ECU closing/opening that half of the MFI relay by supplying/removing control coil ground.

When key turned to start position pump half of MFI closes sending power to pump (thru pump speed relay), if ECU receives a run signal from engine it will keep pump running by holding that half of MFI closed. If ECU doesn’t receive run signal in a given amount of time it will open that half of MFI stopping the pump. So you could have problem with MFI relay, ECU not maintaining ground or ECU not getting a run signal from engine.


If you mean pump speed relay bypass with this statement, that won’t cure your problem, if you’re hearing MFI relay open (click) right before voltage drops to pump and engine stops. MFI relay sends power to fuel pump speed relay which then shifts between high and low speed when ECU determines which speed is needed. So if power is being lost leaving MFI relay, pump won’t run in either low or high speed.


I’d start by monitoring voltage leaving MFI relay on Black wire w/blue stripe (B-L) when starting and running to see if power drops there before engine dies, if does you’d know it’s with MFI relay or ECU control of it.
View attachment 307438
Sorry, I should have been more clear.

I followed this procedure Stealth 316 - Fuel Pump Voltage Measurement so I hooked up the leads at the fuel pump beneath the hatch just as in this tutorial. Started motor, and read 12volts on the multimeter, but then the 12v goes to 0v and the engine shuts off.

When I ran an 8ga cable from the battery directly to the pump, for one I could hear the pump and when the engine started the car continued to run and did not stall.

This is the procedure I was wondering if this would fix my problem: Stealth 316 - Fuel Pump Re-Wire just to be specific. Would this procedure get my car running again, since i already tested it and it runs while directly hotwired so I just assumed that all I would need was the relay and switching circuit to turn it on and off. Or am I not undersanding something?

I am going to go out to the garage and preform the test on the MFi Relay you recommended, checking for power drop before the engine dies @ MFI relay on Black wire w/blue stripe...

That black wire with the blue stripe is the same wire I tested at the fuel pump and monitored it loosing power as the engine dies, would that be an equivalent measurement or should I check directly at the MFi itself on that black wire w/blue stripes?
 

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Discussion Starter · #8 · (Edited)
And can anybody link me to where I can buy a proper data logging cable? I have looked everywhere and maybe its cause i dont know exactly what i am looking for or what not, but I cant seem to find one. any help would be much appreciated!

I am looking for a cable to go from the OBD1 Port to my laptop
 

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And can anybody link me to where I can buy a proper data logging cable? I have looked everywhere and maybe its cause i dont know exactly what i am looking for or what not, but I cant seem to find one. any help would be much appreciated!

I am looking for a cable to go from the OBD1 Port to my laptop
Member Blackstealth on here can build you whatever you need.


I followed this procedure Stealth 316 - Fuel Pump Voltage Measurement so I hooked up the leads at the fuel pump beneath the hatch just as in this tutorial. Started motor, and read 12volts on the multimeter, but then the 12v goes to 0v and the engine shuts off.

When I ran an 8ga cable from the battery directly to the pump, for one I could hear the pump and when the engine started the car continued to run and did not stall.

This is the procedure I was wondering if this would fix my problem: Stealth 316 - Fuel Pump Re-Wire just to be specific. Would this procedure get my car running again, since i already tested it and it runs while directly hotwired so I just assumed that all I would need was the relay and switching circuit to turn it on and off. Or am I not undersanding something?

I am going to go out to the garage and preform the test on the MFi Relay you recommended, checking for power drop before the engine dies @ MFI relay on Black wire w/blue stripe...

That black wire with the blue stripe is the same wire I tested at the fuel pump and monitored it loosing power as the engine dies, would that be an equivalent measurement or should I check directly at the MFi itself on that black wire w/blue stripes?
Unplug your airflow sensor and start the car... I it doesn't die in limp mode, you know it's losing power when it switches to low speed. If that's the case, the relay bypass would in fact fix it, as would fixing the relay (probably full of water)
 

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Member Blackstealth on here can build you whatever you need.




Unplug your airflow sensor and start the car... I it doesn't die in limp mode, you know it's losing power when it switches to low speed. If that's the case, the relay bypass would in fact fix it, as would fixing the relay (probably full of water)
Yeah, Antero (Blackstealth) has a few different products that will work.

Good point, Larry…I forgot that the car starts in high speed mode (no resistor, fuel pump speed relay unenergized), so the FP speed relay is also suspect.


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That black wire with the blue stripe is the same wire I tested at the fuel pump and monitored it loosing power as the engine dies, would that be an equivalent measurement or should I check directly at the MFi itself on that black wire w/blue stripes?
Testing it at MFI relay will confirm if MFI or ECU is causing the problem, or if it's after the MFI like maybe at fuel pump speed relay circuit.

This is the procedure I was wondering if this would fix my problem: Stealth 316 - Fuel Pump Re-Wire just to be specific. Would this procedure get my car running again, since i already tested it and it runs while directly hotwired so I just assumed that all I would need was the relay and switching circuit to turn it on and off. Or am I not undersanding something?
Yeah that would fix it, but the ECU wouldn't be able to turn pump off if engine quit unexpectedly. Like from busted fuel line or wreck, which if fire was involved pump would continue to feed it if you forget or not able to turn switch off.
 

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Yeah that would fix it, but the ECU wouldn't be able to turn pump off if engine quit unexpectedly. Like from busted fuel line or wreck, which if fire was involved pump would continue to feed it if you forget or not able to turn switch off.
Unless I'm missing something, I think he asked if the procedure he linked from Stealth316 would fix his car? That's just a basic pump hotwire that we all use often, and works as stock. (minus the low speed)
 

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Unless I'm missing something, I think he asked if the procedure he linked from Stealth316 would fix his car? That's just a basic pump hotwire that we all use often, and works as stock. (minus the low speed)
OK… So you’re not missing anything, I was because never read that complete re-wire process that still uses the Black wire with blue stripe from fuel pump relay to triggered the added relay in trunk area, instead of another switch source as I assumed :oops:.

BUT….. If that wire is now dropping voltage as he says, it will still drop-out the added relay causing pump to stop. So nothing would be gained with that process, unless it’s simply open circuit on resistor side branch that’s causing the complete drop to 0 volts, instead of ~ 9 volts :unsure:. Which if that's the case, the relay by-pass you mentioned in post #9 would be simplest cure.
 

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BUT….. If that wire is now dropping voltage as he says, it will still drop-out the added relay causing pump to stop. So nothing would be gained with that process, unless it’s simply open circuit on resistor side branch that’s causing the complete drop to 0 volts, instead of ~ 9 volts :unsure:. Which if that's the case, the relay by-pass you mentioned in post #9 would be simplest cure.
You are correct on that, unless you follow his recommendation to bypass the resistor and relay: Stealth 316 - Fuel Pump Relay/Resistor Bypass
 

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Discussion Starter · #15 · (Edited)
Member Blackstealth on here can build you whatever you need.
Thank you!

Unplug your airflow sensor and start the car... I it doesn't die in limp mode, you know it's losing power when it switches to low speed. If that's the case, the relay bypass would in fact fix it, as would fixing the relay (probably full of water)
I did as you suggested; I unplugged the MAF and started the car and it ran without stalling. This is good, I like progress :D Thanks a lot!

So does this for sure pin down the fuel pump relay [the one beneath the airbox] as the problem?

Besides the MFI relay and the Fuel Pump Relay that's beside the Resistor underneath the air box, are there any other relays in the fuel pump circuit that I should know about?

I’d start by monitoring voltage leaving MFI relay on Black wire w/blue stripe (B-L) when starting and running to see if power drops there before engine dies, if does you’d know it’s with MFI relay or ECU control of it.
View attachment 307438
I am going to do this MFI voltage measurement you have suggested and get back with updates! Thank you too! (y)


On Stealth-316 he says you can maybe get away with a 20amp inline fuse between the battery and Terminal 87 on the relay, as long as I've got a stock fuel pump (which I do.). Probably makes sense to just go with the 30amp inline fuse though....

Another question about the rewire... I am going to be using an 8ga wire from battery to relay with the 30-amp fuse in between. Do I need to run the 8ga wire directly to the relay pin or if I get a relay with the connector and wires do I need to run 8ga all the way to the relay?
 

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Discussion Starter · #16 · (Edited)
I’d start by monitoring voltage leaving MFI relay on Black wire w/blue stripe (B-L) when starting and running to see if power drops there before engine dies, if does you’d know it’s with MFI relay or ECU control of it.
View attachment 307438
I completed this procedure. To be clear I exposed the harness below the MFI relay and sought out the black wire with blue stripes ad I exposed a section of the wire and got + Voltage from there; and the negative I just got from the metal of the center console.

When I start the engine the volt meter reads 13.25 volts for a moment, maybe 1 or 2 seconds and then at the same time the voltage drops to zero I can hear the MFI relay click, the car continues to run for a few moments more (approximatly 2 and 1/2, or 3 seconds) then the engine stalls.

So the voltage does cut out before the engine dies.

More Progres (y)

At this point the IAC is still a potential culprit? It seems it worked fine before the fuel pump problem(s) began.
 

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From the test results of the MFI relay, it sounds like at least a defective MFI relay at this point. You can also check to see if the ground signal from the ECU (I think it’s a white/red wire IIRC) also drops. That ground signal is what activates the MFI relay as seen here:


Note: I think the wiring pins at the MFI relay are numbered differently on the 1G cars. But you’re still looking for the ground from pin 8, I believe.


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From the test results of the MFI relay, it sounds like at least a defective MFI relay at this point. You can also check to see if the ground signal from the ECU (I think it’s a white/red wire IIRC) also drops. That ground signal is what activates the MFI relay as seen here:


Note: I think the wiring pins at the MFI relay are numbered differently on the 1G cars. But you’re still looking for the ground from pin 8, I believe.


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I agree with the reasoning provided to this point including beegeezy's. I think we can take it even 1 step further knowing that unplugging the airflow sensor (MAF) kept the pump and the car running. If crank/cam /run signal to ECU was dropping out or B+ voltage into MFI at pin 7 was lost, or MFI was bad and opening the circuit after only seconds,the car would shut down despite the MAF being unplugged...that didn't happen. So the ECU logic and/or some circuitry components failing is the branch point as to whether it gets ground to pin 8 W-R or not to keep the pump running. Confirmation done by seeing if ground suddenly lost on W-R at ECU end or MFI end. Pull ECU and post some good up close pics if that's happening.
 

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I agree with the reasoning provided to this point including beegeezy's. I think we can take it even 1 step further knowing that unplugging the airflow sensor (MAF) kept the pump and the car running. If crank/cam /run signal to ECU was dropping out or B+ voltage into MFI at pin 7 was lost, or MFI was bad and opening the circuit after only seconds,the car would shut down despite the MAF being unplugged...that didn't happen. So the ECU logic and/or some circuitry components failing is the branch point as to whether it gets ground to pin 8 W-R or not to keep the pump running. Confirmation done by seeing if ground suddenly lost on W-R at ECU end or MFI end. Pull ECU and post some good up close pics if that's happening.
This strikes me as perfectly good logic, that's easy for me to agree with especially after reading the below quote from your post #16
When I start the engine the volt meter reads 13.25 volts for a moment, maybe 1 or 2 seconds and then at the same time the voltage drops to zero I can hear the MFI relay click, the car continues to run for a few moments more (approximatly 2 and 1/2, or 3 seconds) then the engine stalls.

So the voltage does cut out before the engine dies.
I don't know why the ECU doesn't drop the ground with MAF unplugged (maybe @RealMcCoy does :unsure:), but it does seem apparent something is going wrong in ECU during some logic change. Pictures of ECU will only help if there's some obvious visual problems, unfortunately there can be problems with no visual evidence.

But it's obvious to me there's no need for added relays, jumpers, etc., until that ground being dropped by ECU is corrected.
 

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This strikes me as perfectly good logic, that's easy for me to agree with especially after reading the below quote from your post #16

I don't know why the ECU doesn't drop the ground with MAF unplugged (maybe @RealMcCoy does :unsure:), but it does seem apparent something is going wrong in ECU during some logic change. Pictures of ECU will only help if there's some obvious visual problems, unfortunately there can be problems with no visual evidence.

But it's obvious to me there's no need for added relays, jumpers, etc., until that ground being dropped by ECU is corrected.
The ECU switches fuel pump speed based on load.(Airflow) Default is high speed. Once you start the engine and it establishes low load, it switches to low speed. If it dies when attempting to make the switch, that tells you the ECU is trying to do it's job, but there is a break in the low speed circuit. As I already posted, the most common issue is the relay full of water, but simply forgetting to plug the resistor back in will do the same... Unplugging the airflow meter simply puts in into limp mode and deprives the ECU any means of establishing load, so it defaults to high speed and never tries to switch.
 
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