Mitsubishi 3000GT & Dodge Stealth Forum banner
1 - 20 of 21 Posts

· Registered
Joined
·
41 Posts
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!
 

· Registered
Joined
·
41 Posts
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!
 

· Registered
Joined
·
41 Posts
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?
 

· Registered
Joined
·
41 Posts
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
 

· Registered
Joined
·
41 Posts
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?
 

· Registered
Joined
·
41 Posts
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.
 

· Registered
Joined
·
41 Posts
Discussion Starter · #23 ·
I missed the part where that was happening... I didn't read all responses, I was just addressing the way the system works, and some common issues I've seen in that system. If it is verified dropping the MPFI BEFORE the engine dies, (which needs to be very carefully verified, as normal operation turns off the fuel pump as the engine dies) that's a pretty clear cut and classic ECU failure.
Okay, so I should inspect my ECU? And attempt to narrow in on the problem circuit?

I am fairly proficient at replacing transistors, diodes, capacitors, etc.
 

· Registered
Joined
·
41 Posts
Discussion Starter · #25 ·
Yes. Shutting off the fuel pump is a classic symptom of ECU failure.
Is this sort of failure common and limited to certain capacitors or diodes etc in the ECU circuit.

It's behind where my car stereo would go right. I've been looking but I have yet to find a decent guide. Anybody know of one? I am itching to go pull the ECU and start testing the various circuits and pathways
 

· Registered
Joined
·
41 Posts
Discussion Starter · #30 · (Edited)
Yes. Shutting off the fuel pump is a classic symptom of ECU failure.
(y) Ty, im pullin out the ECU to check it right now.

Since we know it it the ECU that is the source of the problem, next I am going to attempt to diagnose the ECU itself. The question: is there an exact transistor or diode I should check or a certain circuit that you could show me or do I need to one-by-one test each and every component. I hope I can fix it because I would prefer not to buy a new ECU, but I would more prefer a running car so I will buy one if necessary... and available.

Idle Air Control Valve [IACV] dIagnostics:
I tested my IACV which from what literature I could find on it says that terminals 2&1, 2&3, 5&4, and 5&6 each should have an Ohm reading between Ω28 and Ω33; from the info I have unearthed. When I tested my IACV at the terminals I got these numbers:

Resistance Values
  • Pins 2 & 1: Ω25​
  • Pins 2 & 3: Ω26
  • Pins 5 & 4: Ω25
  • Pins 5 & 6: Ω26
For the record I tested the IACV and got the same numbers as I did after I opened it up and cleaned it properly. I also read that a damaged or misfunctioning IACV could damage ones ECU... Maybe the malfunctioning IACV over time damaged the ECU which lead to the problems I am experiencing where my fuel pump cuts out? Or could it be the malfunctioning IACV with its terminals that are all under the required Ω28 - Ω30 (from what I have read at least since I have not been able to find specific IACV info for our cars. Thank you :)
 

· Registered
Joined
·
41 Posts
Discussion Starter · #33 ·
The most common problems are with the radial electrolytic capacitors failing from age causing erratic current in some circuits, which often have no visual signs. In many cases they leak electrolyte that can corrode and also damage near by components and/or circuit board traces, in these cases there’s usually visual signs of leakage as shown in link @OhioSpyderman linked about removal post #26. Sometimes the electrolyte will damage sub boards attached to main mother board because of ECU being mounted vertically on it’s side, see Important Note: Specific to repair for Stealth ECU (in red) ~ 1/3 down page of the below link.

No matter if there’s visual evidence of leakage or not, original electrolytic capacitors in a ’92 ECU needs to be replaced.


The IACV readings you got of 25-26Ω is probably OK if it is the unit with tan colored top, which should be in ~30Ω rage @ 68°. The later solid black units run ~40Ω @ 68°. Ohm readings a little off or infinity reading from a open coil will not damage ECU, just casue a malfunctioning IAC unit. Damage to ECU from IAC usually occurs when one of four coils shorts to housing (ground), causing ohm readings of near zero ohms and complete continuity to IAC metal housing can be read from pin #s for that coil. When that occurs IIRC what happens is burn driver boards that can be seen as in below picture.

View attachment 307542 click on image to enlarge
Thank you so much for all the info you have helped me with so far. I checked out the link and read the whole page, those radial cylindrical shape capacitors that bulge at the top and sometimes the bottoms leak which are obviously harder to detect than a top capacitor leak. Are these the same ones as in the links below? Or do other components fail often? Or just the faulty 42-year-old electrolytic capacitors that stop functioning I wonder...

Like this kind??? HD 100 Pcs 8 X 11mm Radial Aluminum Electrolytic Capacitors 470uf 25v for sale online | eBay

I still haven't pulled it out, got to tired last night. Going to hopefully go out now and pull it out. Already researched the process last night/this morning (whatever) so it should go quickly. I will pull it out and open it up and examine as well as posting pictures of the board itself.


I currently had a similar problem but the main cause was my ecu fuse under the hood. It starts up fine and the shaking from the motor can eventually move the fuse and stall itself out
Which specific Fuse are you speaking about and where is it located? Is it in the fuse/relay box under the hood located sort of behind the left headlamp bucket from the perspective of standing at the front and looking into the engine bay?

Thank you


Could the speed relay be filled with water or the speed relay coil be toast and directly shorted across itself, or relay pins be shorted to pin 1 causing voltage and amperage to quickly drop as soon as ECU applies ground to pin 1 to shift to slow speed circuit? If so could voltage drop low enough causing the MFI coil to allow the MFI pump contacts to open/click first followed by car stalling just after from pump stopping? Or could a shorted low speed resistor or a partially shorted circuit to ground exist after resistor and before splice connection with high speed wire? Using Ohm's Law at resistor(0.9 ohms) and beyond....V/R=I...so 11-12v/0.9ohms= <15amps fuse ...so even with dead short to ground fuse won't blow. Before relay and partial short to ground.... as voltage drops the MFI acts like circuit breaker and opens before fuse gets hot/amps high enough to blow? I guess if it were me, putting the mental masterbation aside, before I bought a new ECU I would take 15 min and pull the speed relay off the connector, use a 16G piece of wire stripped on both ends, and push 1 end into connector port 3 and the other end into connector port 2..safely set it down so it can't short to metal.....and start her up. If it shuts off buy/fix ECU..if runs make jumper formal,stable and wrapped/insulated.
Just to clarify for me, which relay is the "speed relay" is this the MFI or the Relay and accompanying resistor located beneath the air box? I keep hearing the speed relay referanced and I'm always wondering which one it is. Thanks
 

· Registered
Joined
·
41 Posts
Discussion Starter · #34 · (Edited)
So, I pulled the ECU. In about 3 seconds I spotted a major issue that just so happens to be beside the largest electrolytic capacitor on the board. It has leaked from the bottom its clear to see the leak trail it left, and it devoured what I think was a resistor (perhaps a diode) beside it and it is covered with corrosion as you'll see in the images. It also leaked out another side of itself and corroded two other pins that you can see in the pictures also. I will circle them in red just to be clear.

So far, it is obvious to me that the leaking capacitor(s?) needs to be replaced, as well as that resister labeled "C6" that is circled in red in one of the photos from different angles. The other damage from the same leaking capacitor you will also see from multiple angles and circled in red. You'll be able to see what I am talking about.

If the images below will not load for you; then I made a MEGA Upload Folder to view them: 28.53 MB folder on MEGA

Please, any help will be much appreciated. Thank you.💪🔧🔨🔋








 

Attachments

· Registered
Joined
·
41 Posts
Discussion Starter · #37 ·
Yes similar to ones you linked but those have wrong micro-farad (µF) and voltage wouldn’t work as replacement for the one 47 µF 50 volt capacitor you need. The µF rating MUST be same as one being replaced and the voltage needs to be same as or higher than one replaced. The three correct µF and voltage currently in you ECU is shown at bottom of bellow link.
Yes, thank you of course, I got a lot of info from the link you linked. Thank you. Buying the correct capacitors and replacing them would be child's play for me. The one component I am not sure the exact specs of or where to obtain the specs for is the Surface Mount Ceramic Capacitor labeled C6 that is besides my most obvious leaking capacitor which is labeld "C104" on the motherboard and is 100uf/16v. Of course, if I attempt it, I will replace all three capacitors, but I still need to learn more about that Ceramic Capacitor labeled "C6"that got leaked all over from damn Electrolytic Capacitor "C104"

If anyone can share any insight on the Ceramic Capacitor labeled "C6" I would be much appreciated.

I'm sure he's talking about one below air box as that one only controls the speed of fuel pump and I also often refer to it as pump speed relay. Mitsubishi literature only refers to it as fuel pump relay, which is sometimes confusing since one side of MFI relay actually starts and stops fuel pump by supplying or removing battery voltage.
Thank you for clearing that one up for me. I wonder if with a multimeter I could test the relay to determine if it functions under normal conditions? I also wonder what measurements to take on it to determine if it needs replacing. I could always open it up and make sure it is not "full of water" like others have suggested; last time I had it out while troubleshooting this problem in the beginning and I really don't think there is water in there, but I may as well check it.

Or does the obvious damage to my ECU that I documented with many photos in Post #34 tend to be the source of all my hardships and problems.



You can send off the ECU to get repaired, and from the looks of it, I think that’s the level of repair it needs. It’s not just a capacitor change, but you’re also replacing other components and possibly repairing board traces. You have to remove and reapply the special coating. And then it would be beneficial if you had a testing rig. ECU repairs of this nature are best left to the professionals.

If you plan on keeping the car, you should invest in a new ECU. I would get a chrome ECU if you’re not doing anything wild. IMO, it’s better to start with a new, known quantity than try to repair a nasty 1G ECU.
If I can learn more about the damaged component "C6" (Ceramic Capacitor that got leaked all over) I am more than capable of cleaning up the mess from the leaked capacitor and change out all 3 Electrolytic Capacitors for modern versions. As well as that ceramic "C6" capacitor.

The "Special Coating" looks like thick varnish, maybe a little more sophisticated but it wouldn't be all that hard to find out what they used; or simply use a more advanced modern equivalent. Silicone Potting Compound comes to mind (Once I verified my repair did in fact work)

It's just that I am not a rich guy so If I can fix it myself, I will try to do it myself. Then if I can't fix it, I can send it in to be repaired by the pros.


What is this CHROME ECU all about? Wouldn't that require a whole lot of extra work configuring it to work or is it just plug-an-play. I would probably need a tune afterwards. Putting in an aftermarket ECU for a mostly stock engine makes me feel un-easy. Then again, I don't understand anything about going the CHROME ECU route. Perhaps you could please enlighten me?

Thank You
 

· Registered
Joined
·
41 Posts
Discussion Starter · #39 ·
That’s classic electrolytic capacitor leakage, which requires capacitor replacement and board cleaning with alcohol. That 100 µF, the 22 µF and the 47 µF need to be replaced, with correct polarity installation. You would need to lightly scrap around/under side board legs pins and around C6, then use isopropyl alcohol and tooth brush to scrub those ares good to remove corrosion residue.

I’m not sure if componet in C6 location is damaged or not, possibly just covered with corrosion and/or residue. I can’t tell for sure but it is probable a surface mounted (SMD) capacitor, simular to one above your red circle of C6 and on other side of side-board in location C27.
Thank you for the advice on cleaning the board. I am already aware of polarity on electrolytic capacitors, it's indicated by the grey line running down one side of the capacitor corresponding with the side of the capacitor where the negative pin resides. I would make note of these features before I began.

As far as C6 SMD Ceramic Capacitor being just covered in leakage from the 100uf capacitor and perhaps still functioning fine once cleaned up, that would be a bonus.

I look at it all like this. I could probably fix the ECU myself for $15 or $20. Perhaps even free considering I have hoarded motherboards from all manner of electronics for years now and they are full of those style Capacitors. May just be able to salvage high quality ones if I get lucky and they are of the same Ultra Farad and Voltage rating as the ones I need.

The alternative is spending possibly $200 on sending my ECU away to have it fixed by professionals.

I mean; replacing capacitors and cleaning boards is fairly simple procedure if you have the equipment to do so (which I happen to have). Have other members succeeded in fixing they're ECUs themselves? Even if I didn't succeed in fixing it myself, I could always turn around and send it off to be fixed or go the CHROME ECU way as was suggested just 2 posts ago. I do not know how smart of an idea that would be. Is there a lot of work in converting to chrome ecu?
 

· Registered
Joined
·
41 Posts
Discussion Starter · #42 ·
Sounds like you have tools and knowledge to do the radial capacitor replacements. Knowing that, I’d say just do replacement, clean around C6 and pins for side-boards, then just try ECU to see if it works correctly.

I understand you wanting to do it yourself and could save yourself a lot of money, at worst you’d just have to send it in for repair or replace (as you said) if your repair doesn’t correct it. I’ve fixed my ECU, TCU and Tach by simply doing the same, though I did have to buy a spare used TCU just to see where trace went that was completely burnt away when capacitor burnt up along with burning hole in PCB of my original board. Repaired trace, replaced capacitors in both units, now have one in car and a working spare.

If you don’t have correct capacitors or a electronics store near by where you could purchase them, you could just order set from 3SX for $8.96 that comes with an extra 47 µF that wouldn’t be needed in your TT ECU.
💪 (y) I always try and fix my stuff myself I will not go to a auto shop or stealership unless the sun is falling out of the sky. An added benifit is you get to learn how everything works.

That Capacitor kit from 3SX seems pretty convenient... I am going to look through my spare circuit boards and components first though before I pull the trigger on that.

How is 3SX for shipping times? I live in Vancouver Canada, just wondering if I did go the 3SX route how long (roughly) of a wait I would I be in for?



Read about chrome ECU here: http://chromedecu.org/?page_id=684

Almost everyone with a TT 3S wants to mod at some point. If you ever want more performance, there are several options, including chrome.

However, it sounds like you have the proficiency to do the repairs yourself. Just be aware that since you don’t have a test rig, you might end up chasing your tail if your repairs aren’t 100% or there is some other damage you don’t find. These cars are old and especially the 1G computers are known weak points. A remanufactured ECU will be cheaper and suffice if the remanufacturing process was done correctly. The cost of a reman ECU might approach 50% of a chrome ECU (or be close to equal if you get a used chrome ECU), so plan accordingly.
One day when I do start adding performance parts (it will happen sooner than later), then I will probably do the CHROME ecu, Wide Band 02, FPR, Speed Density, Cat-Back (or full) exhaust, higher cc Injectors, stand-alone MSI ignition, TIEN coil-over suspension, custom made & shaped intercooler piping, etc, etc... oh I can dream. One day when I have the money to do these things I will, and I can't wait until thar time lol.

Already have a Stage 2 clutch lol. Had it installed after I destroyed the clutch on the car shortly after I bought it 10 or 13 years ago when I was in my early 20's. I didnt know much about cars at all back then, so soon after that I got a truck and put my Dodge Stealth into storage under cover for about a decade. I am glad I 'took it off the road' when I did or else, I may not have still had the chance to drive the car today. probably would have crashed it or something would have went wrong due to my lack of understanding of cars at the time...

But alas! Back to reality!
 

· Registered
Joined
·
41 Posts
Discussion Starter · #52 · (Edited)
Great company to deal. Family business! They've been operating since 1998. Incredible 1 day turnaround. a+ communication. 5 year warranty. Good value, the total cost for repair & return is $250(usd). Being as I live in Canada, I had to pay an extra $50 for International expedited shipping; this is to be expected and props to Foreign Auto ECU Repair for communicating this to me almost immediately during our first talks. Here is a link to they're service: Remanufactured Engine Computers w/ 5 yr warranty - 800 241 6689

One repaired ECU:
 
1 - 20 of 21 Posts
Top