2G Eclipse GST - Do I have a dead cylinder?

[Lintu]

Hello!

This is my first real post on the forums, so please forgive me in advance if I’m posting in the wrong section.

I recently bought a 94/95 2G Eclipse GST, and its idle sounds kind of funky — instead of a nice, even purrrr, it oscillates, almost like an RX-7 brap brap brap brap.

Some information:

After sitting overnight, the 4G63 fires right up in the morning. But if it’s still hot from a recent drive, I have to crank it a couple of times before it starts.

Idle stays around 900–1000 RPM, but as mentioned, it sounds uneven or oscillating.

While driving, it feels weak at low RPM, but driving at a higher speed, it feels more normal. When the turbo kicks in, it seems to have decent power.

There’s some liquid that smells like gas coming out of the exhaust, and the exhaust pipes stay really cold even after 20 minutes of idling.

White smoke also comes from the exhaust — not very thick, and it doesn’t smell sweet, just like raw fuel (seems to be running rich).

Coolant and oil levels stay the same, no visible leaks (garage floor is always clean).

Oil is clean and new, with no signs of coolant mixing.

Coolant is new. I flushed and replaced it properly since the previous owner used TAP WATER (oh god... WHY?).

ECU was replaced by the previous owner (original: MD309947, now: MD305162).

All spark plug wires have spark when checked.

Speedometer doesn’t work, but the tachometer does.

It had codes 12, 13, and 25 — which I think are related to the MAF sensor. I carefully cleaned it with maf cleaner spray and the codes went away (I entered diagnostic mode by jumping pin 1 to ground on the “OBD” connector). However, the idle issue remains...

When I got it, ALL the valve cover screws were loose (I could turn most with my bare hands…), but the engine ran.

Well, thats a lot of background info, but I think most are related to the same problem...

What you guys think could be the problem??

Thanks a lot in advance for your help!!

Cheers from Brasil,

Richard.

 

[steve]

You say you had codes 12, 13, and 25. Those would be from a OBD1 ECU not usually found in a USDM 2G. I've not seen a MD305162 ECU, the MD309947 is a standard 95 FWD turbo ECU. So the ECU swap is one open question.

If you think you have a bad cylinder you should check the compression of all 4 and let us know the results.

 

[Lintu]

Hello. thanks for the answer.

I will check compression ASAP and report back.

Regarding ECU, the original one came tossed in the trunk of the car, i have opened it and saw that two capacitors have leaked and corroded several traces and pads. As it is a socketed eprom, in think its worth the shot to try and restore the traces, I think I can do this as Im an electronics engineer. Probably this was the reason they replaced the ECU.

About the one thats currently instaled in the car, I was able to squeeze a tiny camera in there and get a clear picture of the label, please find attached. Im trying to understand if it is a correct ECU for my car.

Thanks!

Cheers!

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[steve]

I'm trying to understand if it is a correct ECU for my car.

The correct ECU would be the MD309947. A MD312464 or MD312464 ECU would be the second choice.
The MD305162 is close in vintage but I can't find the details of what it's from but it's not a US DSM ECU.

 

[Lintu]

yeah, i understand that... I'll try to retrace the original one ( 309947 ).

Thanks, Steve

 

[chrysler kid]

I recently bought a 2g with the firing order from the ignition coils set incorrectly on cylinders 2 and 3. At idle the car sounded like it had a camshaft, or noticeable lope to it.

Have you verified the firing order at the coils matches the ecu desired firing order

 

[Lintu]

Hello,

I also suspect firing order, but as I have an "unknown" ECU installed (Close to NO information about it, MD 305162), I'm not sure what it expects! But don't 2 and 3 share the same coil? (and 1 and 4 sharing the other coil). I mean, inverting them between the same coil shouldn't be a problem, should it?

Thanks for the message!!

The MD305162 is close in vintage but I can't find the details of what it's from but it's not a US DSM ECU.

Yeah, I have only found info about this ECU in a Brazillian listing, that says it is for a 200hp 2.0 Eclipse GST. AFAIK, all Eclipses here in Brazil were imported from the US, so I'm not sure where this ECU came from.

Do you know if the difference between the same connector ECUs is hardware, or its just the EPROM content? Maybe I could just take the EPROM from the non working MD309947 and install in the MD305162, but i don't want to end up with no working ECUs to drive...

Is it worth contacting Mitsubishi?

Thanks!

 

[steve]

Can you take pictures of the circuit boards of both ECUs? Since I've never seen a MD305162 it's hard to say anything about it.

 

[Lintu]

Can you take pictures of the circuit boards of both ECUs? Since I've never seen a MD305162 it's hard to say anything about it.

Sure! Here they are. they seem identical.

309947 has several jumpers, that were soldered by me, as im trying to bring it back to life. No luck so far ( CEL wont go out with this ecu, also engine wont start. )

305162 was also fixed in the past, as i see replaced caps and repaired traces.

thanks!

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[steve]

They are both based on the same PCB JE331B677C but there are minor differences that I can see (like missing transistors) and then there is the software, neither ECU Has an original EPROM. Do you have a way to read them and compare the differences. Do you need a copy of the stock EPROM binary?

 

[Lintu]

They are both based on the same PCB JE331B677C but there are minor differences that I can see (like missing transistors) and then there is the software, neither ECU Has an original EPROM. Do you have a way to read them and compare the differences. Do you need a copy of the stock EPROM binary?

Hello! Yeah, in the photo i was still missing 2 transistors, i already added them ( they fell from the boards corrosion ).

I have tested the "good" ecu 305162 with the eprom from 309947, but it did not work, as soon as i put the key in and turn without starting the engine, i can hear pumps working already etc, so i did not insist in this test.

I am still unsure on how to interface with the ECU, given It is not ecmlink, and i currently only have OBD2 readers, and those wont work.

Whats my best shot in communicating with this ECU?

Well, If you could share the original eprom file, I have some 27c512 ics that I could maybe flash to and test.

Thanks!

 

[steve]

Well, If you could share the original eprom file, I have some 27c512 ics that I could maybe flash to and test.

This is the last version of the EPROM software from the 1995 2G ECU's.
If you do read in your EPROMS chips I'd be interested in looking at the binary files.

 

[Lintu]

This is the last version of the EPROM software from the 1995 2G ECU's.
If you do read in your EPROMS chips I'd be interested in looking at the binary files.

Hey Steve, Thanks a lot for the file!

Ill get my old eprom reader/programmer kit from my folks house this weekend and will try to read both EPROMs, i will surely share the files once I read them.

In the meanwhile, im thinking about how to read the sensors from the car through the "obd" port.

it is the classic 16 pin trapezoidal connector, and the "jumping pin 1 to gnd" trick works to read fault codes through the CEL ( thats how i got codes 12, 13 and 25), which indicates that it is in OBD1 mode, which is weird for a 95 gst 2g. Dont know if it means any difference, but it is actually a 1994 2G gst, 1995 model.

In brazil, it is difficult to find ecmlink eproms and cables to use, and importing them tend to skyrocket the price because of taxes (more or less 10 times the USD price), so im wondering if i could somehow build my own interface to just read live plain Hex code from the ecu and work my way through converting this to actual sensor values, but, to be honest, im kinda lost on what protocol it actually uses, so that I can interface with it...

Any thoughts?

Thanks a lot for your kind help!

 

[Lintu]

This is the last version of the EPROM software from the 1995 2G ECU's.
If you do read in your EPROMS chips I'd be interested in looking at the binary files.

Hello, Steve.

I was able to successfully program a new 27c512 memory with the original firmware you`ve shared, installed it in the 305162 ECU and the car fired right away! Also, now my OBD2 interface is working!!! I was able to read all the sensors and errors for the first time!!

I drove it for a while, and got a CEL regarding O2 sensor ( error P0135 ) - Heated Oxygen Sensor (HO2S) 1, bank 1, heater control - circuit malfunction. Cleared it, drove again, and it came up again.

This should explain why it runs very rich, and struggles to start, but I already noticed almost no white smoke out of the exhaust.

THANKS a lot, now I can at least understand what is going on with the ECU, and I`m sure it is running the firmware it is supposed to run!

I was also able to dump the Binary file from the chip that was installed, please find it in the link below:

MD305162.BIN

1 file sent via WeTransfer, the simplest way to send your files around the world

we.tl

I will also try to dump the binary from the dead 309947 ECU, and will share tomorrow!

Cheers!

 

[Lintu]

Hello!

Now that my OBD is finally working, I was able to move forward with the investigation.

1 – Throttle issue

The throttle reading in OBD was only going up to 65% with the pedal fully pressed. When I moved the throttle directly in the engine bay, it went from 0 to 100% normally. The cable was loose, and the adjustment was already at its limit — so I think the throttle cable is probably not the original one.

I managed to place a nut behind the end of the cable where it connects to the pedal, tightening it, and now I can get a full throttle reading by pressing the pedal all the way down. The performance difference after driving the car was huge!

2 – O2 Sensor (P0135) still triggering CEL

The O2 sensor error P0135 is still showing up as a CEL. I checked the connector from the sensor to the harness, and the female connector had been cut off and replaced. The wire colors before and after the electrical tape are different, so it might be wired incorrectly.

When I remove the sensor, the value read by the ECU changes (with the sensor plugged in, the reading stays at 0V all the time; without the sensor, the reading stays at 0.2V all the time).

The cable coming from the ECU has 4 wires: Yellow, White, Red, and Black.

I couldn’t understand from the service manual what each color corresponds to, so that's something I still need to study.

If you have any advice, feel free to share!

Thanks!

 

[steve]

I believe P0135 is a problem with the heater circuit of the oxygen sensor for Bank 1, Sensor 1, the front sensor.

As you note the factory harness has 4 wires, Yellow, White, Red, and Black.
Pin 1 Red +12v for the heater
Pin 2 Black Sensor ground
Pin 3 Yellow ECU switched Ground for the heater
Pin 4 White O2 Sensor output

The white wire has a metal braid shield that is also grounded to chassis.

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[Lintu]

I believe P0135 is a problem with the heater circuit of the oxygen sensor for Bank 1, Sensor 1, the front sensor.

As you note the factory harness has 4 wires, Yellow, White, Red, and Black.
Pin 1 Red +12v for the heater
Pin 2 Black Sensor ground
Pin 3 Yellow ECU switched Ground for the heater
Pin 4 White O2 Sensor output

The white wire has a metal braid shield that is also grounded to chassis.

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Hello!

Thanks a lot for the info.

I was able to pinpoint the problem to the sensor itself. I replaced it with a new one and the CEL is now gone. Idle still felt a little "rythmic", so I took the spark plugs out and noticed that I have 2 different P/Ns spark plugs mixed... So tomorrow I will buy a kit and replace them ( and the spark plug cables as well ).

I took her for a drive and she feels very healthy!

Exhaust still smells a little like raw fuel, but the pipes are now warming up (they were dead cold before).

I will change the spark plugs and cables and report back!

Thanks for your help guys!

This forum is awesome!