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Discussion Starter #1
Hi everyone,

I'm trying to troubleshoot an issue with my car. Any help or input would be appreciated. I'm working on my 1997 VR4. It's BPU, with 550cc injectors and an SAFCII with a tune, in addition to a handful of other mods in support of a possible future turbo upgrade.

Right now, I have a rough idle and some misfire under light throttle at lower RPMs. At WOT, or at light-mid throttle at higher RPMs, no issues, she pulls like a champ. Gas mileage is poor. If I baby her around, I think I can get 300 miles per tank.

I'm working my way through the spark, fuel, and timing potential issues, and taking into consideration repairing any boost leaks. Pretty sure she's running rich.

I also, however, have Evoscan and a cable. I logged a couple rides around the neighborhood with a short pull or two (gonna try and post link in next post), and I noticed my O2sensor2 is flatlined at zero. I found other members that have posted logs and their O2sensor2 column has values. I'm assuming my O2 sensor is bad, but was wondering if anyone could check this log and confirm? I'm not exactly sure what I should be looking for. 0V on O2 sensor is lean, so system is throwing extra fuel? At higher RPMs and throttle, it's not as much of an issue? Not sure. No CEL for O2 sensor. Also, is O2sensor2 the primary rear O2 sensor?

Thanks,
Steve
 

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Discussion Starter #3
I think I solved the issue. A few hours of searching turned up this thread: O2 sensor requestID in EvoScan 94-95 hybrid The default Evoscan o2sensor2 address is incorrect. You need to change the address from 3C to 3E to get the correct value for the front bank primary O2 sensor (labeled #2 in Evoscan).

This is normal....because Hamish used the wrong request ID. He seemed to spend a lot of time creating a slick interface that worked with the Evos, and then just hoped it would work on other Mitsubishis. For $25, I'm not going to complain too loudly ;)

Anyway, here's what you need to do to fix it. Go to the Logging menu, and chose Edit Data Item List.

Scroll down to oxygen sensor, and click on it. On the right hand side of the screen, and in the "display" field rename it to O2 Sensor-Rear.

Now click on Oxygen Sensor #2. Rename that one to O2 Sensor-Front, and in the box for Request ID, change that from 3C to 3E.

Click ok, and go try logging it. They should both work now.

This should be the same for a 1G car, but I haven't been able to test it yet.
So I switched the ID, hopped back out to my car, and found my front O2 sensor limped between 0.03 to 0.1V at idle, while the other one switches between rich and lean. Giving it a little throttle, the sensor reads rich. So, it's apparently on its way out, but not dead yet, so no CEL.

I'll update after I get a new one installed.

-Steve
 

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Did you try actually driving around once you got the correct sensor reading? Also was the car warm? If the sensor was responding when you revved it, it might not be going out, but i guess its a fairly cheap test to rule that out.

That said, they should both be cycling at warm idle, and light cruise (low load) situations, once the car is warmed up.

Do you have a wideband O2? Also how old are your injectors?
 

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Discussion Starter #5 (Edited)
Did you try actually driving around once you got the correct sensor reading? Also was the car warm? If the sensor was responding when you revved it, it might not be going out, but i guess its a fairly cheap test to rule that out.

That said, they should both be cycling at warm idle, and light cruise (low load) situations, once the car is warmed up.

Do you have a wideband O2? Also how old are your injectors?
I didn't try driving once I was logging the sensor reading. But you make a good point, and once it's warmed up it might be switching, so I will check that out today.

I do not have a wideband. Injectors are 10+ years old, and the car has sat for extended periods a few times (school). Is Ohm testing the injectors even worth it, or should I just pull them off and flow test?

Thanks for the input.


It also looks like we have pretty similar mods. Have you ever tracked your car? How do you like the Gt-347s?


EDIT: Drove around with the car warmed up and logged the data, O2 is definitely on the fritz.
 

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Sounds like a new O2 is in order then. I got my rear O2 from RockAuto a year or two ago and it worked fine. I had a short thread about it - if i recall correctly their listings for front/rear are not always correct, meaning that you could get one with too short/long of a wire (rear needs the longer wire). Let me know if you can't find that.

Regarding the injectors - if it were me, i would pull them off and flow test+clean, especially if you plan to continue doing mods and increasing power. I live local to RC injectors (which is the brand of my 550s). I had fueling/knock issues for years that i could not figure out, because even when i tuned extremely rich, i would still get knock. Turned out my injectors were horribly clogged. Even if they were able to flow fuel, the spray pattern and difference in flow between different injectors was a huge factor in the car not running right. After the flow test/clean, car runs mint. You can read about that here: PSA: How bad are your fuel injectors? Get them cleaned!

NOTE: You will probably need to adjust your SAFC tune after getting them flow tested and cleaned if there is any significant change.

The GT347 were brand new on the car when i bought it in 2007. I daily drove the car until 2018. I never was seeking big XXX HP numbers and liked the responsiveness, so no complaints from me. The engine/turbos have 112k on them (car has 308k) and they are holding up great. I never tracked the car but have done a lot of hard driving in canyons, highway runs, etc. I am now running about E50 mix with ~15-17psi and the car is strong as ever.
 

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Hi everyone,

I'm trying to troubleshoot an issue with my car. Any help or input would be appreciated. I'm working on my 1997 VR4. It's BPU, with 550cc injectors and an SAFCII with a tune, in addition to a handful of other mods in support of a possible future turbo upgrade.

Right now, I have a rough idle and some misfire under light throttle at lower RPMs. At WOT, or at light-mid throttle at higher RPMs, no issues, she pulls like a champ. Gas mileage is poor. If I baby her around, I think I can get 300 miles per tank.

I'm working my way through the spark, fuel, and timing potential issues, and taking into consideration repairing any boost leaks. Pretty sure she's running rich.

I also, however, have Evoscan and a cable. I logged a couple rides around the neighborhood with a short pull or two (gonna try and post link in next post), and I noticed my O2sensor2 is flatlined at zero. I found other members that have posted logs and their O2sensor2 column has values. I'm assuming my O2 sensor is bad, but was wondering if anyone could check this log and confirm? I'm not exactly sure what I should be looking for. 0V on O2 sensor is lean, so system is throwing extra fuel? At higher RPMs and throttle, it's not as much of an issue? Not sure. No CEL for O2 sensor. Also, is O2sensor2 the primary rear O2 sensor?

Thanks,
Steve
I have similar problem on my '94 Vr-4, mostly stock at 166,000 miles. "I have a rough idle and some misfire under light throttle at lower RPMs. At WOT, or at light-mid throttle at higher RPMs, no issues. The problem never occurs on a cold start. It mostly happens on a warm day after I've run the car and park the car between 5 to 120 minutes. When I start the warm engine, I get the rough idle. I replaced the oxygen sensor 3,000 miles ago which did not solve this particular problem (although it did solve the problem of the engine dying at low idle all the time).

What else can I investigate/replace?
 

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Discussion Starter #9
I have similar problem on my '94 Vr-4, mostly stock at 166,000 miles. "I have a rough idle and some misfire under light throttle at lower RPMs. At WOT, or at light-mid throttle at higher RPMs, no issues. The problem never occurs on a cold start. It mostly happens on a warm day after I've run the car and park the car between 5 to 120 minutes. When I start the warm engine, I get the rough idle. I replaced the oxygen sensor 3,000 miles ago which did not solve this particular problem (although it did solve the problem of the engine dying at low idle all the time).

What else can I investigate/replace?
Which oxygen sensor did you replace? Are you Cali-spec? Any chance you have access to a datalogger? You have at least 2 oxygen sensors, so maybe both were bad if you only replaced one?

Three main things you need for your engine to run (with a lot of other things understood to be working) are spark, fuel, and timing. Are your plugs and wires in good shape? Have you checked your fuel system? Voltage to pump, filter is not clogged, injectors?

There are a ton of things that can go wrong, but these are some of the easier, cheaper, and sequentially important things to check.
 

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Which oxygen sensor did you replace? Are you Cali-spec? Any chance you have access to a datalogger? You have at least 2 oxygen sensors, so maybe both were bad if you only replaced one?

Three main things you need for your engine to run (with a lot of other things understood to be working) are spark, fuel, and timing. Are your plugs and wires in good shape? Have you checked your fuel system? Voltage to pump, filter is not clogged, injectors?

There are a ton of things that can go wrong, but these are some of the easier, cheaper, and sequentially important things to check.
Yes, it is a Cali-spec. My mechanic replaced the B1S2 O2 sensor if that means anything. I'll ask him to check the rest of the items.
 

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Discussion Starter #11
B1S2 is bank 1 sensor 2. I think all cali-spec have 4 O2 sensors (2 front, 2 back), but first gen might not. From what I understand, the front banks impact your air-fuel ratio, while the back two are for monitoring your precats. This means you might still have another oxygen sensor that is bad or going bad.

In my current case, one of my front oxygen sensors is stuck toward the bottom of the 0-1V scale, but randomly switches. I assume the ECU sees it switching and so it doesn't throw a code. It is, however, not working correctly. Hopefully when I replace it, it fixes the issue.
 

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B1S2 is bank 1 sensor 2. I think all cali-spec have 4 O2 sensors (2 front, 2 back), but first gen might not. From what I understand, the front banks impact your air-fuel ratio, while the back two are for monitoring your precats. This means you might still have another oxygen sensor that is bad or going bad.

In my current case, one of my front oxygen sensors is stuck toward the bottom of the 0-1V scale, but randomly switches. I assume the ECU sees it switching and so it doesn't throw a code. It is, however, not working correctly. Hopefully when I replace it, it fixes the issue.
This is the correct description of B1S2, however people often confuse or mislabel the O2 sensors they are are describing them. Also, the "banks" refer to either the front or rear of the car, while the sensor # refers to "upstream" (before cats, closer to turbo) or "downstream" (after cats, further from engine). The downstream sensors do not affect engine performance at all. Only the upstream sensors are used by the ECU is closed loop operation to maintain the ideal (~14.7) AFR under warm idle and light cruise (low load conditions). You indicated that there was a noticable difference after replacing the sensor, which makes me think it was an upstream sensor, not a downstream. I would clarify with your mechanic which was replaced.

Does the issue go away shortly after the warm start (i.e., after say 30 sec)? If it is only temporary on a warm start, it could be the fuel solenoid on the firewall that increases fuel pressor on hot starts. I had to bypass mine because it can cause flooding with aftermarket injectors.
 

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Followup to my situation:

Front O2 proved to be tough to remove. I had a clear path from the bottom, but ended up having to remove the radiator, cut the sensor off, and fit a socket over it. No change in idle, maybe a slight change in MPG.

Still working through spark and fuel checklist.. swapped front 3 wires, no difference. 100 miles into my last CEL reset.. P0306!!! Thinking it's old wires, i swap them... and whiiiiiile it's open, lemme just pull a plug (<1000mi on new plugs).

286302


Plug 6.. everything else looks perfect. I'm guessing when my CAS went bad, detonation or timing caused this?

Putting new plugs in tonight. More updates once more progress is made.

Anyone seen this before?
 

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O2 sensor sockets are only like 5-10$ and prevent you from having to cut the wires to remove (and makes it easier to install) :) I got mine from RockAuto when i ordered my sensor.

Anyways, assuming you didnt put the plug in that way, i suppose it could have been knock/detonation, but it would have to be pretty bad... Then, once the gap closed, it fouled. You should have definitely been able to tell if the car was down a cylinder. If you pull the wires one at a time you can usually narrow down cylinder-specific issues also.
 

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......., detonation or timing caused this?........Anyone seen this before?
Timing can’t do that and can’t imagine how detonation could since pressure would be equal top and bottom of plug ground strap. That either had to occur during installation or hit by something in cylinder. Any sign of impact of ground strap?
 

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I have read on various other forums that detonation can cause that to happen. During detonation the pressure is not uniform in the cylinder.
 

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Discussion Starter #17
New plug in, and she's idling like she's young again. Will take her for a cruise tomorrow, but I am assuming I fixed the issue.

O2 sensor sockets are only like 5-10$ and prevent you from having to cut the wires to remove (and makes it easier to install) :) I got mine from RockAuto when i ordered my sensor.

Anyways, assuming you didnt put the plug in that way, i suppose it could have been knock/detonation, but it would have to be pretty bad... Then, once the gap closed, it fouled. You should have definitely been able to tell if the car was down a cylinder. If you pull the wires one at a time you can usually narrow down cylinder-specific issues also.
My O2 sensor socket wouldn't fit past the AC compressor. PITA dude.. i tried 3 different deep sockets (after an open and line wrench) before i realized I was wasting my time, went and got a sawzall, and cut that sucker up. Literally cut the sensor in half right behind the threads. Came off easy, but what a pain omg.

I obviously didn't put the plug in that way so....

I pulled wires 1 by 1 to test if spark could be the issue,, but 3 or so of them didn't change the idle. I knew it couldn't be that many cylinders giving issues, so that's when I found the bad O2 sensor.

Had to circle back around to find this egregious plug after fixing the O2 sensor didn't solve my problem.

I'm almost finished with everything EXCEPT.. i snapped a bolt on my throttle cable bracket (there was only 1), then found that the previous owner (100k+ miles ago) snapped the other one. I tested everything with a pair of vice grips in place, but will prob just helicoil the holes and be done with it. ABQ DRAGWAY here i comeeeeeeeeeeeeee.






PSS

Timing can’t do that and can’t imagine how detonation could since pressure would be equal top and bottom of plug ground strap. That either had to occur during installation or hit by something in cylinder. Any sign of impact of ground strap?
I have read on various other forums that detonation can cause that to happen. During detonation the pressure is not uniform in the cylinder.
Yes - a google search for "spark plug bent closed" lead me to the answer that detonation can cause this. It's not in this post, but my CAS failed and that seems like the only possible time this could have happened.

THANKS AGAIN EVERYONE FOR INPUT!!!!
 
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