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1995 Mitsubishi 3000GT VR-4
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141 Posts
Discussion Starter · #21 ·
Yeah I was going to stick with the damper because it will be my daily driver. 212,000 miles on the original engine makes me want to be kind to the crank.

But $120 for an aluminum that will never fail and add a blip of power, vs. $70 for an aftermarket damped pulley or $300 for OEM!! ...what did I just say about learning a lesson on skimping on parts??
 

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1991 VR4
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Damn just saw that on 3sx... and the fact that 91 OEMs are discontinued. Hope mine lasts for a while.

Maybe check other vendors like Cherry Hill Mitsubishi (i think thats the one) Ninja performance (could be a long wait), etc. There was recently a thread of someone asking about current vendors.
 

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1995 Mitsubishi 3000GT VR-4
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Discussion Starter · #24 ·
I finally had time to reset my FWD bank exhaust cam and install my OEM crank pulley from 3SX. Had to get a little help from the 3D printer to hold the eccentric pulley in place, as I didn't have clearance for my 1/4 drive ratchet and a torque wrench for setting the eccentric pulley and I couldn't find a 1/4 drive breaker bar anywhere locally.



It's good to have the car back on the road, but there are still some issues...

After doing a lot of reading, I'm afraid my car is now one of the many with "rough idle / low power between 2200 and 3000 rpm / hesitation at low rpm" type of issues. Unfortunately not a lot of those threads lead to a conclusive solution.

I have a Chrome ECU, but I'm very uninformed on how to properly datalog. I figure logging, checking, and clearing codes is safe for me to mess with, but I’m not yet confident enough to adjust and flash anything (much more reading to do). Anyway I followed the install readme and have managed to get it far along enough to read and clear codes. I'm getting a repeatable CEL for intake air temperature sensor circuit. I can clear it, and the car seems to run better for a little, but after two or three runs the CEL returns for the intake air temp. and I’m back to really crappy performance.

I logged a few runs and can confirm that my air temp appears to be way off (-50 to -28C on the file attached here). I was really happy about this because I figured that I’ve finally found the culprit. I picked up a remanufactured unit for ~$150 from Advance Auto and proceeded with the install.

While I had both sensors out of the car I decided to test the temperature sensor to see if I could confirm the bad unit. To my disappointment, my original MAF showed the exact same temperature response as the remanufactured part I was going to put in. I was able to take both sensors consistently from ambient resistance (~1.7kOhm at 83F) down to the book specified value of 0.4kOhm at 176F. I cycled each MAF about four or five times and they both appear to respond exactly the same.

Per the book, I also confirmed proper ground and power at the harness for pins 5 and 6. There was a small piece of a leaf that had blocked a few of the honeycomb channels on my original MAF (like 2-3 channels in the six o’clock port). I figured it was a long shot, but before breaking the seal on the $150 part I decided to remove the block and reinstall my original MAF. There was no change however. I had poor response at part-throttle below ~3000rpm. I logged the run which can be found here:
https://drive.google.com/open?id=1bN_8o6UnHAy3jFvVr2-dE_W7VwRe6Vh9

Any suggestions on what to look for? The sensor appears correct when read directly, but the ECU clearly isn’t getting something.

Is it worth installing the remanufactured MAF that I bought to see if that fixes things? There’s a good chance Advance Auto doesn’t accept the return once it’s been used (that’s their policy on sensors anyway).

Some notes on the file:
- I never changed the default injector size in EvoScan, which I think is 500-something (stock should be 360?), so I don’t know if that will cause improper logging of the injector-related parameters.
- I added Fahrenheit columns to coolant and air temp. My coolant reached as high as 215F, but the gage never spiked on me –not sure if that’s normal.
- I left all the default fields checked for logging –I’m not sure if this is too much to log at once over the ODBII port.
- The CEL was not on during this run, but it returned the following morning on my way into work (the next time I drove the car).

I have not yet pieced together my boost leak testing tool (I’m getting there Coop :) ). Perhaps that’s where I’ll start tonight before risking installing the reman’ed MAF. Is it possible that a boost leak would hose up the intake temp reading?

I have replaced the ISC with a new unit (Doorman or AC Delco maybe), but I have not yet gone through the throttle body systems checklist on the Wiki, as I figured it would be a waste until I get the intake temp sorted out. Right now I'm attributing the poor idle to something there that needs adjusting or maybe a boost leak too.

Only other thing I can think of that might be pertinent is that I do have some sort of a grounding issue that I haven’t chased down yet either. I say that because I get a slight dimming of the “Touring” “Check Engine” and “ABS” light that are on when hitting the brakes or while a turn signal is blinking. I only get to work on the car a few hours here and there, so I haven't considered that as high of a priority at this point. Although perhaps I should, given the odd behavior I’m seeing with the MAF.

Appreciate any suggestions!
-Andy
 

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3SNY - HondaTurtleFTW
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I'd say look for grounding issue. Can affect sensors by having a backfeed ti ground

Sent from my SM-G955U using Tapatalk
 

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Color: Arrest Me Red
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Sounds like you have a wire issue.
Check continuity from the maf plug to the ecu.
If you have an issues with the ecu please let m eknow I can help you check it out.
 

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Premium Member
1995 Mitsubishi 3000GT VR-4
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141 Posts
Discussion Starter · #27 ·
Thanks, I'll check the MAF continuity first and see if I can find any breaks. I know the shielding to my front O2 sensor is in pretty bad shape. I see conflicting recommendations on here about whether the shielding is supposed to be grounded at the sensor/connector end here, or at the ECU end, or both.



In any event, I haven't read up enough on reading the datalogs on how to interpret the different O2-related fields, so I don't know if this is hurting me or not.

Am I okay to let EvoScan capture everything on a given run through the Tatrix cable? Or do I need to limit it to a handful of parameters each run?
 

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3SNY - HondaTurtleFTW
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O2s should cycle voltage. don't remember precise numbers(I think .1 to 1v, but don't hold me to that) but it should cycle. if not, it's a bad sensor or bad wiring, iirc.

Sent from my SM-G955U using Tapatalk
 

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Great introduction! Loved the classic pictures! The whole thing reminds me so much of my family... I was just extraordinarily lucky when i spun my VR4 as a stupid teen.

I would return the remanned MAF unless it was extremely cheap.

If your factory MAF is actually bad (sounds like it's ok so far), i would upgrade to the Chromed Jester MAF <img src="http://www.3si.org/forum/images/smilies/new/evil2.gif" border="0" alt="" title="evil2" class="inlineimg" />
 

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Premium Member
1995 Mitsubishi 3000GT VR-4
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141 Posts
Discussion Starter · #30 ·
Great introduction! Loved the classic pictures! The whole thing reminds me so much of my family... I was just extraordinarily lucky when i spun my VR4 as a stupid teen.

I would return the remanned MAF unless it was extremely cheap.

If your factory MAF is actually bad (sounds like it's ok so far), i would upgrade to the Chromed Jester MAF <img src="http://www.3si.org/forum/images/smilies/new/evil2.gif" border="0" alt="" title="evil2" class="inlineimg" />
Thanks Adam, yeah there's quite a history here that I'd like to preserve.

It seems like there's a consensus that I've got a wiring issue, so I'll be returning the MAF while I continue to troubleshoot. Maybe the Jester MAF sometime down the road. If I can get it all back to square soon, I think the next things should be a wideband and then LCDBC. But I don't want to introduce any new variables into the equation just yet.
 

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1995 Mitsubishi 3000GT VR-4
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Discussion Starter · #31 ·
O2s should cycle voltage. don't remember precise numbers(I think .1 to 1v, but don't hold me to that) but it should cycle. if not, it's a bad sensor or bad wiring, iirc.

Sent from my SM-G955U using Tapatalk
If FP_O2Sensor and RP_O2Sensor are the correct fields, then it appears as though mine are cycling, and the front and rear bank look to be pretty well in sync. However my max value when floored (which is only measuring 96 on TPS) seems to be ~0.89V, and there's plenty of instances at or near idle where they both go to flat 0.0V. So I don't know if those are correct.

It's probably all suspect until I sort out the grounding issue and confirm I've got no leaks.
 

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If FP_O2Sensor and RP_O2Sensor are the correct fields, then it appears as though mine are cycling, and the front and rear bank look to be pretty well in sync. However my max value when floored (which is only measuring 96 on TPS) seems to be ~0.89V, and there's plenty of instances at or near idle where they both go to flat 0.0V. So I don't know if those are correct.

It's probably all suspect until I sort out the grounding issue and confirm I've got no leaks.
Below 3000rpm (depending on load/TPS) you will be in closed loop. Above that you will be in open loop, at which point O2 sensor are disregarded and the car runs off the fuel tables. I’m not 100% sure if the ECU still uses MAF temperature in open loop, but it sounds like your car doesn’t have the poor running issue once you enter into open loop.

As far as the stock temperature gauge, I have seen several posts recently where people were logging temperatures from the ECU in the normal range (185-210F) while the stock gauge was reading as high as the red zone on the top. I would trust the ECU temps not the gauge unless you have reason to believe otherwise. The other day I saw 212F on my log and my stock gauge was between 1/3 and 1/2 the way up, so your seems fine.

In terms of logging Im not familiar with the chrome specifically but the problem I saw with torque was that including too many sensors (PIDs) in the log will slow down the refresh rate, so you will get many duplicate values depending on the frequency you have data written into the file. For diagnosing problems it can be useful to output a lot of different sensors but eliminating unnecessary/duplicate things will make it much easier to read the logs and may also increase your “resolution” (right now it looks like you are about 0.5-0.6sec, which is OK for diagnosing maybe but not fast enough to see quick changes).

Your primary O2 sensors seem OK to me. I recently spent a lot of time trying to figure out bad o2 sensor/bad wiring through datalogs. The voltage does go from 0V (max lean) to 1v (max rich). As mentioned they cycle when the ECU is in closed loop mode, generally below 3000pm, to try and achieve the target 14.7 AFR. Under WOT you should be much closer to 1V because you are in open loop running off the fuel tables probably in a 10.5-11.5 AFR range. So your logs line up with expected behavior. As far as being near 0.00V at idle, thats either because you have a vacuum leak or a very lean idle tune. My car has a very lean idle tune, between 16.0-18.0 AFR at idle depending on temperature, and that causes my O2s to read essentially 0v). A vacuum leak after the MAF will cause the same thing because you are letting in unmetered air, making the car run leaner than it otherwise should. Technically the car should be using closed loop at (warm) idle to try and achieve that 14.7 AFR, but it seems like yours is not if the O2 are not cycling at warm idle and are reading near 0V and not moving.

It does sound like you have a wiring problem. Based on your bench test of the unit, it seems like a greater resistance would signal a colder temperature. If there is an extremely high resistance or open circuit there would that cause the very low temperature readings you are seeing? There is also a small chance it is the ECU itself. I know you have a chrome, so that is very unlikely, but generally speaking the ECU becomes suspect when you get MAF codes (usually along with some other ones at the same time) and start to get intermittent poor running, hard start, etc.
 

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Sad that I missed this. What an excellent thread. I love seeing some deep 3/S history/Love like that even if the circumstances are not always good.

Subscribed.
 

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1995 Mitsubishi 3000GT VR-4
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Discussion Starter · #34 ·
Below 3000rpm (depending on load/TPS) you will be in closed loop. Above that you will be in open loop, at which point O2 sensor are disregarded and the car runs off the fuel tables. I’m not 100% sure if the ECU still uses MAF temperature in open loop, but it sounds like your car doesn’t have the poor running issue once you enter into open loop.

As far as the stock temperature gauge, I have seen several posts recently where people were logging temperatures from the ECU in the normal range (185-210F) while the stock gauge was reading as high as the red zone on the top. I would trust the ECU temps not the gauge unless you have reason to believe otherwise. The other day I saw 212F on my log and my stock gauge was between 1/3 and 1/2 the way up, so your seems fine.

In terms of logging Im not familiar with the chrome specifically but the problem I saw with torque was that including too many sensors (PIDs) in the log will slow down the refresh rate, so you will get many duplicate values depending on the frequency you have data written into the file. For diagnosing problems it can be useful to output a lot of different sensors but eliminating unnecessary/duplicate things will make it much easier to read the logs and may also increase your “resolution” (right now it looks like you are about 0.5-0.6sec, which is OK for diagnosing maybe but not fast enough to see quick changes).

Your primary O2 sensors seem OK to me. I recently spent a lot of time trying to figure out bad o2 sensor/bad wiring through datalogs. The voltage does go from 0V (max lean) to 1v (max rich). As mentioned they cycle when the ECU is in closed loop mode, generally below 3000pm, to try and achieve the target 14.7 AFR. Under WOT you should be much closer to 1V because you are in open loop running off the fuel tables probably in a 10.5-11.5 AFR range. So your logs line up with expected behavior. As far as being near 0.00V at idle, thats either because you have a vacuum leak or a very lean idle tune. My car has a very lean idle tune, between 16.0-18.0 AFR at idle depending on temperature, and that causes my O2s to read essentially 0v). A vacuum leak after the MAF will cause the same thing because you are letting in unmetered air, making the car run leaner than it otherwise should. Technically the car should be using closed loop at (warm) idle to try and achieve that 14.7 AFR, but it seems like yours is not if the O2 are not cycling at warm idle and are reading near 0V and not moving.

It does sound like you have a wiring problem. Based on your bench test of the unit, it seems like a greater resistance would signal a colder temperature. If there is an extremely high resistance or open circuit there would that cause the very low temperature readings you are seeing? There is also a small chance it is the ECU itself. I know you have a chrome, so that is very unlikely, but generally speaking the ECU becomes suspect when you get MAF codes (usually along with some other ones at the same time) and start to get intermittent poor running, hard start, etc.
jrhorne: thanks for going through all that! I didn't know what the max temp limit was, other than red on the gage, but I knew low 200s had to be getting close. I wasn't aware of the 3000rpm threshold for opened/closed loop either; good to know that mine appear to be reporting normally (at least for the time being). Per this and Jester's comments, I'm going to make checking the MAF wires and looking for boost leaks my number one priority. Unfortunately tonight all I had time for was an oil change, so I'll have to get cracking on it tomorrow. Aside from the unsatisfying feeling in the right-most pedal and shitty mileage, do you all think there's any harm in continuing to drive it while I work these issues out? The engine seems to be pretty good at protecting itself, and even in it's crippled state it's still a blast to drive.


Sad that I missed this. What an excellent thread. I love seeing some deep 3/S history/Love like that even if the circumstances are not always good.

Subscribed.
Thanks Warzone. I suppose I'm getting a bit off-topic of my own thread, but at this point I think I'll continue it until I get the car back to stock performance. Then maybe start a build thread :)
 

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jrhorne: thanks for going through all that! I didn't know what the max temp limit was, other than red on the gage, but I knew low 200s had to be getting close. I wasn't aware of the 3000rpm threshold for opened/closed loop either; good to know that mine appear to be reporting normally (at least for the time being). Per this and Jester's comments, I'm going to make checking the MAF wires and looking for boost leaks my number one priority. Unfortunately tonight all I had time for was an oil change, so I'll have to get cracking on it tomorrow. Aside from the unsatisfying feeling in the right-most pedal and shitty mileage, do you all think there's any harm in continuing to drive it while I work these issues out? The engine seems to be pretty good at protecting itself, and even in it's crippled state it's still a blast to drive.
just to clarify a few things:

210F is not necessarily a max "safe" temperature. This is just about the upper limit for where the 2nd fan (AC one with AC off) kicks in. So you shouldnt really see temps much above that if your cooling system is working properly and you arent getting heat soaked. I'm not 100% sure what is generally regarded as a maximum safe temp for these cars. I would be worried if I saw anything above 215-220F for sure though.



Also the 3000rpm cutoff of closed to open loop should be regarded as a rule of tumb. you CAN get closed loop above that but you have to be very low throttle (like 10% absolute, which is probably like 20% or less in logs). You can also get open loop below 3000, but you have to be very high throttle/load. There was someone who did extensive testing based on logs and 3000 was just the general cutoff for most conditions. This seemed to agree with what i have seen from my own logs and from me actively monitoring torque for the past several weeks of driving.

There's probably no harm in driving in but i didnt dive that deep into your logs because there were way too many sensors in there lol. I did see a few spots with really high knock, so maybe avoid WOT pulls. I don't think you can do much damage cruising around especially if your O2s are cycling keeping your AFR in check.
 

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1995 Mitsubishi 3000GT VR-4
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Discussion Starter · #36 · (Edited)
So I crack open the manuals to start mapping out my MAF harness pins back to their corresponding pins on the ECM so that I can check them for continuity. It looks like there is a discrepancy between the two volumes.

For example the circuit diagram on the left shows MAF pin 6 going to ECM pin 72, but the MFI inspection section on the right shows MAF pin 6 going to ECM pin 52.



What am I missing? I'm inclined to believe the circuit diagram in volume II is correct. Is the inspection method in volume I showing something other than the terminal numbers in it's diagram?

**CORRECTION**
Wanted to correct this so there wasn't any bad info. out there. I was looking in the wrong section. My '95 FED VR-4 MAF Intake Air Temp Sensor test is on page 13A-215. Those pin numbers align with my circuit diagram. This also jives with Jester's response below: ECM pin 72 is intake air temp. sensor for my car.

 

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My car is a money pit
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As far as the stock temperature gauge... I would trust the ECU temps
Here's my car to his point. Must be corrosion in the wiring somewhere, idk.
https://youtu.be/HUPtta9adww

In terms of logging... including too many sensors (PIDs) in the log will slow down the refresh rate...
This is accurate too.

Great thread. Love how good your posts are!

Edits: Other Notes

TPS will not be 0 -100. I think mine is 12% - 97%... so don't be worried about that.

Max safe temp for coolant is keeping it below boiling, but more importantly, letting the engine come down in temperature evenly so you don't warp the heads. Iron and Aluminum cool at different rates. Coolant at 15psi (radiator cap) doesn't boil till 250+ so keep it below that. Here's a link to show some more info: https://durathermfluids.com/pdf/techpapers/pressure-boiling-point.pdf

Lastly, I can't make heads or tails as to why the two pins are listed differently... but according to our bible (if you don't know about Stealth316, you should check it out... everything in there!) the ECU pinouts for 91-97 all say pin 52, while 99's say pin 62 is for IAT.

http://www.stealth316.com/2-ecu-terminals.htm

Hope some of that helps
 

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Thanks Adam, yeah there's quite a history here that I'd like to preserve.

It seems like there's a consensus that I've got a wiring issue, so I'll be returning the MAF while I continue to troubleshoot. Maybe the Jester MAF sometime down the road. If I can get it all back to square soon, I think the next things should be a wideband and then LCDBC. But I don't want to introduce any new variables into the equation just yet.
Great intro. Check all your tail light sockets for ground. I had similar problems with my 97 SL when I first got it. Turn the lights on with CC engaged would disable it, inside lights would flicker. Took it to a family run Auto-electric shop, the dad ran it down in 10 minutes. The ground wire is embedded in the base of the socket. He played around with it trying to take it out but no dice. Some how he got it to ground so it's OK for now. We put dielectric grease on it after cleaning up the crud. Works great for now but I need to look at replacing it. Had about the same problem with my 97 VR4, cleaned up the sockets, put Dielectric grease, no more problem. Hope this helps.
 

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This is accurate too.

Great thread. Love how good your posts are!

TPS will not be 0 -100. I think mine is 12% - 97%... so don't be worried about that.
Good to know my endless hours of reading on here are producing accurate posts lol :)

And yeah, in a log from ECU TPS should never be below 10%. Mine is 14.5-98.5% in torque. BlackStealth said that if the ECU sees anything below 10% it will throw a CEL.

Note that this differs from something like a SAFC II which is calibrated to read 0-100%.
 

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Color: Arrest Me Red
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for a 95 vr4 ecu pin 72 is air temp. ecu pin 52 is ignition timing adjustment terminal
 
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