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2G GHS GSX Shop Project- Tuning/Idle Help

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gijoe985

15+ Year Contributor
562
20
Dec 13, 2007
Grandview, Washington
Hello all,

We wanted to start a new thread for our high school shop project that has been sitting for the last half year. You can see our old threads here and here.

We have the car turning on now. We've got our timing correct and we have good compression on all cylinders now. Today when we turned the engine on it ran smoothly, but at 1600rpms. It ran well for a couple minutes, but then began to have some hiccups here and there. Eventually the idle lowered some and the idle became rough and then it just died. We tried restarting it and it idled ok and then again eventually died. Wideband originally showed us right around 14. The last time we ran it it was idling at 15:1.

We did a boost leak test and thought things looked ok. Though the psi gauge we had (attached to air gun) may not have been working well. How long does it take to pressurize the system normally? We were pumping in 50psi for 10 seconds or so and that seemed like overkill. It would hold some pressure, but again, I'm not questioning how well that gauge is reading. Sadly maintenance just came to service our compressor, so we may not have air for a few days. But we didn't hear any leaks when we pressurized it as high as we felt comfortable.

I know that the BISS will need to get adjusted, but I was waiting until it seemed to be running better.

Thoughts?
 
I personally use the link voltage value for 0 volts at idle for the TPS adjustment then if I have to vary something, it is the 100%, 5 volt reading in Link. The car is wanting to see 0 volts and 0% at idle and the idle switch is built into the 2g TPS. The ECU is depending on that value. The top end value is sometimes not quite 5, maybe 4.96, but can be adjusted.
 
So, call me crazy, but I stuck the .18 feeler gauge in, and then I set it to .63V, Which gave me like .57v with the feeler gauge removed. Now, I checked it a few times, all was good, but then after starting it, it went up to about .69v when off the throttle. That said, it was trying to idle at around 1100, which is what I currently have link set at. (I figured shoot high until things get hammered out, then go lower.)

So, it still doesn't seem to be running great. I need to figure that out.

I was encouraged to see someone post a video and dyno sheet of 508hp with an almost identical build to ours. He just had larger injectors and a 1g TB. Otherwise very similar. 30psi...

Here is the newest log. I'm going to figure out why the TPS changed...
 

Attachments

  • log.2019.03.27-01.elg
    26.7 KB · Views: 78
Joe did you ever tear the throttle body down and rebuild it? I am wondering if the springs were wound back correctly on it. If you take your hand and physically close the throttle all the way, does the reading for the TPS go back to what you started with? Those 2 coiled springs can be tricky if you don't know how to mark them and get them wound back how they are supposed to be. We use a magic marker before the tear down and mark a straight line across both springs then I tie them together with a zip tie or some string or a bread tie. Just throwing that out there to check off is all.
Looked at the log, the narrow band is cycling and as it shows lean, the ECU will throw fuel at it then when it reads rich the ECU will cut fuel so I bet that thing is surging some, isn't it?
 
The TB is definitely closing all the way. We didn't mark the springs, but I felt pretty confident when we put it back together. And FWIW we had this problem even before we removed the TB. But we did fully tear it down.

So, spring break is here. I'll be gone for 1.5 weeks. Hopefully we'll make more progress when we get back (don't leave us!)

The last time I ran it, it was very rough. So, we shall see.

We had a 3000gt VR4 that had us stumped for over a year and it ended up being a loose knock sensor... So, I'm excited to find out what oddball issue the dsm has. ;)
 
Maybe the TPS is damaged internally and that's why the value is jumping around? I also recommend re-checking the springs on the TB, they're kind of a pain to get right the first time.

At least there is a little progress otherwise and we're seeing some change!
 
If you need a 2g knock sensor Joe, I just posted a link that had 10 left. They are very hard to find. I don't think it is your problem but you might want to look at that one and see. Here is the link and I posted for all to see also.....
https://www.amazon.com/s?k=ks32+knock+sensor&i=automotive&ref=nb_sb_noss

Have a nice spring break and we won't leave you!
 
Well, the day isn't over...

What would be the sign that the springs were not on correctly? Like I said, the throttle plate opens and closes properly. As far as I can tell. They were on there pretty tight.

Also, we still haven't tried the 540s... Might want to do that and just see..
 
You shouldn't have to change anything other than that Joe. If V2 allows for "deadtime" on the injector scaling, you may have to play with that number a little to get Short Term Fuel Trims to within +/- 5%, or that's what I tune to.
Make sure that you put in a NEGITIVE number in the global fuel tab. I have forgot to put the "-" in and it sure doesn't want to start or run that way, LOL
Base fuel pressure at 37.0 - plug in -16.7
Base fuel pressure at 43.5 - plug in - 23.1
You have a 2g so base is considered 42.6 (or 43) which comes out to -22.3 give or take.
Those should get you started.
Marty
 
Yes sir, that is all I used. :thumb:
 
Ok, so we can't tell if it is running better, worse, or the same.

We're kinda getting desperate at this point.Maybe we need to go back to square 1 and check everything from the beginning.

Right now it was roughly idling at around 1100. Bobbling up and down 50 rpm. But once it gets up to temp it dies. But not like component getting hot. The performance just gets progressively worse until it barely idles and then dies. I'll go grab a log from cold until death...
 
Here is the log. I just let it idle until it died. What's odd is that I set the idle position to 0%, but then it was back at 1%.

I restarted it twice after it died. I tried lightly revving the motor some before finishing the log.

The AF was around 12.5 the whole time. But right before it dies it goes to 13, 14, 15 and then dead.

It does idle rough like it is missing, but thus far it doesn't seem to be from 1 cylinder.

I sprayed everywhere with carb cleaner today to see if I had a vacuum leak (even though we boost tested) and it made no difference.

Ideas?
 

Attachments

  • log.2019.04.09-01.elg
    68.5 KB · Views: 81
Does it have a fresh pump and filter? I mean its a shop class so I am sure it does. I will look at the log too but with no way to digitally monitor fuel pressure, it may still be hard to diagnose. Assign one of the students to monitor fuel pressure if you have a gauge.
I wonder if the pump is poopin out? Leaning out its either out of fuel or gets alot more air all of a sudden when warm.
 
hmmm...i dont recall, have we peeked at the ecu to see if its not corroded or jacked up somehow? the log is very erratic, but airflow seems to track accordingly, timing is all whacked and jittery, and the fuel readings we're getting are all over the map. i really wish we could see the wideband in the logs, as im not trusting the AFRest in the log, and the stock o2 is not switching.

how about backing the BISS out some just to see if it will stay running, even at high idle, past where its been dying? other than that @1990TSIAWDTALON has a good idea about taking a student and having them track the fuel pressure, it would be good to see what thats doing at the same time as it shuts down.
 
So, from what I have watched, the fuel pressure stays at 42.5-44 (hard to tell on that small dial. I think we have it set between 42-44.).

The wideband sits pretty happily between 12-13:1 when warming up. That said, if anyone wants to save me the horrifically difficult job of hitting the search button- link me to the easiest tutorial to wire the wibeband in. I guess just let me know which ECU pin is the best... This may be a good time for us to reroute the boost gauge as well. Right now we have wbo2 on the column and the boost is just down by the radio. (or lack thereof).

Todays goals-
1) hook up WBO2
2) Reroute Boost gauge
3) Time permitting- get a log with wbo2 hooked up and manually watch the fuel pressure. I may even take a video to get both fuel pressure and vacuum.

Joe
 
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I took a look at your log. If I remember right, you have V2 Link. I can't find the "simulate narrowband operation" button to let your wideband do all the logging. Every time the O2 sensor goes "hi", the ECU wants to pull fuel since it thinks it is rich, then when the O2 sensor goes "low" the ECU will try to add fuel. It kinda looks like that is why it is surging. I am not very familiar with version2 of Link so sorry if this isn't a good response, but I took a snapshot of my car idling after a pull and you can see the wideband cycling up and down in a square wave form.
Here is a screen shot and I will add that log, so you can just skim over it to see what goes on in my car.
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Attachments

  • log.2018.09.26-01 575hp at 170 seconds.elg
    199 KB · Views: 82
Last edited:
If you can, capture STFT AND LTFT so it will display too. I use the STFT to help get the car dialed in and I am not a pro tuner. It may be helpful to a member that is better at it than me.
 
If the power transistor (ICM) is on its last leg, that could be the culprit. Is the coolant temp sensor in good shape, the one on the thermostat housing that talks to the ECU?
 
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