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Discussion Starter #1
new to the 4-g and just purchased one with problems. what should the fuel trims be? car has a stumbling idle and if try to drive hard falls on its face if you stomp it. cuts completely out till you let off . if you ease into it you can take right up to redline. only code is random misfire.short term fuel trims are around 12 and trying to drop down. help an old tect out been retired for 20 years and haven't kept up with obd 2.

another problem when sitting still after a couple minutes the traction control will cut off (light comes on) switch it off and restart same results:hail:
 

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Fuel trims should be 0. Deviation from 0 means it's either adding more fuel to make up for unmetered air, or pulling fuel to make up for less air than was expected

I know the TC light and all those symptoms can be related to a bad MAF on an OBD2 car.

How are your MAF values at idle? Voltage/flow, then does it go up with load and RPM properly? It sounds like it's running lean, and that's a lean burn/knock you have that is triggering the misfires


Elsewise, it could be a fuel filter, or fuel pump issue. But I've not known those to throw a TC light
 

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Fuel trims should be 0. Deviation from 0 means it's either adding more fuel to make up for unmetered air, or pulling fuel to make up for less air than was expected

I know the TC light and all those symptoms can be related to a bad MAF on an OBD2 car.

How are your MAF values at idle? Voltage/flow, then does it go up with load and RPM properly? It sounds like it's running lean, and that's a lean burn/knock you have that is triggering the misfires


Elsewise, it could be a fuel filter, or fuel pump issue. But I've not known those to throw a TC light
On my hackish tune for my DC Sports CAI, I do have a +15% fuel trim, hackish did make it for the intake I have as to make the MAF scalings correct; dirty MAF? Clogged fuel filter?
It doesn't throw a code because it's still with 25% but I was jw, or it's totally possible that the MAF scaling in the tune really isn't correct
Could trick it by scaling the injectors smaller in the tune 15% but that's a hack
 

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@Kyle

That's wrong. That is so definitely wrong. +15% means your O2 readings were lean, so it's adding 15% more fuel. That's almost enough to throw a check engine light. That leaves very little room for error if something were to ever happen. Go into your tune, disable closed loop, set your MAF scaling properly, and then enable closed loop again. It's a pain in the ass, but I had to for my 3.5" MAF. Also, "dirty" isn't a problem with this style of MAF. Every time it turns on, it does a full power heat cycle to clean itself. With that, if there was oil on it, it will burn up the wire. That's why it's important not to touch the MAF wire, and why you shouldn't use MAF cleaners on it. Most people are lucky and don't have issues with MAF cleaner, but also won't see benefits. Some people are unlucky, because the chance is there that some cleaner may have left a coating in one spot where it didn't full vaporize, and you get the hot spot, or permanently altered MAF values if the entire thing is coated, as it'll change how air moving across it affects it, so MAF scaling will be wrong

Could someone scan their car and grab a MAF idle value for him? Mine's away in storage, so I'm a little screwed on being able to help.
 

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When I leave for work in an hour I’ll grab a reading. I’ll edit this post.



EDIT:
 

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Discussion Starter #7 (Edited)
maf reading

well that's most likely the problem, this one is on .01 up to about 2k then at 3500 jumps to .4.. what do you think and thanks for helping this old critter out. will go to lkq tomorrow and pick up one. what all years will work 06-12?
:fever: mine is a 2.4 if that makes a diff
 

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@Kyle

That's wrong. That is so definitely wrong. +15% means your O2 readings were lean, so it's adding 15% more fuel. That's almost enough to throw a check engine light. That leaves very little room for error if something were to ever happen. Go into your tune, disable closed loop, set your MAF scaling properly, and then enable closed loop again. It's a pain in the ass, but I had to for my 3.5" MAF. Also, "dirty" isn't a problem with this style of MAF. Every time it turns on, it does a full power heat cycle to clean itself. With that, if there was oil on it, it will burn up the wire. That's why it's important not to touch the MAF wire, and why you shouldn't use MAF cleaners on it. Most people are lucky and don't have issues with MAF cleaner, but also won't see benefits. Some people are unlucky, because the chance is there that some cleaner may have left a coating in one spot where it didn't full vaporize, and you get the hot spot, or permanently altered MAF values if the entire thing is coated, as it'll change how air moving across it affects it, so MAF scaling will be wrong

Could someone scan their car and grab a MAF idle value for him? Mine's away in storage, so I'm a little screwed on being able to help.
Thanks for the info Saber, I have never sprayed MAF cleaner on the MAF sensor. And the tune is for my DC Sports CAI and says so in the notes page of the tuning software.
I think it was really about +13% last I checked but never throws any codes except my P0455 evap code
 

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Negative. That's idle. The throttle is never fully closed at idle.


As for your tune, I'm gonna say it's wrong still though. I had mine with the same intake, and had LTFT around 5 usually. 0 is optimal. 0 codes, and zero vacuum leaks when tested with a boost leak tester (which will open up splits that close under vacuum, so is the easiest test method, NA or FI to find damage). Boosted, I managed to get mine to hover around 0 with further tuning. It can even be as simple as a nasty O2 sensor, or the 2 O2 sensors disagreeing. It depends which bank, or if it's both.

It won't affect power, it just leaves you with only half the fuel correction under 40% (I think it's 40% stock) throttle while it runs closed loop. Potentially, you may get better fuel economy if it were running proper (minimal)

EDIT:
At these throttle levels or higher, at the corresponding RPM (or 6000+, 500-), the car is open loop, so won't use O2 data anyway to form LTFT or STFT
 

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I have replaced 3 of the 4 O2 sensors with the OEM Denso parts within the past 2 years and the data on the one I haven’t replaced yet looks good maybe a tad bit slow responsive wise but it oscillates correctly

How likely is it that it could be a clogged fuel filter?
 

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I don't know what gas is like in your area. But for $3, and being a regular maintenance item, it wouldn't hurt to change it
Who knows what the previous owners used for the first 120k miles before I had it, and I guarantee the filter is original.

Under rear seats right, pretty easy to pull out the fuel pump then? I've had the rear seats out before when I was running amp wires to pull the side plastic trims

Possible vacuum leak from 38mm wastegate blockoff plate on my throttle body for the air intake resonator delete?

I'd have to check this by seeing if the STFT goes negative or positive or negative while driving to see if it's a vacuum leak or fuel problem.
 

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btw i also just remembered that running high ethanol gas such as E10 or E15 rather than E0 will cause Positive LTFT, but how much?
 

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Nah, because that would make your fuel trims wrong in open loop, so whenever it's actually important to get them right (otherwise, you can ruin the engine). Injector scaling is similar to how eBay turbo kits "tune" with variable fuel pressure.

You'll want to look at MAF scaling to make sure it adds the right amount of fuel per the amount of air coming in
 

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Nah, because that would make your fuel trims wrong in open loop, so whenever it's actually important to get them right (otherwise, you can ruin the engine). Injector scaling is similar to how eBay turbo kits "tune" with variable fuel pressure.

You'll want to look at MAF scaling to make sure it adds the right amount of fuel per the amount of air coming in
Wouldn’t the MAF scaling be correct since it’s in my tune notes that it’s for that intake?
 
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