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8K views 40 replies 17 participants last post by  damondanner 
#1 ·
I've been experiencing an issue for a few months now. Sometimes the 4G will run fine, sometimes it will feel sluggish. Occasionally, while I'm driving and the car feels sluggish it will suddenly lurch forward and drive normally again. Sometimes it will do the opposite. I had decided it was likely either a flakey TPS or PPS.

I've been to the dealership. They're no help. They told me that the problem is that I'm running premium fuel. They're certain that filling it up with 85 octane will cure the problem, and that Mitsu doesn't know what they're talking about when the manual and filler cap both say premium only. How, I love those discussions...

Anyway, I decide that the only way I'm going to get it fixed right is to troubleshoot it myself. So I buy a DashHawk and start datalogging.

From what I can tell, there are two TPS and two PPS involved. All four are appparently poorly calibrated at the factory, so the ECU averages and normalizes their readings. Easy enough.

What I expected to find was a single PPS or TPS giving an inconsistent reading. I figured when it spiked one direction or the other it would throw the average off and cause the throttle to partially open or close.

Looking at the datalog, I can see the throttle sporadically open/close about 10-15%. These correspond perfectly with my throttle surge issues. Great news, as this confirms that the issue is throttle, not timing or MIVEC engagement. However, when these events occur, the two PPS track perfectly with one another. The two TPS also track perfectly with each other, but both with the big spike. Both TPS also perfectly track the ECU Command Throttle signal. It looks like the ECU suddenly just decides that the throttle needs to open (or close) an instantaneous 10-15%, even though both PPS readings are constant.

I have a hard time believing that the PPS are at fault. Like I said, they track perfectly with one another (though offset in calibration by about 10%) and match my pedal inputs perfectly.

I also have a hard time believing that both TPS sensors are identically flawed. They also track perfectly, though one is really poorly calibrated and reads ~53% when the throttle is really at 2%. However, correct for the offset and it tracks perfectly with the other TPS and both track the Commanded Throttle signal.

So I think, maybe its a bad wiring harness...but the PPS is stable (matches my pedal input) and both TPS track the ECU command signal. So ECU???

So I wonder, perhaps the ECU is seeing another spurious signal which is causing it to occasionally dial back or add throttle. I've tried turning off the TCS, but the problem persists. I've logged timing and IAT, but both act normal when the problem occurs.

So what do you guys think?
1. Two bad PPS that have identical flaws? Too unlikely.
2. Two bad TPS or bad actuator? I don't think so, since they track the ECU commands perfectly.
3. Bad ECU? This would be an awfully specific ECU problem.
4. Bad wiring harness? While the issue is sporadic, it isn't random. The spike always occurs when I'm accelerating and the pull-back always occurs when I'm decelerating.
5. Some other sensor I haven't thought of that would cause the ECU to occasionally pull throttle? I don't see a way to directly track knock with the DashHawk, but I don't see timing getting pulled which I would expect in a knock condition.

What am I missing? There has to be a simple explanation that I'm missing. Otherwise, the ECU seems to be the least unlikely of the options I have.

Any feedback is appreciated.
 
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#3 ·
I have been having the same problem to a long time now... and if I'm not mistaken so has BrianJ.

I've been watching the same things you have and I keep going back to "am I getting a misfire and the ECU is pulling timing" to "WTF"....

I think the only way this problem is going to be resolved is buy a reflash.

I mean I can hit a steady throttle in 2nd and all of a sudden the car will jump foward like I just goosed it... and then sometimes I will be in 3rd and be giving it a little throttle and it is like I hit a wall and my power gets knocked way down. Also when this happens you can feel the power difference. Say you feel it jump forward in 2nd.. now the car feels strong and powerful. Now the car hits the wall in 3rd... now the car feels slow and sluggish.

If this problem is happening to you post up and lets see if we can't get some flow in here to try and get this fixed to keep our cars running top notch!
 
#4 ·
I mean sometimes my car feels like it just has it... it will pull you back in the seat and you will be running 120 before you know it.

Then sometimes it just feels like it isn't there and you watching it slowly go by 80 like WTF!!!
 
#5 ·
bump.... because I think this is something everyone needs to look into.
 
#7 ·
I have this problem all the time... I don't see how having the dash hawk hooked up would cause this... and do you mean the older frimware on the AEM F/IC?
 
#8 ·
Nope the dashhawk firmware. v2.3 would cause weird throttle issues that felt like surges at completely random times. Usually only 1 or 2 times a trip. I took it out for a while then upgraded to v2.4 and put it back in for fuel economy testing. Problem went away.

I just kinda wrote it off as the dashhawk using too much of the CPU runtime for all the scanning while it was installed. Not sure what it really was though.
 
#11 ·
So can you guys describe this as tiny dead spots in the pedal? I have noticed this during city driving lately, and its bugging the piss out of me. I think its in the factory tune.........
 
#15 ·
Not sure if Brian upgraded to the 2.4v... I have his old Dashhawk..

Really though this problem could win or lose a race for you... if the car is close enough to your car.
 
#16 · (Edited)
i also have this problem....but i notice it more when im cruising and then jump on it. the car feels really sluggish. but if im at a stop and gun it right off the line the car feels fine.

but yea sometimes when im on the freeway it feels like my car is broken when i try to pass someone hard....then a few minutes later ill try again and I'm flying by people. pretty weird....sucks its happening but glad to hear its not just my car
ive been meaning to hook up the TPS on the FIC for a while for some other issues im having, but when i finally do ill try and see if i can see what your describing as well.

on a side note...i have no idea how the dashhawk has any effect on this. all the dash hawk does it read in the signals and display them. if your dashhawk is interecepting and modifying signals to the ECU then something is wrong
 
#17 · (Edited)
360jeepboy -You're description matches mine completely - including the 'wall' in third gear. I experience those exact symptoms at random intervals every time I drive. Very annoying. Worth noting that this began long before I purchased the DashHawk. In fact, this was the catalyst that finally drove the DashHawk purchase.

Here is an example (logged with DashHawk v2.4).



The red and yellow lines are the two PPS.
The purple and light-blue lines are the two TPS (note the one TPS that is ~50% out of calibration).
The dark blue line is the commanded throttle signal from the ECU.

Note the PPS stay relatively constant and throttle position is relatively low, and then suddenly - wham - the ECU doubles the throttle for no apparent reason.

I have a logged example of the wall in 3rd gear too. The exact opposite happens. PPS is steady when the ECU suddenly commands the throttle actuator to close.

Anyone else experiencing this?

Any ideas as to what could be causing it? I've thought about replacing the TB, since I do have the one TPS that is 50% off target, but I'm pretty sure it won't fix the problem and then I'll kick myself for wasting $150 on a used TB.
 
#18 · (Edited)
Here's an example of the 3rd-gear wall...



Here I'm watching a few other sensors, but the relevant ones are the PPS in red and the ECU throttle command in yellow.

In this case I'm accelerating lightly in 3rd when the ECU cuts the throttle. PPS was at ~40%. TPS went from 32% to 22% for no apparent reason. 10% doesn't sound like much, but in this case it was about a third of the total throttle opening.

From what I can tell I can always hit WOT if I bury the pedal, so this doesn't cripple the car or anything. However, the difference between the Jekyll and Hyde throttle positions is a night and day difference when you're in the lower gears.
 
#19 ·
I have an '07 GT (automatic tranny) and have been noticing a rather strange issue during acceleration. Launching from a complete stop, the car seems to shift through the gears normally. However, when I am driving between 30-45 mph and step on it, I can feel the car hesitate between 2k-3k RPM. You can actually feel the car jerk (not jarring or anything) a little bit as if it's missing a gear or something. After this hesitation, and the car seems to hit the 3K mark and really pull (as it should). This has been one of the nastiest winters on record, and I have had to dig my car out of heavy snow banks numerous times. I am wondering if it could be something with the transmission.

I installed an AEM full length CAI last November, and the car seemed fine up until now. The weatherguard is still in place, and everything seems solid under the hood. I checked the air filter and it's dry - no clogging either.

The problem is easily reproducible...but the dealership said it was "fine." The issue was definitely not present when I got the car, but now it feels like all the power is lacking overall.
 
#20 ·
Artex...thats cuz the auto at 35mph is in 5th gear and is shifting to 2nd...mine does it...i'll be in 5th gear in the grocery store parking lot....punch it to pull out into traffic and realize it has to take like 4 seconds to shift all the way down to 2nd gear
 
#22 ·
has anyone tried grounding their throttle body, i know that one a lot of car if you do this u can see a small power gain but can alot prolly fix the proble. would be a easy cheap and cheap upgrade if it was the problem. i want to do mine even though i dont have this problem but i havent gotten around too looking at where i can ground to yet but if one of you wants to go ahead and give it a try let me know if it helps any
 
#24 ·
If you're looking for performance gains, TB grounding is a placebo mod - at least in our case. The bolts that secure the TB to the intake manifold already provide a solid ground. Mine reads <0.3 ohms to random chassis points in the engine bay.

I appreciate the suggestion. :)
 
#25 ·
ya your reading the grounding from the TB to the chassis, thats the resistance you would have if your TB was directly grounded. for a better awnser you should be measuring across the the TB to the plenum the from the TB to the motor, then the TB to the engine ground. cuz im sure thats the path it would have to take to the ground i couldnt see any closer grounds. way i see it would only take 5 minutes to do any try it that 5 min might fix the problem. i havent run into this issue at all and i upgraded all my existing ground on the motor, with all the electronics the more grounding the better
 
#27 ·
Mine does this as well, I feel that it has to do with trying to compensate for the intake and the a/f ratio (map sensor, etc are having a huge spike of air coming on decel and it tries to fix it).

Another fun way to screw with the computer is throw it in sportronic, go up to about 3k rpm and set the cruise - it'll try and maintain the MPH which in a way feels about the same (the surging).

The car has a LOT of control over the throttle...

Notice that we don't have a IAC or Bypass? That's because the computer can control the throttle and is no longer limited but it also feels to me its trying to stabilize the idle on decel (or what it feels is decel) and gives a surging feling.
 
#28 · (Edited)
Notice that we don't have a IAC or Bypass? That's because the computer can control the throttle and is no longer limited but it also feels to me its trying to stabilize the idle on decel (or what it feels is decel) and gives a surging feling.
It goes open loop on decel. Maybe the closed map is way different from what would be typical in that rpm range.... actually nm, that train of thought just jumped off the rail.
 
#29 ·
FWIW, I'm convinced that my TPS or PPS is not to blame. I'm convinced that the ECU is reacting to something else and changing the throttle target. I've ruled out IAT, ECT, and engine load as culprits.

My current suspect is the knock sensor, but I don't believe the DashHawk will monitor knock events so I can't datalog it to see whether the events align with the throttle issues. I considered just swapping the knock sensor out to see what happens (though it is a PITA to get to). However, since I can't initialize the learning values for the knock sensor without the MUT-III, I may make matters worse if I swap it out myself.

I wish I could find a way to datalog knock events...
 
#32 ·
Hmmm...I don't think so, I mean, you have the datalogs showing the TPS is definitely erratic per the ECU and nowhere in the factory service manual does it say that the knock sensor has anything to do with the TPS...it will affects timing though, but that don't explain your TPS readings...

You shouldn't be getting knock anyway, unless you're really messing with things...are you tuning?
 
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