The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support Rix Racing
Please Support Rix Racing

MPG/Stuttering Issue

This site may earn a commission from merchant
affiliate links, including eBay, Amazon, and others.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

JBAirborne

Probationary Member
7
0
Feb 9, 2010
Clarksville, Tennessee
I've got one more issue I haven't worked through yet, I'm having *horrid* MPG issues and I can find no real answer. No codes thrown in over 4 tanks of gas, and nothing really abnormal about the car. Only thing I have found so far is a pretty good size boost leak from the TB shaft seals, waiting on parts right now but other than that...

My car pulls really hard up to about 5/6 lbs and after that you can't feel it boost anymore, but my MPG is really bad and I;ve done everything... I get around 9 to 11.5 mpg with conservative driving, shifting at 2700-3200, same affect as shifting at 4500-5000... I just don't understand, new NGK plugs at 0.28, new upstream O2, air filter is good, MAF is good, IAC seems fine no real idle issues except for I have some really hard starts sometimes to where it will start and just die or start and idle at 150-250 until I step in the pedal and help build the vac back up...

Any ideas about the MPG? I think it's causing my stuttering also, but it ONLY stutters in first or reverse when initialy taking off, no matter how high the rpm it will drop dramaticly. First I can almost take off smoothly if I am RPM'd up to 2000 or so but trying to ease off the clutch and ease in the gas gets me a whole car shaking effect but won't die just bogs down a ton. After that drives just fine.

Any help is really appreciated, I really love the car and have sank over 2400 restoring the engine so far because I love the car that much. Thanks!
 
near ## throttle body check how much gas is being delivered in by your gas pedal. . ## running rich if u have to put the clutch in to lower the rpm. . i had that problem and fixed it by adjusting the gas pedal. seemed to me that the previuos owner had it higher since he would go to the track a lot and wanted to get a quick launch.
 
DSM's use a MAS airflow sensor, it is awesome and very reliable, however you CAN NOT have ANY boost or vacuum leaks.

repairing your throttlebody seals is easy, takes about half an hour, google or go to vfaq.com for detailed instructions.

Seriously, if you recently had the engine rebuild, pulling the TB and replacing the two rubber seals is nothing.

If you just dropped 2400 into the engine, drop another 600 or so into DSMLINK/ECMLINK and actually do some tuning with your car, see if you are running rich/lean where the issue is.

you can't really expect to know what is going on with your car without having full access to the ECU.

It is very easy to tune, all you need is someone who will show you the ropes.

but you could always do routine maintence and figure out where the issue is too.

Did you check your timing? it could be way off causing said issues.
 
Thanks for the replies,

I've no luck with anything on the TB, the idle is good it just drinks gas like no other. I idle around 925.

"you can't really expect to know what is going on with your car without having full access to the ECU."

I agree but on a complete stock engine and stock parts I highly doubt the need for something meant for aftermarket performance... The only thing NOT stock on that car is the exhaust... I will absolutely invest in DSMLink a little later, but fact of the matter is that it's a stock car that didn't come with DSMLink to function from the factory, I don't think it's a priority now with the same engine.

And I attempted a "make do" repair on the seals until the actual ones come in, but O Rings just aren't doing the job... I didn't think such a small seal could let such massive amounts (9 to 10 lbs) of pressure escape before entering the IM so fast, but it seems it's possible.

And yes I made sure to recheck and triple check timing, it's set factory spec. Even payed a shop to make sure I wasn't off, 75 bucks and ten minutes later "Yeah man you got it dead on, not bad."

Thanks again for the replies, I guess it's boiling down to one thing... Boost leak, never imagined boost leak would cause power loss AND my MPG to bite the dirt.
 
I know this may be a stupid answer but did you check your air filter? If that's completely clogged the engine would waste more gas than it should.
 
Not stupid at all, it's a common problem with any car to cause decrease in MPG.
I did check it and cleaned and oiled it a month or so back, it's still in good condition. (Not the stock box filter though, round cone.)
 
I was just recently having the same issue with a huge leak. Mine was at my intake manifold however. Really bad idle, really bad gas mileage, it would stumble at certain rpm's, rough starts like you were describing. Did a Boost leak test, and it would even hold 5 lbs of pressure for more than 5 seconds. Replaced my intake manifold gasket, and all my symptoms went out the window. Gas mileage has gone up, bad idle is gone, No more stumbling, no more rough starts, and power has gone up as well.

I would definitely take care of your TB leak, and then go from there.
 
BrandonDSM:

Woah dude, I think you might have helped me pin point my problem actually and I never thought about it...

When I redid all my valves I never took the IM off to replace that gasket, I just disconnected everything hooked to it and pulled the head off... When I did my BLT I couldn't get it to hold 1 PSI at the TB elbow, but I just couldn't find the hiss anywhere and I ***soaked*** my TB with soap/water mix. It sounded like it was the TB shaft seals but it also sounded lower than that...

You might be my savior boss, I'll report back once we pickle uniforms get payed one the first LOL. Thanks again!
 
BrandonDSM:

Woah dude, I think you might have helped me pin point my problem actually and I never thought about it...

When I redid all my valves I never took the IM off to replace that gasket, I just disconnected everything hooked to it and pulled the head off... When I did my BLT I couldn't get it to hold 1 PSI at the TB elbow, but I just couldn't find the hiss anywhere and I ***soaked*** my TB with soap/water mix. It sounded like it was the TB shaft seals but it also sounded lower than that...

You might be my savior boss, I'll report back once we pickle uniforms get payed one the first LOL. Thanks again!


Same here, It sounded like the TB at first but it sounded lower than that. It was the bottom of the intake manifold gasket leaking. Hopefully it fixes it! :thumb:
 
Same here, It sounded like the TB at first but it sounded lower than that. It was the bottom of the intake manifold gasket leaking. Hopefully it fixes it! :thumb:

Mine leaked too, and it was a PITA to replace that gasket. Good luck on a 2g. :cry:
 
Mine wasnt to bad. 3 hours and it was done.

Put when you have a shop to work in and a hoist it makes life easy.
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Innovation Products Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Back
Top