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Running lean, no check engine light.

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DSM IN MN

Supporting VIP
705
23
May 17, 2009
Wadena, Minnesota
My car (1999 GS-T) has had a problem with running lean every since I got it. It does not run lean all the time however.

Up until a few months ago, when the car started to run lean; you were screwed. The only way to get the car to stop running lean was to remove the negative terminal from the battery for about an hour. The only things that seemed to cause the car to run lean was; driving at WOT to say, getting onto the highway "quickly", LOL, or while driving on the highway at a constant speed for more than 20 miles (70MPH for example).


When the car would throw a CEL, it would be something to do with fuel bank 1. Then every now and again it would say insufficient coolant temperature. So I replaced the coolant temperature sensor. That seemed to do the trick.

Then one day it started running lean again, or at least that is what my narrow-band gauge showed. I fixed it though by giving the car 25% throttle from 65MPH to 70MPH then letting off of the gas pedal completely until the car got down to 55MPH. From there the car would run normal.

Today the same thing happened as I was on a 3 hour trip (one way). The first time letting my car coast worked, then it started running lean after going from around 70MPH to 80+MPH. After that it was nothing but lean.

When I got to my destination, I removed my negative terminal. After I put the negative back on, the car ran fine until the same thing happened.

After driving over 100 miles with no check engine light, I do not know where to look to see what is wrong. The only modifications to my car are a SRS Ebay "cat back" exhaust w/the cat deleted, a cone air filter, an Injen intake, hard SMIC piping and a Greddy Type-S BOV. Yes, the BOV is recirculated so that is not the cause.

I would really rather NOT start throwing parts at the car considering I'd probably end up spending more than I need to. Any insight or help would be GREATLY appreciated. Thank you in advance!
 
Start by checking your oxygen sensor start the car and warm it up. Race the engine around 2k rpm and put a DVOM on the out put wires of the sensor(back probe the connector) use the online manual to fine which wires you need to test but I believe the heater wires are all white so it would be the other two. The voltage should bounce back and forth between .6. and 1v. I had a similar issue with oxygen sensors before i found that i had to use the more expensive one i believe ngk or denso, but they would keep going out of range and tripping a lean code. But if you are basing this on the readings from a narrow bad with no codes I wouldn't worry about it unless a code is thrown, a wide band is a good next step if you are really concerned.
 
Start by checking your oxygen sensor start the car and warm it up. Race the engine around 2k rpm and put a DVOM on the out put wires of the sensor(back probe the connector) use the online manual to fine which wires you need to test but I believe the heater wires are all white so it would be the other two. The voltage should bounce back and forth between .6. and 1v. I had a similar issue with oxygen sensors before i found that i had to use the more expensive one i believe ngk or denso, but they would keep going out of range and tripping a lean code. But if you are basing this on the readings from a narrow bad with no codes I wouldn't worry about it unless a code is thrown, a wide band is a good next step if you are really concerned.

I'm going to have to read over that again, LOL, and maybe give it a try. But as far the narrow band goes, it accurately displayes what is happening with the car. I can feel it. It has no power and timing has to be hella' retarded because the RPM range is shortened by quite a few thousand.

Also, I turned the car on this morning to go to work and it ran/drove fine.
 
How do you tune the car, how does your narrow band show your lean? Gonna have to find a way to log or see whats going on. Your gonna have to find a way to see whats going on, or a mechanic, or you may be throwing money at parts. Hard to figure out your issue when your saying you can feel it, what do you feel.
 
A narrowband gauge is just a voltmeter that shows what the o2 sensor is doing, so I'd be willing to bet your o2 sensor is dying. I actually had a very similar series of events, except my o2 was completely dead and I got a check engine light for ECT. Toss in a new sensor and see how that does.
 
How do you tune the car, how does your narrow band show your lean? Gonna have to find a way to log or see whats going on. Your gonna have to find a way to see whats going on, or a mechanic, or you may be throwing money at parts. Hard to figure out your issue when your saying you can feel it, what do you feel.

I have no tuning abilities. The narrow band shows the farthest red or lean light. I can feel the lose of power. I can feel how bad the RPM range is set back. It feels like redline is around 4k.
 
I have no tuning abilities. The narrow band shows the farthest red or lean light. I can feel the lose of power. I can feel how bad the RPM range is set back. It feels like redline is around 4k.

I'll almost guarantee that's your o2 sensor dying, and the ECU not knowing what the hell to do with it. Pull your plugs and see what color/condition they are to confirm the lean condition, then replace the o2 sensor.

By the way, you mentioned a check engine light for "fuel something" might it have been something like "bank 1?"
 
Your narrow band reads at cruise and other various points of light acceleration to gather the current burn conditions and is ignored at wide open throttle. When an oxygen sensor is reading improperly most likely outputting low voltage your ecu is getting informed that your running rich. Your oxygen sensor is actually generating the reading from a reaction of the oxygen in the exhaust system with the component in the sensor I forget what it is made up of but the out put of this reaction is a small voltage. When this signal is week it is telling the car the system is running rich and the car pulls short term fuel trim if this happens long enough you will then start pulling long term fuel trim in-turn causing a lean condition and miss firing, and your poor running condition. You can test this before you replace the sensor to rule it out and save some time and money as well. It should only take a few minutes, if I remember correctly the connector for the O2 sensor is under the thermostat housing and is relatively easy to get to. Gently back probe the two sensor wires (should be the two that are not matching colors the other two are for the heater) with t-pins or paper clips, while racing the engine some where around 2k rpm you should see it jump between .6 and 1 volt. if it does not oscillate some where in this range the sensor is bad and should be replaced.

I hope this helps, I know I some what restated my earlier post but you seemed doubtful it could be an o2 sensor and i thought further explanation would help you understand why it could be this.
 
Well now the car is running on three cylinders. I changed the plugs and cleared the engine code (P0303) but still the car insists on sounding like a damn Subaru. LOL Kind of tired of this thing.
 
Have you checked your wiring for the injectors i found a bad wire recently on the car i just got, i was wondering why it wasnt firing.
 
Have you checked your wiring for the injectors i found a bad wire recently on the car i just got, i was wondering why it wasnt firing.

No I have not.
 
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