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Running lean and misfire

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Th3DooM

10+ Year Contributor
301
3
Jan 5, 2011
Dresden, Europe
Hey there,

I have trouble with running lean and misfire for a while now. The car seems to be a bit slower than usual, it feels like something robs power. Stock n/a 420A with Header.

The inspection 2 weeks ago showed me that I`m running lean,Air/Fuel is 16-17.5 @ idle and @ about 2500rpm when warmed up. I had a couple of exhaust leaks BEHIND the catalytic converter that I fixed, the A/F went down to 16.5.
When I push the accelerator hard the car starts to bog for a sec, than accelerates. When I release the accelerator at higher rpms in gear I think I can hear the exhaust stutter. Yesterday it was pretty warm, the coolant gauge was a bit higher than usual. When I backed up I could hear a louder misfire/detonation from the exhaust.

When the car is cold the idle is between 700 and 1000, rising and falling. When it's about 700, the car shakes a little bit, then it goes back to 1000. When warmed up the idle is rock solid at 800.

I changed the fuel filter about 5000 miles ago, checked the ignition system (coils and wires) both visually and with a volt meter and checked the vakuum lines with flammable spray. There seems to be no problem. Unfortunately I can't get my hands on a fuel pressure tester. I have no CEL or other light in the cluster that's illuminated.

I don't know know where I should start fixing the mess. :confused:
 
It sounds like it's time for a tune up.

When is the last time you changed your O2 sensor? What about your spark plugs?

A bad O2 sensor would cause the issues you describe.

You should also pull your spark plugs and look at them. They will give you a good indication of how your car is running.

NGK Spark Plugs USA

Hope this helps!
 
The upper O2 sensor is about 1 year old, it's a Denso part. Okay, I'll check the spark plugs. Currently I'm running BKR6E and I changed them with the O2 sensor and regaped them to .04"
 
The upper O2 would be the one that would determine your main fuel mixture at idle. A year old shouldn't have gone bad, but I would pull it and check anyway.

You shouldn't ever really re-gap spark plugs. They are so cheap that you should just replace them if you have to re-gap, and keep the other set as a spare for emergencies.

Also, .04in is a little low. By the books the gap should be .048-.053 in. (1.22-1.35 mm).

Most owners, from the look of it, shoot for .045-.050.

Don't forget to check your air filter as well.

Keep us posted.


Also, if you have the time, it wouldn't be a bad idea to check your fuel pressure.

If you have an Autozone near you, they rent a fuel pressure test kit that comes with a tester and multimeter. I can't remember the part number off the top of my head, I'll edit if I can find it. It is not cheap, at about $200, but you will get it all back when you return it. It is a very useful tool.

Good luck!
 
I checked the plugs and they look pretty good (I guess). There's no damage at all, a little bit of brownish dirt at the outer insulator as you can see. But not dramatical dirty. I gapped the spark plugs to 1.2mm =.047" earlier, not to .04 as stated above

This is no.1:
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no.2:
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no.3:
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and no.4:
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I also cleaned my k&n airfilter and look how much dirt came out of there just after the first flush!

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It took me three more flushes to get most of the dirt out of it. Currently it's not dried or oiled so I have to wait until I can see any change...

Another part I checked with the ohm meter is the TPS. The impedance (resistance?) smoothly rises from 0.68kOhms (closed throttle) to ~3.83kOhms (WOT).

Unfortunately we don't have Autozone here in Europe. I work at a european car shop but we don't have a schrader valve-type fuel pressure tester. There are a couple of tester kits on ebay, but I don't know anything about the quality.
 
Those plugs don't look that bad. I would say those aren't the problem.

That air filter was pretty disgusting. Doubtful it's the cause, but ya never know. At least it will be clean now.

Did you get a chance to pull the O2 sensor yet? I would go ahead and pull both just to look at them. Depending on how bad they are replacing them might not be a bad idea.

I didn't even look at the where you were located LOL, my bad. It would defiantly beneficial to check the fuel pressure, but if you can't find a way to do it on the cheap there are a few other things you can do.

First, does the car hesitate/run rough the higher the rpms get? This would indicate a weak fuel pump. Normally though, you will know when the fuel pump is going out since the car will start dying. If you can throw a different or known good fpr on the car and see if that changes anything that might be good as well.

Additionally, check the wires going to the MAF to see if they have a good signal.

Last, when you next fill up on gas, throw some premium in it and put in some fuel system cleaner in their. Ya never know LOL sometimes this clears things up.

Good luck!
 
Well I have a problem with overheating since day 1 so I bought a new radiator and threw out the thermostat last year. The car still gets very warm when staying in traffic (the fan kicks when when it has to). But that's another story. Maybe over winter the car didn't warm up enough so that the extra fuel injected for warming up the engine damaged the new O2 sensor? I hadn't the time to check it, but tomorrow I'll go have a look.

The 420A only got a MAP sensor, but I check that, too. And I'll try to find the best injector cleaner that's legal over here, haha. Seafoam isn't sold in Europe :(
 
check the cam sensor. clean it up and reinstall it. I had similar issues in a neon I had and turned out to be the cam sensor
 
Cleaned the cam sensor today with no luck, the problems remain. I haven't had the time to check the o2 sensors yet. I hope that's the solution because I still haven't found a fuel pressure tester.

When the fuel pressure is okay, could old gummed up injectors cause these problems?

It's sad to feel the car shake an vibrate when idling or driving in lover rpm and light throttle when you drove a brand new car with such a smooth driving pleasure a couple of minutes ago :(
 
Pull your IAC and MAP sensor. IAC is located below the TPS and the IAC is located on the other side of the throttle body, it should have 3 wires coming out of the harness. If you have some carb cleaner I would clean both of these up and spray some carb cleaner in through your throttle body its self.


Also check the fuel injectors, if they are sticking or gunked up it may cause the problem you are having. Also if you have the ability, do a leak down test. If the seals on your valves are worn then you could be losing compression and causing the problem.
 
I cleaned the MAP sensor and the throttle body with brake cleaner earlier that week, and I don't have a proper tool/screw driver to remove the IAC.

I checked the compression last year with superb results, which really surprised me. I have these problems for about 1,5 years and that was the first thing I checked. The car has 186k miles on the odo.

So there's o2 sensors and injector cleaning left. I hope one of these tasks will fix my problems.
 
I cleaned the MAP sensor and the throttle body with brake cleaner earlier that week, and I don't have a proper tool/screw driver to remove the IAC.

I checked the compression last year with superb results, which really surprised me. I have these problems for about 1,5 years and that was the first thing I checked. The car has 186k miles on the odo.

So there's o2 sensors and injector cleaning left. I hope one of these tasks will fix my problems.

the IAC should just take a wrench and screw right in or out. Its right under the TPS
 
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