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Discussion Starter · #1 ·
So my coupe has been having some problems as of the past coupe months. The car is bone stock except for longtubes and exhaust. Idle is ruff and I can tell there's a miss in there as the car rocks from side to side. There some backfiring and poping from the exhaust after a rev or on decel. It also throws cel after about 5-10mins of driving.

Also sometimes it will taking while to crank before it starts when its hot.

Plugs, wires, rotor and cap are about a month old. Timing is at 12 deg.


I ran codes and I got the following:

koeo = 11 (pass)
koer = 41, 91

So by this, its something with 02's or something in the system. So I replaced the 02's and I checked for vacuum leaks and found none. The orange 02 ground is clean and on the back back of the drivers head.

Beside the fuel pump or filter, where else should I look ?
 

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Run a cylinder balance test.
 

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Discussion Starter · #4 ·
MFE...forgot to add that to my original post..I did run the test, actually twice in a row and both times it was 90, system pass code.
 

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Have you cleaned the MAF sensor?? If that is dirty, it will make it run rough.
 

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Discussion Starter · #6 ·
90topdown...when I first got the car in Feb of this year I did clean that ...but I could always try it again. The car has the stock air box and filter< so it should be clean...I'll give it a shot.
 

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Discussion Starter · #7 ·
Update...

So I changed the fuel filter today and it got rid of the idle miss !...

...but it still thows a CEL (same codes (41-91) after couple mins of driving and still backfires and pops form the exhaust on a rev or decel...

Whats next guys ?
 

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Discussion Starter · #9 ·
liljoe07 - Yes they do. I checked the heaters on them and they get hot, with the key turned "on".

I also checked the volts coming from the O2's at the ECU, they are getting power and working. rich when I start the car and they the signal goes lean after driving a couple mins, mainly after a hard pull threw a couple gears.
 

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Fuel pressure when the CEL comes on would be nice. Even the Idle Fuel pressure may tell you something.
 

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Discussion Starter · #11 ·
Dont have a gauge...Yeah the pump is 17 years old...so that may need to be changed :D

I have to have to hit Harbour freight and a get a cheapie gauge and see what its telling me .

Question : How big of a vacuum leak would I have to have to have for it to backfire ?

Pretty big, no ?
 

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Discussion Starter · #13 ·
Lol...no don't have that I could find when I first checked over everything with carb cleaner a while back.

It just seems like that's what's happening somewhere.

Something else odd is my cruise just stoped around the sametime. The little vaccum connector on the brake pedal is connected though.
 

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Discussion Starter · #14 ·
ok..so today I set the timing back to 10 degress just to be safe, and this did nothing.

Also the missing at idle is back. I let the car idle for a few minutes then went to the back, and it's eye watering to say the least. Sounds like there aa cam in it..lol

So I'm guessing theres a lean condition, and the ECU is dumping fuel to cure it.

Anyone ?
 

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Did the problem start after you replaced the cap, rotor, wires, or plugs? Secondary ignition system problems can cause code 41.

Check the fuel pressure as mentioned before anything else. Should be 30-45 PSI at idle.

When you checked O2 sensor output did you see the voltage switching above and below .45V several times in a five second period?

Also since you said the car is missing and appears extremely rich, I would pull the plugs and check them. Perhaps you will find one or two cylinders running lean and the rest rich which could help you isolate the problem further. It will also give you the opportunity to inspect the rest of the secondary ignition system for defects.
 

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Discussion Starter · #16 · (Edited)
Did the problem start after you replaced the cap, rotor, wires, or plugs? Secondary ignition system problems can cause code 41.
No that you mention it, the car did run good with OEM 140k stuff on it, I just changed it as a preventative thing. The problem did start after I changed them, but I'm not sure right after or not.

The 02 sensor output (for both) was pretty steady. the output never jumped or spiked.

Secondary ignition system problems can cause code 41.
Could you explain this a little further ? I would think it would be a rich condition and the fuel not being burned, no ?

Thanks for the help !

***Also, the car idles and drives great when its cold***
 

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misfire is causing the lean condition seen by the 02s.

Then more fuel is added, to cause the rich condition at the tailpipes.

Do you have operating cats?

Also longtubes do not help matters as they place the 02s too far from the exhaust valve.

Why longtubes on a stock engine?
 

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Discussion Starter · #18 ·
misfire is causing the lean condition seen by the 02s.

Then more fuel is added, to cause the rich condition at the tailpipes.

Do you have operating cats?

Also longtubes do not help matters as they place the 02s too far from the exhaust valve.

Why longtubes on a stock engine?

No cats..Dr. Gas X-pipe and a Mac catback...

I know the placement of the 02's in the headers might cause problems, but I know a bunch of guys with longtubes that run pretty well with out the said codes. In therory, would the further 02 placement make them read false lean or rich ?

I had this exhaust laying around from my old coupe that I parted out, so I figured I'd toss it on. The car had a completely stock exhaust when I got it ! :lol:
 

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You need to fix the misfire, then the codes should go away.

Don't like LT myself, had them, hated them, all I'm saying is that it is probably not helping having the 02s that far away from heat.

Any exhaust leaks?

also without cats, and running perfectly you are still going to smell rich at the tailpipes.
 

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The O2 sensor output should be between .1V and 1V and bouncing above and below .45V.

Indy is right, misfire at idle causes lean condition and ECU richens accordingly.

A misfire at idle is a sign that a cylinder or two are not performing their share of the workload. Check your cap, rotor, wires, and plugs. Since code 91 indicates left oxygen sensor lean, I would concentrate on the the left side of the engine.

You can try idling the engine and removing the left side plug wires one at a time. You should see a drop in RPM (increase in roughness) when the wire is removed. If the idle doesn't change you have found your problem cyl.

Also since it idles fine when cold, there is a strong possibility that the left EGO sensor is always indicating lean when the engine is warmed. That is confirmed by the codes 41 and 91 during KOER.
 
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