What Can Be Causing My Rich Fuel Mixture
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Joined: Jun 2001
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From: Malibu CA
What Can Be Causing My Rich Fuel Mixture
My LT-4 has been getting around 13.9 mpg overall for the last 8-10k miles. I reset the mileage every time I fill up. It used to get 16+ mpg overall at least, then something changed. It starts just fine. The exhaust "hunts" at idle and there is a whole bunch of soot inside the exhaust tips. If wiped off, the soot returns within 2 weeks. There is a very small/random miss at idle, too. It runs OK in normal driving and goes like h--l when I push it. It has 70k miles.
I recently replaced the plugs (Bosch +2), wires (Taylor 8mm SpiroPro), had the injectors cleaned with the Bosch system (which I highly recommend), cleaned the K & N, replaced the OptiShark, checked vacuum lines, and cleaned the throttle body as well as I could. The oxygen sensors are original. I had the problem before doing the above work, and it still has it now. Any ideas? :confused:
I recently replaced the plugs (Bosch +2), wires (Taylor 8mm SpiroPro), had the injectors cleaned with the Bosch system (which I highly recommend), cleaned the K & N, replaced the OptiShark, checked vacuum lines, and cleaned the throttle body as well as I could. The oxygen sensors are original. I had the problem before doing the above work, and it still has it now. Any ideas? :confused:
Race Director
Joined: Dec 2000
Posts: 17,551
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From: El Paso Texas
Re: What Can Be Causing My Rich Fuel Mixture (jkingsbury)
Any codes? Sounds like a sensor has gone south. Even without them, at 70K, new O2 sensors are in order. Also, is the car coming up to operating temperature? If the thermostat is stuck open, it could be staying in open loop. You could have a leaking injector. Start with the easy/cheap stuff, and troubleshoot it.
Safety Car
Joined: Feb 2002
Posts: 4,212
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From: Sun City West Az
Re: What Can Be Causing My Rich Fuel Mixture (PTz-92-LT1)
Do you have headers? If so, a leak will fool the O2's into thinking the mixture is lean and the ECM will fatten it up. If the engine is hunting for idle, I'd suspect the IAC is in need of cleaning/resetting or replacing. Dealers use a "top coat" (sold at the parts counter) that you put into the throttle body, let sit for 1/2 hr and fire it up. It cleans the TB, injectors etc. and upon start up it will smoke a lot. If your headers are leaking the smoke "puffs out" at that point and ID the location. Hope this helps.
[Modified by ittlfly, 6:36 AM 2/5/2003]
[Modified by ittlfly, 6:36 AM 2/5/2003]
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Joined: Dec 2002
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From: Riverside CA
Re: What Can Be Causing My Rich Fuel Mixture (jkingsbury)
I got an '87 L98 recently, and it suffered the same problems. Poor mileage and sooty tailpipes. I work around the corner from a school that trains and certifies smog techs. I took my car to their advanced class, and they hooked me up to all of their gizmos. They were able to show me that I had a weak ignition coil, an old oxygen sensor, and (due to some generic "performance chip") catalytic convertors that were cooked. I was lucky in because I was able to register my car with the former owner's recent (and probably pirate) smog certificate. I found out this stuff early, and now I've got almost 2 years before I have to get a smog check again, plenty of time to do it right! The best part is that it cost me $0!!!!
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From: Malibu CA
Re: What Can Be Causing My Rich Fuel Mixture (Frizlefrak)
Well, none of the dash lights like "check engine" have come on, and I don't have the equipment to check codes anyway. Maybe O2 sensors. The car comes up to temperature at 160 degrees when the thermostat opens, and continues up to 180 degrees when the fan comes on. It really never gets above 185 degrees. This is the result of the Ed Wright programming, and I had that done before this problem started, so I don't think that is the cause (although you never know). Yeah, there could be a leaking injector too. Probably I should check the injectors and then replace the O2 sensors (4) if the problems persists. Thanks.
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From: Malibu CA
Re: What Can Be Causing My Rich Fuel Mixture (ittlfly)
No, not headers. Is there a good place to learn about the IAC that you know of? I've had the injectors cleaned and it seemed to make a BIG difference in the overall driveability and power of the engine. Still getting the sooty exhaust and poor mileage, though. Thanks. :seeya
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Joined: Jun 2001
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From: Malibu CA
Re: What Can Be Causing My Rich Fuel Mixture (farhorizon)
Wow, you were really lucky to find that school with all that equipment. It would be great to have that done to my engine. Maybe I'll be able to find someone who knows C4's and has the super equipment necessary to give my car a once over. I think I will try to check the injectors and then the O2 sensors, too. Thanks.
:seeya
:seeya
Melting Slicks
Joined: Feb 2002
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From: The Black Hole LA
Re: What Can Be Causing My Rich Fuel Mixture (jkingsbury)
I believe AutoZone has a scanner that will work on your car and they will scan it for free. My roomates 98 firebird had a miss and it told him down to what cylinder was missing. Although keep in mind that those scanners are meant to scan stock ECM and chip. Not sure if your custom chip will affect it.
My guess from what you have said though is the O2. The engine temp sensor will also make it run rich. I don't know about the LT4 but the L98 has 2, 1 that the guage reads and the other that the ECM reads.
good luck
My guess from what you have said though is the O2. The engine temp sensor will also make it run rich. I don't know about the LT4 but the L98 has 2, 1 that the guage reads and the other that the ECM reads.
good luck
