Bad city MPG
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Bad city MPG
I hate to keep asking you guys for help, belive me. My car is a 93 LT1 A4. But I get like 10 or 11 MPG in the city. I do one WOT run most of the time I drive it. I doubt that's enough to bring the mileage that low. Most drives are in the city, below 10 miles, under 45 mph. I use to get worse, 8 mpg. But take it on the highway for a short trip, I get 23 to 25 MPG. 93 car, so no MAF.
No vacuum leaks, car idles at 550 rpm with a warm engine, no AC on. 650 rpm with AC on. That is perfect, according to the FSM. I even blocked off the TB in July 2016. The car stalled, meaning no vacuum leaks. It runs great, no kidding.
Fuel pressure is 38 PSI running.
Haven't data logged since like August or September. But o2's go from rich to lean very fast. Coolant sensor agrees with what I see on the car's digital readout. Nothing has changed on the car. Just a new opti and coil pack conversion. It is not throwing any codes. If we can't figure it out, oh well. I'll enjoy it like I always have.
Before I give up on finding the cause, where do I start looking?
No vacuum leaks, car idles at 550 rpm with a warm engine, no AC on. 650 rpm with AC on. That is perfect, according to the FSM. I even blocked off the TB in July 2016. The car stalled, meaning no vacuum leaks. It runs great, no kidding.
Fuel pressure is 38 PSI running.
Haven't data logged since like August or September. But o2's go from rich to lean very fast. Coolant sensor agrees with what I see on the car's digital readout. Nothing has changed on the car. Just a new opti and coil pack conversion. It is not throwing any codes. If we can't figure it out, oh well. I'll enjoy it like I always have.
Before I give up on finding the cause, where do I start looking?
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
May 2015. And last time I with data log, it went from rich to lean quickly in closed loop. I can check again later today to verify.
Team Owner
Joined: Aug 2004
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From: Park City Utah
I hate to keep asking you guys for help, belive me. My car is a 93 LT1 A4. But I get like 10 or 11 MPG in the city. I do one WOT run most of the time I drive it. I doubt that's enough to bring the mileage that low. Most drives are in the city, below 10 miles, under 45 mph. I use to get worse, 8 mpg. But take it on the highway for a short trip, I get 23 to 25 MPG. 93 car, so no MAF.
where do I start looking?
where do I start looking?
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
...IF they're not working. All of my cars have their original 02's. Their age and gas mileage is as follows:
'96 Silverado x-cab 4x4; 293,000 miles, 20+hwy, 17-19 around town
'92'Vette; 180k, 28-32 hwy, 20-22 around town
'05 CTS-V; 145k, 23-28 mpg
As soon as one of my O2's fails...I'll replace it.
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Thread Starter
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Joined: Oct 2011
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
My o2 sensors work great. They do cycle rich to lean fast. If bad, one, or both would stay in a certain position. Thank you all for the responses! Tom, didn't know you have that many miles
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Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Melting Slicks
Joined: May 2013
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From: Sacramento California
IMO this is the core of your MPG concern. Based on this one statement, it sounds like your car spends equal time in open loop and closed loop. This will hammer your fuel economy. I'll also go out on a limb and say the oil probably doesn't see full temp very often, which can become a problem if it goes on for a long time, but this is separate from your MPG question.
I bet your "city MPG" would improve if your trips were 20 miles instead of 10... and possibly replacing the O2 sensors (which I might do as well after reading this thread).
I bet your "city MPG" would improve if your trips were 20 miles instead of 10... and possibly replacing the O2 sensors (which I might do as well after reading this thread).
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Injectors we're changed with injectors from him in September 2015. Also put a new fuel filter before doing so. Last time I did a fuel pressure test, it went from 41 psi to 34 psi in twenty minutes. Always 41 or 42 psi at key on.
Last edited by 1993C4LT1; Jan 13, 2017 at 05:49 PM.
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You sure you tucked the o2 wires where they did not melt? Is your digital temp gauge working right that sensor on the water pump can do some strange things.
Last edited by antfarmer2; Jan 13, 2017 at 06:18 PM.