Trying to track down mileage problem.
Thread Starter
Race Director
Joined: Oct 2000
Posts: 16,477
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From: Enter Post Count Here
Trying to track down mileage problem.
Car - 1987 Coupe A4
I used to get consistently over 30 mpg. Then I took the motor/transmission apart and now I'm getting a best of 22 mpg.
Here's everything I've thought to look at. I'm replacing the O2 sensor Friday, although I don't think it needs it.
- 2600 stall torque converter, lock up confirmed
- O2 sensor, new when I bought the car 4,000 miles ago
- Tire Pressure, 35 psi all the way around
- Cam Shaft, slightly hotter than stock, nothing much
- Compression, 10.78:1 Does this make a difference? I'm running 92 octane
- Spark Distribution, All new as of 900 miles ago
What else should I look at?
Thanks.
I used to get consistently over 30 mpg. Then I took the motor/transmission apart and now I'm getting a best of 22 mpg.
Here's everything I've thought to look at. I'm replacing the O2 sensor Friday, although I don't think it needs it.
- 2600 stall torque converter, lock up confirmed
- O2 sensor, new when I bought the car 4,000 miles ago
- Tire Pressure, 35 psi all the way around
- Cam Shaft, slightly hotter than stock, nothing much
- Compression, 10.78:1 Does this make a difference? I'm running 92 octane
- Spark Distribution, All new as of 900 miles ago
What else should I look at?
Thanks.
Le Mans Master
Joined: Feb 1999
Posts: 7,254
Likes: 0
From: Custer SD
Re: Trying to track down mileage problem. (NoWorries)
I don't think there's anything wrong with you car. I highly doubt you were getting 30 mpg before no matter what the gauge says. The new C5's are more efficient than the C4's and they were getting about 26 mpg.
Thread Starter
Race Director
Joined: Oct 2000
Posts: 16,477
Likes: 1
From: Enter Post Count Here
Re: Trying to track down mileage problem. (Romeo Barrera)
Romeo,
I don't trust the dash, never had. The best calculated mileage I ever got was 31 mpg on the downwind leg towards Phoenix from the Grand Canyon. On the reverse trip(more hills), I got 28.
Now, on the way to Phoenix, I pulled off 22, calculated. The dash thought I got 37. :eek:
I don't trust the dash, never had. The best calculated mileage I ever got was 31 mpg on the downwind leg towards Phoenix from the Grand Canyon. On the reverse trip(more hills), I got 28.
Now, on the way to Phoenix, I pulled off 22, calculated. The dash thought I got 37. :eek:
Le Mans Master
Joined: Feb 1999
Posts: 7,254
Likes: 0
From: Custer SD
Re: Trying to track down mileage problem. (NoWorries)
Is that the same convertor you had or is it a higher stall speed? I doubt the tire pressure is causing that much loss, but I try to run 32psi cold. What are your cam specs?
Burning Brakes
Joined: Dec 2000
Posts: 849
Likes: 0
From: Lafayette LA
Re: Trying to track down mileage problem. (NoWorries)
Since some are doubting if you really have a problem, you might clean/check your tailpipes to see if they are getting a lot more carbon buildup than normal. That might be an indication that you really are running too rich.
Are you basing the mileage on actual calculations or the readout? The readout will not be accurate if you changed injector size.
If everything is working right, it should correct the fuel trims to their correct values for optimum mileage. The best way to figure it out is with a scan - any chance you can do that and let us know what it says?
Are you basing the mileage on actual calculations or the readout? The readout will not be accurate if you changed injector size.
If everything is working right, it should correct the fuel trims to their correct values for optimum mileage. The best way to figure it out is with a scan - any chance you can do that and let us know what it says?
Safety Car
Joined: Jul 1999
Posts: 3,946
Likes: 63
From: Marianna FL
Re: Trying to track down mileage problem. (olephart)
Since you've had the engine out recently, go back and check the vacuum line going to the fuel pressure regulator. My mother's car was getting crappy mileage and I found the hose was split on the back side where you couldn't see it. Could be something simple like this.
Safety Car
Joined: Mar 2000
Posts: 3,620
Likes: 2
From: Hillsboro OR
Re: Trying to track down mileage problem. (NoWorries)
Check the fuel regulator as mentioned. Recheck the timing too. Its also possible the motor has not completely broken in. Did you go to a lower temp thermostat. That could account for a loss of mileage. The cam you have is a bit larger than the stock one so you maybe losing some mileage because of it as well. 10% is possible.
Safety Car
Joined: Dec 2000
Posts: 3,767
Likes: 5
From: Jacksonville Fl
Re: Trying to track down mileage problem. (NoWorries)
New motor...new "HOTTER THAN STOCK CAM"...Hehehehehe.
Does that answer the question for you?
One thing is a lot of people make a mistake of setting the valves too tight, especially with stock hydraulic roller lifters ( unless you have stiff springs, going more than 1/8 turn past zero lash is a BIG mistake ). The tell tale signs of over tight valves are a slightly rough idle when in gear and uneven firing sensation on acceleration.
Higher compression will usually help mileage.
One note is with these mods, you may not really help performance that much with the stock ( read: "JUNK" ) overly restrictive exhaust manifolds. Putting even shorty headers will amaze you in the difference.
A big place to pick up mileage is to have a chip burned with less total ignition timing, so you can bump up initial timing and crusie timing without hi rpm preignition.
Other than that, speed cost money...if not parts, then gas ( or usually both )
:nopity
[Modified by BBA, 9:58 AM 12/26/2001]
Does that answer the question for you?
One thing is a lot of people make a mistake of setting the valves too tight, especially with stock hydraulic roller lifters ( unless you have stiff springs, going more than 1/8 turn past zero lash is a BIG mistake ). The tell tale signs of over tight valves are a slightly rough idle when in gear and uneven firing sensation on acceleration.
Higher compression will usually help mileage.
One note is with these mods, you may not really help performance that much with the stock ( read: "JUNK" ) overly restrictive exhaust manifolds. Putting even shorty headers will amaze you in the difference.
A big place to pick up mileage is to have a chip burned with less total ignition timing, so you can bump up initial timing and crusie timing without hi rpm preignition.
Other than that, speed cost money...if not parts, then gas ( or usually both )
:nopity
[Modified by BBA, 9:58 AM 12/26/2001]
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Thread Starter
Race Director
Joined: Oct 2000
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From: Enter Post Count Here
Re: Trying to track down mileage problem. (BBA)
Here are the specs:
Cam- 214/220 .452/.465 center angle 112
Torque Converter- 2600 stall, lock-up provisions
Lifters- Crane Hydraulic Rollers
Rockers- Crane Roller Tip
Springs- Matched to cam-shaft, I don't remember the specs
Exhaust- Hooker SuperComp 2.5 inch exhaust, single Dynomax muffler.
My cheap air/fuel ratio guage says I'm running a little rich, but I not much.
I wanted to get a new top-end before I got a chip burned, I think I'm in a no-win situation with that, other than getting heads/intake then getting a chip burned.
I can live with this for now, I just expected to get at least 26. I'm calculating the mileage from gallons used and mileage traveled. I quit trusting the dash a long time ago. The only things its good for is putting it in neutral at 75 mph and showing your pax 86 mpg. :D
I don't have the provisions to do a scan. :(
Thanks for all the replies.
Cam- 214/220 .452/.465 center angle 112
Torque Converter- 2600 stall, lock-up provisions
Lifters- Crane Hydraulic Rollers
Rockers- Crane Roller Tip
Springs- Matched to cam-shaft, I don't remember the specs
Exhaust- Hooker SuperComp 2.5 inch exhaust, single Dynomax muffler.
My cheap air/fuel ratio guage says I'm running a little rich, but I not much.
I wanted to get a new top-end before I got a chip burned, I think I'm in a no-win situation with that, other than getting heads/intake then getting a chip burned.
I can live with this for now, I just expected to get at least 26. I'm calculating the mileage from gallons used and mileage traveled. I quit trusting the dash a long time ago. The only things its good for is putting it in neutral at 75 mph and showing your pax 86 mpg. :D
I don't have the provisions to do a scan. :(
Thanks for all the replies.
Melting Slicks
Joined: May 2000
Posts: 2,187
Likes: 0
From: Andersonville TN
Cruise-In II Veteran
Cruise-In III Veteran
Re: Trying to track down mileage problem. (NoWorries)
You can also negatively affect your mileage with faulty cylinder firing. If any one (or more) cylinders decides to slack off (bad wire, etc), the engine still turns the same speed at the same MPH, but the remaining cylinders have to work harder, while the slacker cylinder still has gas flowing through it.
Lee
Lee
Racer
Joined: Mar 2001
Posts: 280
Likes: 0
From: Honolulu Hawaii
Re: Trying to track down mileage problem. (NoWorries)
Maybe your foot got heavier since your motor change. I only get 16mpg city/highway and 22highway. When my foot gets really heavy the mpg gets down to like 10mpg.
-Tim
-Tim