Poor gas mileage after clutch job.
10-03-2010, 04:20 AM
#1
Burning Brakes
Thread Starter
Poor gas mileage after clutch job.
First of all, I'm running a stage 2 APE setup. chips are probably ~14 years old now. But I'm comparing my results now, to what they use to be. So stop saying "It's the chips"
Since I replaced the clutch and a few other parts, I've been experiencing fairly bad gas mileage. Driving conservatively in the city (rarely hitting boost), I'm getting ~16-17 mpg, when I usually see at least 20. On a trip from Austin to Houston and back, it was ~21mpg @ 75-80mph in 5th for 350 miles. Usually I see at least 25mpg on highway, that's with some 3rd and 4th gear pulls too. While the car was down (from November '09 - August '10) I had a full rich situation which turned out to be a broken maf sensor. I bought a used take-off APE maf from a vendor on here, same calibration as the old unit. I used my old wiring, but I think the little potentiometer on it might have been turned a bit, although I'm not sure how drastic of a difference that would make. Also, I have a washer on a speed or reference sensor that supposedly isn't supposed to have one, meaning I've gapped one of them 2mm more than spec. Don't know if that would make a difference either. The last thing I can think of that might have an effect on MPG is fouled plugs? Would a full rich situation immediately foul the plugs?
And I do plan to change the chips out eventually. Got more important things to take care of on the car though.
Edit - just remembered some other things. TPS was switched, and the idle screw was turned a tad. It idles (ac off) at just above 1k, and with AC on at ~900. LIttle high, I'll adjust it one of these days
Since I replaced the clutch and a few other parts, I've been experiencing fairly bad gas mileage. Driving conservatively in the city (rarely hitting boost), I'm getting ~16-17 mpg, when I usually see at least 20. On a trip from Austin to Houston and back, it was ~21mpg @ 75-80mph in 5th for 350 miles. Usually I see at least 25mpg on highway, that's with some 3rd and 4th gear pulls too. While the car was down (from November '09 - August '10) I had a full rich situation which turned out to be a broken maf sensor. I bought a used take-off APE maf from a vendor on here, same calibration as the old unit. I used my old wiring, but I think the little potentiometer on it might have been turned a bit, although I'm not sure how drastic of a difference that would make. Also, I have a washer on a speed or reference sensor that supposedly isn't supposed to have one, meaning I've gapped one of them 2mm more than spec. Don't know if that would make a difference either. The last thing I can think of that might have an effect on MPG is fouled plugs? Would a full rich situation immediately foul the plugs?
And I do plan to change the chips out eventually. Got more important things to take care of on the car though.
Edit - just remembered some other things. TPS was switched, and the idle screw was turned a tad. It idles (ac off) at just above 1k, and with AC on at ~900. LIttle high, I'll adjust it one of these days
Last edited by onspeed; 10-03-2010 at 04:52 AM.
10-03-2010, 12:41 PM
#2
Race Director
With tha APE MAF harness, if it goes bad (wiring, potentiometer, etc...) it will make it run rich by default. Sounds to me like your 'new' maf is either bad, or very dirty
10-03-2010, 02:34 PM
#3
Rennlist Member
You are probably running rich. You might hook up a cheap air-fuel gauge to the factory O2 sensor (or just a multimeter) and see if it centers around 14.7 when cruising normally on the highway. Also, are you seeing any black soot at the tailpipe?
10-03-2010, 02:39 PM
#4
Burning Brakes
10-03-2010, 03:28 PM
#5
Burning Brakes
Thread Starter
Haven't gotten around to pulling the plugs. I'll try to get to that today.
No black soot out the tailpipe, although when I went for emissions testing, my results were significantly higher than what I usually get. like 3 or 4x.
CPR, do you know what that potentiometer does? I assume it does some fine tuning to the voltage the DME gets? I don't believe the wiring is bad, because I resoldered the potentiometer after discovering it was broken, and I checked the connections with a multimeter. The MAF... could be dirty. Although it didn't look too dirty from a visual inspection. With the old broken MAF, the car would hardly idle. With this one it runs fairly normal, minus the heavy gas consumption, maybe a little more exhaust fumes.
edit - New magnecor wires too.
No black soot out the tailpipe, although when I went for emissions testing, my results were significantly higher than what I usually get. like 3 or 4x.
CPR, do you know what that potentiometer does? I assume it does some fine tuning to the voltage the DME gets? I don't believe the wiring is bad, because I resoldered the potentiometer after discovering it was broken, and I checked the connections with a multimeter. The MAF... could be dirty. Although it didn't look too dirty from a visual inspection. With the old broken MAF, the car would hardly idle. With this one it runs fairly normal, minus the heavy gas consumption, maybe a little more exhaust fumes.
edit - New magnecor wires too.
Last edited by onspeed; 10-03-2010 at 10:00 PM.
10-03-2010, 10:51 PM
#7
Race Director
Haven't gotten around to pulling the plugs. I'll try to get to that today.
No black soot out the tailpipe, although when I went for emissions testing, my results were significantly higher than what I usually get. like 3 or 4x.
CPR, do you know what that potentiometer does? I assume it does some fine tuning to the voltage the DME gets? I don't believe the wiring is bad, because I resoldered the potentiometer after discovering it was broken, and I checked the connections with a multimeter. The MAF... could be dirty. Although it didn't look too dirty from a visual inspection. With the old broken MAF, the car would hardly idle. With this one it runs fairly normal, minus the heavy gas consumption, maybe a little more exhaust fumes.
edit - New magnecor wires too.
No black soot out the tailpipe, although when I went for emissions testing, my results were significantly higher than what I usually get. like 3 or 4x.
CPR, do you know what that potentiometer does? I assume it does some fine tuning to the voltage the DME gets? I don't believe the wiring is bad, because I resoldered the potentiometer after discovering it was broken, and I checked the connections with a multimeter. The MAF... could be dirty. Although it didn't look too dirty from a visual inspection. With the old broken MAF, the car would hardly idle. With this one it runs fairly normal, minus the heavy gas consumption, maybe a little more exhaust fumes.
edit - New magnecor wires too.
You can't re-solder the potentiometer on the APE set-up....where was the lead broken? At the ceramic ?
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10-19-2010, 10:17 PM
#9
Burning Brakes
Thread Starter
update.
changed the o2 sensors, put a new pot on the APE maf harness, and new set of plugs. also, changed out one of the magnecor wires (broken boot) with the stock one. no change in MPG... maybe a tad lower, although i've only gone through one tank so can't say for sure. Going to try some MAF cleaner once i figure out how I managed to get the filter on in the first place.. there's a lip on the MAF, and it's getting stuck on the lip when I try slipping it off...
Any other suggestions on where my lost MPG's are?
changed the o2 sensors, put a new pot on the APE maf harness, and new set of plugs. also, changed out one of the magnecor wires (broken boot) with the stock one. no change in MPG... maybe a tad lower, although i've only gone through one tank so can't say for sure. Going to try some MAF cleaner once i figure out how I managed to get the filter on in the first place.. there's a lip on the MAF, and it's getting stuck on the lip when I try slipping it off...
Any other suggestions on where my lost MPG's are?
