99 z28 extremely poor fuel mpg
03-02-2016, 09:20 PM
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99 z28 extremely poor fuel mpg Hi I'm new to this forum. Not sure where to post about poor fuel mileage. Ls1 a4 auto, runs great new plugs msd super conductor wires and upstream 02 sensors, Cleaned maf. My question is my fuel mileage is gone? Went from over 200 per tank in town driving to 100 or so in town driving. Noticed mpg was gone so I tuned it up and replaced said items. Still no improvement after new plugs wires and 02's cleaned maf. Looking for ideas anyone got answers?
03-03-2016, 12:08 AM
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It runs awesome great power, cleaned maf with a aerosol maf cleaner. It's got 170,000 miles on it mechanically strong no smoke or ticks or knocks. Just a big loss on mpg went from at least 200 around town town to like 100-135. Doesn't matter if it's driven nice or aggressive. Low mpg. No check engine light.
03-04-2016, 06:32 PM
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It runs awesome great power, cleaned maf with a aerosol maf cleaner. It's got 170,000 miles on it mechanically strong no smoke or ticks or knocks. Just a big loss on mpg went from at least 200 around town town to like 100-135. Doesn't matter if it's driven nice or aggressive. Low mpg. No check engine light.
03-04-2016, 06:41 PM
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No the heating and cooling seems to be fine, I've never had any issues with that or the car mechanically. It's just really odd to run great awesome power can't smell it running to rich not smoking only lil from being rich. No codes, thinking a possible leaky injector or a miss fire but that's alot of off fuel for a misfire. It has a slight bump in the idle is why I'm thinking maybe a coil pack is acting up. It's only gotten 100 miles of easy driving to the 3/4 tank Mark. Before I'd get 200 driving it hard to a tank around town.
03-04-2016, 09:14 PM
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Only mod is k&n filter it's clean, msd wires and new plugs. I took the car on trip did great mpg , soon after trip mpg went away but car still runs great. I'm pretty mechanical and knowledgeable about cars. But this one it's stumping me smh lol. Haven't checked fuel filter yet, but I don't see how a restricted fuel flow can cause excessive fuel usage.
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03-04-2016, 09:58 PM
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have you checked the plugs? Are they wet? Any power loss?
I had the same problem and the cam had ground down. Had power loss and poor MPG.
Also check fuel regulator and fuel filter.
I had the same problem and the cam had ground down. Had power loss and poor MPG.
Also check fuel regulator and fuel filter.
03-04-2016, 10:22 PM
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03-23-2016, 06:19 PM
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Vehicle weight, and rolling resistance are fuel economy hogs. Make sure the brakes do not drag. Make sure it rolls easy and comes to a slow stop with no brake drag behavior.
Do a tune up. plugs, filters, pcv valve, clean everything you can (remove plastic intake ducting and degreaser it), especially the PCV plumbing. DO a compression test, verify all cylinders are hitting the same number. Do a "boost leak test" and/or replace vacuum lines that look cracked, leading around the crank case.
Check the tire pressure, alignment and tread.
Now, once you confirm the tune-up, tires, rolling resistance, compression, all the basics, you are ready to diagnose the computer related problems.
computer related:
1. verify closed loop is working. Use a multi meter on the O2 sensor, or an A/F gauge to verify the closed loop narrowband voltage flips from 0v to 1volt back and forth while driving. Or use a plug-in scanner for this.
2. Verify the ignition timing is set correctly, and that you are getting a full 35-40* of ignition timing during a cruise situation at highway speeds. This is the most likely, final component of fuel economy, is essential to verify once you ensure #1, so do not skip this.
Do a tune up. plugs, filters, pcv valve, clean everything you can (remove plastic intake ducting and degreaser it), especially the PCV plumbing. DO a compression test, verify all cylinders are hitting the same number. Do a "boost leak test" and/or replace vacuum lines that look cracked, leading around the crank case.
Check the tire pressure, alignment and tread.
Now, once you confirm the tune-up, tires, rolling resistance, compression, all the basics, you are ready to diagnose the computer related problems.
computer related:
1. verify closed loop is working. Use a multi meter on the O2 sensor, or an A/F gauge to verify the closed loop narrowband voltage flips from 0v to 1volt back and forth while driving. Or use a plug-in scanner for this.
2. Verify the ignition timing is set correctly, and that you are getting a full 35-40* of ignition timing during a cruise situation at highway speeds. This is the most likely, final component of fuel economy, is essential to verify once you ensure #1, so do not skip this.
03-24-2016, 06:07 PM
#12
