MPG's suddenly tanked - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
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post #1 of 16 (permalink) Old 01-15-2016, 10:40 AM Thread Starter
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Angry MPG's suddenly tanked

1995 LT1, all stock, 120k. New GM o2's, new GM opti, new MAF, new plugs & wires, new GM ICM, new coil, new GM coolant temp sensor, new fuel pump and sending unit, new GM EGR valve, new PCV. All replaced in either May or Nov of 2015. No fuel leaks. No vac leaks that I can see/hear. No fuel pissing out of the FPR, and fuel pressure is where it should be.

Was previously getting 16 or so with a mix of hwy and city. Suddenly, as-in last week, I noticed the level dropping way, way faster than normal. Down to about 8mpg. Car runs perfectly otherwise and wouldn't have any idea that anything changed were it not for the increased thirst. I checked the brakes for any that are dragging and it all appears good. On flat ground the car is easily pushed using one foot out of the driver's door while in neutral.

Hooked up to get a scan and no codes, nor does anything look amiss. I've just ordered new injectors since the ones on there are original to the car and have never been serviced.

Anyone have any other ideas I should be checking into?

Thx!

Last edited by AtlantaDan; 01-28-2016 at 04:13 PM.
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post #2 of 16 (permalink) Old 01-15-2016, 02:48 PM
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Observe fuel trims and O2 readings while driving. When you said nothing looks amiss, it is not clear if you were looking at live data readings.
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post #3 of 16 (permalink) Old 01-15-2016, 03:20 PM
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you threw a lot of parts at it, was that before or after the bad fuel economy?

can you tell us the brand and source of all these "new" parts? you bought a brand new GM maf, or....

also your injectors, what did you order?
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post #4 of 16 (permalink) Old 01-15-2016, 03:20 PM Thread Starter
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Quote:
Originally Posted by shoebox View Post
Observe fuel trims and O2 readings while driving. When you said nothing looks amiss, it is not clear if you were looking at live data readings.
Sorry, yes. I was driving it around while looking at the 02's. They were swinging as they should, at least as far as I could tell. What sorts of things should I be looking for in the data? Better yet, I'll hook the car up and go for a spin while datalogging and post the logs here for review. Thanks for your input

Last edited by AtlantaDan; 01-15-2016 at 03:32 PM.
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post #5 of 16 (permalink) Old 01-15-2016, 03:27 PM Thread Starter
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Originally Posted by steveo View Post
you threw a lot of parts at it, was that before or after the bad fuel economy?

can you tell us the brand and source of all these "new" parts? you bought a brand new GM maf, or....also your injectors, what did you order?
I should have stated above that this problem just started with this past tank (now 2 tanks ago) and the parts were all installed mid/late last year.

I did a complete electronics replacement well before the fuel economy problem. The ICM died and stranded me, and I just replaced everything at the same time to be on the safe side. All parts are AC delco/GM/Delphi with the exception of the wires (new Taylor 8mm), the MAF (new, but AutoZone brand..), and the plugs - NGK's. I kept the OEM GM MAF and swapped it out - no change.

For injectors, I ordered the newer-design 4-hole Bosch 24#'ers.

Last edited by AtlantaDan; 01-15-2016 at 04:24 PM.
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post #6 of 16 (permalink) Old 01-15-2016, 03:31 PM
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For injectors, I ordered the newer-design 4-hole Bosch 24#'ers
what part number? might need a recalibration to get full benefit..


do you have a proper aldl cable or just a crappy code checker? it'd be nice if you recorded a datalog while driving...
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post #7 of 16 (permalink) Old 01-15-2016, 03:34 PM Thread Starter
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Quote:
Originally Posted by steveo View Post
what part number? might need a recalibration to get full benefit..

do you have a proper aldl cable or just a crappy code checker? it'd be nice if you recorded a datalog while driving...
I have the proper ALDL cable. I'll hook it up tonight or tomorrow and log it, then post the log here for review.
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post #8 of 16 (permalink) Old 01-15-2016, 04:02 PM Thread Starter
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Here's a link to a Google Drive folder with 3 scans.
1. Around town cruise - no WOT. Average 35-45 mph. No stops
2. Short near WOT sprint
3. Short cruise with 100% WOT sprint

Thanks for any assistance you can provide
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post #9 of 16 (permalink) Old 01-15-2016, 04:19 PM
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If your problem suddenly started right after getting gas, then maybe you got some bad gas.
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post #10 of 16 (permalink) Old 01-15-2016, 04:23 PM Thread Starter
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If your problem suddenly started right after getting gas, then maybe you got some bad gas.
Excellent point and I'd be 100% behind you, but the trend continues now with new fuel from a different location.
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post #11 of 16 (permalink) Old 01-18-2016, 05:56 AM
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I ALWAYS buy fuel from somewhere with high turnaround, a very busy gas station that you see a lot of other people getting their 93. Little gas stations that don't have a lot of turnaround, especially on the fewer use 93 pumps, can screw you. How is your fuel filter? Does it smell rich?

94 Z28 M6 hardtop power nothing LS1 lid, ported MAF, Pacesetter LT's, ORY, dump, 7/16 NSA Pro Mags, CSR EWP, Bilstein HDs, BMR springs, 32 front 23 rear sway bars, MSD opti, NGK TR55s, Taylor 8.2mm, B&M ripper shifter, underdrive pulley, Trifecta tune, LT4 KM, Poly LCAs and short TA, 3.73s, 295/35/18s
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post #12 of 16 (permalink) Old 01-18-2016, 02:30 PM
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No exhaust leaks?


1995 Camaro Z28 LT1 LE2 355 w/ forged pistons/rods, 230/238 .565/.565" 110+6, 1.6:1 SA RR, LT Headers with ORY, T-56 (rebuilt w/ some upgrades), McLeod Street Twin, Lowered 1.25" (Stagg Shocks and Summit Springs) LCA Relocation brackets, Adj Panhard Bar, Poly suspension bushings, STB , CAI, !emissions crap, Magna Flow Cat Back. 146,xxx miles. Purchased Feb 7, 2012 (168K) 414rwhp
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post #13 of 16 (permalink) Old 01-18-2016, 02:51 PM Thread Starter
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No exhaust leaks. No fuel leaks either.

Anyone had a chance to look at the logs?
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post #14 of 16 (permalink) Old 01-19-2016, 01:55 PM
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Everything on your data logs look alright. It's pulling fuel, but not too much.

I think you need to check the fuel lines (the vacuum ones) for cracks/damage. I wonder if your fuel is evaporating??

I once had the fuel sending unit on top of my Suburban tank crack and it was misting fuel out of it. I couldn't smell it or see a leak for a while, but my gas mileage did drop. Eventually the leak got bad enough that I could smell it, but couldn't see it. Then it progressed to puddling on the ground. Seems unlikely (it is), but it has happened.


1995 Camaro Z28 LT1 LE2 355 w/ forged pistons/rods, 230/238 .565/.565" 110+6, 1.6:1 SA RR, LT Headers with ORY, T-56 (rebuilt w/ some upgrades), McLeod Street Twin, Lowered 1.25" (Stagg Shocks and Summit Springs) LCA Relocation brackets, Adj Panhard Bar, Poly suspension bushings, STB , CAI, !emissions crap, Magna Flow Cat Back. 146,xxx miles. Purchased Feb 7, 2012 (168K) 414rwhp
2014 Ford Focus SE Hatchback- Stock (Wifes Ride)
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post #15 of 16 (permalink) Old 01-19-2016, 03:14 PM
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Have you checked the brakes/calipers for binding ?

Mitch

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