98redorangeta

iTrader: (10)

Ok just trying to think through the simple things my computer is having issues so I can't look at the logs. What was changed headers and y pipe as well as plugs and o2 extensions? Any thermostats or fan temp changes?

Fuel shouldent change much in closed loop as it should be putting in the same amount gas for the air coming in regardless of what the trims are that's what the trims do get you to average 14.7

jaydubb

Same issue here with a 1998 GTP. Installed headers and mileage took a massive dump. I played around with cruise timing. I did the same thing on my G8...

Darth_V8r

iTrader: (4)

Did he ditch the cats as part of the swap? Possibly reduced back pressure affected the O2 readings either by reduced temperature of the sensor and gases or reduced saturation causing false lean?

2000_SS

iTrader: (24)

Cats are gone. That's not the issue. I've done MANY cars with the exact same mods as this one with outstanding results. The only things that are done to it are longtubes, SLP lid, off road Y pipe, and a tune.

The car is still getting poor mileage after dialing the VE in to virtual perfection and adjusting transmission shift speeds.

Sean Goodwin

Just figured I would give an update, as this is my car he is speaking about. Car was purchased 13,600 miles. I have since gotten it up to 18500. The car had all fluids replaced in engine and trans, had msd ignition wires and new plugs put in, had all new seals put on rear end. Car had synthetic oil change at 16k miles with filter, also changed out gas filter which I found to be the original (heh), changed out Tires and rims (which were original). Car was perfect.

Moving forward, recently installed SLP lid, K&N filter, and had the author of this post install BBK LT headers with the included Catless-Ypipe. PRIOR to this install. I always record my MPG by doing full tank fill ups and running it to about 200 miles or 300 depending on city or highway and divide by number of gallons added next fill up. This car was bought from a collector and so I pay attention to details. My 89 IrocZ I built up got better gas mileage than this does now. ANYWAYS, back to the story.

Install was done, and I had to drive from Joplin MO to Springfield for hospital work. So for 2 days straight I went to and from joplin to Springfield MO the drive is exactly 1 hr 15 min. start to stop. I went 70-75mph on cruise control, no gunning it (I am attempting to make sure the tune went ok and to gauge my new MPG). Prior to the install and tune, THIS CAR for 4000 miles. had a nearly consistent 17 mpg city, 23-24 highway (which was in TAMPA FL, in the SUMMER) After the install and tune, the car got, on 2 complete fill ups, I got 17 mpg all highway only miles in winter with virtually 0 traffic. Then poster, looked at the car for me retuned some things but mostly it was all good. the files are of what he posted in his original post. So I kept it for another week after these trips and only did city driving. Posted a 13mpg avg the very next full tank.

So to recap, thats 24 highway, 17 city. To 17 highway/13 city

So needless to say I brought it back to him did a few tweeks but everything looked good. So, after getting it back, I have now taken the car only, to and from work. Which is a 5 mile drive, light to avg traffic for a small town of joplin (nothing like my city driving in Tampa FL) for the last week and a half. Just filled it up today and it was 136 miles on 11.9 gallons!! Thats like 10mpg city! This is NO a/c, no gunning it, no fun in it whatsoever. Simply turn on and go to work and back. 30 to 50 mph.

I drove this car like a madman when I first bought it, enjoying the car, gunning it every light, going 90 on the highway etc, still got 17/24. I haven't driven any car, let alone this camaro or my old one like I have been since the install. (normal/totally babying it/ no fun whatsoever) It literally goes to work and comes home.

With all that said, can someone, anyone please help us figure out what might be up with this primo conditioned Z28? I will buy you beer....seriously.

P.S. I know the numbers pre install are correct. I used Fuelly when I was in FL for 6 fillips and then did my own calcs using fuelly app with no post for the next 10. Every time, it was 17+/23 or 24+ like clockwork. I am a doctoral student, I know how to do simple math. =) My driving habits haven't changed, well that isn't correct. I went from driving it like a Camaro, to driving like an old man with the joy literally stolen from my ride.

LSX Power Tuning

iTrader: (4)

Have you checked everything mechanical, plugs wires etc? Did you adjust the timing any? There are alot of little things that add up making a car get better fuel mileage. Never seen one go backwards like that from doing bolt ons on highway mileage. I have had cammed f bodys get better than stock on the highway. Something is not right somewhere for sure.

Sean Goodwin

I couldn't agree with you more! Just not sure of what....I believe he adjusted the timing, we haven't checked the plugs and wires yet but we had planned to this week. What else might be causing such a dramatic drop with just these changes and a correct tune? 17/24 to 10/17
Perhaps God is angry and siphoning gas out of my ride at night. lol

2000_SS

iTrader: (24)

Yes, timing was added in cruise and partial throttle acceleration areas. I'm going to be looking at the car again in a few days. I plan on checking plugs and plug wires. There were no visible or audible signs of exhaust leaks last time I looked it over but I'm going to check again anyway. Fuel trims at idle don't indicate a leak either.

I've done dozens of cars identical to this one with either retained or improved mileage. I know there's an issue somewhere, just haven't had a chance to thoroughly go over it yet. This is the first car with Bosch iridium plugs I've encountered, and I wasn't the one who installed them, so that's the first place I'm looking since it's the only other variation from OEM.

2xLS1

iTrader: (25)

Get rid of the junk K&N filter. Not saying that is your problem but all they do is oil up everything downstream of them. They don't make any more power than a clean paper filter. I also looked at the tune when it was posted on the HP Tuners forum and IMO there are a few things that could be done to possibly improve the mileage. Also are you using E10 or 100% gas?

2000_SS

iTrader: (24)

Could be either honestly, I don't know where he fills up at but it should be 100% gas. There are a few local stations I advised him to avoid as they typically have poor quality fuel with higher ethanol percentages.

I know there are a few little nit-picky things that could use attention, but none of it would add up to 4-5mpg I don't believe. I've made a few changes to the tune posted online and they seem to have made little difference. I plan on finding & fixing a mechanical issue that has been overlooked then revisiting the tune.

2xLS1

iTrader: (25)

I would put some plain copper core NGK TR55 plugs in it too.

Sean Goodwin

I am okay with both those suggestions. 2000_SS if you want me to get the NGK and the paper filter tomorrow I can do both but I feel like it has to be a bigger issue to be losing 7city and 7 highway. I mean 17/24 to 10/17 is extreme, considering the 17/24 was actually having fun with the new car and this has been babying it completely.

Sean Goodwin

I am using 100% gas, also may I ask what types of changes? are you talking changes that in your opinion would cause massive MPG change or more minor nit picking stuff? I feel like the car runs fantastic since he tuned it, power wise heh.

2000_SS

iTrader: (24)

I totally agree

Nicelysedate

iTrader: (3)

Have you had a wideband on the car yet? I wouldn't trust fuel trims right now because the problem started when the headers where installed.

I would throw a wideband on it and force open loop and see where you are at. Have you checked for exhaust leaks upstream or near the O2's?

2000_SS

iTrader: (24)

Tuned with a wideband....no leaks.

gagliano7

How are the fuel trims after tuning with the wideband? I know on my truck with headers i tuned part throttle with the wideband mileage went down and when i went back to closed loop it showed that i was running lean so the pcm was adding fuel. I tuned part throttle with fuel trims after that and my mileage went up.

2000_SS

iTrader: (24)

LTFTs are within 3% everywhere