My just put 9.5 gallons in my tank, and that was only after 50 highway miles and 40 city miles. And this is all with a light foot. Something isn't right and I cannot figure it out.

Car has:

New wires
New cap
New rotor
Somewhat new plugs
New 02 sensor
90# BBC injectors with a CUSTOM EBL TUNE
motor cannot have more than 75,000 miles on it. No smoke from the tailpipes, not even on startup after sitting for a solid month.
2.73 gear (as far as I know, but I am fairly certain its the stock gear)

There are a couple things I notice. Car is much much faster when it is stone cold. If I fire it up in the morning, for about the first 3 or 4 minutes the thing will put my *** in my seat anywhere under 3500 RPM (engine has nothing up top), but once it warms past that point the engine seems to lose a lot of power and feels "mushy" with hardly any throttle response throughout the RPM range.

I should also mention that my PROM tune is not perfect, but I am constantly tweaking it and any changes I have made, from running the stock 305 PROM to where I am now (Constant tweaking of the VE tables and AE fueling) have had no effect. 4 months ago I thought my bad mileage was due to my PROM tune, but now I dont think so.

Things I suspect:

Car may be running rich. (?)

I know nothing about EGR or how to check if its functioning. Chassis (and EGR system) has 172,000 miles on it.

Perhaps retarted timing at warmer coolant temps, killing mileage and causing bad performance?

 

i have been having the same problem with me 305 rs no real performance mods yet but soon... seems when it starts getting crappy gas milage i take it on the highway and drive it like i stole it for a bit clears itself right out

 

you said your tuning your chip, if you can, post a data log & what program you used to make it with.

 

Alright, any important engine situations that I should log? Or should I just take it through the gears a few times like I normally would drive and post up? It's kind of an ordeal for me to datalog, I'll try to get one up tomorrow morning.

 

Fill it up to the gunnels, and drive it on the highway lazy like. Find your best approximation for highway mileage you can. With an injected 350, 2.73 gears and overdrive it should be over 20MPG.
14mpg around town is something I would expect, around town is really hard to judge, it really depends on driving style, etc.

**faster when cold started** - That raises the red flag. I'm guessing you're running pretty rich, and/or less than ideal timing. I have no idea how that sophistimicated computer timing and fueling works though.

 

Well so much for the datalog. I won't be able to even touch my PROM until I get a new laptop. Any suggestions in the meantime?

 

did you adjust your fuel press? mayb your new injectors are putting too much fuel into your new setup. it could also be your o2 sensor previously was sending wrong info, making your car lean. now your car is running normal (compared to previous condition) and your worried. all you can do to reduce fuel consumption is to reduce fuel pressure or trick the engine into running leaner (bad idea tho).

 

Fuel pressure is 12 psi at idle and with no load on the engine. Haven't tested it in the upper RPM ranges with high MAP values. Injectors have been tuned down to match the engine to the best of my ability, but I'm still working on that. My point was that I've made a lot of progress downtuning the big injectors (via the PROM tune) but still no change in mileage.

 

Maybe I'm just dumb, but mostly from what I've experienced, all cars are a tad bit faster when cold, because the engine is getting that dense cold air, as compared to when the engine bay heats up and it gets the warm air it doesnt like.

Every car I've ever owned felt like it had more kick when cold.

As for mileage, tryin injector cleaner (seafoams), check o2 sensors, tweak the prom, make sure your brakes arnt dragging, that sorta stuff.

 

what all is done to it to need bb injectors? i seen in your sig that you have a basicly stock engine except an unknown cam ,the prom tuning, and the exaust, is that right? Couldn't you try some stock injectors and see if maybe your over fueling it? or have you ran a a/f ratio guage to see? it sounds to me that its rich and the timing is off. check that first. try a stock prom with stock injectors, might make a world of difference.

 

I have the big injectors because they're all I could get my hands on. I was under the impression that these were fine to use as long as I could detune them in the PROM? Before these I had one 61# injector and another 55# injector (mismatched set) running the stock L03 tune and I had the same mileage.

 

Here are two datalogs. The first one is a cold morning start followed by a 5 mile drive. Second one is the same route coming back home about 2 hours after the first one.

http://putstuff.putfile.com/43067/8122675