1baddgarage

iTrader: (3)

Ok, i'm kinda stumped on this one. So if anyone can give me any ideas that would be great. My 94 Z28 with a m6 is only getting 16.5 mpg combined city/highway with around a 35%/65% split and me driving like a grandma. It has brand new Bosch O2 sensors, New Optispark, New plug wires and a new maf sensor. I checked the plugs and they are champions and appear to be in great shape. I have NGK tr55's to replace them if need be. The car runs great, the only problems are it's kinda hard to start when the car is cold, it requires around 5-10 seconds of cranking after it warms up its alot better. Also it has a slight occasional pop at idle. It's not very consistent. I checked the injectors for a leaks and they didn't appear to have any. Any ideas? Thanks

sandman2100

iTrader: (8)

I'd test the coolant temp sensor, but I've had nothing but problems with Bosch O2's.


Best bet is to datalog it if you can so you can get a better idea if sensors etc are operating properly before blindly going through it.

1baddgarage

iTrader: (3)

Ok, the I read all the bad reviews about the bosch o2's after i bought them of course. Are they known to be bad from the get go or just fail sooner than AC delcos/Delphis? How do I test the coolant temp sensor? The one on the water pump, not the head correct? And to datalog I just need the cord to connect to my laptop and to download the program right? Thanks for the help

sandman2100

iTrader: (8)

Correct, I'm not sure if Bosch just go bad fast, just their voltages are just off and slow. The coolant temp sensor is in the water pump, and since you are an OBD1 I'm sure you can just get the cable and software. Mine is OBD2 and I use SnapOn or in the past an AutoTap scanner.

1baddgarage

iTrader: (3)

Ok, I just ordered the Cable and downloaded the freescan software. Thanks for your help, hopefully I can get this figured out soon

LT1

iTrader: (1)

Check your fuel filter if it hasnt been replaced in a while.

1_MEANZ28

iTrader: (4)

fuel filter , fuel pump ??

93M6Formula

I would also check fuel pressure while you're at it since you said it starts hard.

1baddgarage

iTrader: (3)

I don't think the fuel filter or pump could cause bad mpg could they? Definitely could have something to do with the hard start issue though. I do need to get a reading on the fuel pressure though, when they go bad do regulators usually let in more psi or less? The cars has to be running rich

69gto96z

iTrader: (13)

The best i ever got out of my bolt on car was an average of about 17.5 mpg, your not too far off. If you prime your pump 1-2 times when it is cold and then try to start it, and it will start without excessive cranking, your check valve is bad in the fuel pump, and it is time to replace the pump.

ahritchie

iTrader: (1)

How long have you had the car? Has it ever gotten "good" gas mileage? 16.5 mpg seems about normal. The reason I ask is it can vary wildly depending on conditions/driving style. I average right at 16 MPG in my bone stock other than longtubes LS1 car 6spd in a mix of driving with a heavy foot...best MPG on 100% highway driving is about 22MPG (driving 10 over speed limit). My LT1 car got about the same with just bolt ons...190-220 miles a tank...now more like 130-150 per tank with new 383 and 4.10's

93M6Formula

That can't be right can it? i used to get 26 highway with my car in stock form. It would usually do 17/18 in town.

1baddgarage

iTrader: (3)

Priming the fuel system doesn't help at all. So I think the pump is fine. I've only had the car for a month, and I was getting less than 16 till I replaced my oxygen sensors. I thought I should be getting more like low 20s since I haven't been driving it hard at all, and I've been driving highway miles mostly.

englundjd

well i can manage about 18 mpg with about 75%/25% town/highway and have plenty of spirited driving mixed in. i would check your o2 sensors. bosch isnt known to be a good brand. plugs gapped right? might make sure your timing chain is in good condition. check/clean all injectors

ahritchie

iTrader: (1)

Is your cat clogged? They do go bad eventually; gut it! Might want to try a few tank fulls of fuel injector cleaner too. Your starting issues could also ignition related; you might want to see what happens with new plugs and wires and possibly coil and cap and rotor. Still, 16.5 mpg is not THAT bad....if you wanted good gas mileage you shouldn't have bought a V8 muscle car period... get a 4 banger DD and save the LT1 for weekend drives.

1baddgarage

iTrader: (3)

No cat it has an ory. I put sea foam in it Sunday. It has a new opti, wires and I already checked the plugs, they look great. Coil was something I was going to look into. I have a 84 z for the weekends this is my daily for now. 16.5 isnt that bad but it should be getting much better. My 96 mustang gt I just sold to buy this got 20-23 mpg. And they're known to get worse mpg. Also if the bosch 02 are acting up that will show up on the freescan software right?

LT1

iTrader: (1)

This is what i said in another forum ill copy and paste it.

1baddgarage

iTrader: (3)

I got the freescan software hooked up, and the o2's and water temp sensor are reading great. I am however getting code 48 (Maf sensor circuit) and code 43 (esc sensor circuit). Code 43 would be the knock sensor correct? and with the maf sensor not working correctly it would run in speed density. So both of these codes would mess with my mpg right? Thanks

97lt1camaro

iTrader: (3)

I consistently average 17-18mpg city no problem in my camaro. Full bolt on'ss H/C/I bla bla.

Hit the 28mpg mark on roadtrip this past summer. Pure highway. Love it.

EDIT: 6speed

guppymech

iTrader: (7)

When my car was stock I got 17 in mixed driving. Dropped to 16 with 4.10s. Last tank was 13.5 with hotcam and administering some beatings. I have a mail order Ion tune, runs great.