Hello!

I just bought my dream car - 1995 Z28 hardtop 6speed - and the previous owner added a few modifications. Currently, she has 42Ib E-85 Bosch Injectors, 255 Iph Walbro fuel pump, Long tube headers, milled down factory heads, and removed O2 sensors ISO E-85. From what I can tell, the car runs great. However, E-85 is not always accessible and my gas mileage is horrendous - but that is also due to the 4.56 gearing (which I plan to change to 3.73s).

I spoke to the previous owner, who was the 2nd owner for 10 months before I bought it. He informed me that all I have to do is put the stock injectors back on and she will run on 93 smoothly because the z28 never had any PCM tune. From my little knowledge, I do not understand how this is possible without a tune to begin with. Again, I do not understand how this car is running so great on E85 - I have driven it over 500 miles.

I am in the military, so working on my dream car will be periodical when I go to Nashville on leave, but I would appreciate assistance on somehow getting her back to running on 93 or some sort of flex fuel set up. Thank you all, and glad to finally be part of this community!

 

Does the car still have an Optispark and run with the stock ODB I computer, or did someone swap to a flex fuel computer with a sensor? The ethanol mix is varied throughout the year depending on where you live. You might only get 85% ethanol 3-4 months out of the year. You're probably running around on a 50% mix right now that would be running pretty fat with bad fuel economy.

If it's still using the factory ECM you can pull the tune for free if you have the right ODB cable. I would pull the current tune and compare it to a stock one. It was most likely changed at some point. You should be fine leaving the 42lb injectors in and tuning the car for 93 octane gas, but I would want to know exactly how much compression the car has first. They may have jacked it up over 13:1. Make sure the knock sensor is installed, functioning, and the sensitivity hasn't been played with in the tune. heh..

Thanks!

Chad

 

About the rear gear.....My 02 Camaro with a six speed, 4.56 gears, and 25" tall tires turns about 2500rpms at 90mph in sixth gear. I wouldn't spend the money swapping to a 3.73 if you are only doing it for gas mileage. It really isn't worth it. If you are still running the factory 10 bolt rear I wouldn't spend a penny on it. You can probably buy a stock 3.42 rear end complete for $200-$300. Someone that wants a 4.56 setup might even trade you straight up or some cash on the side to swap.

Thanks!

Chad

 

Hmm, this one could be interesting since you are dealing with a OBD1 car.

If you swap to bigger injectors and keep the tune the same, you will run extremely rich

Now, if you then swap out the fuel (like from gas to E85) you are balancing out the bigger injectors.

o2 would still try to maintain stoich when into closed loop. (But you say no o2s at play)

It is a crazy way to do it but
Big Injector flow rate and E85 can be made to equal small injector flow rate and regular gas.

Question is , did they get it right? Any chance to put a wide band on it and see if you are near stoich when not in PE mode?

 

Not the same platform, but I had a 00 Bonneville ssei that I would run 50% e85 and regular gas with stock Injectors. I played around with different ratios, read up, and kept track of mpg and Butt-o-meter performance. Acceleration was outstanding even on the stock tune.

E85 loves timing! Kinda of curious what times your car can turn out

 

Get a Torque Head kit, upload a flex fuel Tahoe file, add the flex sensor wire to the red connector pin 1 to the 411 PCM supplied with the kit add positive and negative. Then plumb the sensor into the fuel line. And your pretty much done.

 

I've been running E85 in my OBD1 TA for over 12 years now. So the 42 injectors work by "tricking" the PCM for the fueling. E85 is 9.8:1 stoich instead of 14.7:1 stoich like gas, so it requires around 30% more fuel. Since the OBD1 PCM can't change the stoich ratio, the way you do this is you tell the computer you are running 30% smaller injectors than you actually are. Since the 42# injectors are 43% larger than the stock 24# injectors, simply switching injectors without changing the tune will make it run that much richer since the PCM thinks it is adjusting smaller 24# injectors. 42# are way too much though at 43% larger, whereas 32# injectors would be more of a good starting point doing nothing but changing from gas to E85. Also, the fact that it is not running O2's to correct for the fueling, you should have an SES light for the no O2's unless they were tuned out of the PCM, and it would be running even richer since the computer can't correct for the fact that 42% injectors are still too large, if the computer thinks it has 24# stock injectors. Someone mentioned possible 13:1 compression, well that's not possible from just milling the heads, you would need a longer stroke to get that or slightly domed pistons.

To go back to 93 octane gas on this car, its pretty simple, and would be just changing the injectors and tune (and re-installing the O2's that shouldnt have been removed). What I would do is get EEHack (free download $EEHack Download – fbodytech) and TunerPro tuning software (also free and corresponding $EE definition file TunerPro and TunerPro RT - Professional Automobile Tuning Software), then order an OBD1.5 tuning cable (OBD Diagnostics, Inc. - OBD2 All-In-One Scan Tool w/ USB (obd1.com)) (only the 1995 cars had this connector). Then pull the existing tune to see what is going on with it and make sure it actually is a stock tune. If it is a stock tune, then simply install O2's and stock size injectors and you are ready for 93 octane. I can help look over the tune as well if you pull the tune off of it.

 

Part of the reason the fuel economy is horrible is that E85 doesn't have the same energy potential as gasoline. It's maybe 25% lower than gasoline. As said before, be careful of compression. If you end up needing race gas that's NOT going to be cheaper....

 

True, that is why E85 typically runs about 30% less fuel mileage vs gasoline. Unless he is running over 12:1 compression (assuming it is a stock short block he isn't) then 93 is fine up to that ratio on the LT1 with the reverse cooling. I've ran 93 a couple times to test it out on my previous 12.5:1 385ci (with large cam) and was able to run it without knock just slightly reducing PE timing vs E85. Now if it has a non-stock bottom end, and is running over 12:1 compression, then yes he may need to step up to beyond 93 octane, depending on the cam timing and dynamic compression. If this car is supposedly on stock tune and stock bottom end, with just headwork and fueling mods, then 93 octane would be fine.

 

Hey!! Thank you for the links. I am fortunately being sent on leave - meaning, I am going home for a week and a half - next week. I am ordering the software and cable right after COB. Regarding the injectors and O2 sensors, where is the best place to purchase the o2 sensors and injectors? Thank you so much for the assistance - this means a lot to me. I cannot wait to be able to daily her.

Another Question I have is will I need to do anything to the fuel system once decreasing the injectors because of the giant walbro fuel pump?