I just bought a 91 Z28, I dont know all the modifactions it has but i do know it has air foil, a cam(dont know the specs of it), light weight pullies, and an exhaust. I am only getting 10 mpg. Is that normal. What could i do to make it get better mpg? Thanks

 

First start by giving it a complete tune up.
which includes:
Spark plugs,
Ignition wires,
Cap & rotor,
Air filter(I would buy a K&N),
O2 sensor,
and fuel filter.
You should notice an improvement in gas milage and performance.

 

Try synthetic lube.

 

Also, if EVERYTHING is in proper tune, you could consider learning how to burn your own EPROM.

There is a "Highway Mode" that you can invoke on your SD 730 ecm. It was put there by GM, but never enabled because the EPA did not want the extra NOx emissions from running lean.

I am just playing with it now, and it does appear to increase gas mileage while driving on the highway. I will know more when I get further chances to test it in the coming weeks on a long road trip.

If I can increase my gas mileage by a couple a mpgs while driving on the highway, the gas savings alone will pay for all my PROM burning equipment within 6-12 months.

 

Glenn, I know you PROM guys don't like to be bothered with questions like this but:

I am having TPIS custom burn a PROM for me, would they know about this "Highway Mode" you speak of?
bsa

 

First, the "Highway Mode" is only on the SD TPI ecm. I have not seen an equivalent on the MAF TPI ecms. It doesn't mean that it doesn't exist. I understand the older MAF TPI ecms haven't been as well "hacked" as the SD TPI ecms.

Assuming you have an SD TPI, I still have no idea if TPIS invokes the "Highway Mode". Ask them. Provided TPIS has not re-written the machine code (highly doubtful, most just modify the various tables), it should be possible. I would probably assume that TPIS does not, as their goal is to make a PROM that has performance in mind. Most hot-rodders assume that price for performance is decreased gas mileage.

But, why not consider burning your own PROM? The amount of money you are about to spend having TPIS custom burn a PROM will easily pay for all the equipment and software. Also, you can re-burn your PROM for FREE. TPIS charges you $100 for each re-burn ... provided you have not altered the displacemnt of the engine, and possibly some other constraints.

Lastly, TPIS is STILL going to burn you a "generic" PROM, but based on their personal knowledge and experience, which SHOULD be a hell of a lot better than JET or ADS Supersh!t (which only play with the spark tables, slightly higher locking speed on the TC and minor changes to the VE tables...and very little at that).

But, I am finding that for an "optimal" PROM, that even factors like air temperature and altitude affect the "optimal" settings. The stock ecm/PROM is suprisingly forgiving and will operate over a very wide range of conditions, but none optimally. I suspect that your TPIS "custom" PROM will be fairly close for your engine, but STILL will not be optimal. The only way to obtain an "optimal" PROM (and probably only for a certain range of air temperature and altitude) is to burn your own.

Once you've invested the time, it is no big deal to burn a different PROM for different conditions...if you feel you need to. Guess, it depends how much of a perfectionist you are.

 

I should also add, that you can burn a custom PROM to take advantage of cheaper gas when you are willing to sacrifice a little performance for economy. And, another PROM to fully take advantage of premium fuel when you want performance. But, you can only consider that option IF you are willing to burn your own PROM.

Once you have developed the two separate BINs, it takes less than 30 minutes to erase, reburn and install the new PROM in your ecm. Less than 5 minutes if you have more than one PROM available (highly recommended).

 

Actually, the Highway Mode is also on the MAF cars, and was actually used from what I've seen from some stock bins. The enable temp is usually at 185 degrees, so is someone is running a lower-temp thermostat and can keep their engine running that cool, then they'll never allow it to be enabled. I changed it to 160 degrees since that's the temp rating of my 'stat and my engine runs at 165-170 degrees consistently (thanks for the monster Griffin radiator). After I did this, I too noticed an increase in gas mileage. I also lowered the enable speed to 50 mph from 55 since I spend most of my commute between 50 and 55 mph.

------------------
Greg Westphal
'87 IROC 305TPI/A4

 

That's good to know Greg. When I looked, I reviewed the 6E.tdf from the 1989 165 ecm, which does not seem to have those constants. This was using Tuner Cat, which is "weaker" on the 165 ecms. So it doesn't mean that just because Tuner Cat doesn't have it (on the 1989 TPI) that it does not exist. I've never looked at the 1987 TPI with Tuner Cat as I do not have a 32 bin for the 1987 TPI.

 

Luckily, GMEPro does have the Highway Fuel and Spark Mode variables in there. You can even change the air/fuel ratio you want to use at different loads (LV8) and how much spark advance you want. I don't know if it's in the '87 .epe file as I'm using the '89 code. The '89 .ecu file for WinBin has the min. enable speed for Highway Fuel Mode, but that's all.

------------------
Greg Westphal
'87 IROC 305TPI/A4

 

That too is good to know Greg, that different Editors work have more features hacked on certain ecms.

I am still "playing" with the "Highway Mode". I found that my ecm had to have the "Canister Purge" operating above 75% for Highway Mode to work on top of meeting the Minimum Coolant Temp and Minimum Vehicle Speed. There is no way to modify or override the canister purge cycle requirement in my version of Tuner Cat. I will be reading the "hack" to see where this parameter is in the machine code so I might alter it.

However, I am still concentrating on getting my VE tables optimal. When Highway Mode "kicks" in, the BLM and INT go to 128 and I am no longer able to monitor my ecm for rich or lean condition beyond the "advertised" AF ratio. However, when I translated the results and overlayed the translated file into an Excel Spreadsheet I use for graphing, I found that my Injector pulse widths had INCREASED instead of decreasing, inspite of displaying a leaner AF ratio.

I know my tables are causing my car to run far too rich, but Highway Mode appears to use those tables instead of the O2 sensor. So if your tables are not "just right" the Highway mode may actually work against you and burn MORE gas. But once I get my tables right, I am hoping to save some money on fuel.

[This message has been edited by Glenn91L98GTA (edited January 03, 2001).]