tuning Haltech on a performance car for FE

[91CavGT]

This is an experiment of sorts. I've recently purchased a "sleeper" of a performance car. It's got plenty of power with a VERY easy potential for consideral more power, but with gas prices as high as they are, I can't drive the car every day while getting 20 mpg. So, I want my cake, and I want to eat it.


The car in question is a 1991 Chevy Cavalier station wagon. Under the hood is a fully built 3.1L cammed and turboed V6. The 2 good things about the car for FE are the 5 speed manual transmission swap the last owner did and the Haltech standalone fully programable ECU.

As it sits right now, the car will/has run a high 13 second 1/4 mile at 105 mph. The last owner told me that it got 20 mpg on a regular bassis, on the highway. That's not acceptable to me.

My goals are to be able to carry my wife and 2 kids anywhere in comfort along with any luggage we have while getting a minimum of 25 mpg city/35 mpg highway AND be able to run a 13 second 1/4 mile.


I've owned the car for just 2 weeks and I'm already learning a great deal about the Haltech and how to tune it for fuel mileage. Here's some things that I tuned......

1. I lowered the idle from 1200 rpm to 800 rpm and it doesn't hunt for an idle anymore
2. I turned closed loop operation on! (I can't believe it was turned off!!)
3. I solved the overheating issue (stuck thermostat wouldn't open till 210 degrees, I replaced it with a 160 degree thermostat)
4. I turned the accelerator pump program down slightly


I've not goen through a full tank of gas yet with these changes, but I can already tell a VERY good improvement in gas mileage!


So, does anyone have any experiance with tuning a Haltech computer? I'll be borrowing a wideband air/fuel meter to help fine tune the air/fuel maps in the next couple of weeks, but that brings up a question. I can run a wide band O2 sensor connected to the Haltech and I can tell the Haltech what O2 sensor voltage to shoot for. So it will effectively adjust the air/fuel mix automatically. However it can only adjust the air/fuel mix up or down 20%. What should I do? Find the money to get a wideband O2 and wire it in, or spend a few days tuning the air/fuel maps with the wideband air/fuel meter?


Once I get the car running where I want it to, I'll be working on aero mods!!

[suspendedhatch]

Tuning is tuning, whether's it's a Haltech, Motec, an AEM EMS, or a lowly piggyback. It's just like getting on the internet. Whether you use Firefox, Safari, Internet Explorer, or Opera; it's still the same internet.

The first thing you want to do is tune the fuel map with O2 feedback turned off until it's within a few percent of your target air fuel ratio for each cell on the fuel map that you can get it into. You can do this on a load bearing dyno or you can have someone drive you around all night. When you are finished tuning, you enable O2 feedback so that it can correct for anything that might change and affect your engine's fuel demand. 20% is a pretty wide margin. Mine is set for +/- 10%. But ideally you should be able to run open loop and be within 3% or less of your fuel target.

Do you even know what your fuel target is? It's going to vary a great deal based on the condition and design of your engine but also it's going to vary across different sections of the fuel map. High load sections are going to require a richer mixture. Light loads you can run lean. Peak torque requires the most fuel.

You are going to want to become familiar with what demand you are putting on the engine at different points of the fuel map. Are you cruising, accelerating hard, accelerating light, are you freeway cruising or city cruising, idling, decelerating, drag racing, are you in too high of a gear, are you driving up a steep hill... then with some reading, experimentation, and dyno tuning, you'll be able to till out your O2 target map.

You shouldn't touch the high load portion of the map at all since it's already been tuned.

And fuel is only half the battle. Ignition timing also plays a big part in FE.

[91CavGT]

Originally Posted by suspendedhatch

Tuning is tuning, whether's it's a Haltech, Motec, an AEM EMS, or a lowly piggyback. It's just like getting on the internet. Whether you use Firefox, Safari, Internet Explorer, or Opera; it's still the same internet.

The first thing you want to do is tune the fuel map with O2 feedback turned off until it's within a few percent of your target air fuel ratio for each cell on the fuel map that you can get it into. You can do this on a load bearing dyno or you can have someone drive you around all night. When you are finished tuning, you enable O2 feedback so that it can correct for anything that might change and affect your engine's fuel demand. 20% is a pretty wide margin. Mine is set for +/- 10%. But ideally you should be able to run open loop and be within 3% or less of your fuel target.

Do you even know what your fuel target is? It's going to vary a great deal based on the condition and design of your engine but also it's going to vary across different sections of the fuel map. High load sections are going to require a richer mixture. Light loads you can run lean. Peak torque requires the most fuel.

You are going to want to become familiar with what demand you are putting on the engine at different points of the fuel map. Are you cruising, accelerating hard, accelerating light, are you freeway cruising or city cruising, idling, decelerating, drag racing, are you in too high of a gear, are you driving up a steep hill... then with some reading, experimentation, and dyno tuning, you'll be able to till out your O2 target map.

You shouldn't touch the high load portion of the map at all since it's already been tuned.

And fuel is only half the battle. Ignition timing also plays a big part in FE.

Idealy, I'd like to hook up a standalone knock sensor and an exhaust gas tempurature gauge in addition to a wideband O2 sensor while tuning. This way I can see exactly what effect each change in air/fuel ratio and timing plays on the motor. I know at full throttle the computer is tuned for 12.0:1 air/fuel ratio. I can probably get away with running 16.0:1 air/fuel as a target ratio while under light load due to the car requiring 93 octane fuel. That is going to be something that I'm just gonna have to play with to see how it does at that mixture. I've got a friend of mine has lots of experiance with Megasquirt and is going to help me tune the car.

I curently see low 30 degree ignition advance right now at low load. Under full throttle and under boost it drops to the high teens to low 20s. I learned on my last turbo car that timing means everything when it comes to power. More timing at any given load as long as there is no knock means more efficient combustion which means better FE.


The 1st tank of gas in the car yeilded 14.5 mpg. That was going 160 miles on 11 gallons of gas. I'm on the 2nd tank of gas right now, and the changes listed in the 1st post were made halfway through that tank of fuel. I've currently got 210 miles on this tank of gas and I'll have to fill up again in about 20 miles or so. I'll get an accurate measurement of FE after the next full tank of gas.

Surprisingly, with the 160 degree thermostat, the car now runs at 180 degrees while cruising in 70 degree ambient temps. This stat has an opening temp of 175 degrees and a closing temp of 160 degrees.

[bobc455]

I have a speed-pro, but it is similar in that it is fully tunable and can handle closed-loop, knock detection, etc. The biggest difference is that mine is on a big-block with a fair-sized cam, and I have the aerodynamics of a rather large sail. Last tank was 14.6MPG, and for me that is mediocre (but I'm working to improve that obviously).

Anyhow, your case seems very similar to the Grand Nationals, who have a turbo 3.8. They get about 27 MPG highway in stock form, and you should be able to beat that because your car is lighter, and you have a 5-speed (they only have autos). Of course tuning is key for that.

I'm not sure about the 3.1, but on the 3.8s they don't like to run leaner than 14.7 (maybe 15.0 at leanest) because the combustion speeds up and tends to hammer the bearings. It's not a detonation thing, it's just that peak cylinder pressure peaks very rapidly instead of getting a smooth increase in cylinder pressure. People on this board have advocated "lean-burn" but I'm not convinced, I need to learn more about the engine designs that permit that. So for the time being the leanest setting I have in my A/F table is 14.7.

BTW the GNs typically start around 11.2:1 A/F at WOT, and that seems to be about average. 12:1 sounds a tad lean, but you can tell the difference on a dragstrip.

I have about 42 degrees of timing for low-load situations (like highway driving). I've tried up to 50 degrees, and sometimes I get that to work well but sometimes I get a misfire. 42 degrees seems to be the highest setting where I can get a consistent combustion. I think my problem is actually within my distributor cap, so with your electronic system you should be able to get 50 degrees of advance - play with it and see.

(If that sounds like a lot of advance, just remember that in the "old days" the distributor would see something like 8 degrees of initial advance + 22 degrees of mechanical advance + 18 degrees of vacuum advance on the highway, this gives 48 degrees of total timing)

I've gotten my VE tables to a point where correction is always less than 5%, and typically is 1.5% to 3%. Of course this took a LOT of trial-and-error, and my unit has the ability to change parameters while the engine is running (some systems require that you stop the engine and re-flash, which I'd find kinda annoying). I think it took me a year or two to get the tuning to a point where all of the tables were so finely tuned!

If your Haltech won't read a wideband, you might have to have someone else do the driving while you read a standalone WB gauge while playing with the laptop - obviously you don't want to do that while driving (and it is a rare passenger than can do the tuning while you do the driving). I don't know enough about the Haltechs, but I'd imagine they must be able to get feedback from a wideband...?

Where are you located? I'd love to help you do some tuning if you are in the northeast US.

-Bob C.

edit: I just saw you are in Texas... Guess I won't be able to help tune in person...

[91CavGT]

Thanx for the info there Bob! I hadn't thought about beating the bearings with too lean air/fuel mixtures. That's some food for thought. Yes, this setup is similar to the Grand Nationals accept for it being wrong wheel drive, 60 degree V6 vs. 90 degree V6, of course the transmission, and smaller displacement.

I can install a wideband and the Haltech can read it. I'm leaning towards this means of tuning and setting the Haltech to automatically adjust the air/fuel mix to where I want it. Then all I need to adjust is timing!


I've got a local friend who has offered his hand in tuning and I'll probably take him up on it, but gas is expensive and it's only getting more expensive.

[bobc455]

Originally Posted by 91CavGT

I've got a local friend who has offered his hand in tuning and I'll probably take him up on it, but gas is expensive and it's only getting more expensive.

All the more reason to do some tuning!

I would advise you to get the minimum adjustment from the WB that you can, and get the system very close to the point where closed-loop is nearly identical to open-loop. The reason for that is "transitional" changes- for example if the top end of your map is rich but your bottom end is lean, the WB correction will be pulling out fuel at the top end of the RPM but after you shift it will still be pulling out fuel even though it should be adding fuel (it takes a few seconds for the closed-loop system to adjust, whereas a shift happens nearly instantaneously). I see too many people just rely on the WB to do their tuning, and that's not how it is intended.

Keep us posted, I'd be shooting for 30 MPG with that setup.

-Bob C.

[91CavGT]

Originally Posted by bobc455

All the more reason to do some tuning!

I would advise you to get the minimum adjustment from the WB that you can, and get the system very close to the point where closed-loop is nearly identical to open-loop. The reason for that is "transitional" changes- for example if the top end of your map is rich but your bottom end is lean, the WB correction will be pulling out fuel at the top end of the RPM but after you shift it will still be pulling out fuel even though it should be adding fuel (it takes a few seconds for the closed-loop system to adjust, whereas a shift happens nearly instantaneously). I see too many people just rely on the WB to do their tuning, and that's not how it is intended.

Keep us posted, I'd be shooting for 30 MPG with that setup.

-Bob C.

Thanks for the tip!

[91CavGT]

Well, I was able to get the car mostly tuned in. Air/fuel ratios were around 9.5:1 to 12.5:1 under cruise!! I lowered air/fuel mix to 13.5:1 to 15.0:1 depending on the load on the motor. I also increased timing to a max of 42 degrees while cruising. This has rewarded me with a best tank of gas so far of 27.6 mpg! There's still work to go though........