Roger Davis

I have an early 91 TA, I think 5.0 with TPI, no mods, 5 speed manual, in good shape. I get about 22 mpg in mixed city / freeway (30% / 70%) driving if I'm careful. I do occasionally use it for highway trips, sometimes in very hot temperatures.

I'm considering changing the chip to use highway mode, but am concerned about reliability. My main concerns are:
- Piston reliability?
- Valve reliability?
- Preignition / Detonation?
- Required fuel : can it still use regular?
- Catalyst reliability?
- Passing California emissions testing?
- What chip changes beyond highway mode settings do I need to make?
- What other mechanical settings or changes do I need to make?
- What real benefits will I get?
- What else did I not know enough to ask about but is important?

Thanks!

Fast355

iTrader: (2)

As long as highway mode is used entirely at a low load cruise, I see no problem with reliability in any way. The combustion temperatures of the leaner mixture are actually lower than they would be at stoichiometric ratios. The pistons and valves might even last longer in lean cruise, not as much carbon or heat. Detonation should never be an issue if lean cruise is setup properly, the second the engine gets the first amount of load on it, it should drop out of lean cruise. Catalyst reliability should not be an issue either. A lean missfire that could harm the cats can easily be detected. I run everywhere on 87 octane. Setup properly, lean cruise will not kick in until you have reached a steady cruising speed of about 50-55 mph, light throttle, and enough time has passed for the BLMs to have stabilized. The emissions test IIRC for California are the IM240, I do not think that the cruise speed maintains 50+ mph long enough to turn on highway mode. I would tune the VE tables with a wideband to deliver the desired air/fuel ratio and set the NBO2 parameters to achieve a BLM of 128 (+/-3). I am getting about 17 mpg in mixed driving and have seen 20-22 mpg @ a steady 70-75 mph on long trips from a 305 TPI powered Fullsize Van.

Theking

iTrader: (1)

Lean /or to lean conditions will cause alot of heat and melt the pistons...
Lean conditions could cause alot of damage if running it to much...
So if you do highway mode, you need to keep track of your BLM.. dont go to lean over time. That will cause big problem with pistons.

Nitsuj86Iroc

I feel similar to what Fast355 said, lean should be ok at low load conditions. how lean im not sure. now when people talk about lean conditions causing a lot of heat and burned parts, they are thinking in terms of racing, WOT, high loads...
im no scientific hotshot, but in a thermodynamics class i had we studied a bit about combustion engines. it was oversimplified in ways that made it somewhat inaccurate, but the concepts were correct. anyways, it was shown that for fuel like gasoline, the most amount of heat created is at a stoichiometric ratio. any leaner or richer caused less heat. now, maybe real world conditions differ, im not sure.

also, i cant find where but i read somebody on here saying they had lean cruise activated for a few years and the catalytic converter was holding up fine. its worth a search.

gta324

I have done some testing with lean burn.

Lean mixture burns slower and the EGT readings dropped some, and you may need some xtra SA to compensate for the slow burn. I wouldnt do much changings and pushing the limits without a WBO2. The numbers that are in some stock bins works if you just enables them. I tuned a built 350 with WBO2 with ARAP values, Closed loop showed 14.0 AFR and HWM gave 15.5. worked great. I think you can go to 16 AFR-17 AFR depending on the tune/combo without any problems.

Learn is usually turned off during HWM so BLM wont change.

Search, there are some info about it.

88 350 tpi formula

iTrader: (9)

not to hijack this too bad but can't I add this table to another gm pcm?($8B) anyone care to teach me how you add stuff?


I guess the gto LS1 cars can turn this on as well. still can't figure out a way of getting the table to enable in the LS1 f-body cars though

DENN_SHAH

iTrader: (1)

i've been running hiway mode for about 3 years now.
i have had no problems with the motor of any kind.
i can't say about the cats, when i put my motor in i put cheap cats on & they didn't last too long. they had melted down long before i made my first change to the chip.
but i don't believe it would hurt them unless you go so lean your getting misfire which would also hurt mileage & driveability.
you can set when you want it to come on using the parameters in TunerPro.

on the hiway i picked up about 3 MPG using hiway mode.
if you already have your tune right, running hiway mode shouldn't be a problem, just go slow with it & watch your data logs. i started playing with the hiway fuel first & later on i turned hiway spark on.
if you don't have a wideband O2, i highly recommend getting one, it makes tuning much easier.