I just got the ARAP bin in my car. I have some questions about the highway mode. In ecm constants i noticed that Highway enabled max speed is set at 55mph? That is saying that high way mode is disabled when you go over 55mph right? Any idea why that would be set that way? What would you guys suggest on the max spark while in highway mode? 17? 14.7? Thanks, Brendan ------------------ 1987 IROC-Z L98,SuperRam,EB 6085's,LPE 219/219 Roller, Crane 1.6RR, EB TPI Base, 58mm TB, ADS 24#, AFPR, K&N, EB TES, Catco Cat, 3" Borla Cat-Back, Accel cap,rotor,distro/other crap, MSD 6AL, MSD Blaster 3, Aluminum DS, 94 Disk Rear, Adjustable Valve, Precision 3.73 Gears, Sub-Frame Connectors, Hotchkis Lower Control Arms, KYB Shocks/Struts, Suspension Techniques Lowering Springs, Polyurethan Bushings all over the place, Moog Upper/Lower Ball joints and Tie Rods ends/Idler Arm, To see the ROC, Check out the webpage Here

leirch, seeing as how you have aluminum heads, you should use a different spark table. I just recently switched mine to that of an 89 vette and noticed that it seemed to pulled stronger. I think as a rule aluminum heads dont need as much total timing (Ive been told 28-32 at WOT) and higher when cruising. If you look at the vette table you will see what Im saying. Go to grumpys ftp site to find the bin.

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355 10:1 , AFR 190 heads, LT4 HOT cam w/ 1.6 roller rockers, complete Superram intake, 58mm BBK TB, 24# injectors, screens out of MAF, MAT relocated, March underdrive pulleys, Streetdampner, Crane HI-6 ignition, 160 thermostat, K&Ns, TES headers(Jet hot coated), Mufflex 4' cat back, B&M shift Kit, 2500 converter, and 3.27s.

I was running the 89vette bin for a while. The ARAP seems to work a LOT better, should i just change the spark tables to the 89vette bin? But keep everything else from the ARAP bin?

Brendan

To answer your first question, you have it backwards. Highway fuel mode wouldn't be enabled until you hit 55 mph. Concerning your 2nd question, you're talking about 2 different things: highway fuel mode and highway spark mode. The max spark advance you'd want to run depends on how much your engine can take, but there's a maximum value in the bin (usually 42 to 45 degrees). For the maximum air/fuel ratio in highway fuel mode, you could easily get by with 15.5 or 16 if you have your engine and PROM tuned up pretty good. 14.7 is the stoichiometric air/fuel ratio for internal combustion engines...

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Greg Westphal
'87 IROC 305TPI/A4

Thats what I did. You might want to give it a try. Seemed to work for me but every combo likes different things. Try the vette spark tables with the ARAP bin and see what happens. That 14.7 and 15.0 sounds like your talking about the A/F ratio while in highway mode. I am still asking people on this board how lean I can while in highway mode.

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355 10:1 , AFR 190 heads, LT4 HOT cam w/ 1.6 roller rockers, complete Superram intake, 58mm BBK TB, 24# injectors, screens out of MAF, MAT relocated, March underdrive pulleys, Streetdampner, Crane HI-6 ignition, 160 thermostat, K&Ns, TES headers(Jet hot coated), Mufflex 4' cat back, B&M shift Kit, 2500 converter, and 3.27s.

Greg, thanks, i hope to get the car on the road this weekend so i will see what it does.

Brendan

Are you sure that "max speed for highway fuel mode" is in fact the minimum speed to engage it. That doesn't make sense to me. Also that means that highway spark mode is never engaged because that value is set to 6350 rpm for all the bins I've seen. I don't understand, why would they define those tables, like highway mode spark advance vs. load but not even use them.
Also I've got an off topic question What does LV8 stand for and how does it convert to grams/second
Thanks

Canadianbeast,
I had the same questions!, if infact Greg is correct which i'm sure he is. Why are the tables all labelled *** -backwards? Another good point that your brought up, why would they even design a "highway fuel" mode if it isn't even enabled!?

Brendan

I don't know why they'd define certain tables and not use them, especially the highway spark mode. I heard (and Grumpy may be able to confirm) that the EPA didn't like the highway fuel mode because the car really isn't in closed loop (O2 sensor is ignored) while in it. Plus, running lean produces more of one of the emissions gases (I think NOx).

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Greg Westphal
'87 IROC 305TPI/A4

For Highway Mode to work optimally, you need your car reading 128/128 perfect as Highway Mode relies on the tables. The GM calibrations are on the rich side (for warranty reasons I suspect), so they wouldn't necessarily give the results you expected.

I found this out when I first got into eprom burning and invoked Highway Mode. My mileage actually decreased and my injector pulses lengthened until I got my VE tables fixed.

And yes, GM did disable them by making the minimum speed 255 mph. They also disabled the Highway Mode Spark Advance by making the minimum RPM very high and the code regarding the 4th gear test needs to be changed.

Lastly, the lockout timers for both HM and HMSA need to be set to 0 to ensure it stays in HM and HMSA. If you don't set it to 0, the routines "drop out" every 60 seconds and do not re-engage until the time set in the Lockout Timer.

This is all with SD cars, but I assume similar tricks were used by GM for the other cars that have this code.

These lockouts are also on the $6E (MAF). Why do you suppose "they" did that? Why would you want to leave highway mode after 60 seconds and take a ten second break? In the absence of contradictory recommendations, I'm going to set the Enable Delay time to zero.



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'87 IROC 5.7l TPI - original owner!

Additionally, while reading posts resulting from a search on highway mode, I got the impression that "everyone" thinks that the spark aspect is locked out because the minimum RPM is set at 6350. Using TunerCat's latest TDF, mine says this is the maximum RPM for higway spark. If this is so, it's not really "locked out" as others have said. Was this simply a case of a misworded title for the constant?

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'87 IROC 5.7l TPI - original owner!

I think I mentioned in another post on this board about why this was done. The 2 concerns I could think of were: running lean for too long might overheat the catalytic converter, and the computer needs to update the block learns since the air quality (temperature, humidity, and pressure) change while you're driving. Of course, the computer is supposed to be able to compensate for those changes, but I (and others) never found it in the $6E code...

Regarding TunerCat's title for the rpm to enable highway spark, it's mislabeled, as well as the mph enable for highway fuel from looking at their definition file:

http://www.tunercat.com/tnr_desc/ecm_sup.html

It should be minimum rpm or mph to enable highway spark or fuel. That's how GMEPro has it listed for the highway fuel...

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Greg Westphal
'87 IROC 305TPI/A4

Thanks, Greg. My new TDF came in just today, and I made those observations. It says, "Max RPM.." and "Max Speed...". They got the RPM title fixed, but it looks like the speed title should read, "Min Speed...".

You've got me concerned about overheating the converter (and exhaust manifolds, and gaskets, and exhaust ports,...), now. Perhaps I should leave those time out settings alone...?

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'87 IROC 5.7l TPI - original owner!

Well, Glenn isn't having any problems with his settings at zero. He just mentioned something to me why GM had them or didn't enable them at all: NOx emissions increase when you lean the engine out. I'm sure the EPA would've frowned on that. I'm gonna try my time out settings at zero instead of the 2 seconds I have now since I haven't had any problem with them at 2. The only thing you could really overheat would be the catalytic converter, but that shouldn't happen since you'll be on the highway and the airflow underneath/around it should keep it cool...

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Greg Westphal
'87 IROC 305TPI/A4

I have one question. I your car is running lean and the timming is set accordingly or should I say correctly for the application, wouldn't this lower converter temps because of less unburned fuel reaching the converter?
I know a lean mixture burns hotter but I thought that a rich mixture is what causes the cat to over heat. Just thought I'd ask.

Steve

Steve: You are correct, it is a rich mixture that makes the catalytic converter heat up. As you said, this is because it has to burn off the unburned fuel that is entering it

I e-mailed TC (at TunerCat) about the lables. He acknowledged that they should read Minimum Speed and Minimum RPM. He sent me a corrected TDF. I assume it's generally available upon request (Version Q).

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'87 IROC 5.7l TPI - original owner!