Inspired by this forum, I recently jumped into the DIY PROM world. Like many folks I started with ARAP as the baseline. One thing I noticed was that the car exhibited extended crank times and did not idle well in open loop compared to the stock APYU3516 bin. Attempts to smooth out open loop via tweaking the open loop air-fuel ratio and timing vs coolant temp tables were unsuccessful.

After reading that other folks having the same problem, I copied all the flags, constants, and tables from my custom ARAP variant back into the original APYU3516 bin. Problem solved! Even though I didn't change the data values when I copied them, "something" changed for the better. I don't know what that "something" is but I do know it worked.

My experience suggests that if you're experiencing extended crank times and poor running in open loop with ARAP, you ought to copy your custom settings back into another GM 6E bin file for comparison.

 

Gauging anything on a small sampling is impossible to do.
When you just blanket copy things, you don't learn what the actual problem is/was.
Gets ya right back to runs OK, vs runs right.

 

very true grumpy, not only does that apply to Prom Tuneing, but when working on the engine... The short way out woulda been nice a few times, but...it woulda ran okay, i don't like okay, i'd rather see perfect.

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
-Gutted Air Boxes

 

What's the cause of the extended crank time? I'd love to kill at least that. Sounds like my starter is getting rung every time I turn her over. Same goes for the little dip into sub-500RPM on initial startup. After a couple seconds its gone, but nonetheless, identification of the problem with these two performance factors in the explicit sense would be very nice indeed.

 

From the parameters available for display and modification in Tunercat, the two bin files are identical yet the response is vastly different. This tells me that the differences exist in a data structure not currently available in Tunercat or in the micro-code itself. Yes I could have spent more time with ARAP trying to smooth things out but if the real difference is currently hidden from view then its likely to be an exercise in frustation. The car now runs very well in open loop. I am very much a newbie. Just my experience so far.

 

Mark, I think you've hit the nail on the head! I've had this and other problems using ARAP. I think there's code we can't get to with TunerCat that we can't change that would "fix" the problem.

If the APYU bin is the GM stock bin for '89 L98's, I might try that as my baseline instead of the ARAP. Good or bad idea?

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'87 IROC 5.7l TPI - original owner!

 

This is interesting because when using an ARAP based chip in my 86, my extended cranking problem disappeared. I start right up, and the idle drops quickly to the desired 625 range, which was not the case with my 86 chip... idle would stay high for quite a while before dropping, and then would hunt in drive.

Before using the ARAP chip, I had tuned my stock chip WOT 02 readings by increasing my fuel pressure (was running lean), all my BLMs were high, but with the higher FP, they dropped into range (130s from 145-150). For the ARAP, I left my fuel pressure where it was (at first), as that was what my motor liked. My BLMs ended up being a little lower, so it now likes a little less FP.

What other tuning have you done to the ARAP? Did you just "plug it in and go"? Have you recorded other information?

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Mike Metzler (Desert86Roc)[*] Check Out:SpeedWorldMotorplex.com[*] Check Out:Chevrolet F-Body Online Part & Illustration Manual[*] My 86 IROC 305 TPI Page (406 build in progress)

ET's @ 1250 ft[*] 14.28 @ 95.461 mph (uncorrected, NOS, no headers)[*] 15.362 @ 88.238 mph (uncorrected, headers, no NOS)
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[This message has been edited by Desert86Roc (edited June 25, 2001).]

 

PJ, I think the APYU is an excellent 6E base code. You can also run AUJM from an 89 IROC 350 w/3.27s if you want to keep it in the family (Camaro vs Firebird). I couldn't find any differences in the data parameters viewable in Tunercat. Both are available from Mike Davis's website.

Mike, I know you're not the only person whose idle improved with ARAP so no general conclusions can be drawn, positive or negative.

I indeed have made more mods to ARAP based on road test and scan tool data. First task was tweaking the MAF scalars to get BLMs back in line. I was pegged at 108 from just off idle through the RPM range with both APYU and ARAP. I attribute this to the modified MAF, SLP airbox, K&N, and maybe some sensor drift over time. Changes on the order of 10-20% were necessary to bring the BLMs to the current range of 124-130 over the complete closed loop operating range.

The most time to date has been spent on the base spark advance table. Simply put, ARAP has WAY too much timing at the lower LV8 values for my stock iron head L98. My EGR system is operational but I had to pull out major timing to eliminate misfires under cruise conditions. The timing curve I run now looks a lot like APYU at lower LV8 values and ARAP in the higher load range (where APYU is seriously lacking IMO).

I've changed many of the constants along with TCC parameters to suit my taste. Currently I'm working on Highway mode fuel, PE fuel, PE spark, and acceleration enrichment but it's too early to see where I'll end up.