87 Vette Owner

Hi -

I'm finally getting around to tuning again (had some valve train geometry issues, but adjustable guide plates solved that).

Anyway, I'm tuning an 87 vette with a 383 Mini Ram engine. 165 ECM, using the $32B mask, Autoprom, LM1 A/F meter, and TunerPro RT. Yes - the MAF is gutted - it was before I knew better .

Cold idle / warm up seems to be my biggest issue right now. It starts up cold nicely and will idle as commanded. However, if I even lightly touch the throttle, it goes lean (I can see it clearly using the LM1 meter graph - as soon as the TPS voltage jumps, AFR gets a nice lean spike). This is obviously acceleration enrichment, right? HOWEVER, when the engine warms up and goes into closed loop, I no longer get the lean AFR spike when I blip the throttle. In fact, it responds nicely . Why would it need A/E when cold in open loop, but not when warmed up in closed loop? It's really interesting because the transition is instant. The second it reaches a certain temp (haven't data logged that yet) and goes into closed loop, it revs fine.

My second question is - in TunerPro RT ($32B mask), what is the best variable to use to tune the acceleration enrichment? The following all seem to relate to A/E:

Accel Enrich % BPW Factor vs Async pulse
No. of accel enrich async pulses vs coolant temp
Accel enrich async factor vs coolant temp
LV8 accel enrich factor vs delta LV8
LV8 accel enrich coolant factor vs coolant temp

Thanks so much for your help!
Dan

8UpAFord

You'll need to play around with the open loop tables, make 10% increases at a time.
Sounds like you need to tune your MAF tables to if you gutted the MAF sensor. Removing the screens will cause the mixture to change. data log data log data log. I plan on slapping a 383 in my vette later on. It's a challage you'll need to do tons of tuning. are you still using the stock TPI unit?


BTW you're using a 32b, I was using a 32b, until i found a 6e bin, the fuel tables are more user friendly to adjust. Plus It's all round a little better chip. I use the 6E with the stock 32b timing tables, seem like my car runs stronger that way.

87 Vette Owner

I made some initial changes to the MAF tables and was starting to get some decent results (was pig rich for a while). I may have leaned them out a bit too much though. The hard drive in my lap top crashed, so while that's being fixed, I'm using my old Auto X-Ray scan tool; not ideal, but enough to get me by. I also data log using the LM1 meter (a/f, rpm, tps). I'm hoping to get some more time in this weekend.

I'm using the TPIS Mini Ram. With my cam and the 4.10s, it works well and is easy to remove. But, tuning it on a MAF engine (as I've come to learn) is a little trickier than something like a Super Ram.

I played around with an APYP $6E bin and didn't notice any major differences, but didn't use the $32b timing table as you did. Maybe I'll give that a try at some point. I've made some good progress starting from a stock ABTC $32b bin - would I just copy everything I've done (timing, MAF, A/E, etc) to a $6E bin?

Grumpy

Given time, you might get it close enough that you'll be happy.
A MAF system has a guaranteed error in it that's hard if not impossible to work around (other then just being *lucky*). A MAF based system will always over report air comsumption during quick throttle openings, since some air is just being used to change the vacumm level inside the plenum, rather then actually being used for the combustion process. The later codes have several tables of corrections to deal with that error, which are lacking in the earlier codes.

Then there's the matter of you manifold....
If you look at the interior of it, you'll see how the rear wall acts as one surface for the last runners, so with the incoming air's inertia, the air doesn't bend very well to actually flow into the last runners. If you look at an HVAC text, you'll see how the last discharge vent on a branch has a *dead area* behind the last vent.

Now with that said, you can try using more delta MAF AE and see if that helps, sometimes, you can run rich enough to get over the inherit faults. But, you might hit the limit of the injectors. TPS AE is basically to cover the throttle blade movement, and the MAF AE to cover as the engine catchs up to the new TB opening.

87 Vette Owner

Definitely not the friendliest of manifolds to tune for sure, especially on a MAF system. I've had to increase idle speed (950 now) and timing at idle (28 degrees) just to smooth things out from the reversion. I probably couldn't have picked a worse combination of cam / intake manifold for a beginning tuner . (In my defense, I was expecting the chip I received along with the engine to be correct and tuned for my specific engine. It was definitely NOT, and really only tuned for WOT, so here I am doing it myself.)

Thanks very much for the insight. I've got 30 pound injectors, so I should be covered from that stand point. I haven't done ANY A/E tuning yet, so hopefully I can make a difference there. I read Twilightoptics post # 4 in this thread https://www.thirdgen.org/forums/diy-...-has-lean.html regarding what he did to fix the issue, so hopefully that will help.