car stumbles on mid- to high-load tip in. if throttle held constant stumbling lasts sometimes briefly, sometimes for several seconds. datalog shows loads up to 200 at or 1-2 intervals after TPS increase. spark drops to min advance (5 degrees) for (subjectively) the same duration as the stumble.

not certain if stumble is too much fuel (quench), too little, or just the spark. HEGOs seem to indicate brief lean-out after tip in, so i'm assuming too little fuel. doesn't last but a couple of intervals, then goes back on the high side, so could be wrong. i have AFR gauge but not logged, generally seems to agree leans out momentarily.

this happening after off-season refresh in which blown head gasket was replaced and heads/deck resurfaced. elderly laptop died w/out proper backup (i know) so rebuilding tune from scratch.

no doubt lots of issues here but let's start with this: would you all advise re-scaling spark/fuel/both? or changing transients for instant fuel add? or I await wisdom dispensed. thanks for any input.

btw, boost is light at about 7-3/4 lbs peak.

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95 GT manual, track only, not street driven
CBAZA-Tweecer-BE-EA
late 70's 302 block stroked 331 w TEA-ported twisted wedge 165 heads, comp cams XE284HR-10, kb 1.5 blower on GT40 lower @ 7-3/4lbs boost, C&L MAF black tube, summit 77mm tb, 60lb injectors, bbk long tube headers, no AC, no emissions (EGR, air pump, or cats), 3.73 8.8, torsen diff

if load is reaching 200 you have an issue, typically 200 load is reserved for crank, i've seen an ecu use the crank pw function when load hit 200 on one occasion, i just multiplied sarchg*2 and rescaled the fuel/spark table and all was well, i don't recommend that unless you have to, for what your doing you shouldn't need to

what did the maf voltage doing during this 200 load tip in ? are you still scaling load or is load set? prldsw scalar?

get your load below 200 and you problem will possibly be resolved, very unlikely though, as it sounds as though you hadn't dialed in fuel yet

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http://www.efidynotuning.com/ford/

thanks, decipha. appreciate the help. i've decided the spark is a symptom, not the problem. I'll take your advice and work on the fuel. various additional info and thinking-out-loud below.

lots of progress since that post, but still have more-or-less the same problem. biggest difference now is that while "stumbling" the load oscillates between near peak (160-200) and about 90, while the throttle is approximately constant.

learned a few things researching: cured one major problem, tossed out vortech FMU variable fuel pressure regulator and replaced with BBK i had before. fuel pressure constant at 43 now. (regulator adjustment screw loses contact w/spring, so won't adjust below 42. prefer to have slight tension on the spring.)

fuel better, at least idles reasonably at 1000, and EA recommends only minimal MAF changes.

to answer your specific questions: have not changed scale. have a tune worked up but was reluctant to get into scale change for fear of screwing up more than i fixed, if i didn't find all the tables/functions to adjust, and reset all the values appropriately.

prldsw=2 but i have not changed FN035. hmm--that the problem, maybe?

mafv fluctuating in a narrow range as the load oscillates.

it would help if anyone could give the literal load calculation. i've searched and found reference to it being flow vs sarchg, but i'm clearly missing something. based on decipha's point, seems my maf curve must be way wrong. at ~8 lbs, seems i should be peaking at under 150 load, but i'm getting 200 and near 200.

agree fuel probably not dialed in still, despite EA MAF results. EA recommends 38 high slope/89 low slope. i used 70/70 because these numbers fall nicely in the middle of the fuel demand shown on the EA chart. i found this advice in a post here, to fit your numbers in the demand. clearly this is way off the EA recommendation. also saw cgrey8's rec somewhere to adjust offset if slopes wildly different. i modified from original values with EA recommendations on the injector offset.

here's the tune and the latest datalog attached. if anyone willing to dig in it would be extremely appreciated. for this datalog, i started in the garage, drove down the road a ways, back to the garage, and out and back again. notable examples of the problem throughout, where the load fluctuates up and down quickly. good example at ET 244-252, also small example at 381-385. counter example, ie constant throttle no load fluctuation at 334-345. load spikes on slight increase in throttle at ET 428.

_________________
95 GT manual, track only, not street driven
CBAZA-Tweecer-BE-EA
late 70's 302 block stroked 331 w TEA-ported twisted wedge 165 heads, comp cams XE284HR-10, kb 1.5 blower on GT40 lower @ 7-3/4lbs boost, C&L MAF black tube, summit 77mm tb, 60lb injectors, bbk long tube headers, no AC, no emissions (EGR, air pump, or cats), 3.73 8.8, torsen diff