Blackbird

I have been unable for months and months to figure out why the car goes 10.1 a/f under decel and will stay there until I touch the gas. Happens no matter what, with maf, without maf, with turbo, without turbo.....

well I noticed yesterday on a drive it goes wacky rich as soon as I hit 21" of vacum. 20 or less, car maintains it's 14.7 a/f. Let off the gas a bit more and hit 21" a/f drops like a rock. slighty touch gas to get it to 20" or less, A/F climbs right back up.

Does this light any lightbulbs for anyone for an area I should be looking into to solve this problem???

dissonance

What does the injector duty cycle show? On decal? Should be like "point" .5% or lower

Blackbird

I would have to log again to find out. have not been logging injector duty cycles.

lets say they were not .5 or lower then what? IE where are you heading with that question.

thanks!

technical

I would look at a couple of things if it were me:

If/when DFCO activates.
TPS values ( PCM getting fooled? )
If you have DFCO turned off, what does the VE look like at those values (rpm, low load)

Blackbird

dfco settings - when stock it will go pig rich then go ridiculously lean as in over 20:1 so for now dfco is off

i have tried plaing with ve for that target area and have had the values so low it's ridiculous (in the teens) no effect.

i dont think it's tps since it will be fine until it hits that 21" of vacum. my eboost will output kpa so I think I am going to switch to that mode and see what that value is and scour tables for anything that jives.

dissonance

maybe a place to start... like technical said maybe ve or something else

are you getting any bucking on decel? like it is burning fuel?

SmokingWS6

iTrader: (1)

you need to log injector pulse width. What injectors do you have? You might need to lower minimum injector pulsewidth, default injector pulsewidth ect if you are running large injectors.

technical

Turn DFCO back on. All engines go rich the moment the throttle is closed. There is a slight delay before DFCO cuts off the fuel. That is why you see it go pig rich for a moment then extremely lean.

Blackbird

well with dfco on it going leaner than 20:1 is not going work well, the car hates it. I don't believe it's supposed to go that lean with DFCO is it? I could investigate if there is a way to minimize dfco, that might work. what bothers me though is I feel I am trying to tune around another issue that I can't track down. I have the same injectors in my buddy's 98 TA that I tune and no such issue exists.

smoking - it does this with both lucas 42's and my current motron 60's, so it's not directly related to the injector.

SmokingWS6

iTrader: (1)

I'd say the motron 60's are to large for stock pulsewidth settings. Log pulsewidth and see what they are reading during decel when afr goes pig rich.

Blackbird

please read above.

also does it with 42's and I have these same injectors in another 98 and it does NOT have the issue.

thanks though, all input is appreciated.

SmokingWS6

iTrader: (1)

I did, i'll still bet a beer on it

Blackbird

Allrighty I have nothing to lose to log and see but they work fine on another car and if it was a widespread issue I think we would see numerous posts about this.

In any case I will log and let ya know.

BLK02WS6

iTrader: (2)

I am seeing the exact same problem with two of our customers cars. Both cars have the exact same 42# injectors, same turbo setups, nearly identical to each other - one does what you describe, one doesn't! If I figure it out, I'll let you know.

Blackbird

as will I.

nice to know know there is at least 2 of us trying to figure it out

Blackbird

Give the man a prize. Dropped the values down to 1.003 and it fixed it!

Now I just have to go fix the low end of the VE table I screwed up so bad trying to overcompensate

Thanks for the tip SmokingWS6! I am glad I wasn't too stubborn to not try your suggestion.

Ragtop 99

iTrader: (7)

Would the same issue of pulsewidth apply to SVO 30# ? I have a similar problem of going pig rich and then starting to lean out. I've probably overcompensated as well.

WS6FirebirdTA00

iTrader: (33)

i have 42# injectors and no matter how lean the ve goes with or without dfco on below like 30 kpa it goes to negative 11 or so, no matter waht kinda fueling i have in the ve. but i havent checked out what it woudl read on WB yet

so you are saying to go lower min pulse width?

WS6FirebirdTA00

iTrader: (33)

so what pulse width were you all seeing on decel? im gonna put the min pulse width to 0.9 because that is as low as those injectors can go and ill see if it helps me out. but i was just curius on what you saw on pulse widths

frcefed98

iTrader: (16)

Heath,
I gotta try that too, same thing is happening with my 98. Goes super rich on decel, especially on the highway. Yesterday when logging my WBO2 was reading 9.1s

So which screen would I go to? Just slap in 1.003 and that should do it?

J