Off-idle stumble

[UnatralyAspiratd]

I've been fighting this problem for as long as I've been running MPI. The car starts and idles great. If i blip the throttle from idle or try to start from a stop it stumbles like its dropping cylinders. Ive tried everything I can think of to work it out but its still there. Accel. comp (TPS based), timing, idle mixture... it drives just fine, pulls from 1200 to 6000 smooth as silk and i am getting decent mileage but this symptom is quite annoying. Its better if i turn the idle up and worse if its lower. It will idle right down to 4-500 (its at about 950 now) and if I add throttle slowly its fine.

 

Magna Manifold

2.5" intake pipes

K&N open cone filter

Aus. Ford TB

3-Bar MAP

Stock Turbo

3" Exhaust

550cc/sec injectors (i think, can't remember)

 

Thanks,

Chris

[heefner]

Do you have a wide band a/f gague? It sounds like its going lean of idle. how big is the throttle body? If you don't have one you need to get one or take it some where and have it professionaly tuned.

[UnatralyAspiratd]

I do have a Zeitronix wide band, unfortunatetly i dont think it reacts to this instance fast enough... It does feel like it is leaning out but i have added acceleration compenation (in incriments of 10% or so) to the point where it worsens without getting better.

 

the TB is 70mm or so, prolly too big for my setup...

 

Chris

[heefner]

No I run a 70mm bbk with no problems. try holding the throttle steady at each of your rpm inputs in your map. Note what the a/f is. Adjust accordingly. If fattening it up dosen't seem to work, try to lean it out a bit. Make sure ego correction is off.

[button]

ignition timing.

i had the same problem at one point.

as soon as you look close at your timing table, you will see.

theres too dramatic of a change from 0-load (~30-40kpa), to light load (just under 100 kpa), to low load (~60-70kpa)

so from a stop it goes:

30-40kpa, ~100kpa, ~70kpa.

but also, the rpms are important.

~900rpm, 1500rpm, 1100rpm.

so it makes a sort of loop.

 

I was blaming my fidanza, but after messing with the timing, problem solved.

 

oh and what stand alone are you using? that would help alot.

**NM, just read your sig**

but heres my table. looks like your using a varient of MS.

My Ign table

[UnatralyAspiratd]

Thanks for the table,

 

THats a bit different than mine. I have more resolution on mine so I will use yours and do some extrapolating and plunk that on there and see what happens.

 

Thanks,

Chris

[heefner]

rather than changing the whole table do low rpm off idle and see where that gets you. Try not to change too many things at one time so you can figure out your problem.

[autoxer]

Altough I am not running MPI I am running FIPPRO and had same issue. And it turn out to be accel enrichment bins set to low. Seems like nobody wants to talk about this subject but it is just as important as VE table. If these settings are to low your car will fall flat on its face when you slam the gas to the floor at take off to high and it will back fire. Here is what I have learned on my own.

First off TPSdot Threshold no Lower than .977 no higher than 2 norm seems to be .977

Accel Bins "2 v/s and 4 v/s" are set for " tip in "on the accel pedal so they get set to help when you just tap the throttle or ease on the throttle also these will affect when you cruising at part throttle like on the highway.

and " 8 v/s and 15 v/s" these are set for when you stomp the gas pedal to the floor. And here is where my problem was, my car would not rev good in park. I stomp the gas and it sounded like a weed eater on crack and from a dead stop I could stomp the gas and the car would not go. So I increased the " 8v/s" to 8.2 and the "15v/s" to 14 and now it revs fast and clean. But like with everthing else all cars will be different. What I did was set all bins to 0 and rev'ed the engine then added some to each until the motor rev'd fast and clean. Don't know if will help anybody but i has made a world of differance in my quest..

[matt88]

YEAH I HAD THE SAME PROB AND I DID THE SAME AND IT WORKS GREAT NOW. (FIPMPI)