Accel Enrich on a mild throttle body injected 302

[svocapri]

I'm hoping someone can help me understand the differences between Accel Time, Accel Taper Time, and End Pulsewidth. I am having a problem where the engine wants to backfire through the intake on rapid throttle changes below 2000 RPM. I originally had the Accel time set to 0.1 and taper time set to 0. The engine would backfire even when I had it set to 25.4ms at 240 TPSdot. It got a little better when I set Accel Time to .3, and it got even better when I set the taper time to .3, but it still goes lean and stumbles; and occasionally backfires if I stab the throttle too fast. I also had set the Accel Time to .5 but had no taper time and it was worse than when I added in the taper time. Can someone take a look at my setup and help me get a handle on this?

Thanks,
Julian Weber

[Matt Cramer]

This diagram shows how the numbers you were asking about work.



Also, please don't turn on Enhanced Acceleration Enrichment until EVERYTHING else is dialed in.

[slow_hemi6]

Keep in mind yours won't look like that because you will have 2 AE pulses superimposed but slightly offset. That is what happens when you run a bit of TPSdot and a bit of Mapdot. I would suggest you just go 100% TPSdot.

[svocapri]

Matt Cramer, Thanks! That picture helps tremendously. I'm sure I have seen it before but this time it clicked.

Slow_Hemi6, Thanks for the explanation of using both. I was wondering where the large spike and then smaller AE was coming from in my logs.

I have some more questions.

1. Since I am running ms2 Exta 3.4.2 is the added field in "Time Based Accel Enrichment" the AE pulse in ms?

2. Does EAE run alongside Time Based Accel Enrichment so that there is the still the AE pulse and there is the quantity added for ATW or SFW? I'm hoping to use EAE once I have things dialed in.

3. Can you confirm that the following is how Time Based Accel Enrichment works?

scenario 1
Base pulsewidth = 2ms
AE pulsewidth = 2ms
Accel time = 0.3
taper time of 0.0
end pulsewidth of 0ms
For .3 seconds every injection event will be 4ms (assuming base pulsewidth doesn't change).

scenario 2
Base pulsewidth = 2ms
AE pulsewidth = 2ms
Accel time = 0.3
taper time of 0.3
end pulsewidth of 0ms
For .3 seconds every injection event will be 4ms
For .3 more seconds it will start at 4ms and taper down to 2ms for each injection event.

scenario 3
Base pulsewidth = 2ms
AE pulsewidth = 2ms
Accel time = 0.3
taper time of 0.3
end pulsewidth of 1ms
For .3 seconds every injection event will be 4ms
For .3 more seconds it will start at 4ms and taper down to 3ms for each injection event.

Julian Weber

[whittlebeast]

If this motor is a typical open plenum American intake, like has been a typical Chevy 350 carburetor motor from the 80s, and the injectors are up where the carb used to be, I have found those motors need a bunch of AE.

This is most likely what got the injectors moved down close to the intake valves real early in EFI development.

Andy

[svocapri]

Andy,
The engine is a ford 302 with a Weiand Stealth dual plane manifold, and a factory HO roller cam. I am finding your experience is correct that this engine needs a lot of AE.

Julian

[whittlebeast]

You simply have to tune it to feel. When you look at the data in MLV, it defies logic. Orders of magnitude more AE that my port injected motors. I tune a similar autocross motor with a Ford 302 and some sort of typical highrise intake.

Andy

[slow_hemi6]

Yeah I have a 1000cfm TBI on a high rise manifold,large hydraulic cam. It needs a good hit of AE. I have mine so I don't feel hesitation in it. You probably don't need what I do but to compare, I have my End PW @ 0.8ms, it tapers but keeps the pulse up for longer. I am using a fairly long Accel time of 0.8s and a taper time of .4s. I use Added/TPSdot of 0.3/20 1.0/100 1.8/140 3.0/500. My TPSdot could react quite differently to yours however. I can run a threshold of 25 without false triggering. Seems like a lot but if you have ever watched what a couple of holley pumps on a 750DP will throw in to cover the transition and over what duration, you will know it takes plenty. Don't be savage on the decell fuel amount either, I tend to stay at 100 or 95. It just messes with transitioning from decell back onto throttle. Use the overrun fuel cut in a much more defined band if that is what you are trying to achieve.

[Matt Cramer]

You got it, and yes, the EAE is applied on top of the regular acceleration enrichment.

[svocapri]

Matt, Thanks for the confirmation.

I have made some real progress finally. I spent about an hour and a half slowly rolling on the throttle at about 1,200 and hitting full throttle around 2000. I got the high load area dialed in without activating accel enrichment. Then I bumped up the Accel time to 0.8 following what Slow_Hemi6 had said, and I bumped the accel taper time to 0.4 with an end pulsewidth of 0.2. The first time I got on the throttle quickly, it stumbled so hard I thought it was backfiring again but this time it was too rich! I reduced the added pulse from 20 down to 7 and things really started to work better.

One thing that I am having trouble with is that autotune keeps bumping the cells too high where I roll on the throttle. I am guessing this is because I don't have enough AE in the low area. The TPSdot appears to be around 40-60 when this is happening. Should I just add more accel time, or do I need more pulsewidth down there? I have attached a log showing it going lean.

So now some more questions.
1. How can I tell if my accel time is too long?
2. Once I get my MAP table dialed in and my accel enrichment is good, how do I start adding in EAE? Do I reduce my accel enrichment and let EAE compensate or do I leave the accel enrich where it is and use EAE to keep the large quantity added by accel enrich from making it go too rich on throttle lift.

Thanks everyone for the help and advice. This car is almost daily drivable.

Julian Weber

[Laminar]

One thing that I am having trouble with is that autotune keeps bumping the cells too high where I roll on the throttle. I am guessing this is because I don't have enough AE in the low area.

Autotune shouldn't be active while you're dialing in AE. Let autotune dial in your VE table at steady state, then disable it to manually set your AE.

[svocapri]

I did some more tuning this afternoon and things were really going well, but then as I was heading back I hit it one more time and it went crazy. Did my distributor pickup just go bad? I have two logs. One with a decent accel enrichment and the other showing the bad RPM signal.

rpm_noise2.png