MAP Fluctuations & Bung Placement

[slowsixtyduece]

So as long as Ive been running my turbo EFI motor, I have had what I consider to be reasonably sized MAP fluctuations. Since my SDS EFI setup uses both TPS and MAP to determine how much fuel to inject, I rely heavily on both. At cruise, with the throttle at a perfectly steady RPM, I watch the MAP reading fluctuate from 11 inHg to 16 inHg and everything in between. Even at idle it is similar but a little less fluctuation. This instability seems to affect my air-to-fuel ratio drastically at times. As I watch the MAP bounce between numbers, I see my AFR fluctuate from 13.7:1 to 11.9:1 and so on. This is a substantial amount in my book - I can be driving down the road at 14.1:1 afr and all of sudden it bounces to 12.7:1. Very frustrating.

I have taken the manufacturers advice and installed a welding torch tip in the line right before the MAP sensor to reduce the fluctuations. This helped somewhat and smoothed things out a little, but its still not enough. So, here are my questions:

1. Is the MAP sensor bung in the right location? I currently have it tapped into the intact tract about 4" before the CB end casting (see pic)?
2. Being this close to an end casting, could reversion be causing these large fluctuations in vacuum?
3. Is it worth the effort to get the bung closer to the throttle body, perhaps before the split in the intake tract (see pic)?
4. What are your MAP and AFR readings like at steady throttle - are they fluctuating a lot or pretty steady? If they fluctuate, how much?

Any other suggestions are welcome. Would really like to get this figured out. Thanks!

Engine-MAP-placement.jpg

[66brm]

Have you tried a vacuum can in the line to try dampen the signal at all?

[rubenski]

You can also use a small fuel filter inline in your vaccum line.

A filter like on you chainsaw of lawnmower.

[Clonebug]

I would think moving it to the center directly under the throttle body would give you a cleaner signal. Depending on how much cam you have you could be getting some reversion from the current position.
I have my map pickup right under the TB but on the shroud side.

[panel]

You can also use a small fuel filter inline in your vaccum line.

This ^^ , and could you run both those locations into a 'T' and then to your MAP sensor ? Might even out the pulses?

[risk]

My setup is very similar to yours, single center mount throttle body w efi end castings. I am pulling the map signal from just below the throttle body. I welded a 1/8" threaded coupling on there, then drilled thru the intake with a small drill bit. Works very well.

Is there a way to smooth the signal in your software?

[slowsixtyduece]

Thanks for all your comments. I am going to try to take it step by step in the following in order and see how much each one helps out:
1. Place small fuel filter inline with the current way I have it setup now
2. Tie both locations in to even out the pulses, making a T and using the filter before the MAP sensor
3. Use a vacuum can to even out the pulses; anyone know who sells a small vacuum can? I am only seeing large brake vacuum canisters online
4. Drill and weld a 1/8" NPT bung onto the intake under the TB. This is my last resort since the intake is powder coated and I dont have immediate access to a welder. But its probably the best way to get a cleaner signal.

Is there a way to smooth the signal in your software?

Unfortunately there is not...as much as I love the simplicity of SDS, it has its fine-tuning drawbacks.

[risk]

Sounds like a plan!

try searching for vacuum storage canister on ebay motors.. older gm cars had one like this:

https://shop.advanceautoparts.com/p/dor ... 22148588-P

Cheap enough to try.. that is basically what the fuel filter idea is just on a smaller scale.

[panel]

Mostly used in the ITB world but Google image this... vacuum canister ITB. Don't know if you'd need one but......

[slowsixtyduece]

Thanks for all the help. After searching around, I finally found a decent set of keywords/phrases that works to pull up results: "engine vacuum manifold" OR "vacuum manifold block", etc. Looks like theres some aluminum one's on Ebay for about $15-$20. Right up my alley.

I picked up a 75 micron lawnmower fuel filter today. Hope it helps calm things down a bit when I get around to putting it on. I think Im going to just mount hoses from each intake intake bung location, bring it to a tee, then run the filter after that. As Panel said, Im hoping it might even out the pulses...

[slowsixtyduece]

Well, I put the fuel filter in the hose and tied both bung locations in and it did help. It has smoothed out my MAP readings enough to keep my AFR generally within the same double digits before the decimal place, ie: 12.0-12.9, etc. So this is certainly an improvement and I can begin fine tuning a bit more here. I may reach out the SDS and see if they have any other suggestions for their own system.

[andy198712]

A restrictor in-line will help too, you can get them from fish shops, they use them in the airline to reduce flow.....

They use this on vacuum gauges for tuning motorbikes, without it the signal is really jumpy! You the. Dial it down till it smooths out and vola

Helped on my ITBs but it’s a fine adjustment needed