EFII map fluctuations

[terry.mortimore]

Hi gang:

I have the dual EFII system and I'm struggling a bit to get the fuel settings dialed in to where I want them.

I now have it programmed so that I get a good start and warm up.

I've noticed on three different occasions that I'll have the RPM/fuel set to where I have AFR readings in the low 13's where I want them only to discover the next time I run the engine a few days later that it will be too lean by quite a bit.

I do put the values lock on each time I have them set, so the fuel numbers have not changed.

The barametric pressure did change quite a bit between the different days.

While running the engine I get a lot of fluctuation showing on the MAP reading on the gauge page. At idle this morning the reading was rapidly changing between 9.8 and 10.5.

At 1750 RPM the MAP was rapidly changing between 16.1 and 17.

By rapidly I mean you can barely read the numbers as they switch back and forth.

Is this normal?

I'm starting to wonder if I have a bad MAP sensor. I thought about switching the MAP sensor from the other ECM but was reluctant to crawl under the dash again.

Thoughts?

Terry.

[Toobuilder]

You should be able to switch between ECU's with a toggle on the panel somewhere, right? Each ECU has its own MAP sensor, so that should isolate the sensor issue.

[rcpaisley]

Hi Terry,
Where is your MAP sensor getting its pressure source.
It should be on the throttle body for the most stable pressure (not on one cylinder). Your kit was delivered with two .020" orifice adapters than can be used to dampen the pressure signal - are these installed?

You can simply switch the plugs between the two MAP sensors if you want to swap them between ECUs to see what they do,
Robert

[terry.mortimore]

The map source is on the aluminum adapter plate between the throttle body and the intake manifold.

I had that apart today and did not notice the .020 orifice. There is a reduction in the aluminum plate, but it was larger than the .042 safety wire I stuck in there to check for obstructions.

I was reading the SDS manual and they suggested a .025 to .035 restrictor to dampen the MAP fluctuations. I installed a .030 restrictor in the line today and it calmed things down quite a bit. If I should have a .020 orifice that might settle it down completely. I'll try that tomorrow.

I still don't understand why the fuel map requirements would change from day to day, but I'll keep working on it.

The next time I notice this I will try running on the secondary fuel injection and or switch the plugs on the two MAP sensors.

The other thing I wonder about is that I have the Dynon map sensor tee'd into this same line, could that be an issue?

Thanks for the help, terry.

[sbrault]

Robert, I didn't see those restrictions in my kit. Do they only ship with some kits and not others?

[rcpaisley]

The orifice adapters are in your vacuum hose kit.
Two of them were in your kit.
They are brass male to female pieces with an .020" hole inside.
They will help settle down MAP signal fluctuation.
They are best installed right at the sump adapter.
Slowing down variations in the MAP pressure signal can adversely affect throttle response. This is why they are an optionally installed item.
The sump adapter has a .040" hole built in. This is present regardless of whether you use the orifice fittings.

Robert

[tspear]

Originally Posted by rcpaisley

Slowing down variations in the MAP pressure signal can adversely affect throttle response.

Can you explain how damping the pressure readings affects the throttle response?

Thanks,

Tim

[rcpaisley]

As you open the throttle, more air enters the engine and manifold pressure rises accordingly.
The ECU is watching the manifold pressure and rpm to determine how much fuel to give the engine.
If you delay the pressure signal to the MAP sensor that the ECU is watching, the ECUs response with additional fuel will also be delayed.
As you add restriction to the pressure signal to the MAP sensor in the effort to dampen the signal you are adding a delay to the fuel response. At some point as you add more restriction, the fuel response will be delayed enough to cause the engine to go lean momentarily as you open the throttle. In the worst case this could cause an engine stumble.
The accelerator pump function can help solve this to some extent.
Every engine is a little different.
The .040" orifice in the sump adapter works fine on most engines.
If the MAP signal is unstable, the .020" orifice adapters can be installed.

Robert