Aftermarket Fuel Injection

[Traveler]

Has anyone replaced their factory ECM on a 350 Mag with anything aftermarket? I'm looking at the Holley 950 or the Accel DFI. Anyone have any experience with these or any other aftermarket fuel injection systems?

[smokediver]

no expert here .. i read that the auto fuel injection systems do not crossover with marine app. something to do with the torque curves and rpm ranges..

[McGary911]

My 502 is controlled by a fastfuel programmable injection system. I havent played with the setup, as the boat runs great as set up, but it is infinately programmable with my laptop. I can program in the actual fuel\air ratio on a sliding scale depending on rpm. Some systems, open loop systems, use an exhaust sensor to monitor what the mixture actually IS, as opposed to a closed system, which knows what is going in, and doesnt pay much attention to what is going out. I hear they can be difficult to set up, but once its done, you save the mapping on a disk, and youre set, unless you want to tweek some more, or make changes.

[Ranman]

It's my understanding that open loop does NOT use O2 sensors. Open loop systems (most commonly used in boats) rely on a fixed map for fuel curves, ignition curves, etc. The reason baots use open loop systems (inferior in my eyes) is because it's difficult to install O2 sensors in the exhaust of boats. O2 sensors and water don't mix.

Closed loop systems (superior in my eyes and most common on cars) use O2 sensors. By using the O2 sensor and "closing the loop", ie. reading the fuel mixture along with MAP, engine RPM etc, the computer can adapt to its situation and alter the fuel, ignition curves, to suit driving conditions.

Anyone else care to explain these concepts as I'm sure I'm not %100 correct.

[McGary911]

Ranman, I did some checking, and I had the open\closed thing reversed. Agreed closed (with sensor) is much better. At 1 time my boat was closed, but even running in fresh H2O, the sensor failed because of the water. I think I'll stay open because of the salt\brackish i run the boat in. My $400 sensor would probably last about 4 hours. I suppose I could swap my exhaust for dry pipes, but even i don't like that much attention! eek!

[GEOO]

I run a F.A.S.T. ECU on my small block. I use a wide band O2 sensor. The first few O2 sensors lasted a few days, I checked my exhaust and found out that I had a slight reversion problem. (idled the boat on the trailer, stop the engine remove the tail pipe off the manifold and saw a small puddle of water.) I changed to dry exhaust and this O2 sensor has lasted over 1 1/2 seasons. I think the Salt kills the sensor not just water. I installed Shot Gun flaps, which accually sit in the water now and the O2 sensor seams to be fine.
I love the F.A.S.T. system. Easy to tune.

[Traveler]

I was hoping there would be some comments on the oxygen sensors. I've never tuned with them or tuned a fuel injection setup for that matter but I have done a lot of carb and nitrous tuning by looking at plugs. O2 sensors seem like a nice tool to accurately tune the fuel map. Anyone have any ideas on mounting a sensor without a new exhaust system? Is there any place you could bore into a wet manifold and get to the exhaust but not hit water? Or how about using an EGR style manifold to get a sample of the exhaust and then sending it into the risers? I don't care much about running closed loop just using a sensor to help tune.

[GEOO]

I have Stainless Marine Alum. Exhaust Manifolds with Stainless tail pipes. SM welded in a bung for the O2 in the elbow.
Tuning is simple. You just set your A/F ratio and the ECU will add or subtact fuel to meet your selected A/F ratio. Example: The ECU will tell you it added 20% or took out 20% to meet your selected 12.5 A/F; you just go into the base fuel map and add 20% or take out were needed. Once you have your base map close (2-3% correction) then the ECU runs off the map and just fine tunes itself with the O2. Or you can take out the O2 sensor and just run off the map.

[CDMA]

George really meant:

Tell Chris to hold laptop while its recording at 104+ mph... eek! eek! eek!

Just kidding. It really is an awesome easy to use system. Someday all my boats will be tunable MPI.

Chris

[Ranman]

I think DougL runs an O2 sensor with his carb setup for tuning. Rootsy was also working on this sort of setup. Maybe they will chime in with some info...

[Rootsy]

Doug does have an O2 sensor bung in his port exhaust pipe. He runs GIL marine exhaust on his sbc. Gil welded this bung in just after the joint at the manifold / riser. His risers dump water at the end WAY back. He also runs MORE camshaft than i do, somewhre in the 230* - 238* @ .050 range. It survived all of his testing last summer.

I run stock merc manifolds with IMCO stainless risers which dump water also at the end of the pipe, just not quite as far back as Doug's do (maybe 10 - 12 inches further back than the merc risers). I run 224*/230* @ .050 and i have seen zero reversion issues. I have turned some SS bungs which i plan to TIG in to at least one of my pipes sometime in the spring.

You use a wideband O2 sensor for an automobile which you can buy over the counter at your local parts store for around 40 bucks. Just make sure it is of the correct voltage range for your meter and enters far enough to have it into the exhaust stream and not buried back in the bung between the inner and outer shell.

Doug uses the autometer LED meter and i have access to a digital (forgetting brand name but NOT the price tag) meter.

I've tuned a number of carbureted engines this way both on and off the dyno and it is the best way to get her as close as possible. especially off the dyno and in the vehicle or boat since you can get readings at cruise, idle, hard acceleration and different loads. :)

[Doug L.]

That covers it!!!


Geo is 12.5 A/F what you run? I thought
unleaded fuel is 14.7 do you stay fat for
the blower??
Doug

[harbormaster]

This is a cool thread. You MPI guys post some photos of your different MPI setups.

[GEOO]

Doug,
I ran my set up on the edge a little, 12.2 A/F with 34 degree advance.
I think most of the marine Super charged engines run around 11.5-12 A/F and natural's run 12-13 A/F. Marine engines are under constant load and run much richer then an Car set-up.

[Traveler]

In searching the web for alternatives for mounting an oxygen sensor I found that Turbo City had made an adapter that goes between the manifold and the riser. Some time next week I'll give them a call and see if they sell the adapter alone. If they don't sell it or it's too expensive I'm thinking of just milling one up on my own.