Undecided on which way to go--- Need Advice

[chadapcb]

I am in the process of converting my Mercruiser 5.7 to TBI.

I have 2 full complete systems.

One from a 94' Chevy Truck with ECM 16197427 with TBI and complete harness?
Second one is from a 92' Chevy Truck ECM 1227747 with TBI and complete harness?

This is where I am needing advice.

Which system should I go with.

I know the Newer one speaks faster than the other.

But here is what I am needing to do.
Run Open Loop system
Minimal sensors. Temp, EST, Knock, MAP, ESC, IAC

If anyone has any insight it would be greatly appreciated.

Thanks,
Chad

[dave w]

The 1227747 is a good, simple, and low cost option for a marine application. If at all possible, I recommend using a 3 wire heated O2 sensor (HO2S) with the 1227747 for closed loop. The 1227747 has a "Park" switch input in the wiring harness that eliminates the need for a Vehicle Speed Sensor (VSS).


One of the challenges I see with the 16197427 is eliminating the requirement for the (VSS). The 16197427 DOES NOT have a "Park" switch input in the wiring harness.

dave w

[chadapcb]

So basically the 427 is out of the question due to the vss
747 will be the simplest and have to ground the parking wire.

I am am good with that.

[Six_Shooter]

So basically the 427 is out of the question due to the vss
747 will be the simplest and have to ground the parking wire.

I am am good with that.

Contrary to what Dave keeps posting, that's not exactly how the '7747 works. It will ALWAYS benefit from a VSS. Grounding the park wire will make it think it's always in park, which is not really what you want, you'd want to leave it open. A better solution would be to use a manual bin, that doesn't look for a park signal, but a VSS will still improve the driveability by a large amount.

If you really can't or don't want to use a VSS, don't use a GM ECM/PCM. I suggest Megasquirt 1 or 2, since it doesn't care if there is a VSS or not.

[chadapcb]

Thanks for the info on the mega squirt. Just don't think that is what I am wanting. It's very hard for me to believe that a module that would work on a pwc would work on a boat that has a 300 hp v8.

Gonna continue to look at the 7747. I believe that it would be the best and switch the bin file.

[Six_Shooter]

PWC?

Anyways, the Megasquirt works on just about ANY internal combustion gasoline engine ever produced, that's how it was designed, to be truly universal. You select the correct settings, connect the correct parts (sometimes some small circuit mods are required that are well documented), and then tune for the engine.

The MS has been used on single digit HP engines all the way up to few thousand HP multi-cylinder engines. The MS1 and 2 had no input or need for VSS, and would be your best bet. MS3 CAN use a VSS, but is likely overkill for your application anyway.

The fact that all GM ECMs OBD1 and newer require a VSS to operate correctly, for driveability, and stable return idle, I would not consider them for an application that doesn't or can't use a VSS, and I love Delco/GM ECMs for their reliability and ease of tuning, they just aren't always the best fit.

[dave w]

I've been thinking the Mercruiser 5.7 is in a boat. I've been thinking the goal is to run a "bare bones" Marine TBI system.

Information from a TBI Painless Wiring Harness: https://www.painlessperformance.com/Manuals/60101.pdf
VEHICLE SPEED SENSOR AND TRANSMISSION LOCKUP FUNCTION
Before you install the harness, please decide the following things:
a.
Are you going to use a 700 R4 Lockup Transmission that you want the computer to control the lockup on?
b.
Does the engine have to be emissions legal; i.e. does the EGR valve and /or air solenoid, and diverter valve need to be connected?
If you answered yes to either or both wires labeled VSS to a vehicle speed sensor that will provide a 2K pulse per mile signal to the computer. The VSS sensor should output a square wave.
.
If you answered no to both of these questions then you may choose not to use a vehicle speed sensor, but the vehicle will operate more efficiently with one.

If you are not going to use a vehicle speed sensor then you will take the orange/black and black/white wires in the dash section and connect them together.

The orange / black wire is the Park input wire. The black / white wire is the ground wire.

dave w

[chadapcb]

Dave

you are correct on wanting to run a bare bones tbi on a mercruiser 5.7

chad

[lionelhutz]

I ran a '7747 for months without a VSS then finally installed a VSS so the computer could control the lockup on a 700R4. I read that it had an effect, but I still couldn't tell any difference in how well it ran either way.

I supposed a single pulse per crankshaft revolution could work. You'd get 30mph for every 1000rpm. But, it would never return to 0 so you'd have to adjust for that.

I think a cooler trick would be figuring out how to retard the timing (or rpm) when switching gears via the programming. I would think your current setup has the typical switches and timing retard module to take the load off the stern drive as you go in and out of gear. On my boat, if I manually close one of the switches the timing retard drops it to about 3-400rpm.

[chadapcb]

Lionel,

The mercruiser is a direct drive straight inboard.

Idle runs between 600-700 RPM the retard is not in the timing at all it is in the transmission.
What I mean by that is I have separate levers one for throttle and one for forward and reverse.

The rpms never go up until I apply throttle no matter if it is forward or reverse.

At 600-700 rpm the prop barely turns thus not having a hard engage in the transmission(Velvet Drive 71C)

Basically the throttle side is not affected when the transmission is put into forward or reverse.
Not like a stern drive with a single lever that when you engage the forward motion it has to reduce the rpm.

Chad

[myburb]

If the computer you were using really needed a vss you could just rig something on the output of the velvet drive. I would think your setup could be made to work just fine without a vss. I wonder what was done with a pto?

[1project2many]

I've helped with marine configuration for TBI. IME the 7747 without speed signal input on the street can suffer from inconsistent idle speed problems. There can be a fair amount of tuning involved in solving that issue. In the marine world it's not as much of a problem. If VSS is desired there are simple paddle wheels that can be affixed to the hull to provide speed information. O2 sensor placement can be a challenge with water cooled exhaust. O2 installed in an exhaust crossover can provide some usable readings although these days I'm less inclined to feel closed loop is necessary. Closed loop enable parameters would need to be adjusted as marine engine temperature is generally lower than automotive engine temperature.

Personally I'm inclined to use the 7427 pcm as I like the faster data updates but the 7747 will work for the marine application. Remember to consider such ancillary issues as fuel vapor accumulation, high humidity, and spark exposure during your conversion.

[chadapcb]

Thanks everyone that has supplied information. I am gonna continued as planned with the 7747 ECM. I am gonna run an open loop to see how it preforms and monitor the fuel usage. I will also run in a closed loop and see if there is any better fuel usage verses the open loop. The way I have looked and study marine engine they are always gonna be gas hogs. Especially in my case with a 2.5 ton boat. I am not looking for speed or increased horse power but that is always a plus. I am mearly looking for stability in the engine. Get the instant crank instead of choke crank, crank, crank, then start. I know there are systems out there that start around $1000 and go up but I have always been the type if I can save cash and be safe about then save cash. Also I have the knowledge and skill to preform such tasks to an engine and if not I have my nephew which is ASE and owns his own shop. Plus on my part. Thanks to all.... Chad

[1project2many]

Please keep us updated and be sure to post plenty of pictures!

[dave w]

I think Wide Band O2 (WBO2) "Tuning" is the best option for programming the PROM Chip.

The attached screen shot shows "Tuning" using actual AFR's, RPM vs. Kpa from a 16197427 PCM that had WBO2 information in the data log.

WBO2 "Tuning" is possible with the 1227747, when using a Moates.net APU1 to have WBO2 information in the data log.

dave w