carb to TBI converions, Marine application

[Fast355]

I see some challenges using a 16168625 PCM for a Marine Carburetor to a Marine TBI conversion. Usually the 1227747 ECM is the Marine TBI computer of choice. The 1227747 has a park switch input, which eliminates the need for a Vehicle Speed Sensor. Setting the 1227747 park switch to Ground (battery -) tells the 1227747 the vehicle is in park. The 1227747 will operate an engine when the 1227747 thinks the engine is in park.

The 16168625 does not a simple park switch input. It might be possible to configure the transmission gear position inputs of the 16168625 to indicate park. (That's something I have not tried to do) The 16168625 uses Vehicle Speed input to select near idle or off idle fuel and spark tables. It might be possible to configure the vehicle speed parameters along with the TPS% parameters to "lock" the 16168625 into using the Off Idle fuel and spark tables only?

I'm sure a Marine engine would run with a 16168625 without a Vehicle Speed input, I'm just not sure how well the engine would run? Perhaps there is a way to have a GPS supply the 16168625 with a vehicle speed input?

dave w

I used the 7427 with a simple park/neutral switch, it is simply a matter of enabling the 700r4 logic. Auto trans/TCC only switches. Input signal on one wire of the 3 (forget which) and it works great.

If it is a Mercruiser several companies make an adaper that sandwiches between the marine manifold and riser and holds an O2 sensor.

I did a TPI 7730 on a TPI marine conversion and simply wired the kill switch into the coil output between the module and coil. Worked beautifully! used a newer marine thermostat housing off a Vortec L31 marine engine thay had the same bolt pattern angle.

7427 works in Open Loop only very well too!

I never use different Idle/Off Idle tables. Would be easy to set the switch over to Zero MPH and disable the Idle parameters completely.

[keaton]

I'm not sure what exactly happens when the manual transmission option is selected. I've converted a few 1227747's to the '8625; I selected manual transmission because they were using either a TH400 or a 700R4 with the factory VSS. I then disabled all the 4L60E / 4L80E transmission codes.

The '8625 needs a VSS input of 2000 (2K) pulses per mile. Here is a link to some VSS options: http://www.jagsthatrun.com/Pages/Spe...eedometer.html Other options include using the speedometer driven VSS from behind the dash of an early 1227747 vehicle (which is a 2K VSS). Maybe connect an electric motor or variable speed electric motor to an aftermarket VSS? The basic idea I have is to provide the '8625 with a VSS speed, so it will switch between Near Idle and Off Idle. Typically the '8625 will switch from near idle to off idle at 6 MPH with 2.1% or greater TPS. The '8625 could be well worth the VSS hassle to use in a Marine application? Imagine having near idle fuel and spark tables for "Wake Free" zones and docking maneuvers along with off idle fuel and spark tables for getting on and staying on the "Plane"!

If your plans are for open loop only, go with the 1227747, I'll gladly swap you two '7747's for the one '8625.

dave w

I would like to do closed loop at some point but for starting off (till i get an O2 sensor in) open would work.

I'm hoping to get better doc behavior with this conversion. currently you set the idle a little high and rich so when you put it in gear the load doesn't stall the motor. hoping with the computer this wont be an issues as the computer should adjust to keep the idle RPM at what ever is set.

I'm going back to the junk yard this weekend, I know where a few more PCM for a TBI system are at. I'll see if I can grab you a 7427 or 8625. Just pay me back and cover shipping ($20 for the PCM + $5 core + ~$3 environmental fee + shipping)

I used the 7427 with a simple park/neutral switch, it is simply a matter of enabling the 700r4 logic. Auto trans/TCC only switches. Input signal on one wire of the 3 (forget which) and it works great.

If it is a Mercruiser several companies make an adaper that sandwiches between the marine manifold and riser and holds an O2 sensor.

I did a TPI 7730 on a TPI marine conversion and simply wired the kill switch into the coil output between the module and coil. Worked beautifully! used a newer marine thermostat housing off a Vortec L31 marine engine thay had the same bolt pattern angle.

7427 works in Open Loop only very well too!

I never use different Idle/Off Idle tables. Would be easy to set the switch over to Zero MPH and disable the Idle parameters completely.

from my research the 7427 & 8625 are basically the same... so shouldn't this one work well in open loop too?

my boat is an OMC. I have seen the adapter that place the O2 in a block between the manifold and riser. this was one of my 1st thoughts but I'm Z-height limited i have about 3/8" between the top of the riser and the sun deck. (see pictures below)

not sure what the T stat housing get me... my Tstat housing has a water in, water to the GM pump, 2 lines out that cool the exhaust.

[Fast355]

I would like to do closed loop at some point but for starting off (till i get an O2 sensor in) open would work.

I'm hoping to get better doc behavior with this conversion. currently you set the idle a little high and rich so when you put it in gear the load doesn't stall the motor. hoping with the computer this wont be an issues as the computer should adjust to keep the idle RPM at what ever is set.

I'm going back to the junk yard this weekend, I know where a few more PCM for a TBI system are at. I'll see if I can grab you a 7427 or 8625. Just pay me back and cover shipping ($20 for the PCM + $5 core + ~$3 environmental fee + shipping)


from my research the 7427 & 8625 are basically the same... so shouldn't this one work well in open loop too?

my boat is an OMC. I have seen the adapter that place the O2 in a block between the manifold and riser. this was one of my 1st thoughts but I'm Z-height limited i have about 3/8" between the top of the riser and the sun deck. (see pictures below)

not sure what the T stat housing get me... my Tstat housing has a water in, water to the GM pump, 2 lines out that cool the exhaust.

I had to use the newer housing because I went with TPI, not TBI.

[Stokes1114]

I have a 16197427 that I would trade for your 16168625 if you would like.

[keaton]

I had to use the newer housing because I went with TPI, not TBI.

Ah ok, that makes since now. I would go TBI or TPI but finding parts on the cheap has been hard. I'm still looking for a TBI Unit. TBI seem easier in my application as i need an adapter plate to bolt it on.

I have a 16197427 that I would trade for your 16168625 if you would like.

let me see if I can make this work for what I need 1st.


do you think the O2 being the the path of 1 cylinder will be enough? I know getting the bank average is better but i have limited options.
any issues with the O2 being right off the port/cylinder head exit?


TBI units. I can find Dodge Units on the V8s all day long but they are high impedance injectors and the ecu needs low impedance. what if i got new injectors and replaced them Low Z injectors and put all the chevy sensors in the unit (IAC, TPS, IAT, MAP). has anyone tried this? will the injector fit? I'm assuming the throttle body bore size will be large enough to flow the air i need as its coming off a similar size V8. thoughts on this?

[dave w]

I'm going back to the junk yard this weekend, I know where a few more PCM for a TBI system are at. I'll see if I can grab you a 7427 or 8625. Just pay me back and cover shipping ($20 for the PCM + $5 core + ~$3 environmental fee + shipping)

Thanks for the offer, at this time I'm good on spare TBI computers.

dave w