Taking the PFI plunge soon

[PJG1173]

Just ordered the vortec v6 marine mpfi intake from flee bay http://www.ebay.com/itm/43L-Vortec-M...-/331490477322

I know a couple members here have successfully converted their 7427 to PFI but I cannot find the threads in where they did them. FAST355 comes to mind as one who did the marine intake conversion on a V8. I tried using the search feature and no luck, so if anyone has a link to the threads I would appreciate it.

Edit: I found this, but I am also looking for info specific to the marine intake as there is a lot of conflicting info on the interwebz.
http://www.gearhead-efi.com/Fuel-Inj...ull=1#post2855

[dave w]

I have not done a V6 MPFI conversion. I do wonder, would the stock CPI settings work? Attached are a couple $8C files I have from a 95 CPI 4.3 Liter V6. I opened the $8C .bin file using a $OD.xdf to figure out the .bin is actually $8C.

dave w

[brian617]

CPI .bin is a good idea. I've been thinking about using one of these intakes on a 4.3 with a turbo.

[PJG1173]

I have the computer from a 94 s10 blazer CPI in my other truck, not sure if I got the memcal with it or not. I'll have to dig around in my box of goodies. this brings up another question though. looking at the tbi - mpfi doc that 93s10v8 made a while back it shows having to solder a jumper onto the memcal. would that have to be done on the 4.3 cpi memcal or is it even required for a v6 conversion at all?

[dave w]

I have the computer from a 94 s10 blazer CPI in my other truck, not sure if I got the memcal with it or not. I'll have to dig around in my box of goodies. this brings up another question though. looking at the tbi - mpfi doc that 93s10v8 made a while back it shows having to solder a jumper onto the memcal. would that have to be done on the 4.3 cpi memcal or is it even required for a v6 conversion at all?

I'm not sure about the 4.3 CPI cylinder select voltage, that sets up the injector firing sequence. The V6 memcal modification might not be needed, depending on how the injector firing sequence is for CPI. I'm thinking the 4.3 CPI is a poppet valve EFI system that fires all poppet valves at the same time? I'm thinking the V8 memcal mod for MPFI sets up the cylinder select voltage / injector firing sequence for every 4th Distributor Reference Pulse (DRP). Maybe a V6 MPFI system needs the injector firing sequence every 3rd DRP? Maybe the CPI injector firing sequence is every 3rd DRP?

dave w

[PJG1173]

I'm not sure about the 4.3 CPI cylinder select voltage, that sets up the injector firing sequence. The V6 memcal modification might not be needed, depending on how the injector firing sequence is for CPI. I'm thinking the 4.3 CPI is a poppet valve EFI system that fires all poppet valves at the same time? I'm thinking the V8 memcal mod for MPFI sets up the cylinder select voltage / injector firing sequence for every 4th Distributor Reference Pulse (DRP). Maybe a V6 MPFI system needs the injector firing sequence every 3rd DRP? Maybe the CPI injector firing sequence is every 3rd DRP?

dave w

um wow. according to the doc I referenced you are correct its every 4th DRP. looks like I may have to do some more research on batch firing...

[PJG1173]

Ok so I looked a CPI injector up. looks like a single tbi injector with 6 poppet valves attached to it. http://www.oreillyauto.com/site/c/de...=fuel+injector

[brian617]

According to ShopKey there is only one power and one ground command from PCM on the early CPI. Looks just like a TBI connector.

[PJG1173]

Yeah I also found this http://www.thirdgen.org/forums/diy-p...ml#post4033676

[dave w]

Ok, as a thought, would it be all bad if 6 MPFI injectors all fired at once? I'm not sure about injector impedance, 6 injectors in parallel compared to the single poppet impedance? If the impedance is close, maybe 6 MPFI injectors could be operated by a single CPI injector driver in the '7427 PCM?

6 MPFI injectors that individually measure 16 ohms impedance each, would be 2.67 ohms when connected in parallel. I wonder what the impedance of a 4.3 CPI poppet valve injector measures?

dave w

[PJG1173]

Ok, as a thought, would it be all bad if 6 MPFI injectors all fired at once? I'm not sure about injector impedance, 6 injectors in parallel compared to the single poppet impedance? If the impedance is close, maybe 6 MPFI injectors could be operated by a single CPI injector driver in the '7427 PCM?

6 MPFI injectors that individually measure 16 ohms impedance each, would be 2.67 ohms when connected in parallel. I wonder what the impedance of a 4.3 CPI poppet valve injector measures?

dave w

I would imagine the same as 1 tbi injector. From the pictures it looks like they just cramed a tbi injector in a fancy housing

[dave w]

I wish I had a CPI injector to measure. Maybe someone will help out?

dave w

[PJG1173]

I wish I had a CPI injector to measure. Maybe someone will help out?

dave w

Looks like the local parts store has one in stock. If I have time tomorrow I'll stop by and see if they will let me measure it.

[dave w]

There is the option of using a resistor box (math required) to keep the PCM injector driver happy, if the CPI injector has a different resistance than the 6 MPFI injectors in parallel.

dave w

[1project2many]

I have measured the resistance across the mode selection terminals on a 4.3 CPI memcal. The memcal is set to "6 cylinder PFI mode" which equates to 1.7V at the mode select pin. The 7727/7730 only has one injector driver so V6 apps with the 7727/7730 will fire all six injectors at once. I'll try and research the resistance of the injector today.