What If? $8D (1227727 ECM) for TBI

[1project2many]

The DRP (Distributor Reference Pulse) signal is the same between the TPI and TBI systems. DRP can be tapped by placing the scope input on the REF line from the distributor and ground on the engine block. What you'll want to view is the injector signal generated when cyl select is at TPI and TBI and that signal is likely to vary between firing all injectors with every DRP or firing alternating injectors with every DRP. There were a few tidbits on thirdgen and some of Ludis' schematics show the signals involved. I can try and narrow it down tonight if I have time.

[EagleMark]

Also if the correct osiliscope signal needed is not available I can look up the sample signal in my Osiliscope. Need year make model of TBI car with 1227727 your looking for and can get sample for it and TPI to compare and make sure you got it right.

[dave w]

The DRP (Distributor Reference Pulse) signal is the same between the TPI and TBI systems. DRP can be tapped by placing the scope input on the REF line from the distributor and ground on the engine block. What you'll want to view is the injector signal generated when cyl select is at TPI and TBI and that signal is likely to vary between firing all injectors with every DRP or firing alternating injectors with every DRP. There were a few tidbits on thirdgen and some of Ludis' schematics show the signals involved. I can try and narrow it down tonight if I have time.

I found a '7727 schematic online. If I'm understanding correctly, I need to connect one of the o'scope channels to distributor reference pulse (REF HI / pin B of the 4 pin distibutor connector / pin R on the module / purple wire with white stripe). The other o'scope channel to one of the injector wires (either Black with Light Green Stripe or Black with Pink Stripe). I'm thinking for the injector pulses, the positive lead of the o'scope probe will go to the injector 12VDC and the negative lead of the o'scope lead will go to either the BLK-LT Grn / BLK-PNK wire. I'm thinking that when an injector is pulsed by the ECM, the o-scope will show a positive looking square wave. My o'scope is old so I can't capture / save any signals.

dave w

[EagleMark]

If you have or find complete schematics send them to me for our inventory.

If you know what signal looks like your fine, but if there's a doubt I can get a picture of the sample stored in my scope for you!

[1project2many]

Dave, yes to connections. Scope connection across injector or from injector - (blk/lt grn, blk/pnk) to ground will show positive pulses when injector is commanded "on." Scope connection from injector + to ground will show positive pulse when injector is "off." Might be nice to use switch or other device to Tee into both bank injector negative wires for easy switching between banks to view alternating or simultaneous firing.

Plenty of old scopes out there. Camera phone still works. :)

[dyeager535]

All feedback / input is

My expert feedback is, please keep going with this! I'm in the process of picking up another 1227727 or two, and may end up needing/wanting to use one in a TBI app, so I'll reap the benefits of whatever you can make work. About the only support I can offer is if you have a need for a 1227727 as a loan for testing. :(

[EagleMark]

I think the coolest thing about this ECM is there are a bizillion out there in JY V6 cars and it's underhood which would make an excellent conversion ECM for off road vehicles. Now to make the V6 Memcal work a V8 TBI...

[dyeager535]

Only thing I don't like about underhood is that the Autoprom cable isn't long enough to reach for driving and tuning. I'm sure an extension can be made.

I assume it's not as simple as doubling up the 4 cylinder MEMCAL or someone would have done it already. :)

[dave w]

Now to make the V6 Memcal work a V8 TBI...

Maybe all that is needed is a '427 PCM V8 Memcal?

Think about it ... Why would GM re-invent the 8192 Baud Knock Filter / Limp Home Resistor Network for the TBI PCM. Makes sense to me, GM would reuse what ever they could to keep production costs down. The TBI injectors will need resitors!

The test bench is set up with both MPFI and TBI stuffs ...

dave w

[EagleMark]

That would simplify things!

That also looks like the Osiliscope I used in high school... late 70's...

I like the MPFI intake with TBI for test bench! I've got some plans started to use aluminum plate for intake, mount TBI, drill and mount MPFI injectors, hole front and rear for distributors, on legs so I can have 2 distributors cut short, mounted and run a fan belt between the 2 on electric varible speed motor! Then I can do a harness front distributor or rear distributor, TBI or MPFI all on one set up!

[1project2many]

Maybe all that is needed is a '427 PCM V8 Memcal?

I got screwed up last night. There's only one injector driver so there's no way "alternating bank" is possible. The only thing to watch is firing on every DRP or every other DRP. You should be firing every DRP with the TBI system. Have you checked both memcals for this?

TBI on PFI... talk about extra fuel for the turbocharged apps.

[dave w]

I got screwed up last night. There's only one injector driver so there's no way "alternating bank" is possible. The only thing to watch is firing on every DRP or every other DRP. You should be firing every DRP with the TBI system. Have you checked both memcals for this?

TBI on PFI... talk about extra fuel for the turbocharged apps.

The '427 PCM Memcal outputs 3.3 VDC for Cylinder Select, or I think it will. I will measure the '427 Memcal for the Cylinder Select voltage very soon. My hope is, I'll be able to "see" if every DRP is possible from a '427 Memcal.

dave w

[RobertISaar]

man, if i had internet access when this thread was first started, i could have cut 90% of the work out for everybody....

[1project2many]

So it's at the point where there's only 10% left? ;)

[RobertISaar]

not necessarily, but it does seem to be very close to a reasonable set of compromises decided on.

what i meant by the 90% was that i had 90% of everything that was already done/discussed(in this thread) either memorized or stored somewhere on my laptop from other people's work or stuff that i've discovered on my own.

10% left probably isn't that far off honestly.