Rebuildman

New install of 1227727 ecm. Using small cap HEI distributor. VATS disabled on chip. I have power through injectors 12v with key on at ecm plug pins B3 & B9. Using a noid light installed in one injector plug grounding pin at ecm will turn on light, injectors click.
Checked wiring from ingition module to ecm, I have ground on ref low wire B19, < 1v on ref Hi wire with key on, voltage increases when engine is cranking.
Swapped in used ecm and ignition module, no help. Have ecm grounds connected to engine and chassis. Do I need to do anything with pin R6, cranking fuel enable input? I tried grounding it but no help there.
Stumped for the moment.

RBob

iTrader: (1)

I'm confused on which ECM you may be using. On the '7727 B3 & B9 are ALDL mode inputs. B19 isn't used.

RBob.

Rebuildman

O.K. well this maybe my problem. I have a 1227727 ecm that is a new install and the motor has the problem I described. Now, I also have a running '90 Corvette with the same ecm p/n, so I used the Vette wiring diagram to connect the new ecm. One thing I did notice when wiring it up was the color of the connectors (4 ea.) did not match the corvette diagram, but physically they would connect in the sockets in both ecm's, so I used the positioning and not the color's. So I have it wired it like my '90 Vette. I have since found a simple list that compares wiring for a 730/749 to a 727 ecm and that shows the pins as you describe. So I am the one confused now.
It lists connectors A,B,C,D and not colors, so what colors are A, B, C, D? And why would the same p/n ecm be wired differently? Also I used a Vette bin to start with, maybe I should start with a Camaro bin, can you suggest which one?
Do you have a link to a detailed wiring diagram?
Thanks in advance!

RBob

iTrader: (1)

At this location:

http://diy-efi.org/gmecm/ecm_info/1227730/

Bottom of page are the wiring diagrams for the Corvette.

HTH's,

RBob.

Rebuildman

O.K. got it, I need to compare this to the manual I have, some how I must have had a brain freeze and messed this up.
Thanks!

Rebuildman

So I checked my Corvette manual, a supplement wiring and troubleshooting manual from the factory. The B3 & B9 are the same as D3 & D9 on the dyi-efi wiring print, B3 is for brown connector, and it indeed is connected to the injectors, as is B9 on the print. So that is interesting and also disappointing because it didn't fix my problem. Tomorrow I will check all the other pins and see what I turn up. Hope I find a mistake somewhere!
So I am not as crazy as I thought, so far!

Rebuildman

O.K. checked wiring on my 'B' (brown) plug which is the same as the 'D' plug on the wiring diagram from DIY-EFI. It is wired correctly, did fine a minor problem with the DIY print reguarding pins C3 and D13. One page list it as reference signal another page list it as bypass. I believe C3 should be bypass and D13 ref. Anyway, my problem is still not fixed. More testing tomorrow, need to double check the distributor hook-up, I am using the small cap HEI, not what is on the print, but I have this same setup in another car and it works fine. Unless someone has a suggestion?

RBob

iTrader: (1)

There is a quick check to see if the ECM is seeing the DRP's: Do a key-on, engine-off and wait for the fuel pump to stop running (about 2 seconds).

Then give it a quick crank (basically tap it over) and leave the key in the 'run' position. If the fuel pump fired up again for 2 seconds then the ECM is getting DRP's.

Can also pull the distributor, ground the housing to the engine block, key-on, and spin it. That to should turn the pump on, fire the plugs, and activate the injectors. (Note that the wiring between the distrib, coil, and ECM needs to be plugged in. And the housing needs to be grounded for this to work).

RBob.

Rebuildman

Great troubleshooting info! I tried the removed dist. spinning, it worked as it was supposed to, fuel pump turned on and my noid light flashed! Re-installed everything turned the starter, nothing on the noid light. Talk about confusing! after about an hour of trying different things I found the problem! I had wired up a relay to supply the power to the ecm for key on power up, worked fine with key in run position, when in start position the relay control power would drop to zero, rewired to a better power supply, problem solved.
Thanks for your help, that distributor technique will be with me for a long time!