7727 wiring questions

[dusterbd13]

im getting further on the harness. hopingto finish tonight.

couple quick questions:
this ECM was an auto car. the new chip will be for a stick. does it need any input from the neutral safety switch? if so, what pin, and what kind of input?

it also has leads for the VSS. does it need it? if so, why?

i read somewhere that i cant use an OBD 1.5 knock sensor with this PCM. true or not?

is it better to ground the ECU to the motor or the chassis?

michael

[robertisaar]

use the knock sensor meant for the motor. you can't use the OBD1.5 knock filter(or at least not easily), but the sensor is fine.

VSS: you can come up to some drivability issues if you don't. the manual trans still uses a VSS.

it's best to ground the ECM to where it was originally grounded. being a 7727, it has to be from a W-body or vette, i don't think anything else got them.

i'll look up the neutral safety switch info, just remind me.

[bszopi]

use the knock sensor meant for the motor. you can't use the OBD1.5 knock filter(or at least not easily), but the sensor is fine.

Are you sure? You should be using the knock sensor which matches the PROM, not the engine. Since the PROM has the KS filter on it, the KS should be matched to that. At least, that's my thought...

[IsaacHayes]

I think it's been determined that you match your KS and KF with the displacement of the motor. The 3.4 Iron head and 3.4 DOHC have the same KS p/n's ... The KF might be tuned a bit different between them though for the different harmonics of the valve train... But the KS should be close enough. Others run 3.1mpfi KS on 3500's and 3400's without issue.

[robertisaar]

the knock sensor is matched to the engine bore. i think it's something like tuned to a 5Khz frequency for a 90mm bore and 7Khz for a 100mm bore.

i've seen it somewhere before, but the filter's purpose is to pass ONLY those frequencies to the ECM to register as knock(since the knock sensor is essentially a microphone and would pick up all noises within it's response range).

so the filter should ideally be matched for bore and valvetrain. i've got a LQ1 filter on the MC, which doesn't match either but it still does register knock, although it may not be as sensitive as it should be.

NINJA'd...

EDIT: i did mention that it wouldn't be easy to use a 1.5 knock sensor in a OBD ECM, but i HAVE seen it done, i just don't know how. there was someone on TGO using a LT4 knock filter on a LT1. here's a pic, but it's not too detailed...

[dusterbd13]

my wiring diagram does not say ehere it was origonally grounded. ECU and harness are out of a 93 lumina.

so what im understanding about the knock sensor is that the obd 1.5 camaro knock sensor is the correct one, and is compatible with the 7727's knock filter and $A1 code. correct? and im assuming the knock filter is built into the ECM.

the VSS in an s10 origonally ran through some form of buffer. i havent had a buffer in my truck for years, ever since i removed the cruise. i run the VSS straight to my autometer speedo. to wire the VSS signal in, what do i do? the wiring is currently purple to the speedo, the other color to ground.

thanks for looking into the NSS, robert.

[robertisaar]

ok, it was originally grounded close to the starter. pins D4 and C6 are to be grounded at G103, pins A22, D10 and D12 are to be grounded at G104.

for the VSS: that would be the DRAC. you should be able to get away without it, assuming you know how many notches are in your VSS reluctor. if not it may require some guessing and testing.

the PCM doesn't look for the NSS, so you should be fine without touching it.

[Scott_68B]

I wired a 7727 into my MGB with a manual transmission, not sure what vehicle you're doing but I didn't do anything with a neutral safety switch and haven't experienced any issues. I believe you'll want to run your grounds to the engine block, that's what I did and I believe that's what was done in the donar car (91 Lumina). You'll want to have a VSS in place. I started out without a VSS and my motor wanted to stall as I came to a stop. That problem disappeared once I added a VSS. In addition, the motor seemed to run better overall...wouldn't go without one. I have a homemade VSS sensor running off my driveshaft and used a magnetic sensor from an early 90's Chevy 4WD truck. I just adjusted the road speed sensor constant. No buffer required for me at least. HTH

Scott

[dusterbd13]

I'm almost done doing the 7727 ecm swap to my 3.4 camaro motor powered S10. its up and running save for a few exceptions. cooling fans and AC system.

are the pins for the fan relays coming from the ECM power or ground?

also, pin C21 is labeled as the AC pressure signal.
pin c17 is AC request
pin a12 is ac control

my origonal TBI motor in my s10 only had two connections to the ECM for the AC system.
pin B8, labeled AC signal
pin A2, ac relay control.

what goes to what?

also, can someone tell me what the pinout for stock fuel pump and AC relays from an S10 are? I've got terminals A,B,C, and D.

thanks
Michael