Few minor questions for the '747 $42 experts.

I have an application with a TH350, and NO VSS. (and I don't want to buy a decoder). I have a '747 w/ harness, TBI, etc.

If I do not have VSS, and uncheck the flag for the vss diag the only thing I'll lose is TCC control (which won't be needed with the TH350) correct?

Will I lose the Knock Sensor routines without the VSS ?

Anyone recommend a good $42 bin to start with for this application? Maybe a manual bin?

-- Joe

 

The KS will still work above 1k RPM. The ECM, however will try to idle whenever the throttle is shut and as you said, there will be no TCC. The ECM is pretty basic so it should still work ok regardless, the only real possible issues are surging or low engine speed when your coasting.

 

Hrmm.. So it won't work as good as my '730 powered vette, but probably better than the quadrabog that was in the truck to begin with?

I'm not a carb guy, but if your off throttle on a carb it's gonna return to idle too, right?

Thanks!

-- Joe

 

One thing about the ECM will be that itll try to control the idle while your coasting, which could mean that it may dip as you slow down due to the IAC possibly being fully closed. With an overrun clutch like a 700 it might not be an issue, but its a potential problem with a trans that has engine braking at all times. With some tweaks you could probably get around it, though.

 

What year is the truck? If it is the 73-87 style, you can switch the instrument panel for a 1983-1987 that had factory cruise. More specifically the speedo head is setup for an optical VSS.

 

Woah wait. The truck is an '84.. Are you saying the cluster might have a VSS out? It had a CC carb computer, like a small standalone module that was powered through the firewall. no wires ran to the dash.

I also have the cluster + wiring, and speed buffer from the '87 I stripped (that I got the TBI setup from) but I don't have any schematics on the in-dash wiring. Jus the '747 schematics from diy_efi.org

-- Joe

 

The VSS buffer is Blue or Yellow (mine is BLUE on my 1983 G20). It has a green/red/and brown wire coming from the gauge cluster to it. It outputs into a yellow wire for the cruise control. Mine had the factory electronic cruise setup on it. All I had to do was tap into the yellow wire and connect the brown VSS signal wire from the PCM into it.

The CC carb computer is simply an ESC modue. Its only function was to respond to the knock signal by retarding the timing. The carb and distributer were a conventional non-computer controlled units. The distributer had vacuum and centrifical advance mechanisms. The carb was sans a mixture control solenoid and TPS, hence the reason it is not tied into the VSS.

 

Finally getting to this point now. The '84 didn't have the VSS or cruise, but I have the cluster out of my 87 which has this buffer. Once I find the connector for it. So the yellow off the buffer (once I find a connector) will be the VSS out to the ECM? Great!

-- Joe

 

I use the 1227747 without VSS on a 3 speed jeep. I think I got lucky with the bin I started with because I dont have any Idle Issues. I will warn you though without vss you do lose DFCO so when you let of the gas on a coast you may get a little putter out of the exhuast. Also I dont have an EGR Valve but Im pretty sure its gonna want to know the speed to work.
Mike