DFI and ECMDiscuss all aspects of DFI (Digital Fuel Injection), ECMs (Electronic Control Module), scanners, and diagnostic equipment. Fine tune your Third Gen computer system for top performance.
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I did a TBI to TPI swap on my 92 RS 305 by repinning the 746 to a 730 everything is working great it started up first try did my timing and it runs great but I am not sure what to do about the VSS buffer do I need to remove it I test drove the car today and got a code 42 VSS but I am not sure if it is from the buffer or the rearend that I installed at the same time it has a 2.73 and I put in a BW 9 bolt with a 3.27 gear any help would be great
If the Car was running before you did the engine and ecm swap it should run now if you have the VSS on the correct pin. Changing the gears will make the ecm and speedometer think you are going faster than you are but it will not keep the VSS from working. Check your wiring, must have missed something.
the 730 ecm has the buffer built into the ecm, no need for the external buffer box anymore, just the high low signal from the vss to the ecm. yellow and purple wires.
Thanks Quick Style
That's what I thought but what do I do with all the other wires on the buffer and will my cruse still work I also would like to find a wire diagram for the buffer.
I went to my local Chevy parts depot and they gave me this chart to calculate my gearing it looks like I need a LT Blue 45 teeth driven gear but they said they cant get it any more and that I should try a tyranny shop
Im not to sure how to post a pic of the chart they gave me
I will keep trying
Thanks for the help
im not familiar with the conversion, i was just giving the info that i know of about the 730 ecm. as for the cruise, with the 730 ecm there is a black box right next to the ecm that i think is the cruise control module.
that 45 tooth driven gear will only work with your rear ratio if your drive gear is the blue 18 tooth, which it should be if your stock ratio was 2.73. The dealer told me that they couldn't get the gear for me also but after talking to the right person i was able to get it but i had to buy it in a pack of 5 for i think like $12 bucks. so i still have some of the gears laying around here somewhere.
The 730 harness:
At the C207 connector (one of two connectors that connects dash harness to engine. computer harness right near the computer) there is a grey wire going from the computer that is suppose to operate the speedometer.
My old harness with the buffer box
has a fan relay right there. Though I know where to connect the wire from a fan relay I need to know which wire from a buffer box operate the speedometer.
I assume connecting the wire I am looking for from now unused speedometer with the grey wire from the C207 connector will make the speed work.
Some more food for thought on the 730.
The 730 has two inputs for the VSS
a.) One is for magnetic VSS = 5 Volt Sine wave
Pins B10 +, and B9 -
4 pulses per revolution, 4000 pulses per mile expected
b.) One for Optical input = 5 volt square wave
Pin C6 +
The nuber of pulses is much higher on this input, searching can find the values. I don't remember right now.
There is a selection bit within the bin to choose which input to use.
You "should" be able to use the buffer box output into C6.
The 730 will output to the dash (B11) and to the cruise control module (C1) at 2000 pulses per mile if you have them connected.
These were for 91-92 SD setups running $8D, If you are running a different mask confirm the wires by the original schematics.
HTH
Actually I do know pretty well about the 730 VSS wires etc...
But I am having this engine in an older body with speed buffer and need to rewire speedometer..
I should connect the B11 wire from a 730 wit a wire that goes to the speedometer in my 88 body (originally 2.8l).. But I dont know which one is that, probably one of those on a buffer box..
And I am too lazy to disassemble dashboard and gauges again to check
I have wiring diagrams in front me from Alldata for the 91 305 TBI VIN E, and they only show one VSS input on pin A10 at the PCM its a brown wire coming from the VSS buffer box. The PCM out of a 91 TBI SD car should be a '7730 correct? Or are my wiring diagrams wrong? This would be great to know because I'm getting ready to swap the 165 computer out of my 87 305 TPI MAF car to the '7730 from a 91 TBI SD car using my factory harness, the pinout wasn't that bad, I have it all done on a chart just by comparing the two diagrams. I was told since the TPI is batch fire I can just hook the wires from my right bank to the RH injector driver and the same for the left bank to the LH injector driver. If there are discreptencies in the diagrams I have it would be great to know before I dive into this lol.
To be sure of what you believe is needed, check here on the schematics page for both of the ECMs. http://www.cruzers.com/~ludis/
Connect items by function and confirm the pins. sometimes just going pin to pin without knowing what it actually is will cause headaches later when you try to fire it up.
There WILL be a pin somewhere wrong when you are done, it just happens.
I tried. And failed :P
I know what an 730 ECM pins where and how does it work..
But I am really unable to make it work with my underdash wiring (with buffer box.. even if I dont need it now.. ) :-P
