I know this isn't exactly thirdgen specific, but it is TPI and I figured this would be the place to go for the answer.

I just helped a fellow MNFBC member swap a TPI equipped 350 GM crate motor (all stock aside from an LT1 cam) into his 1993 K1500 Suburban. It has the stock PCM in it that we left installed to run the 4L60E and used a 727 ECM to run the engine. I am wondering how I can get the VSS signal into the 727 so I can get a VSS and use the highway mode function.... We tried running a feed into the VSS in of the 727 from the 2000 PPM out from the buffer module of the Suburban with the magnetic check flag engaged in the AUJP based bin and 2000 entered as the road speed constant.... Well that got us exactly nothing... The TBI PCM has a glaring SES light since it has no engine to control, but with MAP, RPM, and CTS fed to it, it seems to shift the trans quite well....

I am thinking that the best way to do it might just be to take the signal directly from the VSS as the 727 has a VSS buffer built into it (correct?)..... When I did the 730 in my GTA I ended up using the 4000 PPM road speed constant with the 165 buffer still retained..... I seem to remember trying a few things before it all worked on that project....

Just looking for a good idea on what method would work the best since my first swing was a miss. If pulling it directly off the VSS is the best way, what road speed constant would I use with the factory VSS on the 1993 Suburban (4L60E) ?

TIA,
Matt

 

Lots, er Some, of the truck PCMs have a flag to go from TBI to TPI.

Might write Tuncercat and see if he can do an editor with that flag set for you.

Going to a dry manifold will instantly mean alot less AE.

Then just tune as necessary <G>.
Gonna take some work on that tune, but long term I think you'll be ahead using as many stock parts as you can.

There is a co. making a late model to early model VSS converter, Digitial Dash or some such outfit, was in a Jegs or Summit catalog at one time.

 

Thanks for the info Grumpy.

But just to clarify, because it seems from some of your comments that I did not convey the situation properly, what I have going on is the 727 ECM with an AUJP based $8D .bin running the engine, but the stock PCM from the 93 Suburban (originally a 350 TBI) is still installed to run the 4L60E.... The new engine is actually a Caprice TBI crate long block (he got it for a very good price) with an LT1 cam (used from his 96 Firehawk) and a stock TPI setup on it (Hooker 1 5/8 long tube headers as well). He also fabbed up a mounting bracket so he could use a spare set of 4th gen F-body electric fans on it as well (looks really cool! ).

Everything is actually working quite well aside from no vehicle speed input for the 727 ECM (or at least not the proper signal as Datamaster shows no vehicle speed reading). We tried changing the road speed constant this morning but it still just reads 0 from the 727 (not sure what the PCM is seeing, but we never touched any of it's VSS wiring - just tapped into the 2000 PPM output from the buffer for the 727).

I just want to get the vehicle speed fed to the 727 ECM so the Highway mode function will be available - along with any other vehicle speed related functions like the fan disable MPHs - but Highway mode is the function I would really like to get working as he has seen what others have gotten for mileage with vehicles that I tweaked the PROMs for and enabled the Highway mode in (all totally free, by the way - not making any money on any of it Just for the love of the hobby and to help out my fellow MNFBC members oh yeah..... and to add to my own knowledge base ).

But to sum it up, the PCM from the Suburban is only being retained to run the 4L60E and my goal is to get the proper VSS signal .

Thanks again for the help,
Matt

 

Anybody else have any ideas???? (please )

 

Matt,
I did same set up on my 94 Sub with 502 crate and AS&M TPI. I got a Dakota Digital adaptor box (1" x 1") from Street and Performance that I layed by VSS buffer and ran TBI lead through that to 730-727 input if remember correctly. Was using stock PCM to run 4l60E before swapping to 4l80. S&P should be able to give more info.
http://www.hotrodlane.cc/

DD box has slide switches to set for gears, tires, and etc.

Good luck,

Bob H