MTPFI-MAF

ok i have a question, and I know that this would need to normally go into the interior section but I know that the ECM part of this you guys know better than anybody. I am worried about the signal that the ECM picks up from the vss. I am doing a 4th gen dash swap and it has a v6 cluster. My 1985 Vss is on the Guage Cluster. So I think I need to get a vss that connects to the speedometor cable out put on the T-5 Tranny. What Vss do I need So that the computer Sees it correctly. also How do I make the v6 4th Gen Speedo and Tach get the correct signal.

Grumpy You may jump in any time.

Dave_Jones

That fourthgen dash will need a 4000 pulses-per-mile VSS.

Don't own any T-5's, but I'm pretty sure the '90-'92 T-5's had the same 4000 ppm AC VSS on the tailshaft -- look for two wires coming off the VSS.

However, your '165 ECM will still need the old 2Kppm square wave signal.

I don't know offhand which cars had it, but there were quite a few late '80s-early '90's GM applications that used the 4Kppm VSS, but still had 2Kppm speedometers. Might dig around at the local pick n' pull, and see if you can find yourself one of those yellow buffer boxes, that will change the 4Kppm AC to the 2Kppm signal needed for the 165 ECM.

Also, there should be a file called DRAC2.pdf on DIY_EFI that you may find useful.

Another option would be to go ahead and convert your car to the 1227730 ECM, since that ECM will accept the 4K signal directly. It's not at all a difficult conversion.

Come to think of it, you could also use this as an excuse to swap to a T-56, since it would already have the 4K VSS you need.

Also, I vaguely recall there being an aftermarket device or two that would convert mechanical speedo to VSS (Abbott, perhaps? I can't remember...maybe someone else knows.)

Anyway, I hope that's enough to get you started.

MTPFI-MAF

So Dave_Jones The Vss only Controls the Speedo, and sends a signal to the ECM, Does it have anything to do with the Tach or does the ECM Control Signal to hei Then TO Tach.

Thanks great info u Gave me but I currently have a 870' ECM and was going to convert to a 165' Because For some reason I am still convinced that I like MAF better for a daily driven car that sees State to State Driving. And I wish I could find a T56 In good condition for a farily good price because my T5 Input shaft Is Messed up and Have to double clutch to engage 4th some times tripple Clutch So I am Spending $1000.00 On a Fully Remanufactured One with a 1 year unlimited Milealge Warrany. Can't get a Price and warranty for a T56 That Cheap or I would have one.

Dave_Jones

The tach doesn't really have anything to do with the VSS. (If it did, you'd read zero RPMs until you started moving.) Tach signal comes directly from the ignition. The ECM also knows RPM, because it's connected to the ignition module, but the ECM does not output anything to the tachometer.

Now, on the LT1 fourthgens, the PCM does output a signal to the tach. But it's just a "regular" V8 tach signal, just like you'd feed to any ol' aftermarket tach. Sorry to say, I have no idea what signal a V6 cluster uses! The cluster could be calibrated as a V6 tach instead, or if you're really lucky, it's the same cluster (i.e. a V8 tach), and the V6 PCM tweaks the signal. I guess you'll find out once you hook it up!

On a '730 SD car, the 4K VSS feeds into the ECM, and the ECM can spit back out a 2K signal for the speedometer.

Some other GM apps have the converter box I mentioned, that accepts a 4K input, and outputs BOTH a 2K and a 4K. You'd simply route the 4K to the cluster, and the 2K to your '870 or '165 ECM.

Read the DRAC2 file I mentioned, and you should also take a look at the circuit diagrams in the respective FSMs, to figure out what needs to get connected to what, to make your cluster swap work.

Don't want to kick off a MAP vs MAF debate here, but my '83 T/A is wired so it can run either the '165 in MAF, or the '730 in SD, and I prefer the '730. And it just so happens to be my daily driver. But IMHO either would be an improvement over the '870.

HTH,