Since I'm finally about to start some prom editing, It's dawned on me that I've really got no idea what the consequences are of running the car the way I have been since my T56 swap. At the time (March of 99), I simply left the original A4 park/neutral switch wires jumpered together to fool the ECM to believing that there was still a 700R4 there, but it was always in P or N. I'm running an Autometer electronic speedo off of the T56 output, so I pretty much just left it at that.

With no VSS connection to the ECM, it should have set a code, but it didn't because it didn't look for the input when in Park/Neutral.

I've driven the car like this ever since (20k miles+), and I'm wondering what I have to gain from doing it -right-, now that I'm going to start burning proms.

Thanks in advance,

Andrew Choset
88 IROC-Z !VSS

 

That's interesting. I would have thought this means you've been running in open loop for 20,000 miles. It'll be interesting to hear what someone who knows the answer has to say

John

 

I am curious also. Especially because I am running a similiar no VSS setup( My harness for the vss broke)

 

The lack of VSS can at times be an issue.
Primarliy in so far as you lose the IAC reset. If for some rason the IAC count gets fubar'd, then the idle and throttle follower can suffer.

Plus you may lose some of the DFCO function.

Not to mention TCC in automatics.

Usually just adding an inline speedocable sensor, cures the lack of not having the proper signal.
The electric speedo set ups are another matter.

 

In the '808 cals I'm using, if VSS indicates < 5 km/hr, and TPS is closed, you get Idle Mode and then it runs open loop at 14 :1 AFR after 25 seconds.

Even if his cal was set up like this, obviously he's not running idle mode open loop because he'll have TPS > 0. But it looks like speed has to exceed some preset value (in mine 35km/hr) to get DFCO, so that won't work.

So will it do the normal closed loop/ open loop stuff? (- except DFCO, I imagine).

John

 

Highway mode won't kick on unless a speed threshold has been met.

 

I have been running no VSS with the 730 in my Jeep for a few years. I purchased an adapter for the transmission so the speedo would work and I thought about tapping into it for the ecm. What would the computer think if it was registering speed but still thought it was in park/neutral? I don't have a switch on the tranny for the P/N.

 

That's a good question about the p/n switch. The previous owner of my car didn't have it hooked up and the car ran great. It even idled down near 500rpm solid, never stalled, etc. I would have liked to have had a stock motor to play around with.
I'll get the test bench answer to you shortly weather or not the p/n switch is "important."

 

There is also EGR solenoid issues when the P/N switch is always in park or neutral.

 

An open Prk/Neut wire (no switch, not grounded. . .) tells the ECM it is in drive. This is the behavior of a manual transmission car and will work for an auto also. So un-jumper your connection and all will be fine.

RBob.

 

I'm having issues with my VSS (SGI-5 calibration box) due to six-speed swap. What I did, was disable VSS diagnostics in the PROM. The code went away and my car DOES go into closed loop like normal and it also goes into power enrichment like it's supposed to.

However, I do believe that the VSS controls the gas vapor purge canister (EEC) and sometimes I smell gas coming from it.

My car idles decent in closed loop, but when I start it when it's cold, I have to nurse the throttle until it goes into closed loop.

Since I have no VSS signal right now, my question is: does VSS input have anything to do with open loop (start up mode) idle?

Mike (1bad91Z)