VSS/speed transducer question?

[Mr Bridger]

Got a quick question for you guys. I am in the middle of a LT230 swap on my 1994 RRC. I have done this swap once or twice in the past (but quite some time ago now) and when using a Disco sourced LT230 IIRC I just did away with the Disco VSS unit that sits in the T'case and fitted the external Rangie one as normal.

My question is, can the stock disco transducer be used and wired directly to stock Rangie VSS plug and the external unit removed/bypassed/disguarded, or is the disco unit not compatible?

On a side note, the BW T'case was a SOB to get out with my custom exhaust.


Cheers,
Matt.

[red90rover]

The two units are completely different for different purposes and produce different signals.

[Mr Bridger]

Cheers John, I suspected as much so I installed it as normal but couldn't help wondering.

[red90rover]

I thought you were carbing the rangie?

[Mr Bridger]

Yeah, I collected the parts but almost simultaneously I finally got the EFI to work properly. I am still going to do it when I can find the time, but I may wait until I swap in the 4.2 V8?

[PTSchram]

If you keep the bits from the B-W transfer case,you should be able to transfer everything to the LT-230.

[deepseaoutlaw]

so what exactly is the difference in signals between the old range rover speed transducer that is mounted to the frame and the disco one that is mounted to the transfer case it self? i have the 14cux installed and there are only two wires coming from both units. i ask because my rrc transducers is craping out and having switched out the speedo to a electric aftermarket version i would like to just replace it with the transfer case unit from the later disco 1.

[PTSchram]

I thought about this for awhile and I'm pretty certain the outputs are, if not identical, very similar.

The waveforms in the library of the Snap-On Vantage show identical waveforms-yeah, I know, Snap-On makes mistakes too, but I've successfully swapped ECUs around between pretty much all variations of trucks using the Lucas 13 and 14 CUx EMS and not had a problem with the VSS signal.

[deepseaoutlaw]

so PT your saying i can ditch the old cable driven speed transducer and swap it for the transfercase mounted one from the disco? i thought i could but before spending cash on one or the other o wanted to make sure. also with this part being broken it would cause the rpms to race at nuetral is that right? or is that the stepper?

[PTSchram]

It sure looks like it would work. I've been wrong in the past, I will be again, I'm sure.

Typically, the VSS will exhibit symptoms of cutting out at highway speeds and erratic speedo operation, but the early trucks ahd pass-through cables to the speedo and IIRC, you've replaced the speedo with a GPS.

The early trucks were plagued with ECU problems where the ECU was thinking the truck was going 55 MPH when stationary-I think both of my '88s have later ECUs due to this problem.

Surging at idle can be due to vacuum leaks or TPS problems most often. Somebody's got to find a suitable alternate TPS that doesn't cost an arm, a leg and your first born child!

[deepseaoutlaw]

im going to try and replace the transducer with the later one from the disco and see what happens. i have the 14cux installed already and have changed out the old gauge cluster for all auto meter set up. speedo jumps around from the feed coming off the speed transducer.

[sedat]

The D1 transducer will work. I left the D1 unit intact when I did a Lt230 on a 92' model last year. I didn't have any issues with it.

[PTSchram]

WooHoo! Independent confirmation.

Thanks.

[Colorado Scott]

Would a nonworking VSS (inop speedo) cause a huge dip in MPG? What role does the VSS have other than sending a signal to the speedometer?

Maybe it's coincidence but my fuel mileage has been really crappy since losing my speedo a couple of months ago. Was getting 10-12 now getting 6-8 max.

[PTSchram]

Originally Posted by Colorado Scott

Would a nonworking VSS (inop speedo) cause a huge dip in MPG? What role does the VSS have other than sending a signal to the speedometer?

Maybe it's coincidence but my fuel mileage has been really crappy since losing my speedo a couple of months ago. Was getting 10-12 now getting 6-8 max.

Doubtful, most common cause for diminution in fuel economy is oxygen sensor aging/failure. Assuming good condition ignition components, etc.

[Bentcrank]

Originally Posted by Colorado Scott

Would a nonworking VSS (inop speedo) cause a huge dip in MPG? What role does the VSS have other than sending a signal to the speedometer?

Maybe it's coincidence but my fuel mileage has been really crappy since losing my speedo a couple of months ago. Was getting 10-12 now getting 6-8 max.

If the dummy light is on and your speedo is inop then yes your mileage will suffer. If it's just the upper cable that's fubar'd making the speedo inop then no...it has no effect on mileage. If the Transducer or the lower cable is not working then yes your ECU will go into "limp" and eat gas. With it not working you will get speed sensor, stepper motor, o2, and random misfire codes.

[Colorado Scott]

Originally Posted by Bentcrank

If the dummy light is on and your speedo is inop then yes your mileage will suffer. If it's just the upper cable that's fubar'd making the speedo inop then no...it has no effect on mileage. If the Transducer or the lower cable is not working then yes your ECU will go into "limp" and eat gas. With it not working you will get speed sensor, stepper motor, o2, and random misfire codes.

I'm assuming the O2's are still in good working order- the truck "Fast Passed" the Colorado roller emissions last November. Fast Pass means it was burning so clean during the first part of the test it wasn't necessary to complete/finish the test. The ignition wires, plugs, cap & rotor have less than 10K miles on them and are about 2.5 years old. The stock distributor and coil have about 90K on them and will be looking to rebuild/replace this summer.

No dash lights are on. I haven't taken anything apart yet either; waiting until I get the new LT230 installed. Unless I find a cheap replacement, I'll splice in the D1 style VSS and see what happens.

Thanks guys!

[PTSchram]

Originally Posted by Bentcrank

With it not working you will get speed sensor, stepper motor, o2, and random misfire codes.

My RRC trail rig does not have a VSS. The only code I get is base idle.

[deepseaoutlaw]

ok finally got around to swapping in the disco css into my 88rrc lt230. now i need to wire it up. looking thru the rave manuals i have found the wiring diagrams for both 96 disco and 88 rrc. here is my problem the rrc has a all yellow and all green wire. yellow to the edu green is power in to the vss unit. i dont have a plug for my disco css. which wire goes where on the css unit? if i am looking straight down on the plug and the bolt hole for the vss is at 12 o'clock. does the yellow wire go on the left or right? any help is apriciated.

thanks.