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Replacing the Speedometer Posted by Justin VanAbrahams [Email]  (#32) [Profile/Gallery]
(more from Justin VanAbrahams) on Mon, 28 Mar 2016 14:32:33
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My poor 1985 SPG is going to be the victim of a lot of replacements over the next few months. It's a bunch of stuff I never did on my '90 because it was so original and so low-mileage... but since this '85 probably isn't even really an SPG to start with I don't feel so bad.
First thing is the Walbro 255lph pump, which has hopefully been discussed to death!
The second thing is replacing the power steering pump with an electric pump. I think I more or less have that dialed.
The third and final thing is replacing the speedometer with something aftermarket. Motivation here is mostly curiosity, but also I'm interested in getting rid of the speedometer cable and stupid odometer drive gear... and, I guess, having the correct mileage. The '85 has an LH2.4 swap so the odometer is not even remotely right... plus it's broken. Yeah, I can send it out for $150, have the odometer adjusted and a new drive gear installed, but like I said... I'm curious.
I know the Saab 9000 VSS will pop right into the Saab 900 gearbox, done that before. I know the Saab 9000 VSS puts out AC voltage that increases with road speed, and that the wave is at 4x2458 pulses per mile. The Saab 9000 speedometer converts that to square wave 2458 pulses per mile and sends that to the cruise control and LH ECM. I need a doodad that converters AC 4x -> square wave 1x.
I believe the Dakota Digital SGI-5e will do exactly that. It does convert sine to square and 4:1 should be well within its ability. I *think* I am good in a technical sense.
I'd like to come up with a way to verify things are working as I expect. The VSS should not be an issue - I chucked it up in my drill this afternoon and it appears to work - VAC and Hz varying with speed, eg 200Hz at 700rpm. I'd like a way to equate RPM with road speed, but I have no idea of the ratios in play. I'd also like a way to read the square-wave signal at the LH ECM, but I don't have an oscilloscope. I am wondering if a USB/software based one will do this job... seems simple enough.
So:
1. Anybody happen to know the gear ratio of the Saab 9000 VSS?
2. Anybody played with software-based scopes?
posted by 12.195.130...
, Mon, 28 Mar 2016 14:32:33 <-- Viewing This Message, Thu, 31 Mar 2016 15:56:00
, Thu, 7 Apr 2016 08:51:26, Sat, 2 Apr 2016 21:26:34, Fri, 1 Apr 2016 09:36:58, Mon, 28 Mar 2016 16:27:34, Tue, 29 Mar 2016 09:43:42, Tue, 29 Mar 2016 11:03:25, Wed, 30 Mar 2016 14:39:26, Wed, 30 Mar 2016 16:11:04, Wed, 30 Mar 2016 11:48:04, Wed, 30 Mar 2016 15:55:30, Tue, 29 Mar 2016 11:23:35, Mon, 28 Mar 2016 17:14:45
, Tue, 29 Mar 2016 19:20:05, Mon, 28 Mar 2016 20:05:20, Mon, 28 Mar 2016 14:35:45, Mon, 28 Mar 2016 16:33:10
, Mon, 28 Mar 2016 18:28:35
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