julianco Posted January 24, 2014 Share Posted January 24, 2014 (edited) I've hijacked this thread, but thought the topic belonged in this forum so.... To recap, I have 5 magnets on the driveshaft being read by a hall effect sensor on the tranny. With the Vehicle Speed Sensor wire disconnected, the car runs more or less normally unless I let the RPMs drop too suddenly, and then the engine will stall. I can baby it, and get it to idle, though sometimes doing this, it goes into what I think is "limp mode" and it runs rough, shudders, has no power etc. Turn it off and back on, and it's back to normal - running normally and dying after dropping from higher RPMs. When I hook up the VSS wire, the car runs perfectly until roughly 33mph. It doesn't want to die at stops and seems to run stronger while driving (might be my imagination). But when it hits 33, it seems to cut spark. If I keep it over 33 (going down a hill) the car will die. If it drops below 33ish, it will start firing again. This seems to me like I have the wrong number or readings per rotation so I'm trying to figure out the math as I'd prefer to bust off the magnets and glue them back on only one more time if possible - skipping the trial and error. I'm pretty sure that the VSS wants to see 4000 pulses per mile. The vanagon/EJ swap VSS kit which I'm using a part of, uses 5 pulses per wheel rotation. I'm pretty sure the rear diff ratio is 3.9:1 like the brats? My wheel and tire diameter is ~22.5" which I think give me about 47.5343 rotations per mile.. From here, I'm a bit stuck. Any ideas? Edited January 24, 2014 by julianco 1 Quote Link to comment Share on other sites More sharing options...
julianco Posted January 24, 2014 Author Share Posted January 24, 2014 (edited) Assuming it is 5 pulses per wheel rotation, and the diff is a 3.9:1 ratio, this would give me 1.28 readings per driveshaft rotation, which is problematic. Is it really 5 pulses per wheel rotation though... So I have a ~22.5" wheel diameter. * pi = 70.6858 inches a mile is 5280 x 12 for inches is 63360 63360/70.6858=47.5343 47.5343 x X = 4000 4000/47.5343 = 84.149 Then divide this by 3.9 for the driveshaft..... But 84.149 readings per wheel rotation seems really high, especially when 5 readings per rotation works for the Vanagon guys... Edited January 24, 2014 by julianco Quote Link to comment Share on other sites More sharing options...
Phizinza Posted February 27, 2014 Share Posted February 27, 2014 I used 2 magnets on the tailshaft and it worked without issue. That was using 1990 ej22 Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted February 28, 2014 Share Posted February 28, 2014 i thought the front vss was 4 pulse per rotation. but what ever the number is getting it accurate would seem to me to be important. on the other hand, why not just tap the front sensor wire and feed it to the rear sensor wire? Quote Link to comment Share on other sites More sharing options...
julianco Posted February 28, 2014 Author Share Posted February 28, 2014 So I updated on another thread, but what I ended up doing was swapping the speedo in from an 80's GL which has the VSS built in. It needed some custom fitting, and the black plate that attaches to the front of the speedo unit itself on the first gens wouldn't fit, so it's kinda open which looks unfinished but I think kinda cool, especially after I take off the plates on the temp and fuel gauges. Phizinza : With the 1990, OBDI, the VSS is hardly needed, at least it seems like this is usually the case. Either way, it would not be as sensitive to accuracy as the OBDII's johnceggleston: The 4000ppm is correct, but the issue here is that it is a first gen car with no VSS, and the trans is the 5spD/R when they used the speedo VSSs. In the OBDIIs at least, the VSS was an electronic unit plugged into the tranny where, on the 80s models the speedo cable connects. Anyways, car is running pretty great with the new speedo. Now I just need to figure out why it's always smelling like gasoline after warm up.... Quote Link to comment Share on other sites More sharing options...
Scooner Posted March 4, 2014 Share Posted March 4, 2014 Happy to see you worked your way around that pesky OBD II VSS problem! Now you are romping around boulder turning heads, im sure! Post some pics up on here all I've seen is the pics from the craigslist ad I think? Quote Link to comment Share on other sites More sharing options...
julianco Posted March 4, 2014 Author Share Posted March 4, 2014 (edited) Thanks Scooner! It is fun. Still a few kinks I'm working on, and I moved to Denver.... Anyways, here's a few pics. I think I posted this one already. Here's a few newer ones...I should take some more when I get a chance. Also, update the build thread..... It's real fun to drive in the snow with the little studded snows... Though the handbrake is front wheel, the power to weight ratio makes it a pretty good little drifter. Edited March 4, 2014 by julianco 1 Quote Link to comment Share on other sites More sharing options...
Scooner Posted March 4, 2014 Share Posted March 4, 2014 Man, I love the way them gen 1s look! The coolest part is you've got a powerful modern engine. I bet alot of people get "bit" when they realize its a bit of a sleeper huh? What part of Denver did you move to? Must be for school? Quote Link to comment Share on other sites More sharing options...
julianco Posted March 10, 2014 Author Share Posted March 10, 2014 (edited) No, not for School. Baker neighborhood on south broadway. Come on down for a test drive. Edit: Taking off the studded snows if someone wants to buy... Light use over the past 2 months is all they've seen. Edited March 10, 2014 by julianco Quote Link to comment Share on other sites More sharing options...
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