lgoodson@pacbell.net Posted August 1, 2009 Share Posted August 1, 2009 So the LT1 is in and running fine. Now I am trying to get the tach working. JTR says to use a 280Z tach with the HEI distributor. This is a LT1 and I don't know what kind of a distributor it has besides being the OPTI spark type. But I went ahead and installed the 280Z tach per all of the JTR instructions including calibration and the 15K resister. Using the tach lead off of the coil that my harness guy gave me I am able to get the tach to work (sort of). It jumps around and when you increase the RPMs it goes to zero. Not good. With the resister installed, the tach is dead. Any ideas as to what may be the problem??????? Quote Link to comment Share on other sites More sharing options...
deja Posted August 2, 2009 Share Posted August 2, 2009 There is a blue connector tha come off the engine harness Is the white wire the one you are using for the tach? It comes from the PCM pin A-13. I'm not saying this will work with the Datsun tach, I'm using the GM guage cluster, but that is the tach signal the LT1 puts out. C230...blue 10 pin connector. ............B- brown w/ white stripe (signal out to MIL lite) ............C- white w/ black stripe (diagnostic signal request input to PCM) ............D- white (tach signal out to dash) ............E- dark blue (VATS fuel enable input) ............F- dk green w/ white stripe (AC signal request) ............G- pink (12v 15amp fused ignition switched power feed into PCM, MAF) ............H- AUTOMATIC- lt blue w/ black stripe (TCC switched power in- wire thru Quote Link to comment Share on other sites More sharing options...
lgoodson@pacbell.net Posted August 2, 2009 Author Share Posted August 2, 2009 A13 on my ECM is the engine coolant temp sensor pin. The tack signal comes from the coil. It's a white wire. That is the one that I am using but thanks for the input. I am not using the stock harness. Quote Link to comment Share on other sites More sharing options...
deja Posted August 2, 2009 Share Posted August 2, 2009 If I rememeber you're running a 93 engine right? Sorry about the confusion, my schematics are for the later engines. A13 on my ECM is the engine coolant temp sensor pin. The tack signal comes from the coil. It's a white wire. That is the one that I am using but thanks for the input.I am not using the stock harness. Quote Link to comment Share on other sites More sharing options...
lgoodson@pacbell.net Posted August 2, 2009 Author Share Posted August 2, 2009 Yes, I have a 93 TA LT1 6spd and an aftermarket harness. The harness guy gave me a tach lead off thr coil (white) which is what I am trying to use with mixed results but at least I get something at the tach. Any Ideas? I will call JTR tomorrow and see if they can be of some help. Larry Quote Link to comment Share on other sites More sharing options...
deja Posted August 2, 2009 Share Posted August 2, 2009 I found this on a Z28 site: The white wire in cavity "B" of the ICM plug will probably work. However the 1993 tach gets its feed directly from another white wire on the coil plug that later years do not have. That wire has a little filter on it. No clue what that "filter" would be. You might consider one of these. http://www.camaros.net/techref/electrical/tachfilter/ Quote Link to comment Share on other sites More sharing options...
lgoodson@pacbell.net Posted August 4, 2009 Author Share Posted August 4, 2009 deja, today I talke with Mike at JTR. He couldn't help me with the LT1. Talked to my harness guy and he said that I had it hooked up correctly so I must either have a bad tach or the wrong one as Braap has said that he has not been able to get a 78 tach to work with a HEI system. What do you know about this. Thanks for the link. I probably will build a filter if I need one. I have the filter off the stock harness I could use. Larry Quote Link to comment Share on other sites More sharing options...
deja Posted August 4, 2009 Share Posted August 4, 2009 I would try the factory filter first. When I first got my 77 280Z it had a old school SBC with a HEI. The PO had installed a aftermarket tach mounted on the console, pretty useless. I tried the JTR method to get the stock tach to work with little success. The car had a ballast resistor is series with the stock tach. I tried removing it but then the tach just bounced all over the place. At that time I was unaware of the filter "fix" so I just gave up and used the tach set for 6 cylinders and knew what 6000 rpm was on the 6 cylinder tach. So Brapp might be right, maybe the later tach won't work. deja, today I talke with Mike at JTR. He couldn't help me with the LT1. Talked to my harness guy and he said that I had it hooked up correctly so I must either have a bad tach or the wrong one as Braap has said that he has not been able to get a 78 tach to work with a HEI system. What do you know about this.Thanks for the link. I probably will build a filter if I need one. I have the filter off the stock harness I could use. Larry Quote Link to comment Share on other sites More sharing options...
lgoodson@pacbell.net Posted August 15, 2009 Author Share Posted August 15, 2009 Well It's now 1 78 and 2 76 tachs that I have tried to get to work per JTR and at $40 a pop I might add and still I can't get the thing to work. I have it hooked to the white wire on the negative side of the coil or so I am told. To look at the coil there is no (-) mark to be sure. Who knows how to make the stock tach on a 93 LT1 work? Anybody? Quote Link to comment Share on other sites More sharing options...
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