So I have this recent issue with my dash mounted tach not functioning correctly after a FiTech FI system was installed. At steady speeds above idle the tach will oscillate wildly across a couple thousand RPM or so. It will also drop to zero on occasion. This was not previously a problem before the FiTech system was installed. More detail about it in my other thread: http://www.v8buick.com/index.php?threads/tach-and-speedo-working-intermittently.355095/ The FiTech system I have does not control the timing. My distributor is an MSD ready to run 8552. I'm not currently using any ignition box. The coil is mounted in the stock location between the distributor and alternator. From what I understand there is a way to pull a code off the handheld to see if the FiTech unit is really seeing a noisy tach signal. I had a shop do the install for me so I'm unfamiliar with how to get that code. The engine seems to run fine but maybe there is room for improvement if the tach signal was better, not sure. The handheld did not seem to have an issue displaying a reasonable RPM. I have done some reading online, including here, of people who have had this issue. One suggestion that was found on the FiTech forum is to install EMI/RF shielding over the blue tach wire. This has been tried without success by at least one board member, I forget who. I ordered a length of the shielding and was going to put it in over the blue wire but I'm having second thoughts about it after reading about limited success people had with it. It seems to be a common problem at least, but the fixes are not so common. I think a thread I found on here indicated the problem was solved by installing a 6AL box and hooking the tach to that. My current tach is an old MSD "FAST TACH" p/n 8901. In the future I may be swapping that to one of the reproduction in-cluster tachs. I'm seeing that the MSD tach signal is a 12V square wave, 22.5° duty cycle signal. Does this work with the repro tach or will a filter be needed? Should I proceed trying to install this RF shielding over the blue tach wire or does someone know of anything else that will likely work better? Is there a reason putting in a 6AL box WON'T work or a reason I shouldn't put one in? Would rather not if I don't have to. Thanks for any help.
So there was a fault code for a noisy RPM signal. The issues were resolved after the shop did the following: 1. The coil wasn't getting a full 12 volts, so they "created" a circuit to feed the coil from the ignition switch. 2. The tach was hooked to the wrong side of the coil. Currently it is hooked to the negative side which I thought was the case before, and is the way that FiTech indicates in their diagram it should be hooked up. Not sure what they really changed here. 3. They installed the RF shielding I bought. I had also asked the new shop to lower the engines idle speed since it was a bit high. They did so; and in combination with the above three things the tach issue has been alleviated and the thing runs awesome. The idle speed is near stock, and I believe the fuel injection allows it to run at a lower idle than the moderate street cam would otherwise allow. I like it!
