So at the end of last season I had a shop doing some work on the 70 where they installed a FiTech fuel injection setup on my fresh built 470 motor. They also reinstalled the transmission (200-4R) after it got a freshening up while the motor was out. After I got it back from the shop, a couple issues were present. I had no desire to bring it back to the same shop to fix it (long story) and the car show season was over, so into winter storage the car went. I'm dealing with it in about a month and a half when the car comes out of storage. I suppose I should have posted this thread when I put the car into storage at the end of last season while the issue was still fresh in my head, but I was just too fed up to deal with it much. I'm starting to think about it again now that it won't be long until the car comes out. From what I remember: 1. The tach needle bounced all over the place across a wide range of RPM (even when idling). Can't remember if it did it continuously or there were periods of time it worked normally or had some other problem. 2. The speedometer worked intermittently. It would show the speed correctly up to a point (maybe 30 mph or so) and then randomly drop back down to zero and stay there for a few seconds. Eventually it would seem to work normally again. Rinse, repeat. My immediate intent when I get the car out is to the check the connection at the coil (-) terminal, check that the correct size ring terminals for the stud are used on all the wires, etc., and also add a star washer if there isn't one already to help ensure a good electrical connection. My questions: 1. Could fixing the tach issue also fix the speedo issue? (Do they share a ground, etc.) 2. There is one of those adapter boxes at the end of the speedometer cable where it connects to the transmission (200-4R) that changes the ratio of the speedometer gear. Has anybody ever heard of any kind of binding while using one of these that might cause this issue? 3. Other suggestions on what to look for? Are these symptoms classic indicators of a specific problem? Thanks for any ideas!
The original speedo Drive gear in my 200 was made a bit odd and the speedo cable didn't quite engage like it should. My car did pretty much what you are describing. I was replacing the driven gear in the trans anyway as it was not correct for my rear gear and that cleared it up. Based on your explanation it's likely just a loose speedo cable at the trans or the speedo ratio adaptor. Those adaptors are not particularly sturdy so so if everything is tight I'd suspect it has puked. The tach is purely electrical and the speedo is purely mechanical so nothing you do to one will fix the other. Odds are your shop attached the fitech to the tach output (you have an MSD or some other box?) and forgot to reconnect your tachometer.
I hope the adapter box didn't puke. There are hardly any miles on it. I have no MSD box; however, the tach I'm using is an aftermarket MSD branded one.
It's the hoofprints look for horses not zebras theory here.. Your mechanic installed the fitech which needs a tach signal, wherever that's taken from they probably failed to reconnect the wire for your dash tach. They also pulled your trans and it's easy to not get the speedo cable or adaptor box tight which would cause your speedo symptom. Eliminate those easy things then come back and let us know what happens.
If they forgot to hook up the tach, what makes it bounce all over the place as opposed to not moving at all?
The car is in storage (not at my house). I don't get the chance to look at it until the end of April. Right now I'm just looking for ideas about what to look for when I eventually get it home. The bouncing needle would make sense to me if it was hooked up, but had a crappy connection. This is what I'm going to look for. However, you suggested twice that the tach was probably not hooked up. I don't understand how a bouncing needle is possible if that is the case.
So what ignition are you running? The tach and speedo are two different issues. The speedo is mechanical.
MSD pro billet distributor (p/n 8552), blaster 2 coil. Not using a 6AL box or similar. Plug wires are the ones you cut to length and crimp the terminals on yourself.
That’s an MSD ready to run distributor. The tach should be hooked to the gray out put wire, NOT the coil.
I will also note that the hand held controller that comes with the FiTech setup displays the engine speed correctly without issue. I will check how it's wired once I get the car out. That distributor and ignition setup worked fine for a long time until the engine came out and went back in after the recent rebuild.
Picked the car up out of storage and took a good look at the wiring. The gray wire out of the MSD distributor is not there at all. There is also a single green wire not connected to anything that is coming out of the engine harness bundle on the passenger side of the intake. It has a black connector on the end and I suspect it once fed the electric choke of the Holley carb that used to be on there. The wiring instructions for the FiTech setup are here: https://static.summitracing.com/global/images/instructions/fif-30003_us.pdf Distributor is here: https://static.summitracing.com/global/images/instructions/msd-8552_frm30252.pdf As best as I can quickly tell, both instructions were followed except for the distributor gray wire. No clue where it went. The dash mounted tach seems to work normal up to about 1,000 RPM, then it starts to behave abnormally. At about 2,500 RPM (according to the handheld), the dash tach needle is swinging wildly back and forth across a range of a couple thousand RPM. Have not had the chance to look at the speedometer cable yet.
That was my next guess. In a stock harness, doesn't the tach connect to the coil (-)? What color is it? Memory tells me it's either pink or white, one is the tach, one is the ignition switch and I can't remember which is which.
Pink is the lead to the coil +. The Tachometer lead is brown as I remember. The colored wiring schematic in my 1970 Chassis Manual doesn't show any tachometer lead. Just the clock. There is this page though in wiring diagrams. It shows the tachometer lead separately going through a grommet above the fuse block and exiting into the engine compartment. No color mentioned though. If your car did not come equipped with a tachometer, none of that may be there. Even if it did come equipped, it might not be there today.
Thanks for the diagram. The tach I have now is not factory, it was in the car when we bought it. It's an older MSD branded one. Somebody replaced whatever was originally in the cluster with it.
Found this link: https://fitechefituning.com/fitech-efi-tuning-forum-2/topic/shielding-the-blue-tach-wire/ I kinda suspected electrical noise in the signal wire was the problem, and that link strongly supports the idea. Right now I'm looking into RF shielding and options for the best way to ground it so it will hold up under normal engine vibration.
