Engine Tach Bounce 1989 Mustang GT

[N8ight]

Hello,

Recently switched out my old cap and rotor to an MSD replacement for the factory distributer. Now my tach bounces all over the place. I put the old one back on and it goes away. The car seems to run fine ether way. Any help or suggestions would be appreciated .

 

[Noobz347]

I would say to leave the OEM distributor alone.

 

[Kid wita 5oh]

Only changed the cap and rotor? Not the whole distributor?

 

[N8ight]

Cap rotor and new plug wires.

 

[N8ight]

Same distributor.

 

[AeroCoupe]

Was the erratic behavior at all rpms, down low or up high? Need this information to make any educated guesses.

 

[N8ight]

Its kind of all over. At start up and idle it seems fine once you get in the throttle it seems to struggle to get over 3500 when i know I'm closer to 4500 based on gear and speed. As it struggles to go higher it bounces between 1500 and 3500. When i excel slowly it has a small bounce but still noticeable and gets more aratic at higher rpm .

 

[AeroCoupe]

I would say that those parts are most likely way out of spec in the gap between the rotor tip and the contacts in the cap. Unfortunately MSD’s quality has taken a hit over the past years.

Cap, rotor, and coil wise you are far better off with Standard Ignition and Motorcraft parts like:

Coil:
Motorcraft Ignition Coil - DG470
Standard Ignition Blue Streak Ignition Coil - FD478

Cap:
Motorcraft Distributor Cap - DH411B
Standard Ignition Blue Streak Distributor Cap - FD168

Rotor:
Motorcraft Distributor Rotor - DR374B
Standard Ignition Blue Streak Distributor Rotor - FD307

For plug wires I just run the Motorsport 9mm. You can get better ones but they are twice to three times the cost and I’m not going to gain much for the additional cost. For reference I am referring to the likes of Firecore:

Small Block Ford 302 - FireCore50 Spark Plug Wire Set PF-2000

Firecore50 8.5mm Spark Plug Wire Set for Small Block Ford 302.

firecoreperformance.com

For plugs just run Motorcraft copper core units. I run Motorcraft copper core plugs on my 331 and my 351 with zero issues.

 

[Kid wita 5oh]

.... Unfortunately MSD’s quality has taken a hit over the past years.....

Msd quality was gone long ago... I had multiple bad msd parts 20 years ago... Distributors, coils, tfi modules... Never had one last over 6 months.

 

[AeroCoupe]

The MSD 6AL in both of my cars are 20+ years old and the TFI coils are 10-15 years old. The MSD distributor in the T-Bird is about 10 years old but that car is carbureted. With all of that I haven’t had a failure and I think where their failures are are the TFI distributors but if you put a Ford TFI, PIP, rotor, and cap on their distributor body it works really well…sad.

Their caps, rotors, and coils are highly counterfeited so that’s another problem.

 

[Kid wita 5oh]

.... but if you put a Ford TFI, PIP, rotor, and cap on their distributor body it works really well…sad....

That's exactly what I had to do back then

 

[N8ight]

That's what my thoughts are at this point. I thank everyone for your input and advice. I am going to get the Ford/Motorcraft parts ordered. I will update when the parts are installed .
Thanks again