MFI and CDI failure questions

[wslynn67]

I've spent the evening reviewing MFI information in the archives again just to brush up. I have identified a few questions that I cannot find answers to.

Most of the time when someone suspects an MFI unit is bad, the forum guru's point out that the problem is most likely something other than the MFI pump.

This begs the question, how does an MFI pump typically fail? I find several mentions of fuel in the oil, but that is about it. Is the failure gradual? sudden? obvious? subtle? Would a poll of the people who have rebuilt their pumps prove a useful addition to the archives?

Along those lines, what typically happens when the MFI cog wheel wears out and the belt slips? High rpm fuel starvation with normal running at low rpms (since MFI timing isn't necessarily vital)?

I have a similar question about the CDI unit. Most contributors to the forum point out that they either work or don't work. Do they ever fail gradually? If so, how?

[Bill Verburg]

MFI is a purely mechanical system w/ numerous mechanical adjustments and wear point that gradually over time get out of adjustment due to wear. If there is a sudden issue it is unlikely to be MFI related because they usually don't break, they wear.

[Early_S_Man]

The CDI units can be intermittent ... usually a bad solder joint or cracked/fractured wire that causes occassional problems.

The faults that cause one to go silent, or not trigger ... bad transistor or SCR are permanent and not intermittent in nature. Very basic, discrete semiconductor switching and logic circuitry that is very easy to trouble shoot -- once the disassembly is accomplished.

The Speed Relay is another problem with MFI cars, though not insurmountable ... I have posted the circuit diagram I reverse-engineered three years ago.

WARNING - All '69-on MFI Owners!!! Preventable Failure of $283 Speed Switch module!

[wslynn67]

Thanks,

That was the information I was interested in.

Scott