MFI stuck rack

chauser · chauser's Garage

Tracking down source of fouled plugs I pulled MFI pump (2.4S engine) and injectors for cleaning.
After opening the pump up it was loaded with sludge.

I soaked pump in berryman's B12 chem-dip for 2 days, rinsed that out with carb cleaner.
I was fortunate and was loaned a heated ultrasonic bath - back into berryman's for several rounds of cleaning

Cleaned it all out again w/ carb cleaner then methanol.
Filled it with oil and let that sit overnight.

Pulley turns over fine, but rack is stuck. I put wood dowel in rear hole and w/ mild pressure am unable to get rack to move.
I can rotate the gears above pistons by hand and get rack to move but it does not return.

Suggestions welcomed

RSTarga · 02-10-2022, 05:23 PM

Pacific fuel injection or Mark Jung for a rebuild

icarp · icarp's Garage

sounds like a foreign object is jamming the rack

Ian

stownsen914 · 02-10-2022, 06:35 PM

Have you opened the pump? Pulling a side cover isn't a big deal to do. Might reveal something.

RDM · RDM's Garage

I would suggest that now that the rack is free you put it back through the ultrasound.

Also, the throttle return spring will close the pump; I don't know that pumps are spring-loaded to close on their own (but my experience is from a relative)
Mercedes MFI pump question

hbrand · hbrand's Garage

I got mine to work using GUM Out.
Removing the 6 top parts and working the pistons down with a dowel.
Greetings

chauser · chauser's Garage

Thanks for replies.
I have pump in diesel in ultrasonic cleaner again.
I can now push on back of rack w/ dowel and get it to move, so progress, but still no return.

re spring: perhaps return spring is weak - i'll see if I can source replacement.

re: remove check valves & push pistons down - can you expand on this? I pulled one of the check valves off just to see if it looked clean inside, and it appeared OK. What did you do, spray gumout onto pistons?

thanks
charles

stownsen914 · 02-11-2022, 04:22 PM

Sounds like progress!

Sometimes a good penetrant like PB Blaster can do things oil can't, might be worth a try.

Another thing that wouldn't be evident from external testing - make sure the pistons/plungers aren't stuck. You can have stuck plungers and the pump will still spin (but it wouldn't work in that condition). Plungers are visible with the side cover off. Plungers are another place that some penetrant can help if stuck.