follow-up question for injector cleaning

[tmctguer]

does anyone know what PSI an MFI system is running at when pressurized? i'm trying to figure out how much PSI it would take to run cleaning solvent through an injector to effectively clean it out ?

[Matt Smith]

I'm not sure off hand, but those specs are on Lee Rices stuff in the pelican tech section on MFI. It's unusually high though, and is what gives the mfi system its advantage- excellent fuel atomisation.
Have you investigated ultrasonic cleaning of the injectors? It works nicely- just soak them in B12 or similar in the ultrasonic bath and they clean up well. My bath had a 12min timer on it, so I had to go back and reset it a few times.. I think Warren advocates an overnight soaking? Probably best to get them tested for flow pattern and leakage after you have them cleaned to totally rule out the injectors. I can't give you any local contacts for this service unfortunately, but the other MFI guys may be able to. I wonder what the opening pressure is for diesel direct injectors.. and if test rigs used for them could be rigged up for the Bosch MFI injectors. Worth investigating?

Hopefully the cracks on the flange mountings for the injector stacks will not be causing a leak. I doubt they will as the mounting flange is wide enough to be able to effect a decent seal with the throttle bodies if the gaskets are in good shape or new. The gaskets are inexpensive anyway, and removing the stacks and inspecting will allow you to check and set the throttle butterflies properly. Then you will know the state of the whole induction system. A hassle, but worth it if you are at all curious or concerned. Failing that, try the carb cleaner leak test. Easy
I trust you have checked that the vaccum tubes on throttle bodies 1& 4 are completely clear? You should be able to suck on the other end of each vaccum pipe and get air.
Happy diagnosing!

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'72 911 TE

[kwikt 911]

I believe it's 265psi at the injectors.
GOOD LUCK.

Kevin Kipta
72 911T/E STILL USING ORIGINAL INJECTORS

[Matt Smith]

Same here Kevin. And original un-recond pump. These are tough systems; I think from my experience that their fearsome reputation is largely undeserved. But I do admit to having a soft spot for them

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'72 911 TE

[tmctguer]

i spoke with hergesheimer motors in SoCal (great people, by the way) and they referred me to Pacific Fuel Injection near SF, CA.

i called and spoke with Gus and he said that his company will test and clean fuel injectors for $8.00 each. he will tell you if any are bad and the cost for a new MFI injector is $75.00. you have to mail him the extracted FI's. he can turn them around in 2 - 3 days.

for those who are interested, his contact info is:

Pacific Fuel Injection
153 Utah Ave, Suite B
South San Francisco, CA 94080
650-588-8880

[GIBSON]

Gus is a great resource for anybody trying to keep their MFI systems on the road.
I've had a number of leaky pumps and Gus will sell you a complete gasket set for around 100.00, they are not difficult to install and they really stop the leaks.
I tend to agree that these systems have gotten a bad rap and do function quite well with reasonable maintenace.
I've cleaned injectors in ultrasonic baths too and had pretty good results. I like Gus's cleaning a little better. Seems like I've seen the injectors for around 60.00 each if you look carefully. Of course, if you're going to have Gus clean and check you probably should buy them from him.

Bruce Herrmann
73911S