MFI injector "operating pressure"?

[jkeyzer]

I'm looking into having my injectors cleaned professionally and one of the questions that came up is: what is the operating pressure of the injectors?

The technician said this would be different than the "dead head pressure" but I have no idea what he was talking about. He had done CIS injectors before but not MFI. I guess the limits of his cleaning tools are around 100 psi so I'm concerned that the MFI injectors might be greater than this.

One of the MFI articles refers to greater than 200 psi pressures, is this the number I'm looking for?

Thanks,
Jeff Keyzer
72 911T Targa

[pwd72s]

Yep. MFI is past 100. I've heard various figures, but it's past 100 pounds. Page 95, June 1995 issue of EXCELLENCE quotes a Mechanic named Red McClintock thusly: "...in addition, the fuel system produced 350 psi of pressure in the lines, this atomized the particles of fuel far more efficiently than any other fuel injection system of the time." I don't know how accurate this figure is, but I'd say above 100 pounds. How did I happen to have this quote so handy? Ego... sheer ego. My car was one of the two featured in the article.

[Rot 911]

Jeff the operating pressure at the injector on an MFI is 220-240psi. You can clean these injectors just as well at home using some B-12 cleaner and an inexpensive ultrasonic cleaner. See how here: http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=5882&highlight=Cleaning+MFI+Injectors

If you want to send them off to be done professionally I would recommend Gus at Pacific Fuel Injection. Read about that here: http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=5904&highlight=Cleaning+MFI+Injectors

[pwd72s]

Kurt, thanks...your figure sounds more reasonable to me than the one quoted in the article.

[jkeyzer]

Those high (> 200psi) pressures bring me to another question. Has anyone ever seen hairline cracks develop in their injector lines, causing small leaks? I've got one injector line that I fear may be leaking. The rubber guide on the throttle body where the injector line passes through is somewhat "gooey", and I am not sure if it's from a misplaced blast of carb cleaner or a leaky line.

I'm taking everything apart one day soon to clean out the throttle bodies and throw in new gaskets in an attempt to get good correlation between the stacks. I'll try cleaning up that area to see if it comes back.

With that said are replacement lines even available (pre-bent!)?

[jkeyzer]

Kurt -

Thanks for the info. I think I will try to clean them myself. The pricing ($25-$35 an injector) was not attractive to me as I am just doing this "on the side" as I troubleshoot greater poor running issues.

Where does one find a heated ultrasonic cleaner that will do the job? I have seen one before for jewelry cleaning but it did not have an integral heater. Any stabs at the cost? I'll look around.

Jeff

[tmctguer]

i tried the "jewelry cleaner" route and i had disastrous results. B12 melts any form of plastic it comes into contact with, including plastic jewelry cleaners. luckily, i cleaned up the mess before my wife found B12 all over the place. and i was doubly lucky that the B12 didn't seep all over my (her) cabinets and ruin the finish.

you can search the web for ultrasonic cleaners. i recall that a stainless steel, large volume unit with variable heat control cost around $250. i decided it was not worth the money since i would not be cleaning injectors that often.

i settled for a 1 night soak in techron, followed by a 1 night soak in B12. turns out my problem was elsewhere, but the cleaning didn't hurt anything.

[jkeyzer]

$100-$300 is the ebay asking price too. Soaking them in B12 can't hurt. I'm pretty sure my problem is not injector related, this is more of a "while I'm in there..." thing. By the way - what kind of seals are in there and are they reusable? (Haven't even pulled them out yet!)

[BK911]

Any ultrasonic cleaner with a stainless steel lining will work. The cleaner will generate heat even without the heating option. I soaked my injectors and it didn't make any difference. Then I purchased an ultrasonic cleaner and soaked them overnight and it made a huge difference.

To help defray the cost of my cleaner, I'll soak injectors for $25. That includes return shipping. Email bkolar@centuryeng.com for more info.

BK