backflush CIS injectors
 

From looking around the internet I keep seeing rumours of there being a way to backflush CIS fuel injectors as found in the 911SC.. Is this true?

I have used the "search" and can not find any info on the subject other than people saying they have heard of it being done.

I have seem glimpses of information on the subject, including using a second injector to flush another?!?!??

Logically, if its the fuel pressure heading down inside a CIS injector that opens it, I cant see how its possible... But with all these small snippets of info I have found, I do wonder if there is a cunning way to do it.

Having cleaned a LOT of CIS injectors since 1985, I cannot see any effective way to do this due to their design,...:)

I use the Bosch injector cleaning fixture & solvent to do clean them and it shows opening pressures as well as displays spray patterns which are critical for proper running. In many cases, we find them sufficiently dirty and/or corroded which requires replacement.

Gordon at WitchHunter
 

I happened to have been in email conversation with Gordon @ Witch Hunter today about this very issue and he tests CIS injectors for $8 a piece for his loyal Porsche customers but may be discontinuing that service. He charges $17 for a complete rebuild and calibration of electronic injectors, that are rebuildable, which puts his testing charge into perspective. He told me that CIS injectors are really a disposable item and even new ones are only within 20 to 30% flow rate of each other which is Porsche specs. He shoots for flow rate tolerance of less than 5%. He notes that CIS injectors cannot be successfully backflushed which confirms your remarks, Steve.

:(

rbuswell,

When you say he shoots for a 5% tolerance, are you referring to CIS injectors? It sounds like this is not possible, unless you keep rejecting ones until you get some that are close. Did you mean electronic ones? This seems more likely since he can rebuild and calibrate them.

Well this is what I thought!

Another myth busted! :)

Yes, you are correct ... no way on the CIS injectors
 

Yes, he has a really neat video on his website along with the report he sends out with each electronic set he does. I found it very informational although no help on CIS systems. It really is interesting to see the before and after:

www.witchhunter.com

I soaked mine in a seafoam bath for a few weeks while I was rebuilding some of my CIS stuff. A lot of crud came out I noticed (I'd shake the jug every once in a while, at the end of the soak period there was a fair amount of sediment at the bottom). Replaced all the seals & sleeves, scrubbed them as well as I could with a toothbrush. I think that's about all one can do.

I'll post if things improve once I get the car all back together (one of these days). I may at some point replace the injectors, but for now I know the car ran with the ones on there so no reason to blow the huge amount of $$$ replacing - at least not right away. Once I get it going I'll be able to fine-tune and verify everything is where it should be and replace if necessary.

I suspect a good cleaning wouldn't be a bad idea.

+1 on soaking in fuel injector cleaner for days and then blowing them out with air; new ones would be better.
On SC's, you can check the pattern and the volume by placing all six injectors into glass jars, ignition ON, lift the airsensor plate in the airbox briefly, observe the spray in the jars.
Fire Extinguisher needed!!
There are tiny filter screens in the injectors and in the FD nipples for the discharge lines.

Revealing my ignorance
 

Phile:

I googled Seafoam Bath and only got a body care gel for people. I guess what I'm asking is what is Seafoam Bath?

Adrian Streather's book, "Porsche 911SC: The Essential Companion," features a section about backflushing CIS injectors using a disassembled duff injector and then connecting it to an injector to be cleaned (this is a simplified description). This may or may not be more trouble than it's worth, but it's food for thought.

Brian

Just use any type of injector cleaner: Techron, STP, Bardahl......................
A small Tomato Paste can works well; just right for 6 injectors standing upright fully covered. :)

Just two cans of seafoam in a jug. :)

They also make a product called "deep creep" in a spray can that's a pretty good solvent too, but I think the straight seafoam stuff is probably better for soaking rather than an aerosol product.

The deep-creep stuff is great for cleaning the carbon & crud off of intake valves/ports though. . .

Another method is to use an ultra-sonic jewelry cleaner. These are available via Harbor Freight for around 30 bucks.

Interesting.
I wonder if anyone has had some experience with this. :confused:

I have, that's why I posted this method.

Prior to my 3.2 conversion in my 73, I jumped through a lot of hoops to make my 73.5 CIS work.

I cleaned my injectors using the ultra sonic cleaner filled with injector cleaner. After cleaning, I used air to blow out the injectors. When I installed and tested them, each injector each seemed to work much better than before

Sounds good.
Do you have a picture of the devise?
How big is this thing?
Does it hold just one injector at a time?

I have a small Crest brand, lab quality, heated ultrasonic cleaner that I use. I Can clean all six injectors at once. It is very effective for me. You can find them on e-bay for a feew hundred bucks.

I first clean the injectors with carb cleaner. I them blow them out with compressed air, followed by a good dousing with simple green. I then dump them into the ultrasonic tank, filled with plain water with some dish soap for an hour or so. It works well for me.

Branson is another quality brand. A friend had a cheap jewelry cleaner and I found it to be ineffective and not long lived.

Any ultrasonic cleaner requires a basket. If you have the items to be cleaned on the bottom of the tank you can kill the transducer.

Regards,

Jerry Kroeger

Cross-reference to my backflush experiment here.

Brian

Here's link to a photo of the ultrasonic cleaner I used:

http://search.harborfreight.com/cpisearch/web/search.do?keyword=jewelry+cleaner

I used the one that cost $29.99