Backflushing CIS injectors
 

It's been posted before and here's a few pics I snapped today while backflushing my injectors. I'm redoing the top end of my motor so my injectors have been soaking in techron for around two weeks now.

I clamped an injector pintle end up into a bench vice.
Then took some copper wire and seperated the fine strands and cut 6 of them about 2 or 3 inches long.

Make a tight little v in the middle of the wire and loop it around to an oval O just big enough to stick the end of a hemostat through.

Then very carefully and as light as possible clamp the hemostat on to the injector pintle and lift it up just enough to get the edge of the wire under the pintle and hold it there lighty.
Then loop the wire around the pintle shaft and fold it over the sides of the injector so it holds the pintle open a little.

Take a piece of 8mm fuel line (i used some 8mm brake resovoir line from an old BMW I had) and push it over the end of the injector and hose clamp it.

Now spray some brake clean into the hose filling it up. Then take an air blow gun and push it into the other end of the hose and blast it with 120psi of air pressure from an air compressor.
Any crud that may be on the screen inside the injector will be blown out. Soaking the injector in techron for 2 weeks should help make anything on the screen loosen up first so it gets blown out.

Then loosen the hose clamp and carefully remove the hose without pulling the wires and possibly stretching the pintle spring inside the injector as you work it off.

Test the injector by sticking the plastic straw on a can of brake clean or carb cleaner into the other end of the injector and spray it. The plastic straw fits inside the injector and seals pretty well and the pressure in the can opens the injector and the solvent sprays out the end like gas when the motor is running. You can see if the spray pattern is a nice even cone shape.
In a week or so I hope to have the motor back together with new pistons and cylinders and be on the road again.

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Another great write up. Thanks Jim.

The springs get weak on old injectors. You wouldn't be able to generate enough pressure with a warm brake cleaner can to open a new injector. I'd bet backflush cleaning is about 60% effective anyway.
Does it make sense to thrift injectors in a multi-thousand dollar rebuild? I wouldn't do it.
Just something to keep in mind.

mine dont have a lot of miles on them and i can open them with a can of carb cleaner

When I worked on brand new grey market Mercedes Benz 500SEL's, SEC's, and SL's adding on aftermarket lambda systems and catalytic converters in the early eighties so they could and would pass emsissions and be registered in the USA I took brand new CIS injectors from brand new Mercedes 500 series cars and stuck the straw from a can of carb cleaner in them and sprayed it. Guess what... the injector opened from the can pressure and sprayed exactly like my 930 injectors do.
So maybe you are wrong or just never tried it.

Also, I did this procedure on these same 1987 injectors from my car around 6 years ago the last time I had them out. The car ran perfectly and had a pefect smooth idle afterwards so again I think your wrong.

Another thing I just thought of... I'm basically at sea level a mile west of the Atlantic Ocean in South Florida so the differential pressure between whats in an aerosol can of brake clean or carb cleaner and atmospheric pressure is as high as possible... :)

I've done it more than once and always with the same result.
Maybe you should try it.

I posted a picture of me doing it... you need glasses or open your mind :)

Nice write up Jim.
I've cleaned a lot of these and find if they are not too old/rusty the fix will work for a time and perform acceptably but never as good as new.
The cost of new is prohibitive, however it is a one shot deal as they will last a decade or so. For me the real issue is the difficulty of R&R and the risk of leaks. If the lines are over tightened just once they are ruined. The left bank is fairly hidden so hard to detect a leaker until fuel runs down between the heads onto the heat exchanger. Just something to watch out for.

another great write up Jim and again as usual - appreciate your time and insight

this is very much on my springtime to-do list... not ideal remedy or not, it's better than doing NOTHING - in my case, at least

will make for good piece of mine if nothing more

I did the same thing a year ago. Also did the harbor freight ultrasonic cleaning.

Helped a little bit, 2 of the injectors still didn't have a good pattern.

I did the same thing Jim did, and backflushed with a pint injector cleaner. Brake cleaner easily shot through the injectors, including the new ones.

There is no guarantee this will work, though given the price of new injectors, worth trying!

Bo

Good write up Jim. I posted this on another thread about the insides of an injector. The parts are easily replaced IF one could get inside without ruining the injector body. The filter screen snaps on top of the schrader valve. The spring inside the schrader valve is held in place by a small clip. You can see how back flushing might clean up that double sided screen. So it does make sense to back flush.

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Thanks for posting Jim. I'm gonna give this a try. I usually just soak in Techron and blow carb cleaner through them to check pattern. But you made this look easy! Ignore the trolls...

That's Pretty much the method I used. Had purchased 2 good condition injectors from fellow Pelican and used the best of the 8. After soaking and cleaning I did a flow test WITH the CIS system into plastic soda bottles and matched the best and most accurate flows. Highest flows go to cylinders 2 and 5. Or so I've read. You can also get different flows from different fuel lines (think of it as an afternoon science project). It's definitely worth the time and effort. Still wish injectors weren't so much $$$ but what r ya going to do?

Boy, this is going to come off rude, but it's pent up in me for awhile.....

I read posts like these and I feel like I'm not part of the brand. This mentality of throwing away parts for peace of mind is something I'll never understand.

It's mechanical made of metal parts, not plastic with engineered wear parts making them disposable.

Why the hell would you throw them away? Too many checkbook mechanics, not real mechanics like Mr. Fairman here......

Good job JF.

:) :)

Good post Jf,
I checked the spray pattern on mine they werent round like yours they were sort of intermittent crescent shaped, at first i thought they were made this way because most of mine were only squirting out one side

I didnt soak mine (should have) i dipped mine in injector cleaner and filled them up with the liquid, i then got a Butane lighter gas refill can and stuck it in the end and pushed down, it worked to a point ie from little spray to a nice steady half moon crescent shaped spray, which was steady,

But do all years models need a whole circle spray pattern..?
or are some different in the spray heads?

If they all need a complete round spray,, ill have to take mine out again :(

Hi Rob, unfortunately for you, all of the years have the same round/cone spray pattern . . . sounds like yours are still quite plugged up (the crescent pattern you describe).

The pintle is supposed to move in a high frequency buzzing pattern, and thats what atomizes the fuel into a cone. If it doesnt make a cone, the injector is bad.

Bo

No, I'm referring to trying to open new injectors with a can of carb cleaner.
I have tried to backflush old injectors but the risk/reward wasn't there for me. When I'm at WOT I don't want any nagging thoughts of a burned piston creeping into my consciousnesses :D but to each his own.......The biggest advances in engine emissions and performance have occured due to improvements in fuel delivery and atomization. From carburetors to EFI to direct inject, fuel atomization is the thing that delivers power and economy. Since most of us are running at enhanced boost levels the margin for error in proper fuelling is smaller than a stock configuration. I see new injectors as cheap insurance vs any engine damage that could occur.
Tippy, since you think I'm a checkbook mechanic, your welcome to come to Detroit this weekend and assist me with the installation of my engine/transmission.

it would not hurt just as a routine maint to pull them and clean them every 30k miles. that might ease your conscience at WOT.