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CIS Injector Cleaning

I stumbled across this video today of a Mercedes guy cleaning CIS injectors and thought others here would be interested. It was pretty educational for me and I thought he was pretty thorough in figuring out what does and does not work.

My apologies if it has been posted before:

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Old 03-22-2017, 06:33 PM
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Well, I don't know Rich. How can back flushing work when the injector pintle is seated against its seat with spring tension? It's closed against its seat, and unless really dirty there won't be much cleaner going past the pintle and seat. It would be like trying to force fuel through an intake valve when it's closed.

Tried and true that I and many have used is to take a very thin gauge piece of wire and use it wrapped around the pintle to keep it open just a scant (or other) hair. Then hook up as the dude suggests and back flush with your cleaner of choice.

Why in hell they put a screen in a permanently inaccessible location just floors me. Should have been at the top of the injector and readily removable.
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Old 03-22-2017, 08:21 PM
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Mark, the guy did mention that he propped the pintle open with a small plastic tab he made, so I'm sure it's very similar to your method.
But I did learn that Diesel Purge is an effective cleaner, better than fuel injector cleaner...
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Old 03-22-2017, 08:29 PM
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Quote:
Why in hell they put a screen in a permanently inaccessible location just floors me.
Because injectors are wear items. You don't clean them you replace them, like spark plugs. You can clean these things all you like but a 40 year old worn out injector is never going to be as good as brand new. I learned that the hard way, after cleaning dozens of them just to have them fail a few months later. Plug in new ones and you cannot believe the difference.
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Old 03-23-2017, 04:51 AM
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Quote:
Originally Posted by Jeff NJ View Post
Mark, the guy did mention that he propped the pintle open with a small plastic tab he made, so I'm sure it's very similar to your method.
But I did learn that Diesel Purge is an effective cleaner, better than fuel injector cleaner...
Ah....I missed that piece I guess.
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Old 03-23-2017, 05:01 AM
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I did not watch the entire vid because I was looking for the most important thing he did. that is make a PLASTIC device to hold it open. I did not see it.

I agree with brian. have them tested and replace if needed.
when it comes to cleaning the injectors about all I would do is spray some carb or brake clean in the input to clean the screen.
you start screwing with the needle valve and you risk damaging it and possibly breaking it.


I have tried the back flushing.
I ended up sending them off for testing and 2 of the needle valves broke off when testing.

BTW I too have cut them open.

I ended up buying 6 injectors. best thing I ever did.
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Old 03-23-2017, 07:37 AM
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I've back flushed CIS injectors very successfully.
That doesn't mean everyone has the patience or skill to do it without damaging them somehow.
I don't consider them a wear item like a "spark plug".

Last time I back flushed mine was around 3 years ago and I've done it to these injectors twice now. If these are the original 1987 injectors they have a little over 130,000 miles on them now.
I never tried lacquer thinner because I've heard there's some kind of plastic or nylon fine mesh filter screen in there and I didn't want to take a chance on lacquer thinner possibly breaking them down and ruining them. I agree it would have been nice if the screen was in a threaded on section that could be removed so you can see it and clean it.

I took some pics last time I did this...

With the injector held pintle up in a bench vice I gently grap the end of the spring loaded pintle with a hemostat and lift it up off it's seat about 1/32" and wrap a strand of fine copper wire around it once to hold it open. Copper wire is much softer than the steel pintle and seat so it won't hurt them.


Then slide a piece of 8mm inside diameter hose over the pintle end of the injector and clamp it on with a hose clamp.


Then fill the hose with your solvent of choice and slide the hose on to an air gun.


Then blast 120psi of compressed air through it to back flush it and hopefully rinse any crud off the internal screen and shoot it out the threaded end of the injector.
If you have time to soak the injectors in solvent for a while with the pintles wired open and pointing upwards that can help too.

When pulling the hose off the injector hold the injector tightly in your fingers with the copper wires between your fingers and the side of the injector so when you pull the hose off it doesn't pull the copper wires with it and pull the pintle open more than 1/16" to 1/32" and possibly damage the internal spring that holds the pintle shut until 30 to 35 psi of fuel pushes it open and it sprays.

Then put the small plastic straw on a can of carburetor cleaner into the inlet side of the injector and spray the solvent through it. There should be enough pressure in the can of carb cleaner to open the injector and spray the solvent through it so you can see if the spray is a nice round fine conical spray.


It worked real well for me. The injectors spray a fine conical spray and the car idles smooth at 800 rpms and runs perfect all the time.
Old 03-23-2017, 09:21 AM
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Well thanks guys for all the commentary. I posted it without any commentary because I have no experience attempting to clean injectors. I just found it pretty interesting and educational.

Thanks for the pics and description Jfairmen.

I wish I had seen this before I finished rebuilding my engine. Would have been wise to just test mine and see how they were operating before putting them in the car. I have some spare old ones I can test and practice on.
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Old 03-23-2017, 10:00 AM
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I cured my CIS issues with EFI
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Old 03-23-2017, 10:47 AM
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^^^EFI doesn't help those of us in communist run states.
Don't get me on my soap box about the stupidity of forcing people to rebuild outdated technology instead of simplifying the laws and making the tailpipe emissions the only part that needs to pass.

Good thread, I learned something today.
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Old 03-23-2017, 12:21 PM
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Quote:
Originally Posted by RarlyL8 View Post
Because injectors are wear items. You don't clean them you replace them, like spark plugs. You can clean these things all you like but a 40 year old worn out injector is never going to be as good as brand new. I learned that the hard way, after cleaning dozens of them just to have them fail a few months later. Plug in new ones and you cannot believe the difference.
That makes alot of sense

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Old 03-23-2017, 02:02 PM
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^^^EFI doesn't help those of us in communist run states.
Don't get me on my soap box about the stupidity of forcing people to rebuild outdated technology instead of simplifying the laws and making the tailpipe emissions the only part that needs to pass.

Good thread, I learned something today.
AZ is as strict as CA and more difficult to pass because all our test centers are owned and operated by The State. No deals to be made here, and our customers in CA seem to have an easier time getting their hotrods through emissions than we do.
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Old 03-23-2017, 04:29 PM
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CIS injectors *are* wear items. They are spring loaded, and have specific opening and closing pressure ranges. The springs wear over time, and injectors can leak, or flow at different rates.

Cleaning can improve a used injectors performance, but at some point you'll just have really clean worn out injectors.
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Old 03-23-2017, 04:31 PM
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I guess mine aren't worn out yet and they're clean.
Motor starts right up cold and you can drive off immediately. It runs perfectly smooth all the time.
Only problem I've had with the CIS is the rubber diaphram and o-rings in the aluminum 007 fuel head rotted out from the ethanol in gasoline these days.
I rebuilt the fuel head with a Salvox rebuild kit and it's run perfect since.
I've also had a Brian Leask adjustable control pressure regulator for 9 or 10 years and I dialed it in over a few days of road testing with an innovate wideband AFR gauge back when I got it.
Old 03-23-2017, 06:24 PM
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I sent mine to Larry at CIS Flow tech a couple years ago and 5 were good and one leaked, so I bought one.

A couple weeks ago, I did flow testing and all 6 were remarkably close at idle and at WOT. So 5 29 Yr old injectors are still flowing the same as my one new one. Larry did his magic with cleaning them, so maybe that helped, but for now, no reason for me to replace.
I think it also speaks to the proper care, use and gas the prior owners of my car used. If it sat for years or regularly used bad gas, I am sure I'd have to replace them all by now and many of these cars do sit.
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Old 03-23-2017, 07:39 PM
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Quote:
Originally Posted by 1979-930 View Post
^^^EFI doesn't help those of us in communist run states.
Don't get me on my soap box about the stupidity of forcing people to rebuild outdated technology instead of simplifying the laws and making the tailpipe emissions the only part that needs to pass.

Good thread, I learned something today.
I guess I've been off the forums too long and my sarcasm was lost with this one...
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Old 03-24-2017, 12:13 PM
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We have a DIY where we go over the adjustment and tuning of CIS system, if anyone needs a DIY on it or if this would be handy as an addition to your process; please check out the link below.

Porsche 911 CIS Fuel Injection Tuning and Adjustment | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article


-Dmitry
Old 03-24-2017, 12:21 PM
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Good info.

CIS injectors are no where near as reliable as electrically operated injectors. We find that even new CIS injectors (right off the shelf) have a 30 to 40 % failure from improper flow rates...

CIS injectors may fail due to a weak internal spring. We cannot replace the spring. If the spring is weak, the injector requires replacement. A weak spring will cause that particular injector to open early, and overfuel, or leak, and result in an unbalanced fuel flow of the injector group.


CIS Injector Cleaning Testing Service Mercedes Porsche Ferrari Audi VW Volvo

Anyone used this ?
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Last edited by pmax; 07-20-2017 at 11:03 PM..
Old 07-20-2017, 10:21 PM
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i thought CIS injectors were extremely reliable,
if they are saying new ones are bad I don't think that is reliability, that might be quality control or something like that.
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Old 07-21-2017, 04:51 AM
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Quote:
Originally Posted by T77911S View Post
i thought CIS injectors were extremely reliable,
if they are saying new ones are bad I don't think that is reliability, that might be quality control or something like that.
Do the veteran CIS folks here agree with the 30-40% failure rates ?
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Old 07-21-2017, 10:26 AM
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