? regarding CIS injector spray pattern

[jonbot]

How important is the injector spray pattern at very very low flow? I'm talking about just enough pressure to initially start spraying out of the injector?

Background:

Been having trouble with surging at off-idle operation. Had my injectors tested, and on the test bench one of them was shown to produce a tiny stream rather than a "fanned out", evenly distributed, pattern at very low flow. During high flow, the pattern looks fine. So I purchased a replacement injector.

Upon installation, I decided to compare the spray pattern of the new one at very low flow, with the other injectors in the car. It turns out that the remaining 5 injectors all appear to be delivering poor patterns at low flow when compared to the new one. Some only deliver a half-circle of spray pattern, other ones dribble or produce a tiny stream like the one that was found faulty.

Could this be a reason behind the surging?

[oregonmon]

I hope you get a desirable answer because I have the same symptoms and it seems so do a lot of other CIS owners.

[jonbot]

morning bump

[g rad]

I did a major clean out of all 6 injectors, plus some spares... I broke off a valve using this method... Soaked the lot in a glass jar with nasty Carbosal type carb cleaner.. then got under the tiny valve with a thin piece of wire looped .. pulled the stem of the valve up and to the side of it's outlet, bending the wire down the side of the injector and holding it with my fingers... I put short piece of 3/8 fuel hose over my blow gun outlet.. Was able to blow out trash in reverse of usual fuel flow.... this helped my spray pattern at low pressure.... hope this helps....... This is a bump as much as a reply, radical rad

[LakeCleElum]

I had just one injector with a poor pattern.....It caused the car to stumble and miss between 2 and 4K RPM. I cleaned it myself and back to running like new. In my opinion, the pattern is very important. I think you can have all six cleaned professionally for under $100 or so...

[jonbot]

I replaced all my injectors and it didn't help cure the surging at all...

[RarlyL8]

The fuel injector sray pattern is important for proper atomization of the fuel. The lower the flow the more important it becomes. A bad sray pattern at idle can manifest itself as a burbly or uneven idle caused by the ineficient burn. A dribbling injector can cause a miss at idle and poor throttle response.

Typically a surge is cause by the idle mixture being off or the air metering plate being out of calibration or dirty.

[stlrj]

Originally Posted by jonbot

I replaced all my injectors and it didn't help cure the surging at all...

I wonder if ignition might have something to do with surging? Since all CIS 911's come with CDI and seem to suffer from surging, has anyone been able to solve this with an MSD ignition upgrade?

Maybe someone should post the question.



Cheers,

Joe
74 911 w/ 86 3.2 transplant

[Jim Williams]

For those doing their own checks on the proper spray patterns, here is a excerpt from the Charles Probst book on Fuel Injection.......

[aricaandjustin]

Just to clarify...

Is it surging when its sitting idling without your foot on the gas?

Does it do it whether its cold or warm?

Does the surging get so bad that it eventually stalls?