Flow Testing Results of OEM CIS Injectors

I'd be VERY interested in the rates of the new injectors. I do a lot of work on old Marine Detroit Diesels and it is very difficult to find a new set of 16 (for two V8 engines) that actually have all 16 that work properly. It's very common to have to order three sets to make up two sets that work and then return the ones that are not to spec. Sadly, in the case of DD injectors, it means that you can't know a replacement DD injector is any good unless you test it before you install it. Note that DD injectors are very complicated compared to a gas engine fuel injector so it's not fair to compare them and/or expect a similar fail rate. But it would be interesting to see your old/new.

 

I'd be interested to see that too. I replaced mine in my 328 at 37K miles last winter & the difference is noticeable. When I put the car on a gas analyser afterwards it was running lean for, I suspect, exactly the reasons you describe. It had been set the previous summer on the same piece of kit.

The other place to look for lean running (at idle) are hoses in the CIS warm up system and the vac lines. I found a big hole in the vac line that goes from the plenum via the wheel arch to the ignition box in the back. It was hidden away behind the wheel arch liner & with that particular line, not only was it causing an air leak, but it also meant I was getting no vacuum advance on the ignition.

 

Thanks for this! I'm going through a huge pain right now to replace mine as the threads were all rusted between the fuel lines and injectors, this makes it seem worth the trouble.

I think I actually only have one of the originals that could be tested. The other 7 were destroyed beyond recognition just to get them out. Many don't have threads anymore, one is broken in half....what a mess. I'll just assume they weren't very good.

Please post the results of the new ones, I'm really interested to see what they'll do.

 

Not surprsed you arn't happy - those are all over the place. If you are confidant in the testing i'd be heading back to the guy you bought them from & asking their view of these results.

This might explain a lot about the problems you have been chasing as well

 

You can have them balanced to one another. Can the place you sent them do that too?

 

Bummer - the old ones are better than the new ones! I'm disappointed to see that it's similar to the type of thing we see with DD injectors - where much of the time the old ones are fine and changing to new ones as preventive maint made a problem where one didn't exist before.

As Tom suggests, the only way to do it would seem to be to buy a couple sets and have them tested/matched. I have never pulled one of these injectors - can they be disassembled at all? If so, I assume it's just a spring/pintle? If so maybe the springs can be shimmed to some standard install height (like a valve spring)?

FWIW, from where are the new injectors sourced?

 

How do they do that? I thought the injectors were sealed with no adjustments.

 

OK...I'm thinking about this a bit more and looking at my BOSCH KJET book.

I'm wondering if the difference in opening pressure actually makes any difference in fuel delivery. The pulse/amount of gas is determined by the fuel unit, not by the injector. I'm not sure the opening pressure has anything to do with the actual fuel volume delivered per pulse. I READILY admit that I know virtually nothing about the KJet system from a hands-on aspect. But in reading, the critical part is the atomization produced by the injector which is not affected by the opening pressure.

AGAIN - the above is "out loud" thinking based on what I understand from reading (and I could be understanding it wrong)! Other than measuring the relevant pressures in my 328's system, I have never done any work on a Kjet.

 

My understanding of it is that there isn't any "pulse" as such - all 8 are just firing fuel in constantly. It takes an amount of pressure to get them to open which clearly needs to be more or less the same from one injector to the next so that they open at the same time. Related to this is that they also need to close properly - otherwise you get fuel dripping into the cylinder after shutdown because there is still pressure in the system

As you open up the throttle so the thing just fires in more fuel & the injectors need to flow more or less the same amount of fuel at any given pressure - if they don't you are going to get some cylinders running richer than others. I don't think its any more complicated than that.

 

http://www.jaguarfuelinjectorservice.com/What%20is%20Injector%20Balancing.htm

 

One of the PROS here advised me if I wanted 8 new working ones ...... buy 10 or better yet buy 12.


They are junk. And priced to match.

Even from Bosch.

 

It doesn't -- what matters is that the opening pressure of the injector is above the residual pressure after shutoff (which is ~3 bar) so it doesn't leak, and below the operating pressure in the upper chamber (~5 bar) so it's open when the system is running. More importantly, this sort of injector "flow" testing isn't valid for CIS -- what determines the amount of fuel delivered in CIS is the opening size of the slit in the fuel distributor and the pressure difference across the slit.

As a side note, if you wanted to use this data to compare the injectors themselves, you need to calculate the value:

(volume delivered)/(test pressure - opening pressure)

for each injector, not just look at the raw volume delivered (and the "fuzz" on measuring the opening pressure is probably at least +/- 0.1 bar)

 

Depressing:

I've only driven my car 300 miles in the last year and a half due to fear of the glowing headers (rear bank). Fine at idle but glow after driving. Found good vacuum pressure from plenum and have changed plugs, wires and extenders but same story. I was hoping changing injectors would fix the problem.

Don't know if i should change them now.

 

Trying to understand this: as long as you are testing at a common pressure, say 4.5 Bar for arguments sake, can you explain why it matters whether the thing opened at 3.8 bar or 4 bar in terms of comparing the fuel delivery?

Clearly you want all the numbers to be as close together as possible in terms of when the injectors open, but once the thing is open , surely its open & so at any given pressure, again, you just want the thing to be delivering more or less the same amount of fuel as the next one (with a sensible spray pattern) ?

 

"Don't know if i should change them now."

Yep - nothing worse than the old "paralysis by analysis." OTOH, there's the old "If it ain't broke, don't fix it" as well as the " 'NEW' is the acronym for 'Never Ever Worked'."

One of the three can apply to any proposed operation!

Re "balancing" the injectors - that site seems to indicate that they just keep cleaning them to get them as close together as they will get and if they are not close enough, you buy more injectors until they are!

But if I understand Steve correctly, that service to balance them isn't really going to make any difference anyway.

 

You have either a cam timing problem or an ignition problem. One thing you do not have is a fuel system problem.

 

CIS injectors are non serviceable. They can be cleaned and tested....thats it.


Flow is far more likely to be a distributor problem than a nozzle problem. It is adjustable at the distributor. And testing flow at the nozzle WHEN installed on the system is a valid test, Bosch makes a very good piece of equipment designed to do so. I have 2. When a flow test is done it is done at 3 or more flow rates. There is no assurance that if flow is correct at max that it will be correct at 60%. The Bosch flow tester is designed with that in mind. Testing flow at the nozzle I would think would only be valuable to norrow down the offending component if problems did show up.


Also CIS systems are rather notorious for being inconsistant at low flow. It makes no difference to how they run. At Idle from .3 to over 1% is quite common when reading 8 cylinders. It would be preferable if they were all the same at idle but as a pratical matter it makes little difference. It generally evens out dramatically as soon as there is load and is one of the reasons the system is tested at several different flow rates.



CIS nozzles are very cheap throw away items. Bosch never intended them to be anything else.

 

I heard somewhere that these things will all drip a little after 50-60,000 miles or so. Just replace them then.

 

If you drive 50-60000 in 2 years they are probably still good but if your 328 has 10,000 miles on it I can guarantee the nozzles are trash.

 

Should injectors be replaced as a matter or course at a certain age/mileage, or should the be left alone unless they cause a problem?

 

I replace them at most majors.

In my opinion changing them with the timing belts or at the most every other set would not be too often.

They are not expensive and were never meant to be lifetime parts.

 

Test the new ones before install, or are they always good to go out of the box?

 

Because it's not an ideal check valve that is fully closed below pressure "X" and fully open above pressure "X". It's a spring loaded plunger that lifts off its seat at pressure "X", and as the pressure is raised more, it opens up more, changing the area of the orifice thru which the flow passes.
Another way to say this (if you just wanted to compare the raw data directly) is that the test shouldn't have been run a fixed pressure for all injectors, but rather at a fixed difference above the opening pressure for each injector (like opening pressure + 0.5 bar). If you run that prior calculation, you'll see that they are all fairly close (and the opening pressure values might have +/- 0.1 bar uncertainty, so even though the calculated value for #6 seems a little low, maybe it was really 3.9 and not 3.8).

Yes, the more equal the better, but, the way that CIS works, differences in the injectors have very little affect on the overall operation -- because the "impedance" of the fuel distributor is much, much higher than the "impedance" of the injectors (to use an electrical analogy). Think of the perfect fuel distributor as a 10,000 Ohm resistor and the perfect fuel injector as a 1 Ohm resistor connected in series so the total resistance is 10,001 Ohms. If you have another (bad) injector that has twice the resistance (2 Ohms), the overall resistance only changes to 10,002 Ohms (less than a .01% change).
I know it seems odd, but as long as the opening pressure is OK, and the spray pattern is decent, that's really all that's needed for a CIS injector.