Those injectors look like the ones you’d get at the dealer, minus the star
In regards to the injectors, in general . . . I’m aware that they pass all the pressure tests, but the spray pattern may not be that great anymore, as you surmised. By the way, you don’t still have the old steel injectors, do you?
If so, I’m almost shocked . . . because the insiders know that the newer injectors . . . brass? . . . are more reliable
If you replace the injectors, make sure you replace the plastic injector holders and all o-rings which must be removed. I’d hate for you to create new vacuum leaks.
Unfortunately, I’m not sure what the material of that radiator neck sleeve is. I’d be hesitant to tinker with your new radiator, at this point. Undoubtedly, it will provide many years of good service.
For what it’s worth, if my auxiliary coolant pump was leaking, I also would have bought the Bosch part, in the Bosch box, because they are the original manufacturer for Mercedes-Benz. This was also one of the more common failures. Thankfully, it’s an easy repair.
“…it would seem that being as their fuel flow is modulated by varying the fuel pressure…”
It’s actually “geometrically adjustable passages” that produce the variation of the fuel flow. The fuel pressure prior to these passages (“control pressure”) is – independend from the engine load - (more or less) kept constant by the fuel pressure regulator we talked about last week.
First, the fuel passes metering slits - in the wall of the control plunger barrel – which’s clear opening size is determined by the vertical position of the control plunger.
Secondly, the fuel passes an outlet opening “gap” to the injector pipe. This gap sits in the center of the “pressure differential valve” (1 for each cylinder) and is adjusted by a diaphragm which sits in the center of that pressure differential valve. It divides the upper from the lower chamber of it. That is where pressure is involved, but not the pressure of the fuel which is supplied to the injector. That diaphragm changes it’s position depending on the pressure difference between the upper and the lower chamber. And it is the pressure in the lower chamber, which is modulated by the electrohydraulic actuator (EHA), which is basically nothing else but an “adjustable restriction valve” between the upper and the lower chamber.
“…it would seem that they’d need to be prevented from closing entirely to prevent stalling…”
The engine doesn’t stall with the complete stop of fuel supply to the injectors during coast-down of the engine. Why not?
The fuel supply during coast-down is blocked by above mentioned diaphragm, which then completely block’s the opening gap to the injector pipe. When the engine reaches idle, the CIS-ECU gets information about that by the igniton-ECU. Then the CIS-ECU changes input to the EHA, causing the opening gap to be widened and fuel being supplied to the injectors again.
Compared to the fuel pressure regulator the fuel distributor is a bigger headsratcher.
I hesitate to bore this community with a more detailed description of it’s function.
When I took the old injectors out to test them, they were quite black. But I’m quite sure they’re made of brass. I can check later.
“…If you replace the injectors, make sure you replace the plastic injector holders and all o-rings which must be removed. I’d hate for you to create new vacuum leaks….”
I already bought the black sleeves which are made of rubber and plastic (see picture). Do you thing that the beige plastic holders (see picture) should be renewed too?
When I tested the old injectors I also renewed theses black sleeves when I reinstalled them. Since I also took out the beige plastic holder sleeves (see picture) I renewed the o-ring around them too.
But when I will install the new injectors I don’t plan to take the beige holder sleeves with the o-ring out of the intake manifold again. Because they looked still okay last time. What do you think?
“…I’d be hesitant to tinker with your new radiator …”
You’re right, maybe I should leave it as it is. Eventually the old radiator neck survived 26 years without a metal sleeve. And for over a year, with the ruptured engine mount, it was exposed to severe vibration.
Do you know this brand “Wezel” or “van Wezel”? I think they’re Dutch !?
Sincere thanks for the detailed description. Clearly this is a system that I’m unfamiliar with, and it would appear that some of my assumptions were incorrect.
I’m still curious to find out how the new injectors will affect the operation.
I took out the 10-Amp fuse of the overvoltage protection relay. As a result the CIS-ECU stays switched off. Then I had a test drive. The vibration intensity at idle was the same. However the frequency was a little more irregular.
But what caught my eye was, that idle speed (with the transmission in “P” or “N”) was more stable. With the ECU idle speed swings a little up and down every 4 to 5 seconds (only slighty noticable on the car’s revmeter).
Then I put the fuse back into the OVP-relay to check the o2-sensor emission control.
With the engine at 185°F the duty cycle was as following:
at 2.500 rpm: swinging up and down between 57% and 62%
at idle (about 675 rpm): swinging up and down between 49% and 54%
The idle swinging is definitely caused by the o2-sensor emission control, because it has the same frequency. Idle goes from low to high and back to low within 4.5 seconds.
Isn’t that frequency a little too low for an o2-sensor at idle?
At 2.500 rpm it takes the o2-sensor 1.2 seconds to go from low to high and back to low.
Since the duty cycle values showed that the mixture is too lean, I changed the base setting of the CIS with a 3 mm Allen key through the air filter housing to a higher mixture resulting in the following duty cycle values:
at 2.500 rpm: swinging up and down between 48% and 52% now
at idle: swinging up and down between 42% and 46% now
The Mercedes workshop manual says that the difference between the center value at 2.500 rpm and the center value at idle should not differ by more than 10 %. But 44% is 12 % lower than 50%
But the Mercedes workshop manual does not say, what a bigger difference than 10% means.
I think I should install a new o2-sensor. What do you think?
I also checked the duty cycle of the idle speed actuator (ISA) at idle (with 185°F engine temperature) according to the Mercedes workshop manual. It was 57% (target: 40 +/- 5 %).
What does that mean?
I deinstalled the ISA to clean it inside, but it looked very clean. I connected it to 12 V a few times for a brief moment and it reacts without any drag!?
By the way, I checked the material of the injectors today. It’s brass.
It sounds like like the idle air control valve is doing its job, and is definitely not seized or stuck
As far as the oxygen sensor goes . . . I can’t offer you any CIS-specific advice at the moment
That said, it sounds like the sensor may be switching too slowly.
What I never liked about this system was the ability to mess around with the mixture. In my opinion, that was an open invitation for trouble. I have seen guys messing around with mixture adjustments, not really knowing what they were doing.
I can’t advise you as to whether to buy a new sensor or not, because, at this point, it’s been 5 years since I’ve worked on CIS, and my memory may be faulty
However, if you get a sensor, get Bosch. I’m sure you were going to do that, anyways.
Here’s an idea . . . and it may not be appropriate for your car. I believe the oxygen sensor connector is accessible, if you peel up the passenger side carpeting. If it is, why don’t you just backprobe the connector and measure the signal voltage with your multimeter. Set your meter up to record minimum, maximum and average . . . and whatever else you deem necessary, such as cross counts
“…What I never liked about this system was the ability to mess around with the mixture. …”
I absolutely agree – only touch the mixture adjustment screw, if you really know what you are doing!
I’ve also seen guys mess around with it – having forgot how far they turned the adjustment srew into which direction. One of them even did that without any checking of the duty cycle – he couldn’t even get the car started again and it had to be towed to a Bosch workhshop.
When I adjust a Bosch-KE-Jetronic, I always make notes about the angle and the direction of my adjustments. Plus after every small adjustment angle (about 15°) I check the duty cycle at 2.500 rpm and at idle 2 or 3 times. If I’m not happy with the result, I go for another increment of about 15°. I use a long 3 mm Allen key with a T-shaped handle. That way it’s easier to record the adjustment angle.
Today’s adjustment was finally done with a clockwise turn of about 30°.
Measuring the signal voltage of the o2 sensor connector I already added to my to-do list after adjusting the mixture. But it was already to late to do that today. I want to do that on Monday or Tuesday.
The connector is – as you say - under the passenger side carpeting.
If I buy a new oxygen sensor, I think I will buy one from Bosch directy (it’s only half of the price that the Mercedes dealer charges for it). But I will have to change the plugs – they’re different.
very interesting discussion gentlemen. a little over my head, but interesting none the less. your English is top notch HD, very few errors. Mercedes may be over my head but I m a whiz with words.
your English is good too db …
As for my English, let’s say this . . . I’ve been in both German and American school systems. In fact, I clearly remember the teacher thinking I might literally be stupid. The real problem was my English was almost nonexistent at the time, so my grades naturally reflected it
“Unfortunately” I’ve been in Los Angeles so long now, my German may have suffered. It’s just not of those cities where you have opportunity to speak it every day, unlike some other languages. It seems to come back alright when I visit relatives, but it’s not perfect. But then then again, nothing is.
The funny thing is this . . . while German was my first and primary language, it’s gradually been replaced.
I suppose I’ve assimilated
But this seems to be a common phenomenon in the USA . . . I’m not complaining. I’ve bought 2 houses here, so I’m obviously here to stay.
Wes, I agree with db; don’t shortchange yourself. For me this thread has been like a master mechanic course in 1988 Mercedes fuel injection systems. I’m humbled.
While microprocessors and fuel injection are clearly complementary, it also reminds me that fuel injection systems were used in better cars and controlled in other ways before microprocessors became ubiquitous. The benefit of better fuel vaporization, the benefit of having more surface area per metered fuel volume in contact with oxygen, was recognized a very, very long time ago.
As regards the English language… it never was a strength of mine. German too would be beyond my language capability.
well, I appreciate it but a man should know his limitations. the higher maths just weren t my cup of tea, the English language, however, captivated me. once you jump past, and get to chaos theory and such, it becomes interesting to me again but I don t have the background to really get into it.
let me ask you something, I ve heard string theory explained, and to me it sounded ridiculous.
kinda like 2+3=5, except sometimes it equaled 6, and every great once in a while, just to make the theory work, it equaled 97.
that may not be a good analogy and I may not have the background to understand it, but that’s how I seemed to me.
what do you guys think?
Without hashing through all of this again, I wonder about that spray pattern on those 2 injectors. The pattern should be cone-shaped and if the 2 injectors are “peeing off” as we used to say then that brings up the possibility of flaky injectors or a fault in the fuel distributor slots.
Those fine slots are cut with lasers and it doesn’t take much in the way of a fault to affect fuel flow.
There’s always that nagging issue of an intake air leak. My thought would be to throw a vacuum gauge on it and take a reading with the engine at idle.
The reading will vary based on a number of factors but the manifold vacuum should be substantial anyway and the gauge needle should be rock steady.
Never thought that this thread would lead to a discussion on sub atomic research. LOL
Be careful – research of the micro universe as well as the macro universe can be an invidious affair. People who are active in this field could be very disappointed one day, if and when they find out, that their theory was completely out of reality. Take the “big bang theory”! I know the whole world seems to accept it these days. But is that really what happened - I don’t know.
What I do know though is, that the Bosch guys who started to develop the “K-Jetronic” CIS in 1970 were very much dealing with reality. And they needed to be quite knowlegeable in chemistry and physics in general, especially in hydrodynamics and engineering mechanics and up from the late 70s – when they started to extend the “K-Jetronic” to “KE-Jetronic” with all it’s electronic auxiliaries - also in electronics.
In the attached picture you see the analog Bosch instrument from the 1980s which I use when I check the CIS. With this analog meter you can very nicely check and adjust several things – especially the o2-sensor emission control.
I like this elder hands-on technology! Plus dealing with it takes me back to the 80s – it gives me the feeling of being young.
Oh! – and thanks for the compliment on my English, wesw! - I’m working on it.
And btw wesw – don’t say “…Mercedes may be over my head…”! Basically you find the same CIS technology in cars built by other manufactorers too, like e.g. Volkswagen.
“…if the 2 injectors are “peeing off” as we used to say then that brings up the possibility of flaky injectors or a fault in the fuel distributor slots. …”
These slots in the distributor also crossed my mind, because when I tested the current (old) injectors, I connected each of them to their individual port on the distributor.
Measuring the amount of fuel coming out of each injector port of the distributor simultaneously, is also a point on my to-do list. But I have to build the metering device for that first.
At idle, one injector showed a spray cone consisting of several strings all around (with only little atomization). Another injector showed 2 strings to 1 side with the rest of the spray cone consisting of fairly atomized fuel at idle. The other 4 injectors showed a spray cone of the same quality as the new injectors at idle.
Above idle all current injectors had a nicely atomized spray cone (like the new ones).
What do you think about the picture of the current spark plugs in regard of these 2 injectors, which I attached in my second posting?
“…There’s always that nagging issue of an intake air leak. …”
To be honest – that nags me too!
That’s why I aditionally put a clamp on the hoses of the idle air control valve, when I reinstalled the valve after checking it yesterday. Originally they are just slipped over the connection nozzles of the valve and over the fitting on the air flow sensor housing. Since the hoses felt quite loose I thought it wouldn’t hurt to do that, although another brake fluid spray test at idle didn’t show any leak on them before I clamped them.
But the clamps didn’t change anyway regarding those “tiny kicks” at idle.
Btw: When I sit in the car with the hood completely opened, I can look at the top of the engine underneath the back edge of the hood. And every time when I feel a tiny kick through the seat and the steering wheel, I can see the engine shake a wee bit.
“… the gauge needle should be rock steady. …”
But only if idle is steady as a rock! – which it is not.
And - even if it were – with an untouched false air leak, the manifold vacuum would also be constant, wouldn’t it!?
The quantum guys are never disappointed, just filled with wonderment. As am I.
Many physicists now believe in the “multiverse” theory. Consistent with the theory, many also now believe that the “big bang” was but one of a continuous series of constant “big bang” events that have always gone on and always will.
I for one am grateful that you’ve joined our forum with your challenge. I’m learning a lot from this discussion, particularly from your posts.
Re: your English: I retired from a college, and I only wish that the average incoming student had half your command of the English language. Nay, 1/4 of your command of the English language.
Consistent with the theory, many also now believe that the "big bang" was but one of a continuous series of constant "big bang" events that have always gone on and always will.
I think that’s been going out of favor lately because not only is the universe expanding - it’s expansion rate is increasing.