Author Topic: K-Jetronic: Anybody replace fuel injectors "on principle"?  (Read 943 times)

raueda1

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Sometimes people replace stuff that's old "on principle," as I recently did with radiator hoses of unknown age and condition.  Has anybody done this with fuel injectors in the absence of some kind of obvious symptoms?   And if so, did it make any detectable difference?  By that I mean that the car ran a little better afterwards even though you weren't really aware that it was a bit off in the first place?  Am I even making sense?  :o

Anyway, I ask this because I'm now working through some fuel injection issues.  One extreme school of thought is that, if you want to be sure it's really perfect, get the the WUR and fuel distributor professionally rebuilt (such as CIS Flowtech with bench calibration etc), test injectors and replace as needed.  Better yet, match them to each other!  Then make sure the airflow sensor is set right with a CO meter.

I'm kind of doing this stuff in a piecemeal way as $$ and motivation allow.  A rebuilt WUR is on its way to me now.  Depending on the outcome it may be followed by the fuel distributor.  Since I can't test injectors (more like I'm unwilling to put together the setup to do so), I'm considering replacing on principle.  They aren't that expensive but the car runs pretty well, even with whacky fuel pressures.  So is there any point?

And on a somewhat related topic, has anybody had problems traced to the cold air valve?  My impression is that the valve is amenable to disassembly and cleanup.  I would do this "on principle" (and cause I like to take things apart) as I have no reason to think it isn't working right.  OTOH, I have no reason to think that it is.  Ideas welcome and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #1 on: 25 June 2018, 11:15 AM »
Dave I replaced all my injectors, as I am big fan of the "baseline" approach, though I know most folks despise the "throwing parts at a problem" approach.  But I feel that in the case of the injectors, I figured what the hell, they are (to my knowledge) almost 40 years old, so why not?  Did it make an improvement? Hard to say really, as I replaced pretty much all my fuel related components as well as ignition goodies at the same time, as again, a 40 year old coil or fuel hose does not exactly inspire confidence :o!

What you refer to as the "cold air valve" is what I am assuming the auxiliary air valve, or "air slide"?  If so, then yes, some folks try and clean them out, not sure how successful they are, as I think it is a press fit situation, but also there are some tutorials online of guys who have done this.  New they are super pricey unfortunately, mostly on ebay.

Most common issue on these is that they get stuck open, and thus do not close fully at operating temp.  So then you get hot idle issues as you have too much air entering the system.  It must be fully closed at about 80C if memory serves.  You test it by dumping it into a jug of boiling water from the kettle.  If it does not close up, it's not functioning properly.
Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #2 on: 25 June 2018, 01:07 PM »
I bought a injector cleaner and used it on my 300se .  While it did clean them it didn't fix them from leaking down which caused starting issues.

I think now that unless you have extremely high priced injectors, you should just replace them. Be glad you don't have a M100 6.3 those injectors are $2200 each.

The AAV is really pretty simple to rebuild, as said plenty of YouTube videos to show you how.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

daantjie

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #3 on: 25 June 2018, 01:40 PM »
Be glad you don't have a M100 6.3 those injectors are $2200 each.

Indeed, that is nuts!  Again just shows that the 6.9 is by far the most "keepable" of all the M100 cars.  Bodes well for the future methinks, as K-Jet parts were installed in millions of cars over the years, should always ensure ample part supply.  Compared to $40 per injector (or less even), you are laughing ;)
Daniel
1977 450 SEL 6.9 - Astralsilber

ptashek

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #4 on: 25 June 2018, 03:06 PM »
Has anybody done this with fuel injectors in the absence of some kind of obvious symptoms?   And if so, did it make any detectable difference?

Yes, and not really (with a disclaimer).

Depends on initial condition, but it can make a world of difference especially if the old injectors are leaking heavily. In case of my car two injectors were leaking slightly, the rest were OK (65k miles from new), and there wasn't much discernible difference afterwards. "While in there", as part of the main resto, I've also had the injector holders with both seals replaced, along with all the intake manifold gaskets. All things considered, the entire set of parts was perfectly affordable, so why not.
1993 "Pearl Blue" W124 280TE
1979 "Icon Gold" W116 450SE (history, resto)
1977 "Milan Brown" W116 350SE (parted out)

adamb

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #5 on: 25 June 2018, 03:29 PM »
I replaced my 38 year year old injectors 2 years ago and it made little difference. The car was and is running fine. For my car the occasional and slight misfires at idle are ignition related. I clean the rotor arm and the contacts on the distributor cap and the car runs fine again.

TJ 450

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #6 on: 25 June 2018, 05:43 PM »
The best thing to do would be to test spray pattern with the old ones removed from the car, then you will know for sure if it will be worthwhile.

I used to replace parts “just because”, and that still applies to certain things, but the injectors don’t fail catastrophically so there isn’t much of a concern running old injectors as long as they don’t leak down or have poor spray pattern.

Tim
« Last Edit: 25 June 2018, 06:08 PM by TJ 450 »
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

TJ 450

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #7 on: 25 June 2018, 11:33 PM »
The cost of injectors on the 6.3 is just the tip of the iceberg, K-Jet on the other hand... absolutely marvellous!

Personally I think it’s the best system ever made from a reliability standpoint.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #8 on: 26 June 2018, 02:59 AM »
Here in South Africa, I specialise in the diagnostics and repair of K-jet systems, including rebuild and bench calibration of WURs and FDs.  In general, with an 'unknown' client's car, any time I do major WUR or FD work, I replace the injectors as a matter of course.  It represents a small % of the total bill, and often saves me a lot of time and comebacks chasing down silly issues. 

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

Guru

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #9 on: 28 June 2018, 02:55 AM »
Nope. Rebuilt injectors for my '75 K-Jetronic 450SEL are US$200-300 a piece. That's more than I care to spend for replacing them if they are not broken. So I had an injector service guy come over who cleaned them, replaced the filter and checked the spray pattern and volume for A$380. All were spot on. I then did a bit more cleaning and when I was satisfied I wrapped them tightly in 5-6 layers of Nitto no. 66 self-fusing heat resistant tape (that's the orange stuff in the picture). Not so pretty but should protect them very well because the plastic is getting fragile.
1975 450SEL 4.5 White

Max-NL

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #10 on: 28 June 2018, 05:09 AM »
Those are D-Jetronic injectors. K-Jetronic injectors are completely different :
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1975 450SEL 6.9 #140

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #11 on: 28 June 2018, 07:40 AM »
Nope. Rebuilt injectors for my '75 K-Jetronic 450SEL are US$200-300 a piece. That's more than I care to spend for replacing them if they are not broken. So I had an injector service guy come over who cleaned them, replaced the filter and checked the spray pattern and volume for A$380. All were spot on. I then did a bit more cleaning and when I was satisfied I wrapped them tightly in 5-6 layers of Nitto no. 66 self-fusing heat resistant tape (that's the orange stuff in the picture). Not so pretty but should protect them very well because the plastic is getting fragile.

Yes, generally the D-jet injectors are durable, and my practice is to clean them ultrasonically, and check for spray pattern and matched flow rates.  This is particularly necessary on the 3.5's where no new units are available.  There are aftermarket reproductions available for the 4.5 units, so one does at least have that option.

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

Guru

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #12 on: 28 June 2018, 10:42 AM »
My bad. Of course my model has D-Jetronic... So this is for anyone with D-Jetronic injectors.
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Type17

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #13 on: 08 July 2018, 10:39 AM »
While my 116 has relatively low miles (41,700 at present), and the injectors are fine, I have replaced K-Jet injectors on two of my (4-cylinder) previous cars with noticeable improvements:


An '83 Golf Mk1 GTI @ around 160k miles - one began leaking (hard to start after standing overnight), but I also noticed improvements in low-end torque (moving forward in traffic), idling (smoother) and overall fuel consumption (about 5% more miles to the tank). Later on, when I bought a '93 Audi 80 16v (KE-Motronic, but identical K-Jet type injectors), I changed the injectors at around 150k miles and also noticed similar torque/idling/fuel consumption improvements (the engine had been noticeably easy to stall at low revs - afterwards, in traffic, I was able to lift the clutch and move off and through the gears, whilst still at idle).


The design of the K-Jet injectors means that they wear out with miles and even before they begin to leak at rest, the spray pattern goes off, which means the fuel & air don't mix well, leading to the issues I experienced.


I would replace them on principle at over ~140k miles.


PS: The design means that they constantly self-clean, so cleaning won't improve them.

floyd111

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Re: K-Jetronic: Anybody replace fuel injectors "on principle"?
« Reply #14 on: 08 July 2018, 03:24 PM »
Here in South Africa, I specialise in the diagnostics and repair of K-jet systems, including rebuild and bench calibration of WURs and FDs.  In general, with an 'unknown' client's car, any time I do major WUR or FD work, I replace the injectors as a matter of course.  It represents a small % of the total bill, and often saves me a lot of time and comebacks chasing down silly issues.

So, push to shove, I could send you my WUR's and you could rebuild them and invoice me?