Bosch K-Jetronic Fuel Distributor - Page 2

i can only imagine that cmscott16 is sweating from head to toe about this.

what i usually do in this case is just to replace the parts so it can go for another 6 or more years without worrying about it.

if you are a mechanic and wants to learn, that's fine... it is very educational and can pick-up many things. it took me 2 years to master this one, but that was the last season these models appears. lately it's just new system and much more simple and easy.

on older model, i have to attach many sensor wires from BOSH MOT tester and it's very tricky. you need to read every values in the old fashion way. you can actually see the signals and exhaust gas components. higher oxygen means external leak, high CO or HC means rich, and etceteras, que seras seras, whatever.

once you know the right values and signal, everything is just a piece of cake and full of fun. the fuel system is the most trickiest part especially the fuel distributor. i always keep a new one just for testing purposes... very quick and effective.

My hat goes off to both of you, but especially to cmscott16. I would have bought a new car by now.

Surprisingly, now that i have made some adjustments, the car seems to be running better than it has in a long time. However, I am still a little foggy on one thing.

In between adjustments of the lower control pressure screws, I have been removing all the spark plugs to check for differences in fuel pressure between the injectors. (I don't have a fuel pressure guage or any other equipment except a dwell meter w/tach.) I am absolutely positive that I cannot lean out the mixture any more, because when I do, the acceleration is absoulutely horrible. Yet, when I check the spark plugs, they still appear to be black with carbon buildup. This tells me that the mixture is still too rich.

*Is it Ok to run the car like this, or could the black buildup just be due to bad plugs or incorrect idle settings?

Thank You again for all your help in this matter. And yes, I think that I will think twice about messing around with the fuel distributor without all the necessary equipment.

Also, I forgot to say that I still have the problem with keeping the car running when warm. *Do you think it would help if I richened the mixture via the lower control pressure screws in order to overcome the spring pressure of the EHA once it is warmed up?

blackened plugs means rich.

your problem now is not the warm up phase, but on idling.

there should be a current constantly supplied to the EHA once the temperature reach the operating stage. if you accelerate, it opens more.

before you touch the EHA, check the pressures and electrical signals first.

It is not easy to explain symptoms of my problem by typing, but let me try and elaborate them.

The main thing I notice is that it is running rich. When the car is cold and running, black smoke comes out the tailpipe and flecks of black gunk as well. Furthermore, when cold and running, if I remove the electrical wires to the aux. air device, the car dies.

Since the aux. air device closes when the car is warmed, this would explain the warm-up problem. I think that the aux. air device allows a leaner mixture, since the air is bypassing the sensor plate. This tells me I need to lean out the lower control screws more. However, when I lean these screws out, I can no longer get the car to start. What needs to be adjusted? (The sensor plate? I've been using a 4mm hex wrench and it still does not seem to be making any effect.)

if it's running rich from startup, then it is clear that you have a very low regulating pressure.

the idle speed air does not closes after warm up. it keeps on controlling the air flow all the time, according to the temperature, throttle position, and engine speed. if the engine is normal, you can disable it but the engine must not stall... this is what they call "limp home mode". means even the car got no control unit, you can still drive it back home.

try other size of allen key. 3,4, or 5 mm. you need the LONG one... or else it cannot reach.

i think i got to send you some documents.

i will print them out, scan them and send them online.

Thank You, that would be most helpful. I'm not sure where you were going to send the documents, but if you need my email address, it's lilcorey@comcast.net

Well, I still can't get it right. I would just like to know one thing. Even if I have the lower control pressure screws slightly off, can I compensate for that by adjustment of the air sensor plate?

do not confuse the two.

each got different functions.

sensor plate for idling and basic starting point.

lower or control pressure regulates the fuel flow.

wherever is the fault, you just adjust the relevant part.

Hi Sleepwalker

First of all hats off to cmscott16 - it's good to know there's someone as determined as I am - if not more so!

I've been reading this saga with interest as I'm trying to fix a rough idle when warm problem with my 1979 280CE which has the Bosch K-Jetronic system.

My first guess was an air leak, but I'm now thinking I need to lower my air flow plate height (its neutral height with engine off) but I can't figure out how to do that as I can't find any sort of adjustment specifically for that.

Full details:
1. Engine idles fine at startup, but becomes rough and vibrates once fully warmed (180oF, 80oC, aux air valve fully closed). The engine will die if I put the auto transmission in D (drive) for any length of time. I hear pops from the exhaust - misfires?
2. Under load the engine is great - oil pressures all indicate a healthy engine too - it's only done 75,000 miles.
3. The CO at idle is at 0.2%, far too low. At 1600 rpm it is still 0.2 %.
4. The mechanic at the garage tells me the mixture screw did nothing when he turned it - it is possible that he failed to turn it correctly though.
5. Timing is correct, idle is 800 rpm when warm.
6. I've checked rubber hoses between the meter and the manifold - all seem fine, but of course the inlet manifold gasket may be leaking - don't want to remove it just yet.

Andrew

backfire on intake could mean lean mixture, BLOCKED EXHAUST PIPE, wrong advanced timing, or engine mechanical timing dfference beyond tolerance.

oil pressure stays beyond 3 bar at 2k rpm

CO at 1600 rpm is ok, but must be at least higher at idle.

he was wrong if he is talking about the sensor plate adjustment screw as the mixture screw. he must haven't reached the small allen head (was it 4mm?) inside. it is spring loaded and need to push down while adjusting.

late timing is good at idle, but backfires at sudden acceleration. check the position sensor on plate too.

to confirm the leak, spray everywhere with good quantity of CARB cleaner or water while the engine is idling. if there's a change on the way the engine runs... you got leak.

Thanks for the reply.

I justed tested the mixture screw before reading your reply - the one accessed through a hole between the air flow cone and the fuel distributor. It's an Allen key head but it was 3 mm in size not 4mm. The key locked inside it and it was definitely turning - no doubt about that.

I started the engine - let it warm up and settle down to its rough idle at 800 rpm. Turning the mixture screw clockwise (for enrichment) and made my revs go up and the engine idled more smoothly (as it always does at higher revs) - so I adjusted the idle speed screw (next to the engine block) to bring it back down again. Once back at 800 rpm the engine went back to idling roughly as before. I kept repeating this procedure until I idle speed screw couldn't be turned any further. I think this all confirms what the mechanic found with his CO meter (which I don't have.)

I then read your post and tried spraying water over the inlet manifold and the hoses between it and the air meter. The first time I did it I thought the engine slowed by 100 rpm or so, but on subsequent attempts I wasn't so sure. Perhaps the engine was covered in water and it made little difference after the first time. In any case, if there was a difference it wasn't very noticable.

You say to push down on the mixture screw - but doesn't that just push the lever downwards rather than compress the spring beneath the mixture screw?

Also, can you tell me how I can adjust the neutral height of the plate (i.e. with engine off) as I am thinking that the plate is set too high. Perhaps that might explain why the mixture is tool lean and perhaps also why the mixture doesn't seem to have much effect.

thanks in advance - I'm very puzzled just now!

Andrew

to adjust the neutral height of the plate you have to bend a clip that's underneath the air sensor plate so that it rests just below the bottom portion of the cone shape. (i think it's called an elipse or cortex or something?)

also, sleepwalker, i just ordered a fuel pressure tester for the cis systems and would like to know if you could elaborate on what i should test first, and where the pressure tester should be in-line at. (which hose coming off the distributor should i test at for lower control pressure?)

thanks cmscott

that clip again - I keep hearing about the "clip" or a "leaf spring" - but I don't think I have one. My car is a 1979 280CE (123 coupe) with a downdraft (i.e. air flow is downards into the cone) Bosch K-Jetronic system (not KE).

I've just removed the air flow plate and had a good feel about with my fingers (very dirty inside my cone) but there is definitely no clip below the plate. I read in a service manual that I should knock a "guide pin" inwards to adjust the plate height - but the pin doesn't seem to be connected to the plate or its lever in any way - perhaps a "clip" is missing. I've attached a picture with a green arrow pointing to the top of what I think is the "guide pin".

Any suggestions are most welcome

Andrew


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both of you got different system, but the same principle. discuss more, share ideas, and you will eventually get on it.

scott


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mrtest


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many thanks sleepwalker

however, the guide pin on my unit cannot possibly affect the neutral height of the plate. I suspect a previous owner or mechanic has damaged it and some small part ( a clip or leaf spring) is now missing.

Do you know from your experience how the guide pin's position sets the neutral plate height?

Andrew

i have never done knocking those pins before. the only thing i have done to throttle body is replace the gasket and cleaning. i always leave it to the original position.

OK thanks - I realise that this isn't a common problem.

I'll need to find a similar car and have a look inside its injection unit if I can. Not easy because rust has killed most 123s in Scotland.

Andrew

Well, there seem to be 2 test ports on my fuel distributor, one at the top and one near the bottom. For some reason now my car will only run for about 30 seconds, but i did manage to get a reading of 80psi (5.5 bar) from the top test port, and 70 psi (4.8 bar) from the bottom.

I'm guessing that the top port is upper control pressure and the bottom is lower control pressure. You had said earlier that there needs to be a difference of 1 bar between the two. Since I can't change the upper control pressure, I decided I needed to lower the lower control pressure, to get a difference of one bar. I unscrewed each lower control screw out 1 turn, and tested again. This time the reading from the bottom port was 75psi (5.1 bar.)!!! When I step on the accelerator the pressure drops about 2 psi also. What am I doing wrong? What should I be looking for, and what do each of these test ports actually test? By the way, I couldn't read your chart of pressures you posted, so maybe you could post them again.

not 1 bar. sorry for the error since i got no idea about your engine type till lately. i have mistaken it for a later version. but now i am asking at least the first 6 VIN number before giving info to omit such mistakes.

the difference should be 0.4 bar.

your car is running very rich.

your engine is 103.
system pressure: 5.3 - 5.5
lower chamber pressure: 0.4 bar lower than system pressure. (0.5 is also acceptable).

So, since my lower control pressure is approximately .3 bar too low, does this mean i need to screw in the screws to raise the pressure?

(Note- i did try screwing the screws in about 1 turn and nothing changed. am i doing something wrong?)