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?)