Fuel leaking into air flow sensor KE-Jetronic
 

After being directed towards the fuel distributor as the possible cause of my hesitation below 2000rpm/misfiring issues (m103 engine) I noticed that the inside of my air flow meter was wet with petrol and smelt very strongly of it.
Is the leaking into the air flow sensor caused by the fuel distributor or the fuel pressure regulator? Should I still have my fuel distributor cleaned and recalibrated?

The leakage you describe is coming from the fuel distributor's control piston. Its worn out.

There is a serviceable gasket (from MB dealer ?) for the fuel distributor shaft, if your replace this the fuel leak will stop if it is coming from the shaft. You will need a special tool like a split screwdriver to open the screw because the shaft passes thru the screw. Also you will have to exactly note down the length of the shaft with respect to the outer frame because turning the screw that allows you to replace the gasket also alters how far the shaft drops when you hold the distributor in the right (up/down) position. Take your distributor to a dealer's part store and they may loan you the tool and you can change the gasket right there and return the tool.

Sorry, the measurement of the shaft should me made by keeping the shaft up and distrbibutor down. But here are the instructions.

KE-Jetronic problem?
 

Thank you for your replies but a new seal and recalibration has not solved this problem. All is outlined below...
Okay, brabus has been suffering from hesitation just before around 2000rpm for a while now which clears up after it. It feels like a potential barrier which is overcome and then its fine.
I first thought it was and ignition system fault so I had the car scoped and it checked out fine according to Mercstar, with all cylinders receiving the same spark. I have tried a new coil but to no avail.
I then moved onto the duty cycle,this reads 50% as it should for a non-cat car such as mine. I also measured the EHA current which appears to enrich the mixture under quick acceleration. However, when I disconnect the coolant temperature sensor (CTS) my problem seems to magically dissapear, although the acceleration past 2000rpm isn't quite as strong (due to the lack of enrichment I guess).
I resistance tested my CTS and it checks out. I then noticed fuel in my air flow potentiometer (which I have also previously checked and readjusted to Bosch/Merc spec), and upon removing this my throttle body. So I though leaking fuel distributor.
I bought my pressure regulator, fuel distributor, air flow sensor, injectors and cold start valve to specialist Ken Mills Injection. The fuel distributor was not leaking but he changed the seal anyway and recalibrated it as it was only giving 150cc instead of 175cc. All other components checked out fine. So today I put it all back together thinking all would be okay but :mad:, this car is having none of it, same problem. Where do I go from here guys?

Did the air flow sensor turn out to be o.k. ? If this is a potentiometer type, there is a possibility that there is an open circuit at certain section of the pot contact. With car off, when the air flow sensor is at the top, the resistance should be between 1 and 2K. Now if you gradually depress the plate, the resistance should gradually increase, there should be no jumps greater than 4K. If for certain position of the plate, the sensor resistance is unreliable, you could get hesitation for those positions. Maybe, disconnecting the temp sensor puts your car in limp mode (this thing is car specific, and I dont know about your car) ? And in this mode, the air/fuel ratio is controlled in an open loop maner by the computer, no sensors are read, and this actually tells you that the problem is in one of the sensors. The other possibility is if the position sensor is giving unreliable signal around those rpms. I cannot upload the manual's pages that outline steps to test electrical components of the KE system, send me an email at saumil@swbell.net if you dont have these steps and need them.

Today I decided to change the CTS since it is fairly cheap and the resistance values accross its pins were slightly different to each other. This did not change the cars behaviour at all, hesitation at 2000rpm is still there.
Thanks to saumil I have the ECU pin-out and KE system test procedures so I dabbled a little. First of all I checked the harness to air flow pot, eha and CTS for continuity, all were fine. I then checked the air flow pot as saumil recommended, at rest it is around 1.4kohm, rising quickly and then more slowly until about 9kohms before falling again so no problem there.
Now onto the EHA valve, this passed the resistance test however I never noticed any enrichment whatsoever, it was always at 0ma, KOEO was 0ma too but I believe this is correct as mine is a standard non-cat car. When I had my fuel distributor rebuilt the gentleman checked the EHA and told me it is fine and working as it should be. I can only imagine I have an ecu fault. I have a spare EHA which I performed the quarter turn clockwise trick on, I swapped them over and this was also drawing no current at all.
I noticed one other thing, with my aircleaner assembly removed when I revved the engine white smoke, smelling of oil came out of the hose which goes from the valve cover to the air cleaner. I can't remember seeing this before, but the car still runs okay/no hesitation with the CTS and thus KE-Jetronic system disconnected. Where from here???

The air sensor pot's resistance rising sharply is not a good sign. Infact, the jumps should be less than 2K if you are moving the plate really slowly. Did you get a larger jump than that ? And was the jump close to the zero position, because that could explain your hesitation around 2K rpm.

And you dont have a catalytic converter, but still there should be enrichment current on the EHA. Do you get 10-20 or so ma when you just turn the ignition switch to run, before starting ? Let me check the expected test results on EHA for your car again.

I am also assuming that measuring currents is not a problem, that you are using a series circuit to do that rather than just connecting the meter's terminals across the EHA pins.

I checked, every car must have greater than 15 ma when the throttle is blipped at engine temp of 20 degC. So if you dont get any change in current under this condition, the computer must be replaced if there is not an obvious wire disconnection from the computer to the EHA. What is the exact model that you have ?

I have engine number 103.983 ruf (non-cat) car. I will buy the merc harness and retest with that. I put the ammeter in series with the circuit, read 0ma.
I had the same problem exactly with two different air flow pots so I highly doubt it is that. As you mentioned it is probably that the ECU output to the EHA valve is blown. I was driving around for while without the throttle sensor switch disconnected (unknown to me, realised when I couldn't read the duty cycle), perhaps this caused it.
The file comb1 at the top of page 12 describes my problem, minus the stalling, perhaps it is that? If not I guess the ECU as you say.

Terminals 10 and 12 on the computer connector are connected to the two ends of the EHA connector (do you have the diagram for that connector ?), check for continuity for each wire before buying a new harness. If these two wires show continuity, for sure the computer is not sending the current correctly. The model you described, should either have 10 or 20 ma (depending on the year) as soon as the ignition switch is put on run (position right before the start). I dont know of anything else that can cause the EHA current to be absent, maybe someone else with more experience can pitch in OTHERWISE just replace the computer. Oh, one more thing, try disconnecting the battery for 10 or so minutes, just incase the computer needs a reset.

It is unlikely, but possible that both pots are bad, you should not have a sudden jump (i.e. like an open circuit) at all for any plate position, I can check this on my car and let you know. I dont know if the pot is linear or logarithmic, would expect it to be linear. But in either case, I am not sure if this will cause the EHA current to be absent.

One more thing, check the continuity of the coolant temp sensor terminal (one of the two terminals) to the computer connector (terminal 21). An open circuit in this circuit can put the car in a limp mode.

It's not the ECU
 

I swapped ecu's with one in a breakers yard, no difference. I then realised that I wasn't using the ammeter function correctly, I plugged the wire into the wrong port :dizzy2:. My EHA valve is enriching the mixture on blipping the throttle. I didn't see the +15ma change but I tested the car hot.
I decided to test my engine compressions and I got:

13 bar
13 bar
13 bar
12.5 bar
13.5 bar
12 bar

Cylinder 5 & 6 are just within the mercedes 1.5 bar tolerence in their literature. The compressions are slightly higher than 300E compressions due to Brabus raising the compression ratio. Cylinder 6 is leaking slightly from the rings. I introduced a teaspoon of oil and then read 13 bars from it's compression test. However I don't think my compressions should be giving me the problems I am seeing at the moment?
The crankshaft position could also apparently be causing this? I have never seen this mentioned on any forums as being such a cure.

O.K., so the ECU is ruled out. It is not the compression causing this either. You can also check the air sensor pot while the car is running, this may allow you to examine if there is erratic change in sensor voltage when you get the hesitation. The same pins (middle pin and one of the two neighbouring pins, I dont remember which one but you can figure this out) you checked resistance across, now measure the voltage. Note, to do this test, the sensor connector must be conected to the pot, so you can use alligator clips to firt make all the connections. At idle, you should get between 0.5 and 1V, ideally 0.7V. Then as you smoothly press the gas pedal, the voltage should increase gradually. Notice what happens around the hesitation point. Do you see a voltage that dips down.

Not the crankshaft position sensor either
 

I resistance checked the crankshaft position sensor, it checked out fine with 845 ohms.
I then checked the air flow pot as you recommended saumil, at idle in drive I get almost bang on 0.7V, fluctuating around 0.71 as the idle is slightly unsteady. As the revs are raised the voltage slowly raises with them, no jumps at all. I went upto 3500rpm, way beyond my problem zone.
I will check the throttle valve switch next for completeness. Where do I go from here?! Is the TDC sensor important?

I think the air sensor is ruled out also. Did you verify the EHA function when the car is cold ? Can you check intake vaccum ? At idle, it should be between 16-22 inch Hg. If it is too low, there could be an exhaust clog OR a EGR valve (if your car has one) malfunction. Also what happens to intake vaccum when you press the gas pedal ? Can you check the vaccum that controls the EGR valve ? That valve should be closed at idle, i.e. the vaccum should be lower than 2 inch Hg. Then as you accelerate, at 2000 - 2500 rpm, the vaccum at EGR port should be 5 to 6 inch Hg, enough to open the valve. If this valve does not work like this, idle would be rough and you would also have hesitation during acceleration. These are some other possibilities I can think of. My 87, 260E does not have an EGR valve so would not know its location but should be somewhere around the exhaust manifold since its job is to ricirculate the exhaust.

I also do not have an EGR valve on my car or the means to check the vacuum. I'm considering seeing a 'reputable' mechanic later this week though so he can do such a check. I replaced the boot underneath the airflow sensor, the hoses to the idle control valves and the thin vacuum hoses for the injection system though. Is there anything else I can check without a vacuum gauge?

Possible solution!
 

I thought the air intake temperature sensor was pretty unimportant to be honest. Anyhow, running out of ideas I looked on alldatadiy.com where I read "The intake air temperature sensor which is located in the induction system measures incoming ambient air temperature. Information concerning the incoming air temperature is sent to the CIS-E and EZL control units and is used to calculate necessary adjustments to the air/fuel ratio and ignition timing. Low ambient air temperatures will tend to enrichen air/fuel mixtures and high ambient temperatures will tend to retard ignition timing."
So I resistance checked it, it should have the same resistance profile as the CTS. At room temperature I got 16kohm, telling the KE-ecu that the air is -30C and so enriching the mixture. This would explain my sooty black spark plugs too. I'll have to wait until wednesday for the part to come from the big merc warehouse in MK to find out though but I'm hopeful. Also would explain why without the electronic side of things the car performs better, as the base mixture is good.

I think it should contribute as you read, but I am not sure how much it is weighted in the air/fuel ratio calculations. The reason I am saying this is because my 87, 260E does not have this sensor. But this is an inexpensive part and if you done see a decrease in resistance with increase in air temp (you can use a hair dryer), it is bad.

No change
 

The air intake sensor was definitely bad, an ohmeter across the new one gave ~2kohms (old one was 16kohms) but still no joy. I'm running out of ideas, but I think I'm going to go though the entire KE-Jetronic test procedures before bringing it to a mechanic.

Throttle position sensor checked out okay, only just below 1ohm, but below nonetheless, cleaned up the pins too. Looked inside my ecu connector and all was well, no corrosion. I also had the wrong fuel pump installed, with one pin (87H) missing, put the correct one back, no change. It's off to a Merc shop tomorrow.

Yes, check the KE system one last time (though you have done most of the tests already), and if it is not the KE system the only thing I can think of now is vaccum. Perhaps a clog in the exhaust system.

You should confirm that the sensor signals are indeed reaching the ECU (i.e. if the harness is o.k.) Specially the coolant temp sensor cables.

Okay I visted Lymington motors where they told me they had fixed another tuned car earlier on in the day. They were meant to check and adjust my EHA valve. When they eventually got the pressure tester onto the fuel distributor (it measures the upper or lower chamber pressure) the tool seemed like a compass, changing reading as you moved it. Anyway they seemed to establish that the pressure differential was only 0.3 bar when it should be 0.4.
They removed the valve and were put off by the screw which they though was the adjustment. The prats were trying to turn it clockwise almost rounding off the threads! I informed them that you undo the screw and an allen key is adjusted underneath. Bottom line was no change and really not much of an idea either except that they initially did a leakage test, all cylinders over 50% so I'm going to strip the engine down and do the rings. Also going to check for a vacuum leak by blacking off vacuum lines one-by-one.

I dont think press diff of 0.3 compared to 0.4 would cause the hesitation at 2000 rpm, for that rpm, the diff would be quite larger, unless ofcourse for some reason the pressure difference becomes erratic around 2000 rpm. The difference should increase smoothly as your rpm smoothly goes up, this happens by reduction in lower chamber pressure (upper chanber pressure is constant between 5.3 and 5.5 bar) as you depress the gas pedal.

The 0.3 vs. 0.4V may cause a difference during startup. Do you have a problem starting the car or idling ?

The hesitation, does it occur around 2000 rpm also when you gradually depress the pedal past it ?

Forgot to ask, is the fuel still leaking in the air sensor ?

I know I posted the solution elsewhere but in case anyone stumbles upon this thread after a search...

The black sooty spark plugs were due to the base CO adjustment being VERY rich (I'm talking 5 rotations rich, over 10% CO). How it got there I don't know but that's what it was.

The hesitation was due to the ignition control unit which mounts on the inner fender and uses vacuum and an R16 resistor value to calculate the spark signal should be sent. See my later post for more details on this.

Thanks to everyone to helped me solve this, especially Saumil who sent me lots of KE test literature and zakh who spotted the solution!