Guys,

I have tested my MB 92 car, last friday in my dealers shop, and it gave me the below results, they told me that I have a problem and they would like to fix it, when I asked them what is it, they replied, "Don't worry we will fix it". and they gave me a paper ;from a testing device called SUN; that printed on it the below things...

For me I don't know what is it, so can any MB professional body analyze the below readings for my engine and tell me what is the problem.


Hints: = Constant
=====================

Vehicle Under Test

Model Name:124

Limits valid from:09.84 - >>
IGNITION TYPE :TRANSISTORISED
ELECTRICAL COOLING FAN :YES
POWER STEERING :YES
FIRING ORDER 1-3-4-2

IGNITION TEST
--------------

RPM 0
BATTERY VOLTS 12.23=
CURRENT AMPS -11.1=
COIL +/KL.15 VOLTS 12.13=

STARTING SYSTEM TEST
----------------------

ENGINE RPM 234=
BATTERY VOLTS 11.18=
CRANKING CURRENT AMPS -102=
COIL +/KL.15 VOLTS 10.55=
COIL -/KL.1 VOLTS 7.24=
DWELL 4.1 (DECREASING)
VACUUM MBAR 9=

CYL AMPS
1 31=
3 30=
4 31=
2 28=

CHARGING SYSTEM TEST
----------------------

ENGINE RPM 2879=
BATTERY VOLTS 13.84=
CURRENT AMPS 3.6=
ALT.RIPPLE %2.4=

IDLE AND EMISSIONS TEST
-----------------------

ENGINE RPM 759=
CO %VOL 1.37=
HC PPM VOL 176=
CO2 %VOL 13.99=
O2 %VOL 1.40=
LAMBDA 1.014=

LOW SPEED SECONDARY KV TEST
----------------------------

ENGINE RPM 761=

CYL FIR.-KV SPARK-KV MSEC
1 11.7= 0.7= 2.0=

3 12.9= 0.6= 1.8=

4 12.0= 0.7= 2.0=

2 10.8= 0.7= 2.0=


HIGH SPEED SECONDARY KV TEST
-----------------------------

ENGINE RPM 1260

CYL FIR.-KV SPARK-KV MSEC
1 4.8= 1.2= 1.0=

3 6.8= 1.2= 1.2=

4 6.9= 1.1= 1.7=

2 6.5= 1.1= 1.5=

OK I'll stick my neck out.

Two factors make this rather difficult. One is that different test equipment bracket testing in different format/criteria. (I have no specific experience with that specific equiptment). Second I am not where I can look up exact numbers.

Third all diagnostics should start with verification of symptoms. I have no idea what are the symptoms. I presume there are symptoms.

After reading the whole sheet I only see one definite problem. That is the "High Speed secondary KV Test". Cyl #1 is lower in activation voltage (the amount of potential voltage necessary to ionize the molecules in the spark gap or whatever greatest gap. The possible causes for low voltage include shorts, rich mixtures, low relative compression and timing.

The even more important factor is the reduced "burn" time. Normal minimums here are around 1.0 to 1.3ms. The fact that it is so much lower than the third and fourth in the order is very important. All the spark energy is burning out in only 60% of the time on the first two cylinders in the order.

The fact that all the activation voltages dropped at "High Speed" is normal and a result of the lowered effective compression incurred by the advance in timing . The fact that the low speed test showed no difference is something to consider. It eliminates shorts as the reason for the reduced high speed voltage (the shorts would be more apparent to the higher KV of the low speed test).

The next test should be a snap KV test, but since it isn't here I will speculate that a reduction in compression would cause a reduced firing KV but it would probably lengthen the firing time. The relationship is higher activation voltage - lower time, lower activation voltage - higher time. The total spark energy is always the same (with a single coil).

The next possibility would be a rich mixture (that isn't there at low speed - tricky condition). I tend to see this as the condition although the condition of spark plug/plug gap could tell a lot. If I could draw it here I would. The normal firing condition involves a build-up of voltage as the coil primary field collapses. At the point where the greatest source of resistance is overcome the voltage is discharged through the new connection. In normal ignition systems this resistance is the plug gap and because the connection is bridged on ionized fuel molecules there is a large activation voltage (spike) followed by a steady firing voltage (much less) which uses up the the rest of the energy. In a good designed and running system the spark lasts long enough that the fuel gets thoroughly burned this means that at the end of the line a natural increase in voltage occurs before the spark dies out do to all the hydrocarbon molecules beeing used up. On a scope the whole thing is: a vertical line to 10kv a burn at .7kv for 1.7 milliseconds, a small curl up and then a drop and maybe oscillations depending on the type of electronic coil control.

In the case of the high speed kv pattern for this car I imagine the low firing spike is broadened and sloped to the end of energy with all the energy disapated to ground in a hump and a reduced time.

To try and make actual diagnostics from this single issue is only relavent for discussion. I would look at that plug first, check the compression second. Actually I would have also done a snap kv test and probably done a relative compression test with the scope by comparing cranking current with an inductive amp probe triggered off #1 cyl secondary kv (spark plug wire). In this test with a scope attached to the battery cable with an inductive amp probe the amps necessary to crank each cylinder through its compression stroke is graphed on the screen. The peaks are easily compared to get a simple non intrusive compression test.

After all that I'm not sure I would do anything if you have no SYMPTOMS.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I regret that I am unfamiliar with the test equipment but I note two items:-

1. The CO %age is 1.37 for an engine with a catalyzer this would normally be less than 0.5%. This suggests the mixture is too rich.

2.The lambda voltage appears to be 1.014 volts. This indicates that it is sending a signal to the ecu to weaken the mixture.

For whatever reason the mixture is NOT being corrected. As a first check is the air filter needing to be changed? If it is OK, then you are on to the fuel injection system.

Guys,

Thanks a lot, even I didn't understand any thing from what Steve said, but I can see that he is really brillint in MB technition.

Anyway, about the spark plugs they are new, and about the compression test, they did it, and they gave me a small sheet of paper which was graphed on it some arcs.
About the compression test arcs they are all above 11.5, one of them is 12.3,And they didn't say anything wrong in it.

Guys, Do you think, it's the spark plug wires who make those problems, and they need replacement please advise.

Actually what I should have said is listen to Alan. I missed the the Lambda voltage as I was thinking adaptation values for some reason. The thing is pegged rich on Lambda.

Which does validate a bunch of what I was saying. The voltage drop on the cylinder #1 is undoubtably from the rich condition.

Spark plug wires are NOT the problem. Does it have a misfire???

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

About Spark plug wires, No they don't have misfire..but may be because they are old, they have a little bit big resistance that make the engine with less than it's full capability. Do you think this is true guys!!


but I'm feeling that my car is consuming a lot of fuel for ,it goes 6Km/litre.

...................

__________________
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