Hi I own a UK 300e-24V 1991 W124. The chassis no is 124.031 and has the USA 300ce 24v (124.051) 104.980 3 litre 24v engine with CIS Ke or CFI fuel injection.

On checking my engine fault codes, I discovered using Socket 3 (Data Link Connector 16-pin), that I had fault code 9 – “Current to EHA is Illogical”

This was the only fault present and cleared it using the known techniques. I the drove the car and the fault code 9 reappeared. I the disconnected the 55-pin connector from the CIS-E unit and performed a continuity measurement between pins 55 and37 and the value read 19.7ohm. Great I thought, the cable harness from CIS-E to EHA is correct and the basic resistance of the EHA is in tolerance.

On connecting the DVM in series with the EHA, with ignition on engine off, the EHA only drew 11.4 mA - ( I thought it should have been 20mA). On start up the current rose to about 20mA. It only went negative with deceleration fuel cut off, dipping to about -30mA and then returning back to 11mA.

The engine starts fine and drives without fault apart from a poorer fuel consumption and poorer performance, than when I first owned the car. I have had the car nearly two years. I had to replace the MAS control unit for Dealer replacement and the part number of the new one supersedes my old one. When I then took it for its annual emissions check, it failed and was running at about 3.0%. It was then corrected and this year it passed at 1.0%

1) My problem is there is no catalytic converter fitted to my vehicle nor is there a 02 sensor (lambda) and hence my system is an open loop system so why does it need an EHA to correct for rich or lean?

2) Can any one tell me what the current measurements should be for a UK spec 104 and why does it need an EHA any way?

3) what causes incorrect current readings at the EHA on my system anyway?

Any help would be very much welcome.

Thanks

Tony

EHA is the electronic mechainsm to fuel correction.

Fuel correction for cold running, starting enrichment, acceleration enrichment, decel cut-off, and others are effected by EHA. In countries with catalytic convertors feedback control is also effected.

Code enabling criteria is what you are looking for and I don't know what the controller cares about actual EHA current.

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

Thank you for your response Steve. Yes you right, I’m just a bit slow at the moment!

The EHA obviously works in some form as it performs cold start enrichment and engine warm-up, and the engine does not stall or miss during this time (or any other). Also all the usual sensors’ feeding the CIS, MAS and EZL are obviously working fine to give the EHA some sort of corrective information.

Would adjusting the base line fuel/air mixture with the allen key alter the EHA baseline current readings?

Is it also normal the when turning the ignition off and removing the key that the CIS unit sill provides the EHA with a small voltage and hence a small current flow of about 11mA through the 20 ohm actuator coils? (perhaps a capacitor in the CIS unit??)

Once again thanks

Tony

I don't think any current should flow after the key is off. That could be illogical.

BTW, I have always looked for the 20ma KOEO (key on engine off) to verify control and calibrate my test tool, but one day I happened upon the list of actual ma values for all motors for various conditions (wish I knew where that document existed - might have been here) and noticed a number of engine combinations that only had 10ma KOEO and even rarer was another value that escapes me (could have been 40 or 50ma).

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

Once again thanks.

Just for confidence, I have checked the current with my other DVM and they were within 0.1mA. Also, on disconnecting and reconnecting the DVM (from being in series with EHA and CIS) with key off and out of ignition, the voltage/current does returns to zero on reconnection.

I also have access to another 300e 1990, but with 12v 103 engine fitted and going to check its EHA currents. Just one potential problem though, its not a very good state of tune and has 300,000miles on the clock but I will see what it brings. This car also has no cat or o2 sensor.



Once again many thanks for your time and trouble.

Tony

The current readings for the various engines and conditions (for the 103 engines at least) are on page 13 of the "KE Injection Tests" section of the 124 CD.

Also, that same document specifies testing the EHA for the "implausible/illogical" condition you mention. The tests all appear to be for continuity in the wiring.

But all of this is in the National Versions (with cat and lambda) section. I have no idea what this would mean in a UK car with a US engine. Maybe the ECU finds this situation confusing.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thanks Chuck for the response.

I do not have access to the 124 CD that you refer to so I’m unable to check the data. My 300e_24V is a UK standard car just like the US 300Ce_24V but without the cat and lambda sensor.

I checked out another UK standard 300e 12V (103) today and the current readings for the EHA were 18.9mA KOEO. Slowing falling to about 2.1mA at normal operating temperature. Increasing positive 2 to 4mA as the throttle was opened and on fuel shut off, going negative to about -38mA. This engine does not have a MAS control unit and I was unable to check fault codes. There is only the 9 pin “x11” connector next to the EZL unit, and I don’t have the pin outs or fault codes for that connector. However from engine start and through warm-up, it did not show any operating faults but I did not drive the car.

I do not have access to a CO meter so I do know the state of tune but the current readings for this engine do not seem too far from the nominal values I would have expected, unlike my own 300e_24V. So it would appear that the fault code 9 I am getting is correct but I don’t know what’s at fault. The CIS unit not out putting the right correcting current, or a faulty EHA is perhaps its only the base mixture that’s out of spec.

Once again, any thoughts greatly received.

Tony

The comment on the page in the CD was meant for Steve B, to remind him of the reference.

I can't help you with a 104.980 engine - that is the "standard" version, and they did not put it on the US CD. The 24V engine did not make it to the US until 1993, with a 104.992 engine, according to the CD.

FWIW, the spec on the 103.980 "standard" engine, which is on the CD, says 0mA KOEO, 0 +/- 3 mA idling - the 11 reading you got would seem to be high.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thanks Chuck.

All the information and software I have, has been generated for the US market and I even subscribe to www.Alldata.com. The closest vehicle data which matches my car is for a 1990. 300ce with the 3.0 litre 24v 104.980 engine but Kat and lambda fitted.

As for the 300e (103 engine) car I tested, it was just to give me some confidence that the EHA current measurements for an open loop system made some sort of sense, unlike my own 104.

I take it that on any system the KOEO state should be in specification/tolerance, or bearing in mind that all the other senses should be providing active data apart from the inductive type sensor eg crankshaft position sensor with the ignition on. Or does it need the engine to have been started before the EHA starts to operate actively?

Thanks Tony

Thanks for the ref info Chuck, I may try and read it again this week end.

I am never too worried about whether its a 20ma KOEO car or a 10ma KOEO car as I am very confident in my test hook-up. The actual figure plays no other part in my diagnostics. I use it as a reference when hooking up new meter.

In the case of this fault, I would think the controller is seeing an open circuit at times causing instantaneous current changes which can't happen in real life. If it system is tracking -2ma and the circuit opens to 0ma this can't really happen that quick but it will probably make no difference in performance that one would notice. I am just speculating or what the controller thinks it is seeing.

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

Hi,

I’ve just been looking at the readings in greater detail and are as follows.

KEKO 29.6mA

Start-up from cold rises initially to 35.2mA

Then quickly falls in regular steps to about 12.4mA

Then as it approaches normal operating Temp. 10.9mA


If I open the throttle quickly it rises to approx 20mA and the return to about 10.9 -10.8mA.

The only worry I have is that when the engine is off – key out there is a current flow of 11.2mA for a few minutes and then it returns to 0.0mA.

It is as if there is a dc offset causing all my current measurements to be 11mA out.

I also check the fault codes on pin 14 (MAS controller although my model or 300ce 24v was not on the list.)

It listed fault 9 – Circuit 50 Failure. I have replaced this unit with a dealer supplied new one months earlier and the part number is newer.

Any more thoughts greatly received

Tony

I think that you need to find the specs for a 104 Standard version.
But absent that, the 103.980 specs would seem (at least to me) to be more relevant than a KAT/lambda car.

Thinking about it last night, pretending it was in my garage with my less than state-of-the-art diagnostics and training:

I am suspicious of your KOEO reading. What happens if you clear the fault, and do KOEO without starting the engine? Does the fault reappear?

What is the current reading at hot idle? I couldn't tell from your first post. I think 11 mA at hot idle could generate a fault of some sort.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Hi Chuck,

Just got back in and it’s late. I will perform this test tomorrow morning but what I can tell is that the fault will reset but not performed the KOEO measurement straight after without starting engine yet.

11mA is the hot idle current.

Will post another tomorrow after test.

Thanks for your support


Tony

Hi,

Cleared fault codes and checked for fault code 1. – OK

Started engine from cold and checked EHA current readings. Allowed engine to warm-up to operating temp. Increased engine speed a few times. Current stabilised to 11mA each time.

Re-read fault codes and still fault code 1 – no fault found. I was unable to drive today as I was blocked in. Last time I cleared the faults and took it for a drive, fault code 9 reappeared. Will check again as soon as possible.

Thanks

Tony

After more reflection, I think you need to focus on the 11mA reading at hot idle. That is just 'way too much enrichment. On a cat/lambda car, we would have a go at the mixture and read the on/off ratio of the lambda control valve.

But in your case, I think what is happening is

a. the CIS control unit is getting a bogus signal telling it to enrich. This could come from the air or throttle position sensor, temp sensor, or a vacuum sensor (if it has one).

b. the control unit has gone around the bend - the KOEO current is wrong, and it should not be sending anything with key off. If my suspicion is right - that the correct KOEO reading should be 0 like the 103.980 - then a hot idle reading 11 mA too high may be more than a coincidence.

And, I would not rule out a vacuum leak somewhere as a culprit or contributor.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe