Hello All,

I have a 1988 300E that idles rough, and dies intermittently. Some days it won't die at all, other days it won't stay running at a stop sign unless my foot is on the gas.

I read a lot of the posts here and have started troubleshooting, but could use a little help.

I checked the OVP relay (Pin 3 on the round test socket, supposed to be 2.5 to 5 volts I read) Mine measures 1.8 volts. Do I need to replace the OVP relay?

I also checked what I believe to be the lambda adjustment (Pin 3 on the round test socket supposed to be 55% duty cycle I think) Mine gives no reading (00.0%). Is this an error code? I disconnected the battery ground with the ignition on as I was told this would clear error codes. No change to the 00.0% reading. Any ideas?

I see three relays near each other behind the battery.

1) Silver with a 10A fuse on top. Part# 201 540 32 45. Appears to be Mercedes genuine part. This is the OVP relay, right?

2) Black relay marked "KVS Kickdown" Part# 002 545 52 05. This one also appears to be a Mercedes genuine part, but appears to be used as it has "300E 124/86' written on it in with a paint pen. Which relay is this?

3) A black relay marked "KAE Relay" 3.701.130 12*99 PA6 GF-30. This appears to be a non-Mercedes part. Is this the fuel pump relay or a different one?

Also, where is the decel micro-switch located. Apparently this could be the culprit also.

Anything I'm overlooking? What should be my next step?

Any assistance greatly appreciated.

Thanks,
Gebhard

Kickdown is the fuel pump relay.

The decel switch is at the end of throttle cable. It is a small grey switch w/roller wheel.
The KAE relay is for A/C. This diagnosis is very difficult even for MB tech. You might do search on air flow sensor as it can be a common fault in stalling & hesitation.

Thanks for the info on the switch and the relay.

Anybody know if 1.8 VDC on the OVP relay is acceptable or a failing metric? Should I replace the OVP relay?

Thanks,

Gebhard

Got a 93 300e that coughs and backfires thru the engine compartment. New fuel filter, MAF one year old, running premium fuel. Idles fine and revs up good in neutral, but under load it likes to "Pop" under the hood. Need to build a code reader. Have 16 pin near battery. I have code sheet but don't know how to use a reader. Engine running or off? When and how do I push the momentary switch?

Fixed the problem with a new #1 coil, made a code reader to figure it out. I now sell code readers on Ebay for $32. They work good and include code definations and instructions.

http://cgi.ebay.com/ebaymotors/Mercedes-Diagnostic-Code-Reader-W124-300e-and-others_W0QQitemZ330387628521QQcmdZViewItemQQptZMotors_Automotive_Tools?hash=item4ceca321e9

(Fixed now) Very annoying. Suggestions appreciated.

Sincerely,
Rick Potter
Potters Barber Shop
Osage City, Kansas

Rick,

Here are instructions I found on this forum (from Battlecat714):

Reading Fault Codes

- Turn ignition key to “on” position, all dash warning lights will be on.

- Remove cover on 16 plug diagnostic connector near battery.

- To read check engine light codes (DM), hold down built in button next to LED light for 3 to 4 seconds, LED light should be on, release button, count the number of LED flashes that follows. Hold button down for 3 to 4 seconds again to check for another code. Keep doing this until all codes have been read and first code comes up again.

- To clear codes - hold down button for 10 to 12 seconds, turn ignition key off for a few seconds, repeat to clear additional codes. Ignition must be turned off between each code cleared.

To check other modules using code tester – insert black plug into socket #1 (ground). Insert red plug into socket #16 (12V power). Insert yellow (third color) plug into socket to be tested, for example #8 or #14. Repeat steps above for LED button using code tester button and LED. Same process for deleting codes as with LED button.

Check appropriate fault code list to determine fault.

Checks codes as quickly as possible at the first sign of a problem. Codes spread from one module to another and will often show up twice or cause other codes. The sooner you check the codes the more likely you are to identify the source problem.

****

I've been reading codes for the last few days, so my old brain is rather fresh on the subject. So...yell if you need a hand. Plus, I have links to the code results. And, I just built the home brew tester...after putting it off for months...and it's easy. So just yell if you need advice.

Now...what to do after you get the codes...well, that's where I fall short and need advice from others on here.

Jim

__________________
Syntax26

1995 MB E420 (lowered)
1989 MB 300SE (sold to brother)
1975 MB 280 (sold)
One damn fine jacked-up golf cart

First check is to see if you have CAL. or FED. version. If Fed , you do not have a DM ...only Cal Emmssions had Bullt-in Led/SW for DM /N59 module in 1993/124.032 chassis.

Do you have a CE Indicator lamp on the Dash???
....if yes, you have Cal, if No , you have Federal and NO DM.

__________________
A Dalton

Fed Version. No California here. Mechanic told me that I need plug wires or ends as a cylinder is not firing. I will tear it apart this weekend. Built code reader and here they are, hope someone can send me a code list as I cannot find a description for my pins.

Pin 6 error - 3,6,8,9
Pin 7 error - 1
Pin 8 error - 1
Pin 10 error - No Blinks
Pin 14 error - 5,11

Any comments would be appreciated.
Sincerely,
Rick Potter
Potters Barber Shop , Osage City, Kansas

Rick,

You can see pin descriptions and read code explanations here.

http://www.geocities.com/MotorCity/D.../cs1000_mb.pdf

__________________
Syntax26

1995 MB E420 (lowered)
1989 MB 300SE (sold to brother)
1975 MB 280 (sold)
One damn fine jacked-up golf cart

I've looked at the cs1000_mb document many times and cannot find the codes for my 1993 300e 2.8 124. 16 pin connection and I can't find #6 #7 or #10. Any advice would be appreciated.

Rick,

On page 11 you'll find the explanations for each pin for the 16 pin connector.

Then you need to find the correct page - for your car - the code explanations by pin.

__________________
Syntax26

1995 MB E420 (lowered)
1989 MB 300SE (sold to brother)
1975 MB 280 (sold)
One damn fine jacked-up golf cart

Change these 3 connectrs for the misfire

http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=2AO123CS42D712BYJQ&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1993&product=F1010-84561&application=000357363


Your 124.028 chassis has no Built-in Led or DM, but you can use codes for
123.032 on some pins.

Single Flash is not an ERROR..it means there are NO codes stored in that module.
[Your - 14]-EA cable may need to be adjusted or lubed. ..you want 1/4 slack
Your SRS codes are on page 114.

I would clear all codes and see what returns.
You do NOT have to turn key off for each code clear...you turn key off for 10 sec , on for 10 and then restart.

Yoy also have a 129/RST code pin listed that is not applicable to your car.

__________________
A Dalton

I've looked at the cs1000_mb document many times and cannot find the codes for my 1993 300e 2.8 124. 16 pin connection and I can't find #6 #7 or #10. Any advice would be appreciated.

I agree with you completely as it sounds simple and I see the page you talk about, but I cannot find a page(s) detailing pins 6, 7 and 10 for a 16 pin 2.8 300e. It's not there.... what a puzzle.

6 is SRS on page 114
7 is AC and 124.028 does not have a/c diagnostics in '93
10 is RST/129 and not applicable.

__________________
A Dalton

Ordered wires and plugs today. Hope the rough engine problems go away. Read codes an hour ago. Can't seem to clear them, I'll try again.

Pin 6
3 - Driver Air Bag
6 - Front passenger seat belt buckle switch
8 - Voltage supply interrupted
9 - SRS warning Lamp

Pin 8
4 - Load sensor in EAL/AKR control module faulty

Pin 14
5 - Stop lamp switch
11 - Fuel safety shut-off to LH-SFI control module