I've been having poor MPG lately and went to check my CO reading and got a fixed 70% on my multimeter. This fixed reading was verified by a tech using a Bosch diagnostic computer, and he told me the problem is no power to the connector.

Looking at the schematic, pin 3 is supplied power via pin 23 of the CIS-E control unit.

Is this where I should start? If I do find battery voltage at this pin, what should I check next? The OVP was recently changed FWIW.

TIA!

Iodyn
'91 300E

When I look up 70% duty cycle for a 91 300E I get Starter signal (circuit 50) recognized.

You should first check that your hook up is correct by checking the duty cycle key on engine off. BTW was that the way you got the 70%, because all federal cars give 70% key on engine off. To get real values the engine must be running.

Also if you do the key on engine off test and you get 85% you have a California car.

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

Thanks Steve for your prompt response!

I got 70% with car both off, and running/revving. There was no fluctuation at all. The Bosch readout may have been a different %, I don't recall, but nonetheless was a constant reading with engine running.

I see your circuit 50 on the schematic and it relates to the plug connection on the starter lockout switch. This is on the X26, 12 pin plug connection of the engine wiring harness.

How do I go about testing this circuit for voltage? Is there a fuse for this circuit 50 that I can check?

Thanks again!

Iodyn
'91 300E

The 50 terminal is the wire that activates the starter. The act of starting puts the car into different mapping for fuel control.

I have never seen this code, but would imagine from the description that tern 28 on the KE controller will think it is seeing the start signal. Note: the start signal is not just the battery voltage that occurs at this point during starting. It actually is the lack of ground. Notice that the 50 terminal (28 at N3) goes to the windings of the starter solenoid. When there isn't battery voltage (as in starting) there is ground through the windings. Thus if this wire is not connected the controller also sees the same thing as starting; the lack of ground.

Check this circuit. I would also advise looking at the EHA current as this will really tell you what the electronics are doing.

Have you tried the impulse codes at the other diagnostic connector by the battery? These will be more specify as to the fault.

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

Steve,

In an earlier post, like waaaaay earlier (March, 2000) you stated:

Ok, I'll bite. In that same thread you didn't elaborate on how to do this. Instead of searching through your almost 3000 posts, I was hoping you could briefly rehash this technique for me.

I would appreciate it very much!

TIA!

Iodyn
'91 300E

Look in the DIY section under the article "Evaluating engine controls". It shows and discusses various methods to get the codes without special tools.

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

Well, I threw together a homemade pulse counter (thanks Arthur) and pulled some codes from my X11/4 diagnostic socket, and erased some others that had been fixed awhile back (O2 sensor ).

First thing I noticed is that my 16 pin X11/4 connector on firewall across from battery only has pins 1, 3, 6, 7, 14 occupied. According to my CD's and a diagram sent to me (thanks again Arthur) these pins diagnose the following:

1. ground
3. not used (why is a pin there?)
6. SRS control module
7. ACC push button control module
14. electronic accelerator control module/cruise control amplifier

No codes out of pin 14. Codes 3 and 29 from pin 3. These correlate to:

3 - Coolant temperature in KE control unit implausible
29- difference in coolant temperatures between KE control unit
and EZL ignition control unit.

WHICH TEMP SENSOR DO I NEED TO DIAGNOSE? ;D The test steps in CD manual mentions nothing about the 2 pin blue coolant sensor that cuts in high aux fans at 105 and cuts out AC at 115, rather the EZL coolant temp sensor (B11/2 -- big round 4 pin connector at back of head). Does the two pin blue coolant sensor have nothing to do at all with the CIS-E control unit??

Manual says to "measure temperature sensor connections diagonally and compare both readings -- they must be the same".

This is on the EZL sensor (4 pins) no doubt, so is this the 29 fault code I'm getting?

Thanks in advance for any insight any might have here ... my engine is still in FOM and the gas mileage is terrible.

'91 300 E

I forgot to mention that I'm also getting fault code 8 from pin 6. (bad altitude pressure signal from EZL ignition control unit).

~Paul

___________________
'91 300E, 215K miles

(my son's account that I accidentally logged into to start this thread)