89 420SEL Running/ECU Problems - PeachParts Mercedes-Benz Forum

wbain5280 · #1 05-23-2007, 12:09 AM

Ok sports fans, I've been workin on my 420SEL for a while now. I've overhauled the intake manifold and vacuum lines, switches and gaskets. The check engine light is still on. I've got some really strange readings, like no current at the EHA, easy starting but stalling when cold. I've got a X92 or X11/4 diagnostic connector with a push button but no LED and connectors at Pins 1, 6 and 7.

The idle speed goes up and down which indicates a vacuum leak. I didn't replace the rubber CIS air horn base because it looked OK. When I unplug the idle air valve, idle speed goes way up.

Here are some pics:

X11/4 or X92 http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0026.jpg

Only pins 1, 6 and 7 http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0027.jpg

Pin 1 Brown wire or ground http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0028.jpg

Pin 6 pink and pin 7 green http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0029.jpg

Pushbutton wires http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0030.jpg

Builder's plate http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0039-1.jpg

Air horn gap http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0042-1.jpg (while running)

No duty cycle http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0037-1.jpg (KOEO)

I suspect the ecu is shot http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0035-1.jpg

The idle valve works, I made sure it worked OK and was clean http://i19.photobucket.com/albums/b177/wb300se/MB_420SEL/DSC_0031-1.jpg

There doesn't seem to be any voltage at either the CIS-E air flow pot despite it's position.

I think I need a similar 420SEL to use as a basis for testing.

just-n-time · #2 05-23-2007, 01:13 PM

Go to the post I have, youwill find some on the EHA reading and the pot, It may help you the test are of a 90 420sel.

david s poole · #3 05-23-2007, 05:35 PM

have you checked the ovp relay?these cars will run pretty well in limp mode and your ecu may not be getting power.

wbain5280 · #4 05-23-2007, 08:19 PM

Thanks Guys.

JNT, I read over your posts because you did so much work on your 420.

David, I resoldered the OVP a while ago. I'll test the voltage at the ecu connector in the morning, it's getting a little dark.

wbain5280 · #5 05-24-2007, 11:58 AM

12 volts at pin 1 of the ECU plug, OVP OK.

I think the O2 sensor is bad.

wbain5280 · #6 05-31-2007, 10:12 PM

I gought a generic, read Ford Mustang, generic BOSCH 13943 O2 sensor for $44 from Auto Zone. I went to the Ford dealer and the the mating connector cost $42 bux. Yikes, I'm going to the junkyard for a connector or just solder the new one in to the existing harness.

I was checking the car's schematics and the 'check engine light' is really an O2 sensor is bad light. I hope that once it's replaced, it will run better or at least give me some diagnostic eadings from the X11.