[V8] very little audi content

[Tony and Lillie]

That relay is a common failure point, and not on any other CIS system I've 
ever worked on. Just replaced it on Dad's 2.6 as well. Gotta love MB for a 
few of their "better engineering" ideas. Also, the series fuel pumps. Which 
will bring me to a point in a sec.

BTW, I'm a pretty big fan of CIS. It's not super easy, but it's simple and 
relatively low maintenance when done correctly.

So, let's start with the basics. Fuel pressure and flow. There are plenty of 
info sources for the specs, I'll just cover what you need to check from my 
experience.

Check those, if one or both are low, make sure both pumps are running. There 
are two, they run in series. They are located right inside the LR wheel, on 
a sort of plate that mounts to the car. Also houses the filter, which might 
need replacement.

The airflow pot does not have a huge affect on the system, relative to a few 
other componenets. Unless something has gone terribly wrong with it. Either 
way, it's shared with most CIS vehicles, so take a trip to the salvage yard 
and grab one. Plenty around at my local ones. That system was used on 
everything from Audi's and VW's to Porsches, Volvo's, Saabs, Deloreans, 
M-B's, and I'm sure I've forgetting some.

The next thing I'd check is the voltage on the O2 sensor signal wire 
(typically black). This is a DC voltage from 0-1v. Should hover around .5, 
fluctuating from .2 to .8 fairly rapidly. The ECU only uses this info once 
the engine has reached a certain temp (just like the V8, and every other car 
for that matter).

You can also check the DPR current, but that's typically a little farther 
in. Also, check the coolant temp sensor with an ohm meter, and compare it to 
the recommended specs at different temps.

This should give you some decent info to start with, report back with what 
you find.

Carefully take any hardened hoses/vac lines off that look like $$ 
(everything on an M-B, IME), and soak them in water that is about 180 deg. 
Softens them right up. I also use just a bit of Mr Clean in the water when I 
do this.

Tony (who daily drives a CIS '86 4000Q and a CIS 100 Avant)

----- Original Message ----- 
Subject: [V8] very little audi content


I had an Audi (4000 S) that had CIS fuel injection. There is the
content...

I have been trying to get my sons new to him 1989
Merc 190E 2.6L up to snuff and that means diving headfirst into the CIS
guts of this machine. WOW. this is one complex system that is
guarenteed to fail due to the huge number of microswitches,
potentiometers, vacuum lines, and bla bla bla.

To finally get
it working smothly I had to dissamble a goofy thing called the
"Overvoltage Protection Relay" and scrape/clean the relay
contacts. This ingenius device causes all sorts of seemingly unrelated
things to happen. Next was the air flow meter potentiometer.
It was givving very eratic readings and apparently new ones are crazy
expensive as well as no longer available. I ended up fixing this one
by drawing over the carbon trace with a big fat graphite pencil to give it
better conductivity. After that, it is starting easy and running
smooth.