1991 300CE (M104) sluggish upon acceleration - timing advance issue? - PeachParts Mercedes-Benz Forum

rgnprof · #1 08-14-2010, 03:44 PM

I have been running down a sluggishly accelerating '91 300CE with the M104 engine. Recently, gas mileage has suffered as well, down maybe 4-5 mpg...although part of that may have been due to a plugged fuel filter - which has been changed.

Car still seems to have a "dead" spot when I hit the gas pedal, and I'm beginning to think - after reading thru a bunch of old posts - that I may have a timing advance issue. I have located 2 vacuum pods behind the windshield washer bottle on the passenger fender wall. One runs to the air pump...

Can someone explain what these do and how to test them??

Thanks, ryan

Gilly · #2 08-14-2010, 04:07 PM

IIRC one is for the EGR switchover valve and the other for the air pump switchover valve.
I can't remember what changes the cam advance, but (again IIRC) you can jump power and ground to the cam advance and you should hear the engine sound different as you jump power on and off to the solenoid.
I really don't think vac has anything to do with the cam advance solenoid, it's electric.
Gilly

david s poole · #3 08-15-2010, 02:56 PM

the timing is regulated by a vacuum hose that goes to the ignition module behind left h/light.if no vacuum timing will be retarded causing loss of power.

rgnprof · #4 08-15-2010, 03:07 PM

David,
Thank you for the reply. Can you be a little more specific about the 'ignition '
module' - and where the hose runs from and to?? Is there any way/procedure to test the vacuum advance on this motor?

Also, I have made an additional observation which I should have made sooner!

This car runs a lot smoother with more power and less hesitation when it is cooler outside - and the temp gauge is reading approx 85-90 C. We have had a miserable heat spell here in OK - temps ranging from 100-106 F...This car normally runs very hot in this heat - anywhere from 100-110 C. I talked to the best local Mercedes indy, and he confirms that it will run that hot. I think his quote was these cars "run like a dog in this hot weather"... The PO had the same shop replace the thermostat because the car was not heating up enough - this was done about 20,000 miles and 2 1/2 years ago.

Anyone else have a similar observation? Can the temp at which the engine is operating at affect the performance like this?

ryan

rgnprof · #5 08-15-2010, 03:16 PM

I found the hose running from the EZL to the intake manifold...not sure how to test it???

ryan

Ferdman · #6 08-15-2010, 06:11 PM

Ryan, when was the Oxygen sensor changed last? Replacing the Oxygen sensor in our sluggish 1991 300CE resolved the problem.

rgnprof · #7 08-15-2010, 06:34 PM

Dont think it has been changed - I have one coming on Tuesday. Car has 72,500 miles...

david s poole · #8 08-16-2010, 10:02 AM

if you unhook the vacuum hose from the ignition module and with engine running put your finger over the end you should feel good vacuum.also if you put it back on the module with engine running there should be a noticable improvement in the smoothness[if it has vacuum].