Quote:
Originally Posted by EricSilver
Is this the procedure? (From a 2004 post of yours):
Although there is a reasonable chance that the egr tube is blocked,[common 104 prob], an easy test for vac. flow is to simply apply some vac [ hand pump or vac source] to the egr while at idle. This opens the egr and will cause the engine to stumble..[ go lean]...if it does ,the tube is not blocked and other parts of the egr system are suspect...
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Yes .. here is another
http://www.peachparts.com/shopforum/showthread.php?t=137068&highlight=egr+hand+pump
The basic concept of the test is the EGR is never called for at idle when car coolant is up to temp. So, if you manually cause the egr to open at that time , the engine will go very lean and stumble [ what you are basically doing is causing a very large intake vac. leak] If the tube is plugged , this can not happen as the air the egr is allowing to pass can not pass a blocked tube , so there will be no noticeable effect on the engine running.
NOTE**-The engine will not stall b/c engine management will try to correct a/f mix.
There are 5 parts to egr operation:
The ECU sends an electric sig to a SOV at the front of the engine [ SOV is just an electrically operated air valve.] It lets engine vac pass on to the egr diaphragm, which opens the egr actuator.
The common faults on 104s are the plastic vac supply line that is under the front engine cover cracks from heat fatique. This stops vac from ever getting to the SOV supply side. So, code 5. But if you have vac at SOV, then the SOV has to open.. That is also a probable for code 5 [ they get gummed up]
And if the SOV does get vac to the EGR , the EGR on 104s was changed via Benz TSB [ Technical Service Bulletin 518 or such] b/c the shaft did not have the needed clearence and they would Hang Up, causing a Code 5. These where changed to a new part and usually the Dealer would put a White paint dot on the new unit to let Techs know it was upgraded , b/c the part # never changed, just the shaft tolerence diameter design. [ but many got changed without being indexed, and some never got changed]
So , you can see why it is best to do a couple of test to see which one of these common faults are causing the ..well you get it ..code 5.
Anyway , a hand vac pump does the testing and you are looking mainly for rough running at idle when you open the EGR and you are also looking for a SNAP SHUT when you relaese the vac supply to EGR.
That, along with verification of vac supply [ hoses/sov/etc] are the test.
Good Luck ..not a hard thing to check out, but easily mis-diagnosed