EGR PLUG - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 11-28-2010, 09:12 AM Thread Starter
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Deleting EGR system from a 420 SEL. Would anyone know the thread size and pitch of the threaded female hole in the exhaust manifold? Just from inspection it's a fine "bolt" or straight (untapered) pipe thread. This same thread type is common all over the engine. Detroit irons always use a standard tapered pipe thread (NPT). Just wondering if they use a bolt, or straight metric pipe thread? Have sone other things to plug and this would be useful info.

TIA, Dave
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post #2 of 3 (permalink) Old 11-29-2010, 03:07 PM
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If the EGR valve is vacuum operated you only need to plug the vacuum hose leading to the EGR valve to keep it from opening. Cut the hose near the EGR valve and put a solid rod matching the inside diameter of the rubber hose between the two hose ends. This allows you to remove the plugged hose part and regain the EGR function for smog checks.

If your engine has an electrically operated EGR valve part of the systems built in testing involves the ECU momentarily cycling the EGR to its limits and looking for a change in engine operation. If the measured change is not within the expected limits the system will log a DTC. Your car is old enough to where the vacuum operated EGR without the self test is probably what is fitted, but you need to check it carefully first.

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post #3 of 3 (permalink) Old 11-30-2010, 08:57 AM Thread Starter
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No smog to worry about and it's vacuum actuated. Looking to remove and "clean" up so it appears it was never there.
What I've since discovered is MB's don't use tapered pipe threads on their engines for tapped holes for sensors etc.
What they use is a fine 1.0 pitch bolt thread with an aluminum crush washer to seal. The EGR is a M14 (1.0 pitch) and the vacuum switches and water temp. sensors etc. are M10 (1.0 pitch). Cut them to the desired length if not available. Instead of plugged vac lines and such, (Trailer Park) all you see now is a hex bolt head that disappears in the cloud of other fasteners.

Thanks for the feed back. Dave
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