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Old 03-05-2002, 07:58 AM
Registered User
Join Date: Aug 2001
Location: New Jersey USA
Posts: 28
Cool EGR Valve

Greetings All -

I hope someone can answer this question about my EGR valve.

My car's (87 560sl) performance is not up to par when the throttle is pressed down. I have disconnected the EGR vacuum line that runs from the EGR check valve to the EGR. The engine runs with much more gusto and my feul mileage increases by almost 2X.

Does this condition indicate a bad EGR or thermo valve?

Also, will my engine be harmed in any way with the EGR disconnected?

Thank You in advance for any help.

87 560 SL
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Old 03-05-2002, 10:20 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Leave it that way for a while and see how it does. It is there for emissions only. It sounds like there is a problem with vacuum getting to the valve when it is not supposed to.
Donnie Drummonds
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Old 03-06-2002, 08:19 AM
Registered User
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,768
If that car has an egr switch/over valve, check the vent on the valve for blockage.
When a sw/o valve is de-energized, the vent lets air back into the vac line. If it doesn't, the egr can not pull back to the closed posistion because of the vac. holding in the line.
[ kind of like when you hold your finger over the tip of a straw and pull liquid when lifting it.]

That goes for most switch/over valve set -ups.
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Old 03-06-2002, 09:42 AM
Registered User
Join Date: Aug 2001
Location: New Jersey USA
Posts: 28

Guys - Thank You for your feedback.

I just replaced the check valve with a new one. Still the same problem.

Can someone explain to me the action an EGR valve goes through upon acceleration? Does the EGR valve open or is it forced closed? And how does the thermo valve relate to all of this? The service manual does not explain the theory of these mechanics. UUUGGGG

Or am I simply worrying about a minor problem.

Thanks Again.

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Old 03-06-2002, 04:46 PM
Posts: n/a
EGR valve

I am in the UK and was speaking to a MB tech today about the egr valve , basically his comment was disconnect it they are a waste of time!!! and cause more problems than they are suppose to sort. (and anway they rarely work properly if at all)

A friends 93 300d had problems starting, after many hours (including tank out because we thought bad fuel) the second the egr valve was disconnected it started? The state of the inlet manifold after it was amazing, full of tarry substance reducing the diameter by at least 50% I cant see that being an advantage.

I believe they were put on in the first instance in cars for the American market. They claim to reduce the burn temperature and reduce the Nox emmissions

With it disconnected my mates car was quicker and more economical, which follows, that it is also more efficient so emissions are lower?

Mine does not have one
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