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Old 07-28-2011, 04:54 PM
Scott_S_OC's Avatar
Join Date: Jul 2011
Location: Orange, California
Posts: 6
Another Warm Up Regulator Question -

1976 450 Sl, Mechanical CIS - Starts Up only by Pressing Down on Air Diaphragm - Runs Up Rough for a Min, Smooths out.

I just got a 76 450SL, was not running, replaced the Fuel Pump Car Starts now. However it will not start unless with the Key in the Ignition turned far right (not starter engages) and pressing down on the air diaphragm to let fuel into the injectors for 10 sec or so to get 'The screeching sound' then I can crank the engine and it will start. It ‘runs up’ a bit rough for a min or so till I press the gas down and get revs up then it smooth’s out and idles and runs great.

With those symptoms’ and further reading I took apart my Warm Up Regulator and soaked it in gas, used some compressed air through the 2 fuel lines (not the small vac diaphragm though). and reassembled it. It did not make any difference. However today in looking at some Drawings of the WUR's I see there appears to be a "Rod' or "Pin" (see pic) between the Top inside where the Fuel Enters the WUR Chamber and the top of the Cont that sits on the Spring. Mine did not have any "Rod" or "Pin" as illustrated. Just the 2 Springs The Cone and Thermal Element. Should there be a "Rod" or "Pin' between the Cone and the Top Inside of where the Fuel is delivered? See Red Arrow on my attachment.

What else should I check? I have not checked the Pump Pressure yet.



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Old 07-28-2011, 05:47 PM
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Join Date: Jan 2003
Location: Matthews, NC
Posts: 1,356
Yes, you must have the rod.

84 500 SEL (307,xxx miles)
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Old 07-28-2011, 06:25 PM
Scott_S_OC's Avatar
Join Date: Jul 2011
Location: Orange, California
Posts: 6
Ah... Very Good, Thanks Paul !!

That would explain a lot, I recon the previous owner must have lost or failed to put the
rod into the WUR, it appears it might have been leaking due to the RTV they had for gasket,
and was resealed at one point, such it is not functioning correctly.

Anyone know of a parts source for that little Rod or Tube or Pin that goes between the
Cone and the Fuel Distribution Disc?

Guess have to spend $170.00 for another WAU for a 50 Cent part...

Thanks a million,


Last edited by Scott_S_OC; 07-28-2011 at 06:35 PM. Reason: spelling
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Old 07-28-2011, 10:14 PM
Senior Member
Join Date: Nov 2002
Posts: 736
i've not swapped internal parts for a control pressure reg., but i would surmise they have to be different for each application. unless you find the same part number reg., another pin might be a problem. good luck, chuck.

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