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Apparent fuel delivery issue in 1990 740 Rex Regina

posted by  rstarkie on  Wed Nov 7 07:30 CST 2012
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last visit: Fri Oct 24 10:14 CST 2014
[RELATED]

I posted earlier about referrals for a Volvo friendly garage in the Lexington area:

http://www.brickboard.com/RWD/volvo/1546295/volvo_friendly_garage_south_lexington_ky.html

In an effort to avoid a tow to a garage I have continued to try to diagnose the problem from afar.

I sent a known good coil assembly and a fuel pressure gauge setup (image below). Replacing the coil did not solve the problem but the pressure results were telling.

The car will sometimes start and run poorly, but not for long. Once the gauge was installed it initially showed just shy of 30psi pressure during cranking and the car started. It ran for several minutes all though it required a feathering of the throttle to keep it running.

During the time the car was running the pressure fluctuated between 15 and almost 30psi. The pressure fluctuations did not correlate to throttle position. The fuel pressure regulator does not have a fuel smell at the vacuum side.

I don't remember what the specs are on Rex Regina fuel pressure but I believe it should be over 40psi. (43?)

So while I think we have found the source of the problem I wonder if it is the pump or perhaps the filter? If the pressure was constantly low I would have a better feeling about pointing a finger at the pump failing. With the varying pressure I wonder if there could be debris moving around inside the filter occasionally allowing a better flow of fuel?

Thanks for any hunches and the pressure specs of the Rex Regina system if you have them.

Randy

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