'91 EB runs rich.

Which is it? Running Lean or Running Rich?

Hmmmm......Jim Warman where are you? ( I says in my best "Car 54" voice )

BOTH codes?

I hate it when that happens

I'd reset the computer in case one code was a fluke and see which code reappears. You won't lose anything because you already wrote down the codes.

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There is a pressure test port on the fuel rail. It shouldn't cost that much to have a shop check it. The port looks like a Schraeder tire valve, though I can't recommend using a tire gauge on it.....(grin).

Mike

There are less than a handful of things that can make a motor run rich but a real host of things that can drive them lean. These 4.0s of all flavours like to eat intake gaskets (I'm starting to think that it is because the manifold bolts to the block rather than the head like most V motors). The most common things that will drive mixtures lean are (in no particular order) dirty fuel filter, fuel pressure too low, leaking intake gaskets (when mine went, it developed a real taste for oil) and dirty MAF..... all these are common problems with the Ex.

My suggestion would be (especially if there are no real noticeable drivability concerns) to clear the codes and complete two drive cycles and recheck but only if you have done a KOER first...... this is an important step because continuous memory codes can be misleading.

HTH