'92 Grand Prix running too rich.

I had a stalling problem on my 1992 Grand Prix LE (V6 3.1L) which was fixed by changing the ignition module (used one but kept my old coils). Ever since, the car is running extremely rich in fuel.
Prior to the stalling problem, it used to do on average 425 km (264 miles) on a 60L (15.85 gal) fuel tank, however, it now only does 280 km (174 miles). It also has an hesitation when i give it gas from a standstill position (or even a slow roll). That problem also started after the stalling repairs and may or may not be linked to the same problem.
I've had two mechanics look at it and they can't find anything apparent. Any clues, guys?
TIA
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First rule of thumb - when a "repair" appears to create another problem...
--

-Mike-
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You may have gotten a bad coil pack. Try taking it back and getting a new one.
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I took the car to a mechanic yesterday and wasn't able to find any vacuum or wiring problem.
He did connect his Snap-On computer to a connector underneat the dashboard and received a "No communication" error.
The previous mechanic who changed the ignition module hooked his without a problem many times and never mentioned a problem there. Could he have shorted out my ECM computer somehow? Could that be the cause of my fuel consumption and hesitation problem?
Yesterday's mechanic said he'd have the Snap-On rep come and take a look at it since it is a new $12,000 computer he bought and although he's used it a few times and never had problems, he just wants to makes sure he isn't missing something before telling me that my ECM needs to be replaced.
TIA
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Cars of this age can develop connector and grounding problems. Try opening and re-seating all connectors. Look at the contacts to see if there is any problems. Loosened and re-tighten grounding screws.

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In article

And he didn't investigate any further?

Doubtful.
Fuel pressure regulators leaking is a very common problem on GMs, and it fits the symptoms exactly. Is the engine stubborn to start after a hot soak of 10 minutes or so?
Your original post infers that a used ignition module was used, if so, how do you know it is the right one and how do you know it too isn't defective?

He's missing how to enter "Legacy" mode on his shiny new Modis. (or Snap-Ons' software is still full of bugs)-: The worst time to learn a new piece of equipment is when you're trying to fix a car.

There are a lot of things hat should be checked WRT a no communicate error message before an ECM is condemned. On a 92 it would start with something as basic as jumpering pins A to B in the ALDL and reading the flash codes.
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Sounds like it was running rich before also (425 km (264 miles) on a 60L (15.85 gal) ). Did you check fuel filter , pressure, plugs-wires? A bad plug wire or wires may show up under a load. Did the original shop reset the DTC lamp?

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